S

A substitution box, a lookup table that replaces small groups of bits with other groups of bits. It adds non-linear mixing to a cipher.

Plain language A lookup table in encryption replacing bit patterns nonlinearly.

Used in RFC 2612 RFC 4009 RFC 5794 RFC 5830 RFC 6114

Straightforward-Naming Authority Pointer, a DNS lookup method in which NAPTR records, chosen by an application service tag and a protocol tag, lead step by step to the server for a service in a domain.

Plain language A DNS-based method for progressively finding service locations.

Used in RFC 3958 RFC 5928 RFC 8973

Secure/Multipurpose Internet Mail Extensions, a way of signing and encrypting email that uses CMS to hold the protected data and certificates to identify the people involved.

Plain language A standard for digitally signing and encrypting email messages.

Used in RFC 2311 RFC 2312 RFC 2316 RFC 2480 RFC 2630 RFC 2633 RFC 2634 RFC 2649 RFC 2785 RFC 2798 RFC 2984 RFC 2985 RFC 3114 RFC 3157 RFC 3218 RFC 3274 RFC 3327 RFC 3335 RFC 3369 RFC 3370 RFC 3372 RFC 3420 RFC 3428 RFC 3524 and 95 more

A request method whose defined semantics are essentially read-only, so a client does not request or expect any state change on the origin server. GET, HEAD, OPTIONS and TRACE are safe.

Plain language A request that only reads data without changing server state.

Used in RFC 2310 RFC 2976 RFC 5789 RFC 7231 RFC 7237 RFC 7252 RFC 8132 RFC 8470 RFC 9110 RFC 9875 RFC 10008

A prime number p such that p = 2q + 1, where q is also prime. Diffie-Hellman groups built on safe primes are the kind adopted in this RFC.

Plain language A mathematically special prime number providing stronger security for key exchange.

Used in RFC 4419 RFC 8268

A random value mixed in before hashing a secret so that each stored hash is unique to its own value.

Plain language Random data added before hashing to make password hashes unique and stronger.

Used in RFC 2898 RFC 2945 RFC 3112 RFC 3447 RFC 3826 RFC 3961 RFC 3962 RFC 4309 RFC 4543 RFC 4568 RFC 5054 RFC 5802 RFC 5869 RFC 7292 RFC 7664 RFC 7677 RFC 8018 RFC 8146 RFC 9106 RFC 9154 RFC 9276 RFC 9901

A browser rule that stops a script from reading responses from a server other than the origin it came from. It keeps each site's scripts in their own isolated sandbox.

Plain language A browser security rule preventing scripts from accessing other websites' data.

Used in RFC 6454 RFC 8615 RFC 8826

Security Assertion Markup Language, an XML-based framework that allows organizations to exchange identity and authentication information securely.

Plain language An XML format for securely sharing authentication and identity information.

Used in RFC 6595 RFC 7499 RFC 7773 RFC 7831 RFC 7833 RFC 7930 RFC 8409

The Simple Authentication and Security Layer, a framework in RFC 4422 that lets protocols plug in authentication mechanisms such as SCRAM or PLAIN. XMPP carries SASL exchanges as XML elements.

Plain language A framework allowing protocols to use flexible authentication methods.

Used in RFC 1731 RFC 1734 RFC 2222 RFC 2244 RFC 2245 RFC 2251 RFC 2384 RFC 2444 RFC 2449 RFC 2554 RFC 2595 RFC 2636 RFC 2645 RFC 2703 RFC 2808 RFC 2829 RFC 2830 RFC 2831 RFC 3062 RFC 3080 RFC 3117 RFC 3163 RFC 3195 RFC 3207 and 72 more

A standardized process for normalizing and validating Unicode strings used as user names or passwords, defined in RFC 4013. It removes certain ambiguous characters and prevents spoofing attacks.

Used in RFC 4013 RFC 5721

A congestion control where the average time from one congestion signal to the next stays the same as the flow rate grows. DCTCP is an example.

Plain language Network congestion control scaling proportionally with traffic growth.

Used in RFC 5651 RFC 5775 RFC 9330 RFC 9331 RFC 9332

Static Context Header Compression, a compression and fragmentation mechanism for constrained networks. Two ends share a static context made of Rules.

Plain language A compression method for IoT devices using pre-shared rules.

Used in RFC 8824 RFC 9011 RFC 9363 RFC 9391 RFC 9442

System for Cross-domain Identity Management, a standard way for systems to create, read, update and delete user and group records over HTTP using JSON.

Plain language A standard protocol for synchronizing user accounts across systems.

Used in RFC 7643 RFC 8417 RFC 9865 RFC 9944 RFC 9967

In OAuth, a value naming a kind or amount of access, such as reading a profile. Scope values are defined by the authorization server and a token carries only the scopes it was granted.

Plain language A permission label on an access token indicating what resources it can access.

Used in RFC 6749 RFC 6750 RFC 6755 RFC 6819 RFC 7522 RFC 7523 RFC 7591 RFC 7628 RFC 7635 RFC 7662 RFC 7853 RFC 8414 RFC 8628 RFC 8693 RFC 8707 RFC 8898 RFC 9068 RFC 9126 RFC 9200 RFC 9396 RFC 9431 RFC 9560 RFC 9635 RFC 9700 and 3 more

A Protocol Data Unit that includes a context engine ID and context name along with the actual management request or response, allowing the message to be routed within a specific management domain.

Used in RFC 2272 RFC 2571 RFC 3826

A data structure maintained by a TCP sender that tracks which octets or ranges of octets have been cumulatively acknowledged or selectively acknowledged.

Plain language A TCP sender's record of which data blocks the receiver confirmed.

Used in RFC 3517 RFC 3708 RFC 6675

Salted Challenge Response Authentication Mechanism (RFC 5802), a password-based SASL mechanism that does not send the password. SCRAM-SHA-1 and SCRAM-SHA-1-PLUS are mandatory to implement in XMPP.

Plain language A password authentication method never transmitting the password itself.

Used in RFC 5802 RFC 5803 RFC 6120 RFC 6331 RFC 7677 RFC 9266

A set of graphic characters used for the written form of one or more languages.

Plain language The set of characters used to write a language, like Latin or Arabic.

Used in RFC 3536 RFC 3660 RFC 5646 RFC 6365

Small Computer Systems Interface, a standard for communicating with storage devices such as disk drives and tape drives.

Plain language A standard protocol for computers to communicate with storage devices.

Used in RFC 2143 RFC 3720 RFC 3980 RFC 4018 RFC 4173 RFC 4455 RFC 5046 RFC 7143

The Stream Control Transmission Protocol, a reliable, message-oriented transport protocol with multiple streams per connection and support for several IP addresses per endpoint.

Plain language A reliable protocol for transporting messages with multiple simultaneous connections.

Used in RFC 2960 RFC 3057 RFC 3127 RFC 3257 RFC 3286 RFC 3309 RFC 3320 RFC 3331 RFC 3332 RFC 3347 RFC 3419 RFC 3423 RFC 3436 RFC 3530 RFC 3539 RFC 3554 RFC 3588 RFC 3708 RFC 3758 RFC 3788 RFC 3807 RFC 3816 RFC 3836 RFC 3868 and 116 more

A unit of information inside an SCTP packet, either control information or user data. A packet can bundle several chunks after one common header.

Plain language A labeled unit of data or control information within an SCTP message.

Used in RFC 4820 RFC 4895 RFC 5061 RFC 6096 RFC 6525 RFC 6951 RFC 8832 RFC 9260

Signing Domain Identifier: the domain named in the d= tag of a DKIM signature. It is the domain that takes responsibility for the message and the one whose DNS holds the public key. It does not have to match the address in the From header.

Plain language The domain that digitally signs an email message and proves authenticity.

Used in RFC 5585 RFC 6376

A Self-Delimiting Numeric Value is a number encoded in as many octets as needed. The top bit of each octet says whether more follow, and the other 7 bits hold the value.

Plain language A compact number encoding indicating when it continues across multiple bytes.

Used in RFC 5326 RFC 9090 RFC 9139

Session Description Protocol. A text format that describes a media session, such as which codecs and addresses to use. SIP messages commonly carry it as an offer and an answer.

Plain language A text format describing media session details like codecs and network addresses.

Used in RFC 2198 RFC 2326 RFC 2327 RFC 2543 RFC 2705 RFC 2848 RFC 2974 RFC 3015 RFC 3016 RFC 3108 RFC 3190 RFC 3261 RFC 3262 RFC 3264 RFC 3266 RFC 3303 RFC 3311 RFC 3312 RFC 3313 RFC 3323 RFC 3372 RFC 3388 RFC 3389 RFC 3398 and 326 more

A negotiation model in which one party sends an SDP description as an offer and the other replies with an answer describing what it accepts. Both then set up the session accordingly.

Plain language A session negotiation method where one party proposes and the other accepts.

Used in RFC 4117 RFC 5576 RFC 5583 RFC 6184 RFC 6190 RFC 6947 RFC 7345 RFC 8285 RFC 8373 RFC 8841

A condition that must be met for a media stream before session establishment or modification can proceed. Progress is delayed until it is satisfied or the session fails.

Plain language A requirement that must be met before a media session can start.

Used in RFC 5027 RFC 5898

A string in LDAP syntax that specifies criteria for matching entries, such as (cn=John*) for names starting with John.

Used in RFC 1959 RFC 2254

A domain name directly beneath a top-level domain (TLD). In EXAMPLE.COM, EXAMPLE is the second-level domain; in LTD.UK, LTD is the second-level domain.

Used in RFC 2146 RFC 2240

A cookie carrying the Secure attribute, which tells the browser to send it only over a secure transport such as HTTPS.

Plain language A browser cookie transmitted only over encrypted HTTPS connections.

Used in RFC 2964 RFC 6797

SEND, a set of protections for IPv6 Neighbor Discovery that uses cryptographically generated addresses and signatures to prove who sent a message.

Plain language Cryptographic protections for IPv6 network announcements preventing forgery.

Used in RFC 4429 RFC 5269 RFC 6105 RFC 6496 RFC 6980

The shared state two peers keep for protecting traffic: the algorithms, keys and other parameters. IKE has an IKE SA for its own messages and creates Child SAs for ESP or AH traffic.

Plain language Shared encryption keys and algorithms between two communicating peers.

Used in RFC 1135 RFC 1777 RFC 1825 RFC 1826 RFC 1829 RFC 2002 RFC 2006 RFC 2084 RFC 2085 RFC 2207 RFC 2228 RFC 2230 RFC 2262 RFC 2344 RFC 2356 RFC 2367 RFC 2394 RFC 2395 RFC 2401 RFC 2402 RFC 2403 RFC 2404 RFC 2405 RFC 2406 and 170 more

The shared state that two peers build by exchanging tokens, after which they can protect messages to each other. Several contexts can exist at once between the same peers.

Plain language Established secure communication state between two endpoints.

Used in RFC 2078 RFC 2743 RFC 2744 RFC 7546 RFC 8353 RFC 8613 RFC 9172 RFC 9173

A signed JSON Web Token that describes a security-related event, such as an account being disabled. It is defined in RFC 8417 and abbreviated SET.

Plain language A signed notification of security events like account disabling.

