IXP Route Server Ops: Internet Exchange BGP Route Server Operations

Internet Engineering Task Force (IETF)                       N. Hilliard
Request for Comments: 7948                                          INEX
Category: Informational                                      E. Jasinska
ISSN: 2070-1721                                               BigWave IT
                                                               R. Raszuk
                                                            Bloomberg LP
                                                               N. Bakker
                                                Akamai Technologies B.V.
                                                          September 2016


             Internet Exchange BGP Route Server Operations

Abstract

   The popularity of Internet Exchange Points (IXPs) brings new
   challenges to interconnecting networks.  While bilateral External BGP
   (EBGP) sessions between exchange participants were historically the
   most common means of exchanging reachability information over an IXP,
   the overhead associated with this interconnection method causes
   serious operational and administrative scaling problems for IXP
   participants.

   Multilateral interconnection using Internet route servers can
   dramatically reduce the administrative and operational overhead
   associated with connecting to IXPs; in some cases, route servers are
   used by IXP participants as their preferred means of exchanging
   routing information.

   This document describes operational considerations for multilateral
   interconnections at IXPs.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7948.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  Bilateral BGP Sessions  . . . . . . . . . . . . . . . . . . .   3
   3.  Multilateral Interconnection  . . . . . . . . . . . . . . . .   4
   4.  Operational Considerations for Route Server Installations . .   6
     4.1.  Path Hiding . . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Route Server Scaling  . . . . . . . . . . . . . . . . . .   6
       4.2.1.  Tackling Scaling Issues . . . . . . . . . . . . . . .   7
         4.2.1.1.  View Merging and Decomposition  . . . . . . . . .   7
         4.2.1.2.  Destination Splitting . . . . . . . . . . . . . .   8
         4.2.1.3.  NEXT_HOP Resolution . . . . . . . . . . . . . . .   8
     4.3.  Prefix Leakage Mitigation . . . . . . . . . . . . . . . .   8
     4.4.  Route Server Redundancy . . . . . . . . . . . . . . . . .   9
     4.5.  AS_PATH Consistency Check . . . . . . . . . . . . . . . .   9
     4.6.  Export Routing Policies . . . . . . . . . . . . . . . . .  10
       4.6.1.  BGP Communities . . . . . . . . . . . . . . . . . . .  10
       4.6.2.  Internet Routing Registries . . . . . . . . . . . . .  10
       4.6.3.  Client-Accessible Databases . . . . . . . . . . . . .  10
     4.7.  Layer 2 Reachability Problems . . . . . . . . . . . . . .  11
     4.8.  BGP NEXT_HOP Hijacking  . . . . . . . . . . . . . . . . .  11
     4.9.  BGP Operations and Security . . . . . . . . . . . . . . .  13
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   Internet Exchange Points (IXPs) provide IP data interconnection
   facilities for their participants, using data link-layer protocols
   such as Ethernet.  The Border Gateway Protocol (BGP) [RFC4271] is
   normally used to facilitate exchange of network reachability
   information over these media.

   As bilateral interconnection between IXP participants requires
   operational and administrative overhead, BGP route servers [RFC7947]
   are often deployed by IXP operators to provide a simple and
   convenient means of interconnecting IXP participants with each other.
   A route server redistributes BGP routes received from its BGP clients
   to other clients according to a prespecified policy, and it can be
   viewed as similar to an EBGP equivalent of an Internal BGP (IBGP)
   [RFC4456] route reflector.

   Route servers at IXPs require careful management, and it is important
   for route server operators to thoroughly understand both how they
   work and what their limitations are.  In this document, we discuss
   several issues of operational relevance to route server operators and
   provide recommendations to help route server operators provision a
   reliable interconnection service.

1.1.  Notational Conventions

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].

   The phrase "BGP route" in this document should be interpreted as the
   term "Route" described in [RFC4271].

2.  Bilateral BGP Sessions

   Bilateral interconnection is a method of interconnecting routers
   using individual BGP sessions between each pair of participant
   routers on an IXP, in order to exchange reachability information.  If
   an IXP participant wishes to implement an open interconnection policy
   -- i.e., a policy of interconnecting with as many other IXP
   participants as possible -- it is necessary for the participant to
   liaise with each of their intended interconnection partners.
   Interconnection can then be implemented bilaterally by configuring a
   BGP session on both participants' routers to exchange network
   reachability information.  If each exchange participant interconnects
   with each other participant, a full mesh of BGP sessions is needed,
   as shown in Figure 1.

