Glossary
O
53 terms.
- O/R Address
In X.400, the structured address used for mail routing, made up of hierarchical attribute-value pairs like Country, Organization, and Personal Name.
Plain language An X.400 address built from attributes like country and organization.
- OAM
Operations, Administration, and Maintenance: the tools and data used to monitor, test and troubleshoot a network.
Plain language Tools and methods for monitoring, testing, and troubleshooting a network.
Used in RFC 3429 RFC 4454 RFC 4717 RFC 5317 RFC 5586 RFC 5654 RFC 5860 RFC 5921 RFC 5950 RFC 6136 RFC 6291 RFC 6310 RFC 6370 RFC 6371 RFC 6372 RFC 6426 RFC 6435 RFC 6905 RFC 7023 RFC 7174 RFC 7260 RFC 7338 RFC 7439 RFC 7455 and 13 more
- OAuth
An authorization protocol, specified in RFC 6749, that lets an application obtain limited access to a resource on a server on behalf of a user without the user handing over their password to the application.
Plain language A way for an app to ask a server for permission to act for you, without seeing your password.
- Object class
A directory definition that lists the attributes an entry must have and may have. Entries are classified by one or more object classes.
Plain language A directory definition specifying required and optional attributes for entries.
Used in RFC 1274 RFC 1309 RFC 1430 RFC 1609 RFC 1803 RFC 2247 RFC 2252 RFC 2254 RFC 2256 RFC 2798 RFC 2969 RFC 3703 RFC 4104 RFC 4512 RFC 4519 RFC 4523 RFC 4524 RFC 7612
- Object identifier
A globally unique dotted-number name, such as 1.2.840.113549.1.7.2, assigned by a hierarchy of authorities. Protocols such as CMS use them to label content types, algorithms and attributes.
Plain language A globally unique dotted-number identifier for protocols, algorithms, or attributes.
Used in RFC 1023 RFC 1065 RFC 1085 RFC 1155 RFC 1156 RFC 1157 RFC 1158 RFC 1187 RFC 1212 RFC 1213 RFC 1215 RFC 1227 RFC 1229 RFC 1230 RFC 1231 RFC 1232 RFC 1233 RFC 1238 RFC 1239 RFC 1253 RFC 1274 RFC 1285 RFC 1303 RFC 1381 and 367 more
- Object Identifier (OID)
A globally unique numeric identifier in dotted notation (for example, 1.3.6.1.4.1.5) used to identify protocol elements, schema components, and other structured data.
Plain language A globally unique dotted-number identifier for protocols and data elements.
Used in RFC 1274 RFC 2021 RFC 2256 RFC 2654 RFC 2829 RFC 2830 RFC 3295 RFC 3410 RFC 3621 RFC 3674 RFC 3703 RFC 3826 RFC 4398 RFC 4520 RFC 4531 RFC 5272 RFC 5755 RFC 5758 RFC 5934 RFC 6482 RFC 7427 RFC 7693
- Objective Function
In RPL, the rule that decides how a node computes its Rank and which neighbors it selects as parents, for example by minimizing hop count.
Plain language A rule determining how a device selects the best path to send traffic.
Used in RFC 5541 RFC 5862 RFC 6550 RFC 6551 RFC 6552 RFC 6719 RFC 8233 RFC 8413 RFC 8685
- Observation Domain
An IPFIX concept identified by a 32-bit Observation Domain ID that is locally unique to the Exporting Process. A Collecting Process can use the Transport Session and the ID to separate export streams from the same Exporter.
- Observation point
A location in the network where packets can be observed. Passive measurement methods collect data at one or more of these points.
Plain language A network location where traffic can be observed for measurement.
Used in RFC 5101 RFC 5472 RFC 5475 RFC 5476 RFC 6313 RFC 6615 RFC 7011 RFC 7799
- OCSP (Online Certificate Status Protocol)
A protocol, defined in RFC 2560, for asking a certificate authority's responder whether a certificate has been revoked. RFC 6066 lets the answer travel inside the TLS handshake.
Plain language A protocol for checking whether a certificate has been revoked.
Used in RFC 2560 RFC 3125 RFC 3379 RFC 3647 RFC 3820 RFC 4366 RFC 4386 RFC 4557 RFC 4738 RFC 4806 RFC 4945 RFC 5019 RFC 5055 RFC 5126 RFC 5216 RFC 5276 RFC 5755 RFC 5912 RFC 5940 RFC 6024 RFC 6066 RFC 6187 RFC 6277 RFC 6283 and 23 more
- OCSP responder
A server that answers certificate status requests, either by building a response on demand or by serving pre-produced signed responses. The responses say whether a certificate is good, revoked or unknown.