Used in RFC 8417 RFC 8935 RFC 9967

An intermediate system that implements IPsec, for example a firewall or router that has been IPsec-enabled. It protects traffic passing through it on behalf of other hosts.

Used in RFC 1825 RFC 4301

A set of security attributes attached to a subject or object, such as a sensitivity level and compartment or an SELinux identity, role and type.

Plain language A security marking showing data sensitivity and access permissions.

Used in RFC 2634 RFC 3114 RFC 5570 RFC 7204 RFC 7444 RFC 7569 RFC 7861 RFC 9478

How much protection a message gets: noAuthNoPriv (none), authNoPriv (authentication only) or authPriv (authentication and encryption).

Used in RFC 2571 RFC 3412

An SPI is a 32-bit value that identifies a security association for incoming packets. In HIP it is a compressed stand-in for a pair of host identities, so the two ends agree it during the handshake and each picks the value it wants to see in packets from its peer.

Plain language A short number in the packet header that tells the receiver which keys to use.

Used in RFC 1826 RFC 5202 RFC 7402

A formal statement of the rules that people given access to an organization's technology and information assets must follow.

Plain language Formal rules governing how employees must protect systems and information.

Used in RFC 1244 RFC 1281 RFC 2196

The ordered IPsec database that matches packets by selectors and chooses whether each one is protected, discarded or allowed to bypass IPsec.

Plain language IPsec's rules database deciding which traffic is encrypted or blocked.

Used in RFC 2401 RFC 3585 RFC 4301 RFC 4945 RFC 5858 RFC 6027 RFC 6071 RFC 7619 RFC 9061

A service that validates security tokens it is given and issues new security tokens in response. In OAuth token exchange, the authorization server plays this role.

Plain language A service validating credentials and issuing temporary tokens.

Used in RFC 7521 RFC 8693

The starting value fed to a pseudo-random generator. All the unpredictability of its output comes from the seed, so a seed with only a few bits of entropy gives a small set of possible outputs no matter how complex the generator is.

Plain language The initial value determining all random numbers a generator produces.

Used in RFC 1750 RFC 1760 RFC 2243 RFC 2289 RFC 4086 RFC 4162 RFC 4777 RFC 5632 RFC 5669 RFC 5748 RFC 8479 RFC 8682 RFC 9881 RFC 9935 RFC 9964 RFC 9986

A value that identifies a segment in Segment Routing, for example a prefix or an adjacency.

Plain language An identifier for a routing segment or hop in segment routing.

Used in RFC 8402 RFC 8476 RFC 8491 RFC 8660 RFC 8665 RFC 8666 RFC 8667 RFC 8669 RFC 8754 RFC 9020 RFC 9085 RFC 9086 RFC 9256 RFC 9259 RFC 9513 RFC 9524 RFC 9602 RFC 9631 RFC 9716 RFC 9800 RFC 9831 RFC 9855 RFC 9902 RFC 9933 and 2 more

A way of steering traffic in which the sender lists the segments, or steps, a packet should follow through the network.

Plain language A routing method where senders specify the exact path packets take.

Used in RFC 8287 RFC 8402 RFC 8403 RFC 8426 RFC 8476 RFC 8491 RFC 8604 RFC 8660 RFC 8661 RFC 8662 RFC 8663 RFC 8664 RFC 8666 RFC 8669 RFC 8754 RFC 8814 RFC 8986 RFC 9085 RFC 9086 RFC 9087 RFC 9125 RFC 9252 RFC 9256 RFC 9350 and 27 more

The label ranges a router sets aside for global SIDs. A SID index is turned into an actual label by counting through the ranges in the order they were advertised.

Plain language A router's reserved label range for global segment identifiers.

Used in RFC 8660 RFC 8665 RFC 8667

An IPv6 routing header used by SRv6 that carries the list of segments a packet must visit and can also hold TLVs with extra metadata.

Plain language An IPv6 header extension listing segments a packet must traverse.

Used in RFC 9259 RFC 9352 RFC 9800 RFC 9947

An acknowledgement that names individual segments received out of order, instead of only the last one received in sequence. It lets a sender resend just the missing segments.

Plain language Acknowledging exactly which data arrived for efficient retransmission.

Used in RFC 908 RFC 2883

A TCP option that lets a receiver tell the sender exactly which blocks of data arrived. The sender can then retransmit only the missing segments.

Plain language A TCP option reporting exactly which data blocks the receiver got.

Used in RFC 2018 RFC 2488 RFC 2757 RFC 2883 RFC 3042 RFC 3155 RFC 3465 RFC 3708 RFC 4653 RFC 5326 RFC 5690 RFC 6349 RFC 6582 RFC 6675 RFC 7414 RFC 7661 RFC 8257 RFC 8985 RFC 9937

A token that can be used only by a client that proves it holds a particular key, unlike a bearer token that works for anyone who has it. DPoP is one way to do this.

Plain language An authorization token usable only by the device that created it.

Used in RFC 9449 RFC 9700

Sensor Measurement Lists, a data format for carrying sensor readings as a list of records. It is defined in RFC 8428.

Plain language A standard format for recording and transmitting sensor measurements.

Used in RFC 9100 RFC 9193

A 32-bit counter that numbers every byte TCP sends, so the receiver can put data in order, detect duplicates and acknowledge exactly what it has.

Plain language Numbers in TCP identifying each byte for proper ordering and acknowledgment.

Used in RFC 442 RFC 512 RFC 516 RFC 675 RFC 683 RFC 700 RFC 761 RFC 793 RFC 869 RFC 889 RFC 905 RFC 908 RFC 916 RFC 938 RFC 964 RFC 1072 RFC 1110 RFC 1144 RFC 1151 RFC 1201 RFC 1216 RFC 1263 RFC 1323 RFC 1582 and 189 more

A 32-bit counter that TCP-AO keeps beside TCP's 32-bit sequence number to form a 64-bit space. It tells apart segments that repeat the same sequence number after rollover.

Plain language An extended sequence counter preventing confusion after wraparound.

Used in RFC 5925 RFC 9187

A way of comparing counters that wrap around, so that half of the values count as newer than a given number and half as older. It lets a small counter be reused safely.

Plain language A method for comparing sequence numbers on wraparound-capable counters.

Used in RFC 1982 RFC 9302

The process of converting a Java object into a byte stream so it can be stored or transmitted, and later reconstructed from the bytes.

Used in RFC 1085 RFC 2713

The server_name extension (type 0), in which a TLS client states the DNS host name it wants to reach, before the server picks a certificate.

Plain language A TLS extension allowing clients to request a specific domain certificate.

Used in RFC 1013 RFC 3958 RFC 4366 RFC 6066 RFC 6186 RFC 6353 RFC 7525 RFC 7590 RFC 7671 RFC 7673 RFC 7712 RFC 7838 RFC 7924 RFC 7925 RFC 8143 RFC 8323 RFC 8336 RFC 8461 RFC 8737 RFC 8744 RFC 8765 RFC 9174 RFC 9325 RFC 9460 and 9 more

An optional HTTP/2 feature in which a server sends a PUSH_PROMISE and a response for something the client has not yet asked for. A client can disable it with SETTINGS_ENABLE_PUSH set to 0.

Plain language HTTP/2 feature allowing servers to send unrequested resources to clients.

Used in RFC 2177 RFC 3995 RFC 5465 RFC 5551 RFC 6202 RFC 7540 RFC 8030 RFC 8297 RFC 8336 RFC 8620 RFC 8764 RFC 8887 RFC 8895 RFC 9113 RFC 9114 RFC 9218 RFC 9569 RFC 9749

A way for a server to keep an HTTP connection open and push a stream of text events to a client, using the media type text/event-stream.

Plain language A web protocol for servers to continuously push updates to clients.

Used in RFC 6202 RFC 8040 RFC 8650 RFC 8895

An identifier (typically one byte) that specifies which process or service on a station should handle a particular frame, similar to a port number in IP.

Plain language An identifier directing frames to specific services on a network station.

Used in RFC 1008 RFC 2106

A network entity that advertises the availability of a network service, registering itself with directory agents or broadcasting its service description.

Used in RFC 2614 RFC 3082 RFC 3528 RFC 3822 RFC 4018

An abstraction of a network reference point where network services can be, or already are, delivered to customers. It can be bound to one or more attachment circuits.

Plain language A logical point where customers connect to network services.

Used in RFC 9408 RFC 9834 RFC 9835

The region within which all locations map to the same service URI or set of URIs for a given service. It may consist of several non-contiguous shapes.

Plain language The geographic or logical area covered by a particular service.

Used in RFC 5222 RFC 6739

The definitions of the semantics and parameters of a specific type of quality of service. The Integrated Services model defines two service classes, Controlled Load Service and Guaranteed Service.

Plain language A named kind of service, such as a guaranteed one, with its own rules and numbers.

Used in RFC 2386 RFC 4594 RFC 5127 RFC 8100

A field in the DCCP connection handshake that describes the application-level service the client wants to reach. It helps middleboxes and reduces reliance on well-known ports.

Plain language A code identifying which application service a connection request targets.

Used in RFC 4340 RFC 5238 RFC 5595 RFC 5597

The logical point where slice-specific treatment begins or ends, typically where an Attachment Circuit connects to the provider network at a PE.

Plain language The boundary between customer equipment and network provider responsibility.

Used in RFC 7398 RFC 9889

Finding where a service is running, meaning which hosts and ports, without hard-coding them in the client. DNS SRV records are a classic mechanism for it.

Plain language Automatically locating available network services without hardcoding addresses.

Used in RFC 462 RFC 620 RFC 623 RFC 830 RFC 887 RFC 1491 RFC 1789 RFC 2052 RFC 2165 RFC 2248 RFC 2413 RFC 2552 RFC 2608 RFC 2609 RFC 2610 RFC 2614 RFC 2782 RFC 2843 RFC 2915 RFC 2968 RFC 2969 RFC 3059 RFC 3082 RFC 3088 and 34 more

A sequence of network functions (such as firewall, then load balancer, then DPI) through which traffic for a service must pass.

Plain language An ordered sequence of network processing functions traffic passes through.

Used in RFC 7665 RFC 8459 RFC 8568 RFC 9145

An architecture in which packets are steered through an ordered set of service functions, such as filters or NAT, so each can apply its own processing.

Plain language Network architecture directing traffic through multiple processing stages.

Used in RFC 8300 RFC 8459 RFC 8595 RFC 8596 RFC 8677 RFC 8924 RFC 8979 RFC 9015 RFC 9192 RFC 9263 RFC 9451 RFC 9491 RFC 9516

The component responsible for reading service path information and forwarding packets to the next service in the chain, then to the next SFF.

Plain language A component directing packets to the next step in a service chain.

Used in RFC 7665 RFC 8300 RFC 8459 RFC 8596 RFC 8677 RFC 8924 RFC 9015

The specific sequence of Service Functions that packets of a given classification are sent through. In the NSH it is identified by the Service Path Identifier.

Plain language The ordered sequence of network functions a specific packet type traverses.

Used in RFC 7665 RFC 8300 RFC 8459

The process of determining what user-level communication service is being invoked in a SIP session, such as a voice call, a video conference, gaming, or media streaming.

Plain language Identifying the type of communication service in use, like calls or video.

Used in RFC 5897 RFC 6050

A target value or range for a measurable aspect of network performance, such as bandwidth or latency. A customer can check it by measuring traffic.