                               ___      ___
                              /   \    /   \
                           ..| AS1 |..| AS2 |..
                          :   \___/____\___/   :
                          :     | \    / |     :
                          :     |  \  /  |     :
                          : IXP |   \/   |     :
                          :     |   /\   |     :
                          :     |  /  \  |     :
                          :    _|_/____\_|_    :
                          :   /   \    /   \   :
                           ..| AS3 |..| AS4 |..
                              \___/    \___/

               Figure 1: Full-Mesh Interconnection at an IXP

   Figure 1 depicts an IXP platform with four connected routers,
   administered by four separate exchange participants, each of them
   with a locally unique Autonomous System (AS) number: AS1, AS2, AS3,
   and AS4.  The lines between the routers depict BGP sessions; the
   dotted edge represents the IXP border.  Each of these four
   participants wishes to exchange traffic with all other participants;
   this is accomplished by configuring a full mesh of BGP sessions on
   each router connected to the exchange, resulting in six BGP sessions
   across the IXP fabric.

   The number of BGP sessions at an exchange has an upper bound of
   n*(n-1)/2, where n is the number of routers at the exchange.  As many
   exchanges have large numbers of participating networks, the amount of
   administrative and operation overhead required to implement an open
   interconnection scales quadratically.  New participants to an IXP
   require significant initial resourcing in order to gain value from
   their IXP connection, while existing exchange participants need to
   commit ongoing resources in order to benefit from interconnecting
   with these new participants.

3.  Multilateral Interconnection

   Multilateral interconnection is implemented using a route server
   configured to distribute BGP routes among client routers.  The route
   server preserves the BGP NEXT_HOP attribute from all received BGP
   routes and passes them with unchanged NEXT_HOP to its route server
   clients according to its configured routing policy, as described in
   [RFC7947].  Using this method of exchanging BGP routes, an IXP
   participant router can receive an aggregated list of BGP routes from
   all other route server clients using a single BGP session to the
   route server instead of depending on BGP sessions with each router at
   the exchange.  This reduces the overall number of BGP sessions at an
   Internet exchange from n*(n-1)/2 to n, where n is the number of
   routers at the exchange.

   Although a route server uses BGP to exchange reachability information
   with each of its clients, it does not forward traffic itself and is
   therefore not a router.

   In practical terms, this allows dense interconnection between IXP
   participants with low administrative overhead and significantly
   simpler and smaller router configurations.  In particular, new IXP
   participants benefit from immediate and extensive interconnection,
   while existing route server participants receive reachability
   information from these new participants without necessarily having to
   modify their configurations.

                               ___      ___
                              /   \    /   \
                           ..| AS1 |..| AS2 |..
                          :   \___/    \___/   :
                          :      \      /      :
                          :       \    /       :
                          :        \__/        :
                          : IXP   /    \       :
                          :      |  RS  |      :
                          :       \____/       :
                          :        /  \        :
                          :       /    \       :
                          :    __/      \__    :
                          :   /   \    /   \   :
                           ..| AS3 |..| AS4 |..
                              \___/    \___/

           Figure 2: IXP-Based Interconnection with Route Server

   As illustrated in Figure 2, each router on the IXP fabric requires
   only a single BGP session to the route server, from which it can
   receive reachability information for all other routers on the IXP
   that also connect to the route server.

   Multilateral and bilateral interconnections between different
   autonomous systems are not exclusive to each other, and it is not
   unusual to have both sorts of sessions configured in parallel at an
   IXP.  This configuration will lead to additional paths being
   available to the BGP Decision Process, which will calculate a best
   path as normal.

4.  Operational Considerations for Route Server Installations

4.1.  Path Hiding

   "Path hiding" is a term used in [RFC7947] to describe the process
   whereby a route server may mask individual paths by applying
   conflicting routing policies to its Loc-RIB.  When this happens,
   route server clients receive incomplete information from the route
   server about network reachability.