- OCSP Stapling
A TLS feature where a server provides a signed OCSP response for its certificate during the handshake, eliminating the need for the client to query an OCSP server separately.
Plain language A TLS feature where servers provide certificate status instead of clients checking.
- Off-path attacker
An attacker who cannot see the packets of a connection and so must guess the values that identify it, such as the client's port number.
Plain language An attacker without access to a connection who must guess its identifying values.
- Offer/answer
A model in which one party sends an SDP offer describing the media it wants to use and the other replies with an SDP answer that accepts, changes or rejects each part.
Plain language A negotiation where one party proposes media and the other responds.
Used in RFC 4568 RFC 4788 RFC 5018 RFC 5956 RFC 6236 RFC 8829 RFC 8839 RFC 8843 RFC 8866 RFC 9143
- Offer/answer model
A two-step negotiation in which one party sends an SDP offer describing what it can do and the other replies with an answer that picks from it.
Plain language A negotiation where one party proposes media options and the other selects.
Used in RFC 3311 RFC 3312 RFC 3407 RFC 3959 RFC 3960 RFC 4145 RFC 4568 RFC 4597 RFC 4975 RFC 5188 RFC 5547 RFC 5939 RFC 6364 RFC 7006 RFC 7362 RFC 7866 RFC 8373 RFC 8840 RFC 8848 RFC 8853 RFC 8858 RFC 9335 RFC 9429 RFC 9584
- OLSRv2
Version 2 of the Optimized Link State Routing Protocol, a proactive routing protocol for mobile ad hoc networks. It distributes topology control messages describing the links between routers.
Plain language A routing protocol for wireless mesh networks that keeps every router informed about the shape of the network.
- On-link
Describes a destination that can be reached directly on the same link without going through a router. Hosts decide this from the prefixes advertised with the L flag and from Redirects.
Plain language A destination reachable directly on the same network link.
- One-time password
A password that is valid for a single use, so a copy captured by an untrusted client or an eavesdropper cannot be used again.
Plain language A password valid for a single use preventing reuse of compromised copies.
Used in RFC 1731 RFC 1938 RFC 2196 RFC 2284 RFC 2289 RFC 2444 RFC 2504 RFC 3169 RFC 3888 RFC 6030 RFC 6560
- One-time signature
A signature key that is safe to use for only one message. Using it for two different messages lets an attacker create forgeries.
Plain language A signature key usable only once; using it for two messages enables forgery.
Used in RFC 8391 RFC 8554 RFC 8708 RFC 8778 RFC 9802 RFC 10033
- One-way delay
The time a packet takes to travel from a sender to a receiver in a single direction. Measuring it needs clocks at both ends that agree closely.
Plain language The time a packet takes to travel in one direction.
Used in RFC 2330 RFC 2679 RFC 2680 RFC 2681 RFC 3357 RFC 3393 RFC 3432 RFC 3763 RFC 4656 RFC 6808 RFC 6817 RFC 7312 RFC 7497 RFC 8382 RFC 8698 RFC 9341 RFC 9342
- One-way key chain
A sequence of keys where each key is computed from the next by a one-way function. Anyone can step backward along the chain from a later key, but nobody can step forward without knowing the start.
Plain language Sequence of keys where each is computed from the next by a one-way function.
- Opaque LSA
A kind of OSPF link-state advertisement that carries extra application-specific information in a general format. Its scope can be link-local, area-wide or domain-wide.
Plain language An OSPF advertisement carrying application-specific information.
Used in RFC 2370 RFC 3623 RFC 5250 RFC 5252 RFC 6827 RFC 7471 RFC 7770 RFC 8379 RFC 8444
- Opcode
A number in a packet that says what kind of message it is. ARP uses 1 and 2 for request and reply, and RARP adds 3 for request reverse and 4 for reply reverse.
Plain language A number in a packet indicating the message type like request or reply.
Used in RFC 120 RFC 265 RFC 281 RFC 550 RFC 826 RFC 903 RFC 1350 RFC 1996 RFC 2136 RFC 2748 RFC 2929 RFC 5395 RFC 6455 RFC 6895 RFC 7843 RFC 8160 RFC 8490 RFC 8618 RFC 8906 RFC 9619 RFC 9669
- Open redirector
An endpoint that uses a parameter to send a user agent to the location in the parameter without validating it. Attackers use it to leak codes or tokens, or to borrow the trust a user has in a site.
Plain language An endpoint that redirects users to any URL without validation, exploitable by attackers.
- Open Relay
A mail server that accepts and forwards email from any sender to any recipient without authentication, allowing spammers to bounce their messages through it to hide their origin.
Plain language A mail server accepting messages from anyone, abused by spammers to hide origins.