Plain language A performance target for network services customers can measure.

Used in RFC 4176 RFC 8316 RFC 9543 RFC 9544 RFC 9551

A set of parameters that define the service (such as bandwidth, latency and loss rate) offered to a traffic stream by a Differentiated Services domain.

Plain language Technical specifications for network service quality and performance.

Used in RFC 2998 RFC 3260 RFC 4176

A protocol in which User Agents find services through Service Agents and Directory Agents. Version 2 is defined in RFC 2608.

Plain language A protocol for network devices to discover available services.

Used in RFC 2375 RFC 2609 RFC 2614 RFC 3059 RFC 3421 RFC 3528 RFC 3822 RFC 3832 RFC 4018 RFC 4173

A YANG data model that describes a network service from the customer perspective, including requirements like bandwidth, latency, and security, without specifying underlying technology.

Plain language A description of network service requirements from customer perspective.

Used in RFC 8299 RFC 8969 RFC 9315

A document that describes the syntax of the service URL for a given service type, and defines all the service attributes for that type including their meaning, their defaults and the constraints on the values they may take.

Plain language The published description of one kind of service: what its address looks like and what information a provider may attach to it.

Used in RFC 2609 RFC 2614 RFC 3822 RFC 4018

A specification of performance requirements for a network service, including bandwidth, maximum end-to-end delay, delay variation, and maximum loss ratio.

Plain language A contract specifying guaranteed performance for a network service.

Used in RFC 2430 RFC 2475 RFC 2758 RFC 3387 RFC 4176 RFC 4190 RFC 7536 RFC 9439 RFC 9732 RFC 9938

A protocol for announcements of multimedia sessions using multicast. SAP sends announcement packets to well-known multicast addresses and ports on a periodic basis.

Used in RFC 2114 RFC 6695

A signaling intermediary, commonly used by SIP domains, that sits between networks and handles signaling and media, including relaying media for devices behind NATs.

Plain language A network device controlling and relaying phone calls between domains.

Used in RFC 5853 RFC 7362 RFC 8688 RFC 10006

A protocol for describing multimedia sessions, carried in the body of SIP messages. Contains information about media types, codecs, ports, and connection addresses.

Used in RFC 3556 RFC 4597 RFC 5118 RFC 5369 RFC 5956 RFC 8285

The set of parameters (ingress point, protocol, IP address, port, and routing policies) that a SIP service provider needs to route a call to another provider's network.

Plain language Information needed to route calls to another phone provider's network.

Used in RFC 6461 RFC 6567 RFC 7877

A random value, often stored in a cookie, that a server uses as a key to look up information about one visitor. Keeping data on the server and only the identifier in the cookie limits the damage if the cookie leaks.

Plain language A unique identifier linking a browser to server-stored session data.

Used in RFC 2059 RFC 2246 RFC 2326 RFC 2741 RFC 2964 RFC 3018 RFC 3033 RFC 3436 RFC 3451 RFC 3576 RFC 3652 RFC 3749 RFC 3783 RFC 3817 RFC 4081 RFC 4252 RFC 4346 RFC 4454 RFC 4462 RFC 4656 RFC 4817 RFC 5077 RFC 5191 RFC 5247 and 26 more

An application-layer protocol for establishing, modifying, and terminating real-time sessions such as phone calls and video conferences. SIP messages carry addressing, routing, and other call information.

Plain language A protocol for setting up and managing phone and video calls.

Used in RFC 3325 RFC 3427 RFC 3841 RFC 4190 RFC 4245 RFC 4579 RFC 5356 RFC 5360 RFC 5364 RFC 5411 RFC 5922 RFC 7044

A fresh symmetric key generated by the KDC for a client and a service to share. It appears in the ticket and in the reply to the client, and is used for only a limited time.

Plain language A temporary encryption key shared between two parties for one session.

Used in RFC 1045 RFC 1446 RFC 1510 RFC 1731 RFC 1851 RFC 1949 RFC 1964 RFC 1991 RFC 2093 RFC 2222 RFC 2440 RFC 2451 RFC 2522 RFC 2548 RFC 2695 RFC 2716 RFC 2930 RFC 2941 RFC 2942 RFC 2944 RFC 2945 RFC 2946 RFC 2947 RFC 2948 and 61 more

A SIP user agent function that acts as the source of recorded media and metadata, sending them to a recording server. It may be a phone, a gateway, a border controller or a media server.

Plain language A device or software recording calls and metadata for archival.

Used in RFC 7245 RFC 7866

The party in SIP-based recording that receives the copied media and the metadata describing the recorded communication session.

Plain language A server storing recorded calls and related communication data.

Used in RFC 7245 RFC 7865 RFC 7866

A way to start a new TLS or DTLS association from an earlier one, deriving fresh traffic keys without repeating the expensive public key operations.

Used in RFC 5077 RFC 5764 RFC 6101 RFC 7924 RFC 8548

A blob a TLS server gives a client after a handshake. The client can present it later to resume the session as a PSK. In TLS 1.3 the NewSessionTicket message carries it.

Plain language A token allowing a client to resume a TLS session without renegotiation.

Used in RFC 4217 RFC 4507 RFC 4851 RFC 5077 RFC 5422 RFC 5723 RFC 5868 RFC 7170 RFC 7301 RFC 7525 RFC 7925 RFC 8472 RFC 9001 RFC 9149 RFC 9190 RFC 9325 RFC 9369 RFC 9427 RFC 9813 RFC 9846 RFC 9887 RFC 9930

A protocol that helps a client behind a NAT discover its external IP address and port by querying a STUN server.

Plain language A protocol helping clients behind NAT discover their external address.

Used in RFC 3605 RFC 5128 RFC 5245 RFC 5626 RFC 5766 RFC 5902 RFC 6156 RFC 6314 RFC 6679 RFC 7051 RFC 7064 RFC 7345 RFC 7350 RFC 7362 RFC 7443 RFC 7478 RFC 7584 RFC 7675 RFC 7825 RFC 7982 RFC 7983 RFC 8016 RFC 8445 RFC 8656 and 4 more

The TWAMP role that receives each test packet from the Session-Sender and sends a test packet back in response.

Plain language A network test endpoint echoing received test packets.

Used in RFC 6038 RFC 8762 RFC 9503 RFC 10052

A one-second interval during which a large number of line coding violations occur, indicating serious signal degradation. For example, a P-bit PSES is a second with 44 or more coding violations.

Plain language A one-second period with excessive transmission errors indicating problems.

Used in RFC 2496 RFC 2558 RFC 3592

Standard Generalized Markup Language, a system for defining markup languages by specifying rules for how tags describe document structure and meaning.

Plain language A meta-language for creating markup languages like HTML and XML.

Used in RFC 1049 RFC 1866 RFC 1874

The Secure Hash Algorithm 1, a hash function that turns any input into a fixed-size digest. It produces a larger hash than MD5.

Plain language A cryptographic hash function producing fixed-length fingerprints of data.

Used in RFC 2104 RFC 2404 RFC 2459 RFC 2574 RFC 2945 RFC 3110 RFC 3174 RFC 3217 RFC 4050 RFC 4122 RFC 4162 RFC 4194 RFC 4366 RFC 4432 RFC 4777 RFC 4880 RFC 4895 RFC 5053 RFC 5201 RFC 5702 RFC 5754 RFC 6234 RFC 7166 RFC 7645 and 4 more

SHA-256 is a hash function used here as a one-way computation: it turns an input into a fixed 32-octet value that cannot be run backwards to recover the input. The same input always produces the same value.

Plain language SHA-256 is a one-way calculation that turns some bytes into a fixed 32-byte result.

Used in RFC 4432 RFC 4701 RFC 4871 RFC 5077 RFC 5758 RFC 6209 RFC 6380 RFC 6812 RFC 7183 RFC 7693 RFC 7924 RFC 8624 RFC 8731

An extendable-output function from the SHA-3 family, written SHAKE(M, d), that hashes a message M to a digest of d bits. SHAKE128 and SHAKE256 are the two defined instances.

Used in RFC 8692 RFC 8702

A manually configured, unnumbered OSPF link between two PE routers that makes the route across the VPN backbone look like an intra-area link. It is optional.

Plain language A logical link configured in OSPF to optimize paths over VPN backbones.

Used in RFC 4577 RFC 6565

The process of working out which flows traverse the same bottleneck link, so that their congestion can be controlled together. This RFC does it by comparing summary statistics of each flow's one-way delay measurements.

Plain language Working out which data streams pass through the same congested link.

Used in RFC 8382 RFC 8699

A recovery scheme in which preconfigured protecting paths for several disjoint working paths share resources, and one is activated by the APS protocol when needed.

Plain language A backup system where multiple paths share protective resources.

Used in RFC 7412 RFC 9270

A set of links that can fail together because they share some underlying resource, such as the same physical port or line card.

Plain language Network links that would fail together due to shared underlying resources.

Used in RFC 4054 RFC 4202 RFC 4203 RFC 4220 RFC 5286 RFC 5298 RFC 5307 RFC 5521 RFC 6119 RFC 6414 RFC 6457 RFC 6825 RFC 6981 RFC 7446 RFC 7926 RFC 8001 RFC 8390 RFC 8800 RFC 9479 RFC 9492 RFC 9855

A set of network links that share a common risk of failure, such as links in the same fiber optic cable or sharing the same physical path.

Plain language Links that would break together because they share the same physical path.

Used in RFC 4209 RFC 4428 RFC 4874 RFC 5521 RFC 7916 RFC 8355 RFC 8779 RFC 8919 RFC 9917

A key known to both sides of an authentication exchange. In TOTP the prover and the verifier each hold the same secret key, and it is never sent along with the code.

Plain language A secret key both parties know without transmitting it.

Used in RFC 1472 RFC 1852 RFC 1994 RFC 2058 RFC 2085 RFC 2104 RFC 2138 RFC 2139 RFC 2195 RFC 2243 RFC 2274 RFC 2403 RFC 2404 RFC 2522 RFC 2539 RFC 2548 RFC 2574 RFC 2607 RFC 2631 RFC 2661 RFC 2759 RFC 2841 RFC 2845 RFC 2865 and 85 more

A multicast distribution tree rooted at the Rendezvous Point and used by all sources of a group, written (*,G). Source-specific groups avoid it.

Plain language A single multicast delivery tree used by all senders to a group.

Used in RFC 2189 RFC 2201 RFC 4608 RFC 7438 RFC 7761

A tunnel header that is not sufficient on its own to forward the packet as an outer header. It sits between two IP headers or between an IP header and a Layer 2 header.

Plain language A lightweight tunnel header nested between other headers.

Used in RFC 3035 RFC 5129 RFC 9599 RFC 9601

Dijkstra's algorithm as OSPF uses it: each router builds a tree of shortest paths with itself at the root and derives its routing table from the tree.

Plain language A routing algorithm calculating shortest paths from each router to destinations.

Used in RFC 981 RFC 1074 RFC 1131 RFC 1245 RFC 1247 RFC 1583 RFC 1584 RFC 2178 RFC 2328 RFC 2362 RFC 2702 RFC 3626 RFC 3684 RFC 3784 RFC 3787 RFC 3847 RFC 3906 RFC 3945 RFC 4061 RFC 4062 RFC 4063 RFC 5286 RFC 5302 RFC 5305 and 36 more

An attack that learns secrets from how a system behaves, such as how long a calculation takes, rather than by breaking the math itself.