   There are several approaches that may be used to mitigate against the
   effect of path hiding; these are described in [RFC7947].  However,
   the only method that does not require explicit support from the route
   server client is for the route server itself to maintain an
   individual Loc-RIB for each client that is the subject of conflicting
   routing policies.

4.2.  Route Server Scaling

   While deployment of multiple Loc-RIBs on the route server presents a
   simple way to avoid the path-hiding problem noted in Section 4.1,
   this approach requires significantly more computing resources on the
   route server than where a single Loc-RIB is deployed for all clients.
   As the BGP Decision Process [RFC4271] must be applied to all Loc-RIBs
   deployed on the route server, both CPU and memory requirements on the
   host computer scale approximately according to O(P * N), where P is
   the total number of unique paths received by the route server, and N
   is the number of route server clients that require a unique Loc-RIB.
   As this is a super-linear scaling relationship, large route servers
   may derive benefit from deploying per-client Loc-RIBs only where they
   are required.

   Regardless of whether any Loc-RIB optimization technique is
   implemented, the route server's theoretical upper-bound network
   bandwidth requirements will scale according to O(P_tot * N), where
   P_tot is the total number of unique paths received by the route
   server, and N is the total number of route server clients.  In the
   case where P_avg (the arithmetic mean number of unique paths received
   per route server client) remains roughly constant even as the number
   of connected clients increases, the total number of prefixes will
   equal the average number of prefixes multiplied by the number of
   clients.  Symbolically, this can be written as P_tot = P_avg * N.  If
   we assume that in the worst case, each prefix is associated with a
   different set of BGP path attributes, so must be transmitted
   individually, the network bandwidth scaling function can be rewritten
   as O((P_avg * N) * N) or O(N^2).  This quadratic upper bound on the
   network traffic requirements indicates that the route server model
   may not scale well for larger numbers of clients.

   In practice, most prefixes will be associated with a limited number
   of BGP path attribute sets, allowing more efficient transmission of
   BGP routes from the route server than the theoretical analysis
   suggests.  In the analysis above, P_tot will increase monotonically
   according to the number of clients, but it will have an upper limit
   of the size of the full default-free routing table of the network in
   which the IXP is located.  Observations from production route servers
   have shown that most route server clients generally avoid using
   custom routing policies, and consequently, the route server may not
   need to deploy per-client Loc-RIBs.  These practical bounds reduce
   the theoretical worst-case scaling scenario to the point where route
   server deployments are manageable even on larger IXPs.

4.2.1.  Tackling Scaling Issues

   The problem of scaling route servers still presents serious practical
   challenges and requires careful attention.  Scaling analysis
   indicates problems in three key areas: route processor CPU overhead
   associated with BGP Decision Process calculations, the memory
   requirements for handling many different BGP path entries, and the
   network traffic bandwidth required to distribute these BGP routes
   from the route server to each route server client.

4.2.1.1.  View Merging and Decomposition

   View merging and decomposition, outlined in [RS-ARCH], describes a
   method of optimizing memory and CPU requirements where multiple route
   server clients are subject to exactly the same routing policies.  In
   this situation, multiple Loc-RIB views can be merged into a single
   view.

   There are several variations of this approach.  If the route server
   operator has prior knowledge of interconnection relationships between
   route server clients, then the operator may configure separate
   Loc-RIBs only for route server clients with unique routing policies.
   As this approach requires prior knowledge of interconnection
   relationships, the route server operator must depend on each client
   sharing their interconnection policies either in an internal
   provisioning database controlled by the operator or in an external
   data store such as an Internet Routing Registry Database.

   Conversely, the route server implementation itself may implement
   internal view decomposition by creating virtual Loc-RIBs based on a
   single in-memory master Loc-RIB, with delta differences for each
   prefix subject to different routing policies.  This allows a more
   fine-grained and flexible approach to the problem of Loc-RIB scaling,
   at the expense of requiring a more complex in-memory Loc-RIB
   structure.

   Whatever method of view merging and decomposition is chosen on a
   route server, pathological edge cases can be created whereby they
   will scale no better than fully non-optimized per-client Loc-RIBs.
   However, as most route server clients connect to a route server for
   the purposes of reducing overhead, rather than implementing complex
   per-client routing policies, edge cases tend not to arise in
   practice.