- Open Shortest Path First
A routing protocol where routers exchange information about the network topology and each router computes the shortest path to every destination.
Plain language A routing protocol where routers share network topology to compute shortest paths.
Used in RFC 1238 RFC 1245 RFC 1246 RFC 1370 RFC 1403 RFC 1586 RFC 1745 RFC 1765 RFC 2105 RFC 2334 RFC 2370 RFC 2375 RFC 2642 RFC 3101 RFC 3137 RFC 3623 RFC 3719 RFC 3906 RFC 4061 RFC 4062 RFC 4750 RFC 4812 RFC 4915 RFC 5250 and 36 more
- OpenPGP
A standard format for keys, certificates and signed or encrypted messages, defined in RFC 4880. An OpenPGP certificate can hold a primary key and several subkeys.
Plain language A standard format for encryption keys, certificates, and signed messages.
Used in RFC 3156 RFC 4398 RFC 4880 RFC 5585 RFC 6091 RFC 7681
- OpenPGP cleartext signature
A way of signing text with OpenPGP while leaving the text readable. The message is wrapped between a signed-message header and a signature block, as described in RFC 4880, Section 7.
Plain language An OpenPGP signature kept readable with the signed text and signature block.
- Operational attribute
A directory attribute that the server maintains for its own use, rather than ordinary user data. Attributes such as entryUUID are marked with the usage directoryOperation.
Plain language A directory attribute maintained by the server rather than user data.
- OPES
Open Pluggable Edge Services, an IETF framework in which an OPES processor passes application messages to callout servers that adapt them, for example by filtering, translating or logging.
Plain language A framework where network devices can adapt application messages via callout servers.
Used in RFC 3724 RFC 3836 RFC 3838 RFC 3897 RFC 3914 RFC 4236
- OPES Processor
A network element that adapts (modifies, filters, or transforms) application-layer messages according to OPES services.
Plain language A network device that modifies or filters application messages.
- Opportunistic Encryption
A method of automatically setting up encrypted tunnels between systems without prior bilateral arrangement, by looking up encryption capability in DNS.
Plain language Automatically encrypting traffic when both sides support it without prior agreement.
- Opportunistic privacy
Using encryption when it is available but carrying on without it, or without verifying the peer, when it is not. It protects against passive eavesdroppers but not active attackers.
Plain language Using encryption when available but proceeding without it if not, protecting against passive listeners.
Used in RFC 6973 RFC 7435 RFC 7525 RFC 7619 RFC 7671 RFC 7696 RFC 7787 RFC 7858 RFC 8004 RFC 8110 RFC 8280 RFC 8310 RFC 8460 RFC 8862 RFC 9063 RFC 9289 RFC 9462 RFC 9505 RFC 9672
- Opportunistic Security
A design in which a client uses an encrypted channel when the server offers one but does not insist on authenticating it. The connection proceeds even when the authentication check fails, so the client must not treat the channel as trusted.
Plain language A design where the client accepts encryption when it is offered but does not insist on proving who the other side is.
- OPT record
A pseudo resource record, type 41, in the additional section of a DNS message. It carries control information for one exchange and is never cached.
Plain language A DNS pseudo-record carrying control information for one exchange.
Used in RFC 2671 RFC 3225 RFC 5001 RFC 6891 RFC 6975 RFC 7830 RFC 7871 RFC 8145 RFC 8764 RFC 8914 RFC 9567 RFC 9660 RFC 9664
- Optical Cross-Connect
A device that switches light signals from input ports to output ports, either all-optically or by converting to electrical form temporarily.
Plain language A device switching optical signals between ports.
Used in RFC 3471 RFC 3604 RFC 3717 RFC 4054 RFC 4202 RFC 4209 RFC 4847
- Optical Transport Network
A network technology, defined by ITU-T G.709, that carries client signals over optical links inside containers called ODUs and OTUs.
Plain language A fiber-based network technology carrying signals in standard containers.
Used in RFC 3591 RFC 4054 RFC 6827 RFC 7096 RFC 7139 RFC 7449 RFC 8779 RFC 9376
- Option negotiation
Telnet's WILL, WON'T, DO and DON'T exchange, used to agree on features beyond the Network Virtual Terminal. Refusing leaves the connection as a plain NVT.
Plain language A Telnet exchange for agreeing on extended features.
Used in RFC 435 RFC 461 RFC 471 RFC 495 RFC 513 RFC 560 RFC 562 RFC 651 RFC 652 RFC 653 RFC 654 RFC 655 RFC 656 RFC 657 RFC 658 RFC 669 RFC 679 RFC 701 RFC 702 RFC 718 RFC 726 RFC 727 RFC 729 RFC 732 and 63 more
- Options Template
An IPFIX template that describes records carrying extra information about something else, such as a whole message or session, instead of describing flows themselves.