Plain language An attack exploiting observable behavior like timing instead of cryptography.

Used in RFC 6989 RFC 7664 RFC 7696 RFC 7748 RFC 8125 RFC 8645 RFC 8731 RFC 8937 RFC 9106 RFC 9576

A smaller conference that some of the participants of a main conference move into for part of the time. A conference allows sidebars only when its allow-sidebars element is set, and a sidebar records the main conference as its parent.

Plain language A separate small meeting that a few people break away into during a bigger one.

Used in RFC 6501 RFC 6504

A language for writing email filtering scripts, defined in RFC 5228. Extensions add new tests and actions to it.

Plain language A language for writing email filtering scripts with tests and actions.

Used in RFC 3431 RFC 3685 RFC 3894 RFC 5173 RFC 5228 RFC 5229 RFC 5230 RFC 5231 RFC 5232 RFC 5260 RFC 5429 RFC 5435 RFC 5436 RFC 5437 RFC 5463 RFC 5550 RFC 5551 RFC 5703 RFC 5784 RFC 5804 RFC 6009 RFC 6134 RFC 6468 RFC 6609 and 8 more

Signaling Compression, a scheme for compressing signaling messages such as SIP. It is defined in RFC 3320.

Plain language A compression scheme for signaling messages like SIP to reduce size.

Used in RFC 3485 RFC 3486 RFC 4077 RFC 5049 RFC 5112

A signaling agent at the edge of an IP network that receives and sends native signaling from a switched circuit network. It may relay, translate or terminate SS7 signaling.

Plain language A translator at network edges passing control signals between phone and Internet.

Used in RFC 2719 RFC 3094 RFC 4165 RFC 4190 RFC 4233

A system of signaling protocols used by the public switched telephone network (PSTN) to control call setup, routing, and management. SS7 is separate from the voice traffic itself.

Plain language Control signals that tell the telephone network how to connect calls.

Used in RFC 3094 RFC 3332 RFC 3372 RFC 3482

A set of rules for creating and validating electronic signatures. When a signature names its policy, every verifier can apply the same rules and reach the same result.

Used in RFC 3125 RFC 5126

A digitally signed record, issued by a Certificate Transparency log, that proves a certificate was submitted to the log at a specific time.

Plain language A receipt proving a certificate was submitted to a transparency log.

Used in RFC 6962 RFC 9162 RFC 9163

A family of protocols for carrying telephony signaling messages over IP networks, using SCTP as the transport protocol.

Used in RFC 3788 RFC 4233

The Stateless IP/ICMP Translation Algorithm, which converts IPv4 packets to IPv6 and back without keeping per-connection state.

Plain language A stateless translator converting between IPv4 and IPv6 without per-connection state.

Used in RFC 3142 RFC 6145 RFC 7755 RFC 7756 RFC 7757 RFC 8368

A performance degradation that occurs when TCP sends many small segments instead of accumulating data into larger segments, causing severe throughput reduction and excessive network traffic.

Used in RFC 813 RFC 2525

A TCP technique where both endpoints try to open a connection to each other at the same time. In ICE TCP it is signaled with the S-O candidate type.

Plain language A TCP technique where both endpoints open connections at the same moment.

Used in RFC 5382 RFC 5596 RFC 6544

Session Initiation Protocol. A text-based application-layer protocol for creating, modifying and terminating sessions such as voice and video calls.

Plain language A text-based protocol for creating, changing and ending phone and video sessions.

Used in RFC 1209 RFC 2458 RFC 2543 RFC 2824 RFC 2848 RFC 2871 RFC 2916 RFC 2976 RFC 2995 RFC 3002 RFC 3027 RFC 3050 RFC 3087 RFC 3108 RFC 3136 RFC 3204 RFC 3219 RFC 3261 RFC 3262 RFC 3263 RFC 3264 RFC 3265 RFC 3298 RFC 3303 and 465 more

A lasting peer-to-peer SIP relationship between two user agents, such as an ongoing call, identified by Call-ID and the From and To tags.

Plain language The complete conversation between two phones from setup to termination.

Used in RFC 2543 RFC 3261 RFC 3262 RFC 3265 RFC 3311 RFC 3323 RFC 3326 RFC 3428 RFC 3486 RFC 3515 RFC 3578 RFC 3608 RFC 3665 RFC 3680 RFC 3725 RFC 3840 RFC 3841 RFC 3856 RFC 3857 RFC 3891 RFC 3893 RFC 3910 RFC 3911 RFC 3959 and 88 more

A concrete use of the SIP event notification framework for one class of events. It names the event and says what subscriptions and notifications carry.

Plain language A ready-made notification topic with rules for update messages.

Used in RFC 3427 RFC 3515 RFC 3680 RFC 4575 RFC 4579 RFC 4662 RFC 5366 RFC 5589 RFC 6086 RFC 6502

A named definition of what a particular kind of SIP INFO request carries and how it is used, as set out in the INFO framework of RFC 6086.

Plain language A named definition of what a particular SIP INFO request carries and how it is used.

Used in RFC 6086 RFC 8840

A server that forwards SIP requests and responses on behalf of other user agents, and may apply routing and policy.

Plain language A helper in the middle passing calls and applying routing or policy.

Used in RFC 2543 RFC 2824 RFC 2848 RFC 3050 RFC 3087 RFC 3261 RFC 3262 RFC 3263 RFC 3265 RFC 3311 RFC 3319 RFC 3323 RFC 3324 RFC 3325 RFC 3326 RFC 3327 RFC 3329 RFC 3361 RFC 3372 RFC 3398 RFC 3428 RFC 3455 RFC 3486 RFC 3487 and 137 more

A server that accepts REGISTER requests and stores where a user can currently be reached.

Plain language The office keeping a list of where each user is currently reachable.

Used in RFC 2543 RFC 2848 RFC 3261 RFC 3327 RFC 3455 RFC 3515 RFC 3581 RFC 3608 RFC 3665 RFC 3680 RFC 3764 RFC 3840 RFC 3841 RFC 3880 RFC 4083 RFC 4457 RFC 4740 RFC 4780 RFC 5039 RFC 5049 RFC 5360 RFC 5373 RFC 5589 RFC 5626 and 29 more

A carrier or operator that provides VoIP services to customers, using the SIP protocol for call setup and management.

Plain language A phone company providing VoIP services using the SIP protocol.

Used in RFC 5486 RFC 5589 RFC 6405 RFC 6406 RFC 6461

A single request and all the responses to it, up to and including a final response.

Plain language A single request and all the responses to it.

Used in RFC 2543 RFC 3261 RFC 3262 RFC 3263 RFC 3265 RFC 3311 RFC 3312 RFC 3428 RFC 3515 RFC 3578 RFC 3581 RFC 3665 RFC 3725 RFC 3891 RFC 3911 RFC 4028 RFC 4117 RFC 4168 RFC 4320 RFC 4321 RFC 4475 RFC 4579 RFC 5057 RFC 5359 and 19 more

An endpoint that sends or receives SIP requests, such as a phone or softphone. It acts as a client when it sends a request and as a server when it answers one.

Plain language An endpoint sending or receiving SIP requests like phones or softphones.

Used in RFC 2543 RFC 2848 RFC 3261 RFC 3262 RFC 3263 RFC 3265 RFC 3311 RFC 3312 RFC 3323 RFC 3324 RFC 3325 RFC 3327 RFC 3329 RFC 3351 RFC 3372 RFC 3398 RFC 3428 RFC 3486 RFC 3487 RFC 3515 RFC 3524 RFC 3578 RFC 3581 RFC 3608 and 160 more

Stateless Address Autoconfiguration. A host builds its own IPv6 address from a prefix in a Router Advertisement (with the A flag set) plus an interface identifier, without a DHCP server holding state.

Plain language IPv6 hosts building addresses from router announcements plus their own identifiers.

Used in RFC 2461 RFC 2462 RFC 2464 RFC 2467 RFC 2497 RFC 2529 RFC 2894 RFC 3146 RFC 3315 RFC 3484 RFC 3590 RFC 3756 RFC 3927 RFC 3971 RFC 4242 RFC 4293 RFC 4294 RFC 4338 RFC 4429 RFC 4489 RFC 4861 RFC 4862 RFC 4919 RFC 4941 and 80 more

The Stateless Hash-Based Digital Signature Algorithm, a quantum-resistant signature scheme standardized by NIST in FIPS 205. It was previously known as SPHINCS+.

Plain language A quantum-resistant signature method built from scrambling functions.

Used in RFC 9814 RFC 9909

The most recent stretch of data that a compressor or decompressor can point back into. In DEFLATE it is the previous 32K bytes, and it moves forward as new data is processed.

Plain language A short memory of recent data that moves forward as new data comes in.

Used in RFC 700 RFC 714 RFC 813 RFC 935 RFC 998 RFC 1323 RFC 1381 RFC 1663 RFC 1951 RFC 1967 RFC 1974 RFC 1979 RFC 2018 RFC 2118 RFC 2203 RFC 2395 RFC 2402 RFC 2488 RFC 2562 RFC 2637 RFC 2661 RFC 3081 RFC 3095 RFC 3124 and 23 more

A simple way to carry IP packets over a serial line. The version this RFC refers to has no packet type field, no version numbers and no option exchange.

Used in RFC 914 RFC 1144 RFC 1207 RFC 2138 RFC 2341

A group of timeslots that repeats over and over in a TSCH network. Each cell in it is a timeslot and channel offset pair that can be scheduled for sending or receiving.

Plain language A repeating timetable telling each device when it may transmit or receive.

Used in RFC 7554 RFC 8180 RFC 9030

The initial phase of a congestion control algorithm, in which the sender raises its sending rate step by step to find how much the path can carry.

Plain language The initial congestion control phase raising sending rate gradually.

Used in RFC 2309 RFC 2416 RFC 2488 RFC 2525 RFC 2581 RFC 2757 RFC 2914 RFC 3155 RFC 3390 RFC 3465 RFC 3738 RFC 3742 RFC 4341 RFC 4654 RFC 5681 RFC 5682 RFC 5690 RFC 5783 RFC 6349 RFC 6928 RFC 7661 RFC 8257 RFC 8337 RFC 9002 and 4 more

A TCP control variable that marks the boundary between slow-start (exponential growth) and congestion avoidance (linear growth). It serves as a memory of recent network conditions.

Plain language A record of how fast data could go before, for safe speed-up.

Used in RFC 2001 RFC 2488 RFC 2581 RFC 2861

An attack on static Diffie-Hellman keys in which a bad public key lets an attacker learn information about the private key. Validating the received public key helps to prevent it.

Plain language A trick using rigged numbers to learn parts of a secret key.

Used in RFC 2631 RFC 2785 RFC 6989

A small, resource-constrained device with limited memory, processing power, and battery capacity that connects to the Internet and may sense, process or control physical systems.

Plain language A small internet-connected device like sensors or smart bulbs.

Used in RFC 6574 RFC 7397 RFC 7452

A language and framework for defining management information used by SNMP and MIB (Management Information Base) specifications.

Plain language A language for describing network information managed by SNMP.

Used in RFC 1065 RFC 1109 RFC 1155 RFC 1229 RFC 1285 RFC 1724 RFC 1902 RFC 2287 RFC 3216 RFC 3295 RFC 3410 RFC 3584 RFC 3780 RFC 4113 RFC 6632 RFC 8096

An attribute that lists the algorithms a mail system supports, so that a sender can pick one the recipient will understand. Each entry is a capability identifier with optional parameters.

Plain language A list of the algorithms a mail system can handle. Senders read it to choose a method the recipient will understand.

Used in RFC 2633 RFC 3274 RFC 5703 RFC 5754

Structure of Management Information, Next Generation. A protocol-independent data definition language for describing network device attributes, events and capabilities more expressively than earlier management information languages.

Used in RFC 3780 RFC 3781

The Structure of Management Information Version 2, which defines the data types used by SNMP management information bases. Many YANG types have an equivalent SMIv2 type.

Plain language The rulebook for describing network information in SNMP management bases.

Used in RFC 1447 RFC 1512 RFC 1748 RFC 1749 RFC 2021 RFC 2579 RFC 3216 RFC 3273 RFC 3289 RFC 3295 RFC 3410 RFC 3621 RFC 3705 RFC 3780 RFC 3813 RFC 3877 RFC 4546 RFC 6933 RFC 9911

The Simple Mail Transfer Protocol. A sender-SMTP and a receiver-SMTP exchange commands and replies to pass a message and its envelope addresses from one host to the next.

Plain language The protocol for passing mail messages from server to server.

Used in RFC 469 RFC 543 RFC 751 RFC 759 RFC 771 RFC 772 RFC 773 RFC 784 RFC 788 RFC 800 RFC 801 RFC 808 RFC 817 RFC 821 RFC 822 RFC 832 RFC 833 RFC 834 RFC 835 RFC 836 RFC 837 RFC 838 RFC 839 RFC 840 and 252 more

An SMTP extension, defined in RFC 4954, that lets a client prove who it is to the server before sending mail. RFC 6409 requires submission servers to support it and to require it by default.

Plain language Showing identification to the mail server before sending messages.

Used in RFC 2476 RFC 2505 RFC 2554 RFC 2645 RFC 2821 RFC 3013 RFC 3207 RFC 3848 RFC 3865 RFC 4405 RFC 4409 RFC 4468 RFC 4616 RFC 4870 RFC 4954 RFC 5068 RFC 5248 RFC 5550 RFC 6409 RFC 6710 RFC 7001 RFC 7601 RFC 8601 RFC 9057 and 1 more

A three-digit number that starts every SMTP server reply. The first digit gives the class: 2 for success, 3 for a request for more input, 4 for a temporary failure and 5 for a permanent failure.

Plain language A three-digit code indicating success, waiting, temporary failure or rejection.

Used in RFC 821 RFC 1211 RFC 1651 RFC 1652 RFC 1653 RFC 1845 RFC 1846 RFC 1861 RFC 1869 RFC 1870 RFC 1893 RFC 1894 RFC 1985 RFC 2033 RFC 2034 RFC 2476 RFC 2505 RFC 2789 RFC 2821 RFC 2852 RFC 2920 RFC 3030 RFC 3207 RFC 3461 and 17 more

The SMTP extension for internationalized email. It allows UTF-8 characters in the local part of an address and U-labels in the domain.

Plain language An extension to SMTP, the protocol that delivers email, that lets email addresses use letters from any writing system instead of only basic English letters.

Used in RFC 6531 RFC 6532 RFC 6533 RFC 6783 RFC 9873

Systems Network Architecture, IBM's networking architecture for connecting terminals, controllers and hosts.

Plain language IBM's networking architecture for connecting terminals and computers.

Used in RFC 1538 RFC 1576 RFC 1593 RFC 1795 RFC 2114 RFC 2166

A protocol that extends the LLC layer to carry multiple protocol types by including an organization code and protocol type identifier.

Plain language A protocol identifying message type so networks know if it's Internet or other.

Used in RFC 1103 RFC 1188 RFC 1329 RFC 1356 RFC 1932 RFC 2297 RFC 2390 RFC 2427

The Sub-Network Access Protocol header, which follows the 802.2 LLC header and carries an organization code and a protocol type such as an EtherType.

Plain language A small label on a message saying what kind of message is inside.

Used in RFC 1188 RFC 1390 RFC 1490 RFC 2684

The Simple Network Management Protocol. It lets a management program read and set values on a remote device by talking to an agent on it.

Plain language A protocol for reading and changing remote network device settings.

Used in RFC 1021 RFC 1023 RFC 1052 RFC 1060 RFC 1065 RFC 1066 RFC 1067 RFC 1089 RFC 1098 RFC 1109 RFC 1123 RFC 1147 RFC 1155 RFC 1156 RFC 1157 RFC 1158 RFC 1161 RFC 1162 RFC 1180 RFC 1187 RFC 1189 RFC 1207 RFC 1208 RFC 1212 and 591 more

Software running on a network device that receives SNMP requests from managers and responds with information from the device's MIB.

Plain language Software on a network device answering a manager's questions remotely.

Used in RFC 1098 RFC 1157 RFC 1229 RFC 1270 RFC 1285 RFC 1441 RFC 1442 RFC 1448 RFC 1449 RFC 1904 RFC 1905 RFC 1906 RFC 2287 RFC 2571 RFC 2575 RFC 3295 RFC 3410 RFC 3512 RFC 3705 RFC 3813 RFC 4639 RFC 5343 RFC 6933

A collection of management information accessible by an SNMP entity, identified by a contextEngineID and a contextName. The same item of information can exist in more than one context.

Plain language A labeled collection of management information in an SNMP entity.

Used in RFC 1447 RFC 2571 RFC 2575 RFC 3411 RFC 4088 RFC 5343 RFC 6933

The part of an SNMP entity that sends and receives messages, authenticates and encrypts them, and controls access to managed objects. It is identified by an snmpEngineID.

Plain language The core system handling SNMP message transmission and processing.

Used in RFC 2571 RFC 2574 RFC 2575 RFC 3410 RFC 3411 RFC 3412 RFC 3826 RFC 3877 RFC 5343 RFC 5592

A message an SNMP entity sends to report that an event has occurred or a condition is present. It is either an unconfirmed trap or a confirmed inform request.

Plain language An alarm a device sends when something notable happens.

Used in RFC 1446 RFC 1904 RFC 1905 RFC 2576 RFC 3014 RFC 3295 RFC 3512 RFC 3812 RFC 3877 RFC 3970 RFC 4547 RFC 4639 RFC 5592 RFC 5675 RFC 5907

An unsolicited notification an SNMP agent sends to a manager when something notable happens, instead of waiting to be polled.

Plain language A device notification sent when something happens without being asked.

Used in RFC 1215 RFC 1227 RFC 1246 RFC 1448 RFC 1628 RFC 1666 RFC 1697 RFC 1905 RFC 3512 RFC 3805 RFC 3877 RFC 4750

A conceptual execution context in SNMPv2 with defined security policies, authentication and privacy protocols, and permissions to access specific managed objects.

Plain language A user account with security rules for accessing specific information.

Used in RFC 1353 RFC 1441 RFC 1447 RFC 3826

The Simple Network Time Protocol, a simplified way for a client to synchronize its system clock with a time server.

Plain language A simple way for computers to synchronize clocks with time servers.

Used in RFC 2030 RFC 4075

The Start of Authority record at the top of a DNS zone. It holds the zone's primary server, contact, serial number and timers, and its last field sets the negative-answer TTL.

Plain language The DNS zone record holding authority, contact and timing information.

Used in RFC 883 RFC 1033 RFC 1183 RFC 1537 RFC 1713 RFC 1912 RFC 1982 RFC 1995 RFC 1996 RFC 2136 RFC 2181 RFC 2182 RFC 2308 RFC 3007 RFC 5936 RFC 6303 RFC 7477 RFC 7534 RFC 7706 RFC 8020 RFC 8765 RFC 8976 RFC 9103 RFC 9432 and 1 more

Simple Object Access Protocol, a protocol for exchanging structured information in distributed environments using XML as its message format.

Plain language A protocol for exchanging structured information using XML messages.

Used in RFC 4227 RFC 4743 RFC 5381 RFC 7878

The XML wrapper element containing a SOAP message, with optional headers and a required body containing the actual message content.

Used in RFC 3288 RFC 4227

An IP address together with a port number, identifying one end of a TCP connection. A connection is identified by the pair of sockets at its two ends.

Plain language An IP address and port number identifying one end of a connection.

Used in RFC 1 RFC 33 RFC 36 RFC 39 RFC 44 RFC 46 RFC 48 RFC 49 RFC 54 RFC 55 RFC 56 RFC 57 RFC 60 RFC 65 RFC 66 RFC 74 RFC 76 RFC 80 RFC 93 RFC 97 RFC 98 RFC 100 RFC 101 RFC 105 and 126 more

SOCKSv5 is a protocol (RFC 1928) for routing network packets and DNS lookups through an application-layer gateway or proxy server, often used for firewall traversal and now for protocol translation in the IPv6/IPv4 gateway mechanism.

Used in RFC 1928 RFC 3089

A type of circuit that combines aspects of permanent and switched connections, with a pre-provisioned permanent segment that can be associated with temporary switched segments dynamically.

Plain language A circuit combining permanent backbone with dynamic access segments.

Used in RFC 3474 RFC 4139 RFC 5493

State that has a limited lifetime and disappears unless it is refreshed in time. If the owner goes quiet, the state cleans itself up.

Plain language Information that disappears unless refreshed within a time limit.

Used in RFC 1102 RFC 1633 RFC 1853 RFC 2205 RFC 2961 RFC 3210 RFC 3903 RFC 4080 RFC 4094 RFC 4733 RFC 5973 RFC 5978 RFC 9176

An approach that separates control elements from forwarding components, so software running in a centralized controller can program the devices in the network to behave in specific ways.

Plain language Centralized control programming network devices to behave in specific ways.

Used in RFC 7426 RFC 7576 RFC 8192 RFC 8283 RFC 9050

A tunnel encapsulating one protocol family within another, for example IPv4 packets within IPv6.

Plain language A tunnel carrying older-style addresses inside newer-style network envelopes.

Used in RFC 5512 RFC 5565 RFC 5571 RFC 5619 RFC 5640 RFC 6334 RFC 6674 RFC 6908 RFC 7040 RFC 7596 RFC 7785 RFC 8026 RFC 8513 RFC 8539 RFC 8658 RFC 8676

A link-local multicast address computed from the low-order bits of a unicast address. Neighbor Solicitations for that address are sent to it, so only the few nodes that share those bits need to listen.

Plain language A small group address limiting neighbor discovery to relevant devices.

Used in RFC 2373 RFC 2375 RFC 2461 RFC 2462 RFC 2470 RFC 2491 RFC 2529 RFC 3146 RFC 3513 RFC 3590 RFC 4861 RFC 4862 RFC 5798 RFC 6059 RFC 6164 RFC 6820 RFC 6957 RFC 7048 RFC 7219 RFC 8929 RFC 8981 RFC 9131 RFC 10028

Synchronous Optical Network, a standard for transmitting data over fiber-optic lines at high speeds, developed in North America.