Plain language An IPFIX template for metadata about flows rather than flow data itself.
- OR Address
The originator/recipient address used in X.400 mail. It is built from attributes such as country, administration domain and private domain names.
Plain language An X.400 mail address built from hierarchical attributes.
- ORCHID (Overlay Routable Cryptographic Hash Identifier)
A 128-bit IPv6-like identifier format defined by RFC 4843 for use in overlay networks, with a fixed prefix in the first 28 bits to mark it as cryptographically derived and globally routable within the overlay.
Plain language An identifier format for overlay networks with a fixed prefix marking it as cryptographic.
- Organizational domain
The domain at the top of the namespace hierarchy for a given domain, while still having the same administrative authority over it.
Plain language The domain that owns the one you are looking at, such as example.com for mail.example.com.
- Organizationally Unique Identifier (OUI)
A 3-octet (24-bit) prefix assigned by the IEEE Registration Authority to uniquely identify an organization, forming the first half of a 48-bit MAC address.
Plain language A 24-bit identifier in a MAC address assigned to the manufacturer.
Used in RFC 1968 RFC 2153 RFC 2685 RFC 3772 RFC 5342 RFC 7042 RFC 9542
- Origin server
The server that holds or generates a resource and answers requests for it, as opposed to a proxy or cache in between. Cookies are set by and returned to origin servers.
>Plain language The server holding a resource rather than a proxy or cache.
Used in RFC 2295 RFC 3466 RFC 3568 RFC 6265 RFC 6770 RFC 7230 RFC 7231 RFC 7235 RFC 7807 RFC 7838 RFC 8006 RFC 8010 RFC 8164 RFC 8297 RFC 8336 RFC 8470 RFC 8615 RFC 8674 RFC 9110 RFC 9112 RFC 9211 RFC 9674 RFC 9729 RFC 9842 and 1 more
- OSCORE
Object Security for Constrained RESTful Environments, a way to protect CoAP messages end to end using COSE. It can also secure HTTP.
Plain language A method for end-to-end encryption of CoAP and HTTP messages.
Used in RFC 8824 RFC 9031 RFC 9203 RFC 9528 RFC 9668 RFC 9820 RFC 9953
- OSPF area
A group of OSPF routers and networks that share a link-state database. Dividing an AS into areas reduces the routing information each router handles.
Plain language A group of OSPF routers and networks sharing routing information.
Used in RFC 1131 RFC 1245 RFC 1247 RFC 1248 RFC 1252 RFC 1253 RFC 1584 RFC 1587 RFC 1722 RFC 1765 RFC 1793 RFC 2154 RFC 2178 RFC 2328 RFC 2370 RFC 2740 RFC 2791 RFC 3101 RFC 3166 RFC 3167 RFC 3386 RFC 3509 RFC 3623 RFC 3630 and 94 more
- Ossification
The loss of a protocol's ability to change because middleboxes and implementations come to depend on the exact details of what they see on the wire. QUIC encrypts nearly all of its headers to reduce this.
Plain language Loss of a protocol's ability to change because intermediaries depend on exact details.
Used in RFC 7663 RFC 8546 RFC 8558 RFC 8701 RFC 9000 RFC 9065 RFC 9369 RFC 9419 RFC 9607 RFC 10049
- OTN
Optical Transport Network. The layer 1 technology that carries client signals in optical containers over wavelength links, with those containers multiplexed together and the wavelengths combined by wavelength division multiplexing.
Plain language The part of the network that carries data across fibre as light.
- Outbound Route Filter (ORF)
A filter that a BGP speaker sends to a peer so that the peer limits which routes it sends back. It lets a speaker pull the routes it wants on demand.
Plain language A BGP filter that allows a peer to request only certain routes.
- Overlay network
A network built on top of another network, where participants route messages and store data for each other without a central server.
Plain language A network built on top of another where participants relay messages and data.
Used in RFC 4981 RFC 5693 RFC 5694 RFC 6029 RFC 6940 RFC 7348 RFC 7364 RFC 7365 RFC 7650 RFC 7851 RFC 7890 RFC 7904 RFC 8014 RFC 8345 RFC 9217 RFC 9299 RFC 9521
- Overload bit
A flag in a router's own link state PDU that tells other routers not to compute routes through it. It is used here to signal that the router's database is not yet synchronized.
- Overload control
Mechanisms by which an overloaded node asks others to reduce the traffic they send to it. Senders react by throttling, which rejects some requests, or by diverting requests elsewhere.
Plain language Mechanisms allowing overloaded nodes to request traffic reduction from senders.