Plain language A standard for very fast data transmission through fiber-optic cables.

Used in RFC 1595 RFC 1619 RFC 2173 RFC 2174 RFC 2175 RFC 2615 RFC 2761 RFC 2823 RFC 3471 RFC 3473 RFC 3592 RFC 4207 RFC 4842 RFC 6310 RFC 6383

Synchronous Optical Network and Synchronous Digital Hierarchy, standards for sending digital data over optical links, which MAPOS uses as its underlying transmission.

Plain language Standards for high-speed data transmission over fiber-optic cables.

Used in RFC 2171 RFC 2172 RFC 2175 RFC 2615 RFC 3255 RFC 3592 RFC 3604 RFC 4139 RFC 4207 RFC 4842

One entry in an LDAP sort key list: an attribute type, an optional matching rule that says how values are compared, and a flag that reverses the order for that key.

Plain language One field to sort results by, together with the rule for comparing its values and whether to reverse the order.

Used in RFC 2891 RFC 4790

An MSDP message that tells peers a source is actively sending to a multicast group, so other domains can learn about it. It is abbreviated SA.

Plain language A notification that a sender is actively broadcasting to a multicast group.

Used in RFC 3618 RFC 4611

Forging the source IP address of a packet to impersonate another host or network.

Plain language Forging a packet's source address to impersonate another host.

Used in RFC 5210 RFC 6959

Checking that the source address of a packet is one that the sender is actually allowed to use. It helps stop address spoofing.

Plain language Checking that a packet's source address belongs to the sender.

Used in RFC 6620 RFC 7039 RFC 7219 RFC 7513 RFC 8704

A group of consecutive source packets that are protected together as a unit by an FEC scheme, assigned a unique source block number for identification.

Plain language A group of packets protected together by error recovery mechanisms.

Used in RFC 5052 RFC 5445 RFC 6363 RFC 6681 RFC 6801

The ability for a listener to ask for multicast traffic only from named senders, or from every sender except named ones.

Plain language Choosing to receive multicast from named senders or all except named ones.

Used in RFC 3376 RFC 3810 RFC 5186 RFC 9776 RFC 9777

An ICMP message that a gateway or host sends to a datagram's source to ask it to cut back the rate at which it sends traffic to that destination.

Plain language A message asking a sender to reduce transmission rate.

Used in RFC 896 RFC 970 RFC 1016

An IP option in which the sender lists the routers a packet should pass through. It can be strict, where each hop must be adjacent, or loose.

Plain language Listed routers a packet should pass through on the envelope.

Used in RFC 1383 RFC 1702 RFC 1812 RFC 6997

A bridging method in which the sender places the path to the destination, a list of bridge and LAN segment numbers, in a routing information field of the frame.

Plain language The sender listing the route through bridges on the envelope.

Used in RFC 1638 RFC 2470 RFC 3518

Specifying the path that a message should take through multiple hosts to reach its destination, including intermediate relay points.

Plain language Specifying the exact path a message should take through the network.

Used in RFC 780 RFC 805 RFC 1383 RFC 1454 RFC 1525 RFC 1749 RFC 4728 RFC 6550 RFC 6554 RFC 7855 RFC 8138 RFC 8218 RFC 9914

A form of multicast where a receiver subscribes to a channel written (S,G): traffic from one specific source S sent to a group address G.

Plain language Multicast where receivers choose both the source and the group.

Used in RFC 3678 RFC 3738 RFC 3810 RFC 3913 RFC 3956 RFC 3973 RFC 4604 RFC 4605 RFC 4607 RFC 4608 RFC 4609 RFC 5132 RFC 5135 RFC 5374 RFC 5740 RFC 5757 RFC 5760 RFC 5790 RFC 6051 RFC 6128 RFC 6308 RFC 6450 RFC 7450 RFC 7667 and 7 more

The API or protocol a controller uses to communicate with and control network devices (switches, routers, etc.). Common examples are OpenFlow and NETCONF.

Plain language The API letting a controller communicate with and control network devices.

Used in RFC 7426 RFC 8456

The Layer 2 protocol used by 802.1 bridges to avoid loops by blocking redundant ports, so frames follow a single tree of active links.

Plain language A Layer 2 protocol blocking redundant ports to prevent frame loops.

Used in RFC 1459 RFC 2174 RFC 4605 RFC 4957 RFC 5556 RFC 6325 RFC 6439

A bridge protocol that forms a tree over connected bridges by blocking some links, so that forwarding loops are avoided.

Plain language A bridge protocol avoiding loops by blocking redundant links.

Used in RFC 1220 RFC 1493 RFC 1638 RFC 2643 RFC 3518 RFC 4188 RFC 4318 RFC 5171 RFC 7727 RFC 7938

A domain name reserved for a particular purpose, which software may handle differently from ordinary names. The name resolver.arpa is one example.

Plain language A domain name reserved for a particular purpose like testing.

Used in RFC 6761 RFC 7686 RFC 8244 RFC 8375 RFC 9462

An IMAP mailbox with an attribute that marks its purpose, such as drafts, sent messages or junk mail. Clients find it by attribute rather than by name.

Plain language An IMAP folder with a label saying what it stores, like drafts.

Used in RFC 6154 RFC 8579

Sender Policy Framework. A way for a domain to say which hosts may send mail using it, checked against the SMTP MailFrom or HELO/EHLO domain.

Plain language A way for domains to list which mail servers may send using their names.

Used in RFC 4408 RFC 4871 RFC 5303 RFC 5451 RFC 5518 RFC 6652 RFC 6686 RFC 7001 RFC 7489 RFC 7960 RFC 8601 RFC 8617 RFC 9989 RFC 9990 RFC 9991

A DNS TXT or SPF record published by a domain that lists the IP addresses and hostnames of mail servers authorized to send mail from that domain.

Plain language A DNS entry listing mail servers authorized to send for a domain.

Used in RFC 4406 RFC 7208

Security Parameter Index. A number that identifies a particular Security Association. IKE headers carry two 8-byte SPIs, and ESP and AH use 4-byte SPIs.

Plain language A number identifying which security agreement a packet belongs to.

Used in RFC 1825 RFC 1829 RFC 1851 RFC 2006 RFC 2085 RFC 2205 RFC 2207 RFC 2332 RFC 2367 RFC 2401 RFC 2402 RFC 2406 RFC 2521 RFC 2522 RFC 3102 RFC 3104 RFC 3173 RFC 3554 RFC 3585 RFC 3715 RFC 3753 RFC 3957 RFC 4004 RFC 4106 and 34 more

A fingerprint, usually a SHA-256 hash, of a server's Subject Public Key Info. A client that holds a set of pins accepts only servers whose keys match one of them.

Plain language A fingerprint of a server's key that clients verify to avoid interception.

Used in RFC 7469 RFC 7858 RFC 8310 RFC 9464

A rule that a router does not advertise a route back out the interface from which it learned it. With poisoned reverse it does advertise it, but with an infinite metric (16 in RIP).

Plain language Not advertising a route back out the interface you learned it from.

Used in RFC 1058 RFC 1075 RFC 1582 RFC 1918 RFC 2080 RFC 2091 RFC 2453 RFC 4762 RFC 6147 RFC 6368 RFC 6550 RFC 6957 RFC 7432 RFC 7623 RFC 7782 RFC 8317 RFC 8361 RFC 8365 RFC 8388 RFC 8560 RFC 8598 RFC 8695 RFC 9014 RFC 9464 and 8 more

A CAPWAP mode in which the 802.11 MAC functions are divided between the WTP and the AC. In Local MAC mode, by contrast, the WTP handles encryption itself.

Plain language Dividing Wi-Fi functions between the access point and its controller.

Used in RFC 4564 RFC 5414 RFC 5415 RFC 5416 RFC 7494

A VPN setup that sends only traffic for chosen destinations through the tunnel. All other traffic goes out directly and is not carried by the VPN.

Plain language Sending only office traffic through a VPN while other traffic goes directly.

Used in RFC 4093 RFC 7359 RFC 8598

The registry client, usually a registrar, that is responsible for an object and is allowed to change it.

Plain language The company responsible for a registry entry and allowed to change it.

Used in RFC 5730 RFC 5732 RFC 8590

A retransmission timeout that fires even though the original data was not actually lost, only delayed in transit.

Plain language Resending data that wasn't lost, only delayed in delivery.

Used in RFC 3481 RFC 3522 RFC 4015 RFC 5682 RFC 7765

An ordered list of segments that represents a source-routed policy, identified by headend, color and endpoint. It holds one or more candidate paths, of which one is active.

Plain language A named travel plan telling routers which segments to write on packets.

Used in RFC 9256 RFC 9831 RFC 9857 RFC 9862 RFC 9933 RFC 9960

The Segment Routing Global Block, a block of labels configured on a node and used for global segments. A node's block is a local property and can differ from other nodes.

Plain language The range of numbers a router sets aside for its segment identifiers.

Used in RFC 8669 RFC 8670

The Secure Real-time Transport Protocol. A profile of RTP that encrypts and authenticates media packets and protects them against replay.

Plain language RTP with encryption and authentication protecting all media packets.

Used in RFC 3323 RFC 3550 RFC 3711 RFC 3830 RFC 3951 RFC 3952 RFC 3959 RFC 3960 RFC 4040 RFC 4046 RFC 4102 RFC 4103 RFC 4170 RFC 4184 RFC 4348 RFC 4352 RFC 4383 RFC 4396 RFC 4425 RFC 4442 RFC 4563 RFC 4566 RFC 4567 RFC 4568 and 138 more

A DNS record type (RFC 2782) that tells a client which hosts and ports provide a given service for a domain, with priorities and weights. XMPP uses _xmpp-client._tcp and _xmpp-server._tcp.

Plain language A DNS entry saying which hosts and ports provide a service.

Used in RFC 2168 RFC 2219 RFC 2782 RFC 3088 RFC 3123 RFC 3263 RFC 3319 RFC 3340 RFC 3361 RFC 3403 RFC 3404 RFC 3486 RFC 3529 RFC 3596 RFC 3620 RFC 3832 RFC 3861 RFC 3887 RFC 3920 RFC 3958 RFC 4038 RFC 4077 RFC 4085 RFC 4168 and 60 more

A prefix configured on a node that covers the set of SRv6 SIDs provisioned there. It is advertised as a Prefix NLRI with the SRv6 Locator TLV.

Plain language A prefix covering all segment identifiers provisioned on a node.

Used in RFC 9352 RFC 9514 RFC 9723 RFC 10038

A 128-bit identifier for a segment in Segment Routing over IPv6. It has locator, function and argument parts, and a behavior is bound to it on the node that owns it.

Plain language A 128-bit identifier for a segment in IPv6 segment routing.

Used in RFC 9352 RFC 9514 RFC 9819 RFC 9831

Secure Shell, a protocol for secure remote login and other secure network services over an insecure network. It combines a transport layer, user authentication and a connection layer that carries channels.

Plain language A protocol for secure remote login and network services.

Used in RFC 2179 RFC 2504 RFC 3535 RFC 3871 RFC 4111 RFC 4250 RFC 4251 RFC 4252 RFC 4253 RFC 4255 RFC 4256 RFC 4335 RFC 4344 RFC 4345 RFC 4419 RFC 4432 RFC 4462 RFC 4716 RFC 4742 RFC 4778 RFC 4819 RFC 5114 RFC 5277 RFC 5590 and 60 more

A numbered, flow-controlled stream inside an SSH connection. Shells, commands, X11 windows and forwarded TCP connections each get their own channel, and many channels share one encrypted connection.

Plain language One of many separate conversations sharing a single encrypted connection.

Used in RFC 4250 RFC 4254 RFC 4256 RFC 4335 RFC 4742 RFC 4819 RFC 5592 RFC 6242 RFC 8160 RFC 8308 RFC 9987

A predefined service with a host-independent name that a server can start on a session channel, such as a file transfer service, instead of a shell or an arbitrary command.

Plain language A special named service a server can start on a session channel.

Used in RFC 3411 RFC 4254 RFC 4742 RFC 4819 RFC 5592 RFC 6242

The SSH message, number 20, with which each side starts key exchange. It carries a 16-byte random cookie and comma-separated, preference-ordered lists of the key exchange, host key, cipher, MAC and compression algorithms the sender supports.

Plain language The SSH_MSG_KEXINIT message where each side sends its list of preferred algorithms.

Used in RFC 4253 RFC 8732 RFC 9142

Synchronization source identifier. A 32-bit number in each RTP header that names the sender of a stream. SRTP mixes it into the encryption IV.

Plain language A 32-bit number in media packets identifying the stream's sender.

Used in RFC 1889 RFC 2508 RFC 2658 RFC 2762 RFC 2862 RFC 2959 RFC 3158 RFC 3550 RFC 3611 RFC 3711 RFC 4568 RFC 4571 RFC 4585 RFC 4588 RFC 4695 RFC 4696 RFC 5104 RFC 5109 RFC 5135 RFC 5404 RFC 5506 RFC 5576 RFC 5725 RFC 5760 and 78 more

Any property a client discloses that does not change over time, or changes very infrequently, and is unique for that client in a given context. A MAC address, a client-id and a hostname are examples.

Plain language A property of a device that stays the same or changes very infrequently.

Used in RFC 6973 RFC 7819 RFC 7824

A route that a Receiving Speaker has kept from a peer whose session ended but has not yet deleted. It is still used for forwarding until the peer returns or the stale timer runs out.

Plain language An old route kept until the peer returns or a timer expires.

Used in RFC 8538 RFC 9494

A protocol specification that has completed the Internet standardization process and is recommended for use on the Internet.

Plain language A protocol specification approved and recommended for Internet use.

Used in RFC 3000 RFC 3300 RFC 7841

The multi-stage procedure by which the IETF moves a technical specification from Proposed Standard through Draft Standard to Internet Standard, based on implementation experience and consensus.

Plain language The stages moving specifications from proposed to official standard.

Used in RFC 2700 RFC 2800 RFC 2900 RFC 3935

An international, open, voluntary organization that develops technical standards and specifications for use on the public Internet, such as the IETF, ITU, W3C, or ETSI.

Plain language A group developing technical standards for Internet technology.

Used in RFC 2690 RFC 2691 RFC 4052 RFC 5704

The path of maturity levels a specification follows on the way to becoming an Internet Standard.

Plain language The path a specification follows to become an Internet Standard.

Used in RFC 72 RFC 804 RFC 1007 RFC 1100 RFC 1120 RFC 1140 RFC 1199 RFC 1200 RFC 1250 RFC 1264 RFC 1280 RFC 1310 RFC 1311 RFC 1360 RFC 1396 RFC 1399 RFC 1410 RFC 1500 RFC 1540 RFC 1599 RFC 1600 RFC 1601 RFC 1602 RFC 1610 and 158 more

A top-level XML element sent over an established XMPP stream. There are three kinds: message, presence and iq.

Plain language A top-level XML element sent over an XMPP stream.

Used in RFC 3920 RFC 3921 RFC 3922 RFC 3923 RFC 5122 RFC 5437 RFC 6120 RFC 6121 RFC 7247 RFC 7395 RFC 7572 RFC 7702 RFC 8600

A Short-Term, Automatically Renewed X.509 certificate. It has a short lifetime and is renewed automatically through ACME instead of being revoked when it is no longer needed.

Plain language A short-lived certificate automatically renewed instead of revoked.

Used in RFC 8739 RFC 9538

A command that upgrades an existing, unencrypted connection to TLS in place, instead of using a separate port for encrypted traffic. In XMPP it is the <starttls/> element.

Plain language A command upgrading an unencrypted connection to TLS in place.

Used in RFC 821 RFC 2222 RFC 2595 RFC 2829 RFC 2830 RFC 3062 RFC 3207 RFC 3501 RFC 3502 RFC 3656 RFC 3788 RFC 3848 RFC 3887 RFC 3909 RFC 3920 RFC 4217 RFC 4261 RFC 4314 RFC 4409 RFC 4422 RFC 4468 RFC 4511 RFC 4513 RFC 4521 and 50 more

Data the SCTP server puts in its INIT ACK so it need not keep any state until the client echoes it back in COOKIE ECHO. This protects against SYN-flood-style attacks.

Plain language Data a server uses to avoid keeping state until connection confirmation.

Used in RFC 2960 RFC 4732 RFC 4895 RFC 4960 RFC 6013 RFC 9260

A path computation element that remembers the label switched paths in the network, so messages can refer to a tunnel by an identifier instead of describing it again.

Plain language A route planner remembering previously calculated paths.

Used in RFC 7399 RFC 7491 RFC 8623 RFC 8637 RFC 9050 RFC 9357 RFC 9504

An NFSv4 identifier the server returns to the client to reference the state of a file, such as an open or a delegation.

Plain language A ticket proving what you are allowed to do with a file.

Used in RFC 3010 RFC 3530 RFC 5661 RFC 5662 RFC 7530 RFC 7531 RFC 7862 RFC 7863 RFC 7931 RFC 8881 RFC 9754

A method for IPv6 hosts to automatically configure their own addresses using information from routers, without requiring a DHCP server.

Plain language Hosts automatically configuring addresses using router announcements.

Used in RFC 2462 RFC 2590 RFC 3316 RFC 4076 RFC 4852 RFC 4864 RFC 4941 RFC 4968 RFC 5375 RFC 8106

A protocol in which each request is handled on its own, and the server keeps no memory of earlier requests from the same client. HTTP is stateless, so sessions have to be built on top.

Plain language A protocol where each request is independent and servers keep no memory.

Used in RFC 1094 RFC 1305 RFC 1436 RFC 1546 RFC 1769 RFC 1813 RFC 1945 RFC 2056 RFC 2639 RFC 2765 RFC 2965 RFC 3041 RFC 3091 RFC 3181 RFC 3263 RFC 3320 RFC 3321 RFC 4241 RFC 5969 RFC 6026 RFC 6434 RFC 6436 RFC 6437 RFC 6503 and 18 more

A translation method that needs no per-connection table. It works out the result from the packet itself and from pre-configured information in the translator.

Plain language Translation following fixed rules without keeping conversation tables.

Used in RFC 6144 RFC 6219

A fixed list of common strings that a compressor and decompressor both already know. It lets even the first message be compressed against it.

Plain language A shared list of common strings used to compress even first messages.

Used in RFC 3485 RFC 5112

An identifier of a Tagged Buffer on a node. A peer advertises it, together with an offset and length, so the remote side can place data directly into that buffer.

Plain language A label on a buffer telling the sender exactly where to place data.

Used in RFC 5040 RFC 5041 RFC 5046 RFC 7145

Secure Telephone Identity Revisited, the IETF framework for cryptographically protecting the identity of callers in real-time communications such as SIP calls.

Plain language A framework cryptographically protecting caller identity in real-time calls.

Used in RFC 8816 RFC 8862 RFC 9118 RFC 9795

A dedicated network that connects servers to storage devices such as disks and tape drives. Its job is to give servers fast access to shared storage.

Plain language A dedicated network connecting servers to shared storage devices.

Used in RFC 2625 RFC 3821 RFC 3831 RFC 4171 RFC 4297 RFC 5046

A delivery method in which each host keeps a complete copy of the message and passes it on to the next host, so the sender and the final recipient do not need to be online at the same time.

Plain language Each hop keeping a complete message copy before passing to the next.

Used in RFC 187 RFC 821 RFC 1935 RFC 2542 RFC 2821 RFC 3528 RFC 3997 RFC 4141 RFC 4838 RFC 5050 RFC 5546 RFC 5598 RFC 6257 RFC 7242 RFC 8238 RFC 9052 RFC 9171 RFC 9172 RFC 9174 RFC 9265 RFC 10036

A server's distance, in NTP hops, from a reference clock. Stratum 1 servers are synchronized directly to a reference clock; each step down adds one, up to 15, and 16 means unsynchronized.

Plain language A server's distance in hops from a reference clock in NTP.

Used in RFC 1059 RFC 1305 RFC 1769 RFC 2030 RFC 4149 RFC 4330 RFC 5905 RFC 5906 RFC 5907 RFC 7384 RFC 8633 RFC 9249 RFC 9327 RFC 9769

An independent, bidirectional sequence of frames inside an HTTP/2 connection, identified by a 31-bit integer. Client-initiated streams are odd-numbered, server-initiated even.

Plain language Independent bidirectional frame sequence inside HTTP/2 connection identified by integer.

Used in RFC 7540 RFC 8441 RFC 8650 RFC 9113

A cipher that encrypts data by combining it with a continuous stream of pseudorandom bits called a keystream. RC4 is an example.

Plain language Encryption combining data with a continuous stream of random-looking bits.

Used in RFC 2628 RFC 3686 RFC 4503 RFC 6229 RFC 7008 RFC 7465 RFC 7539 RFC 7905 RFC 8439 RFC 8758

Sending frames from many streams interleaved on a single connection, so that many requests and responses are in progress at once.

Plain language Many requests taking turns on a single connection simultaneously.

Used in RFC 4666 RFC 6084 RFC 8441 RFC 8859 RFC 9113 RFC 9297 RFC 9308 RFC 9621 RFC 9622

A TCP acknowledgment that covers more than two segments of previously unacknowledged data. It can happen by design, because of implementation bugs, or when ACKs are lost.

Plain language One acknowledgment covering many previously unacknowledged segments.

Used in RFC 2923 RFC 3449

A method that converts a passphrase into a symmetric key. OpenPGP defines several, and recommends Argon2 because it is memory hard.

Plain language A method converting a passphrase into a symmetric encryption key.

Used in RFC 2440 RFC 4880 RFC 9580

An older technology for preparing and comparing non-ASCII strings, defined in RFC 3454. XMPP's Nodeprep and Resourceprep were profiles of it.

Plain language An older technology for preparing and comparing non-ASCII strings.

Used in RFC 3454 RFC 3490 RFC 3491 RFC 3722 RFC 4013 RFC 4282 RFC 4518 RFC 4690 RFC 5122 RFC 6122 RFC 6885 RFC 7247 RFC 7564 RFC 7622 RFC 8264 RFC 8265

Spreading a file across several storage components in fixed-size pieces, taken in turn. It allows several devices to serve one file in parallel.

Plain language Spreading a file across storage devices in pieces taken in turn.

Used in RFC 5664 RFC 8881

A part of a syslog message made of named elements, each with a set of name and value parameters. It lets programs attach machine-readable data to a message.

Plain language Named elements with parameters in syslog for machine-readable information.

Used in RFC 5424 RFC 5675 RFC 5848

A common syntax for HTTP header fields, defined in RFC 8941, built from types such as List, String, Token, Integer and Boolean. Cache-Status uses it.

Plain language A common HTTP header syntax for Lists, Strings and other types.

Used in RFC 8941 RFC 9211 RFC 9651

A suffix on a media type name, such as +cbor-seq, that signals the type is built on another media type as its foundation.

Plain language A suffix on media types showing what format they are built on.

Used in RFC 6839 RFC 7303 RFC 8742

A field value composed of multiple components separated by semicolons, such as an address broken into street, city, region, and postal code.

Used in RFC 2426 RFC 9555 RFC 9651

An area into which AS external advertisements are not flooded. Routing to outside destinations uses a default route injected by an area border router.

Plain language A quiet routing area reached outside using a single default route.

Used in RFC 1245 RFC 1246 RFC 1247 RFC 1583 RFC 1765 RFC 2370 RFC 3101 RFC 4915 RFC 5250 RFC 5340

A gateway that is the only link between a local network and the rest of the internet. It is not meant to carry traffic that neither starts nor ends in that local network.

Plain language A gateway that is the only connection between a local network and Internet.

Used in RFC 827 RFC 888 RFC 914

The small DNS client built into a device or operating system. It does not look names up itself; it sends queries to a recursive resolver and uses the answer.

Plain language A small DNS client asking a recursive resolver instead of searching alone.

Used in RFC 1034 RFC 1536 RFC 2845 RFC 3833 RFC 4033 RFC 4035 RFC 4074 RFC 4697 RFC 4986 RFC 5358 RFC 5452 RFC 5625 RFC 6055 RFC 6147 RFC 6731 RFC 6742 RFC 6975 RFC 7706 RFC 7849 RFC 7858 RFC 7871 RFC 8027 RFC 8094 RFC 8244 and 17 more

A TLV nested inside another TLV to add extra information to that one TLV. Receivers ignore and skip sub-TLVs they do not know.

Plain language A labeled field packed inside another labeled field.

Used in RFC 3784 RFC 5305 RFC 5640 RFC 6439 RFC 6827 RFC 7471 RFC 7557 RFC 7981 RFC 8570 RFC 9012 RFC 9352 RFC 9356 RFC 9479

A domain name that sits below another one, such as www.example.com or mail.example.com under example.com.

Plain language A domain name sitting below another, like mail.example.com.

Used in RFC 819 RFC 881 RFC 882 RFC 920 RFC 921 RFC 941 RFC 1032 RFC 1480 RFC 1530 RFC 1535 RFC 1591 RFC 1816 RFC 2146 RFC 2240 RFC 2352 RFC 2377 RFC 3982 RFC 6763 RFC 6797 RFC 7469 RFC 7489 RFC 9272 RFC 9444 RFC 9965 and 1 more

One TCP connection over a single path, used as a part of a Multipath TCP connection. A Multipath TCP connection can have several subflows.

Plain language One TCP connection over a single path in a Multipath TCP connection.

Used in RFC 6182 RFC 6356 RFC 6897 RFC 8041 RFC 8684 RFC 9897

An X.509 certificate extension that lists the identities the certificate is valid for, such as dNSName host names or iPAddress addresses. RFC 2818 says a dNSName here must be used for the host name check if present.

Plain language A certificate extension listing all names it is valid for.

Used in RFC 2818 RFC 2830 RFC 3860 RFC 3923 RFC 4043 RFC 4683 RFC 4945 RFC 4976 RFC 4985 RFC 5734 RFC 5922 RFC 6047 RFC 6125 RFC 6187 RFC 6614 RFC 7817 RFC 8310 RFC 8550 RFC 9115 RFC 9289 RFC 9310 RFC 9462 RFC 9525 RFC 9549 and 6 more

A key derived from a main secret key rather than chosen separately. AES-CMAC derives two subkeys, K1 and K2, from its one key.

Plain language A key derived from a main secret key rather than chosen separately.

Used in RFC 4493 RFC 6091 RFC 9580

The component of a CCSDS URN that categorizes the type of resource (such as "document" or "schema"). Each SNID has its own assignment rules defined by a CCSDS document.

Plain language A category label saying what kind of thing a resource identifier points to.

Used in RFC 6453 RFC 7738

A richer exchange, framed by the Telnet commands SB (250) and SE (240), that carries the details of an option once both sides have agreed with DO/WILL that they understand it.

Plain language A richer exchange settling option details after both sides agree.

Used in RFC 562 RFC 580 RFC 651 RFC 653 RFC 654 RFC 655 RFC 656 RFC 657 RFC 726 RFC 732 RFC 749 RFC 764 RFC 779 RFC 854 RFC 855 RFC 859 RFC 861 RFC 1041 RFC 1043 RFC 1073 RFC 1079 RFC 1091 RFC 1096 RFC 1184 and 7 more

One of several physical networks, such as LAN cables, that share a single Internet network number. A subnet is identified by a subnet number carried in part of the host bits of the address (RFC 950).

Plain language One physical network segment with a single Internet address number.

Used in RFC 917 RFC 919 RFC 922 RFC 925 RFC 932 RFC 936 RFC 940 RFC 950 RFC 985 RFC 995 RFC 1009 RFC 1027 RFC 1044 RFC 1118 RFC 1175 RFC 1209 RFC 1219 RFC 1256 RFC 1366 RFC 1466 RFC 1519 RFC 1709 RFC 1724 RFC 1797 and 46 more

A 32-bit value with bits set for the network number and subnet number of an address (the RFC calls it the address mask). A host ANDs it with two addresses to see whether they are on the same subnet. Written 255.255.255.0 or as a prefix length such as /24.

Plain language A stencil showing which address part is the network and which is the host.

Used in RFC 917 RFC 940 RFC 950 RFC 985 RFC 1027 RFC 1195 RFC 1219 RFC 1338 RFC 1395 RFC 1519 RFC 1533 RFC 1721 RFC 1722 RFC 1723 RFC 1860 RFC 1878 RFC 2096 RFC 2131 RFC 2226 RFC 2453 RFC 3011 RFC 3021 RFC 3442 RFC 3527 and 5 more

An IPv6 address, formed from the subnet prefix with all zeros in the rest, that reaches any one router on that link. It is defined in RFC 4291.

Plain language An address reaching any router on a subnet link.

Used in RFC 3627 RFC 5375 RFC 6164

A request from one user to receive notifications of another user's presence status changes.

Plain language A request to be notified when someone comes online.

Used in RFC 2778 RFC 3265 RFC 4660 RFC 7248 RFC 8641 RFC 9685

A value used with BGP multiprotocol extensions to identify a specific type of network layer reachability information, such as unicast routes, multicast routes, or VPN routes.

Plain language A BGP identifier specifying the type of routing information being exchanged.

Used in RFC 2858 RFC 3107 RFC 4684 RFC 5512 RFC 8277

A set of public cryptographic algorithms for key exchange, digital signatures, hashing and encryption, announced by the US National Security Agency in 2005. It was chosen from algorithms approved by NIST.

Plain language An approved list of cryptographic algorithms for government security.

Used in RFC 6239 RFC 6318 RFC 6380 RFC 6460

Application-level information sent inside a TLS handshake message. TLS itself does not process it; it is meant for the protocols and applications above TLS.

Plain language Application information sent inside TLS handshakes for the application.

Used in RFC 4680 RFC 5878 RFC 7562

The IEEE 802.1X name for the end of a link that responds to the authenticator and asks for network access. EAP calls the same role the peer.

Plain language The device or person asking for network access and authentication.

Used in RFC 3580 RFC 3748 RFC 7268

A caching server in a content network that stores copies of content and serves requests from clients, reducing the load on the origin server.

Plain language A caching server that stores content copies and serves them to reduce load on the origin.

Used in RFC 3040 RFC 3454 RFC 3466 RFC 3507 RFC 3568 RFC 3570 RFC 6707 RFC 6983 RFC 7337 RFC 7937 RFC 8006

Two UTF-16 code units that together represent a character outside the Basic Multilingual Plane. In JSON strings such a character can be written as two \uXXXX escapes.

Plain language Two code units combined to represent a character outside the standard Unicode range.

Used in RFC 2781 RFC 3629 RFC 5137 RFC 7159 RFC 7493 RFC 8259 RFC 9839

A DNS record type, Service Binding, that tells a client how to reach a service, such as which protocols, ports and alternate names to use.

Plain language A DNS record that tells clients which protocols, ports and names to use for a service.

Used in RFC 9462 RFC 9463 RFC 9540 RFC 9848

A group of peers participating in the distribution of the same streaming content at a given time.

Plain language A group of peers sharing the same streaming content at the same time.

Used in RFC 5594 RFC 5632 RFC 5694 RFC 6972 RFC 7574 RFC 7846

A Software Identification tag is a record that identifies and describes a software component, patch or installation bundle. It is defined in ISO/IEC 19770-2:2015 as XML.

Plain language A record that identifies and describes a software component, patch or installation bundle.

Used in RFC 8412 RFC 9393

A provider edge router in the middle of a multi-segment pseudowire that switches the control and data planes of the segment before it to the segment after it.

Plain language A provider edge router that switches control and data planes between segments of a pseudowire.

Used in RFC 5254 RFC 7267

An attack in which one person creates many fake identities in a network to gain disproportionate control or influence.

Plain language An attack where one person creates many fake identities to gain disproportionate control in a network.

Used in RFC 5694 RFC 5765 RFC 7416

Encryption where the same secret key is used both to encrypt and decrypt; the sender and receiver must share the key beforehand.

Plain language Encryption using the same secret key for both encryption and decryption by both parties.

Used in RFC 1446 RFC 1898 RFC 2660 RFC 3565 RFC 3766 RFC 4880 RFC 5794 RFC 6031 RFC 9640

A NAT that may map the same internal address and port to a different external address and port for each destination. It accepts packets only from hosts the internal host has already sent to.

Plain language A NAT that maps the same internal address to different external addresses for each destination.

Used in RFC 4380 RFC 5128 RFC 6081 RFC 6780

A denial-of-service attack that sends many TCP SYN packets to make a server hold state for half-open connections until it has no room left for real ones.

Plain language A denial-of-service attack sending many TCP SYN packets to exhaust a server's connection capacity.

Used in RFC 2267 RFC 4732 RFC 7430

An MPLS label that causes the same behavior at the egress router as the label it replaces, but also triggers extra actions agreed in advance, such as counting packets.

Plain language An MPLS label causing the same egress behavior as its replaced label, plus extra agreed actions.

Used in RFC 8957 RFC 9571

A standard way for devices to send log messages to a log server. Each message carries a facility and a severity level.

Plain language A standard protocol for devices to send log messages to a central log server.

Used in RFC 4778 RFC 5425 RFC 5426 RFC 5428 RFC 5675 RFC 5676 RFC 5848 RFC 6012 RFC 6632 RFC 7922 RFC 9232 RFC 9662 RFC 9742

The number at the start of a syslog message that combines the Facility and the Severity. It is calculated as the Facility times 8 plus the Severity.

Plain language A number combining the source facility and severity level of a syslog message.

Used in RFC 3164 RFC 5424