4.2.1.2.  Destination Splitting

   Destination splitting, also described in [RS-ARCH], describes a
   method for route server clients to connect to multiple route servers
   and to send non-overlapping sets of prefixes to each route server.
   As each route server computes the best path for its own set of
   prefixes, the quadratic scaling requirement operates on multiple
   smaller sets of prefixes.  This reduces the overall computational and
   memory requirements for managing multiple Loc-RIBs and performing the
   best-path calculation on each.

   In practice, the route server operator would need all route server
   clients to send a full set of BGP routes to each route server.  The
   route server operator could then selectively filter these prefixes
   for each route server by using either BGP Outbound Route Filtering
   [RFC5291] or inbound prefix filters configured on client BGP
   sessions.

4.2.1.3.  NEXT_HOP Resolution

   As route servers are usually deployed at IXPs where all connected
   routers are on the same Layer 2 broadcast domain, recursive
   resolution of the NEXT_HOP attribute is generally not required and
   can be replaced by a simple check to ensure that the NEXT_HOP value
   for each received BGP route is a network address on the IXP LAN's IP
   address range.

4.3.  Prefix Leakage Mitigation

   Prefix leakage occurs when a BGP client unintentionally distributes
   BGP routes to one or more neighboring BGP routers.  Prefix leakage of
   this form to a route server can cause serious connectivity problems
   at an IXP if each route server client is configured to accept all BGP
   routes from the route server.  It is therefore RECOMMENDED when
   deploying route servers that, due to the potential for collateral
   damage caused by BGP route leakage, route server operators deploy
   prefix leakage mitigation measures in order to prevent unintentional
   prefix announcements or else limit the scale of any such leak.
   Although not foolproof, per-client inbound prefix limits can restrict
   the damage caused by prefix leakage in many cases.  Per-client
   inbound prefix filtering on the route server is a more deterministic
   and usually more reliable means of preventing prefix leakage but
   requires more administrative resources to maintain properly.

   If a route server operator implements per-client inbound prefix
   filtering, then it is RECOMMENDED that the operator also builds in
   mechanisms to automatically compare the Adj-RIB-In received from each
   client with the inbound prefix lists configured for those clients.
   Naturally, it is the responsibility of the route server client to
   ensure that their stated prefix list is compatible with what they
   announce to an IXP route server.  However, many network operators do
   not carefully manage their published routing policies, and it is not
   uncommon to see significant variation between the two sets of
   prefixes.  Route server operator visibility into this discrepancy can
   provide significant advantages to both operator and client.

4.4.  Route Server Redundancy

   As the purpose of an IXP route server implementation is to provide a
   reliable reachability brokerage service, it is RECOMMENDED that
   exchange operators who implement route server systems provision
   multiple route servers on each shared Layer 2 domain.  There is no
   requirement to use the same BGP implementation or operating system
   for each route server on the IXP fabric; however, it is RECOMMENDED
   that where an operator provisions more than a single server on the
   same shared Layer 2 domain, each route server implementation be
   configured equivalently and in such a manner that the path
   reachability information from each system is identical.

4.5.  AS_PATH Consistency Check

   [RFC4271] requires that every BGP speaker that advertises a BGP route
   to another external BGP speaker prepends its own AS number as the
   last element of the AS_PATH sequence.  Therefore, the leftmost AS in
   an AS_PATH attribute should be equal to the AS number of the BGP
   speaker that sent the BGP route.

   As [RFC7947] suggests that route servers should not modify the
   AS_PATH attribute, a consistency check on the AS_PATH of a BGP route
   received by a route server client would normally fail.  It is
   therefore RECOMMENDED that route server clients disable the AS_PATH
   consistency check towards the route server.

4.6.  Export Routing Policies

   Policy filtering is commonly implemented on route servers to provide
   prefix distribution control mechanisms for route server clients.  A
   route server "export" policy is a policy that affects prefixes sent
   from the route server to a route server client.  Several different
   strategies are commonly used for implementing route server export
   policies.

4.6.1.  BGP Communities

   Prefixes sent to the route server are tagged with specific standard
   BGP Communities [RFC1997] or Extended Communities [RFC4360]
   attributes, based on predefined values agreed between the operator
   and all clients.  Based on these Communities values, BGP routes may
   be propagated to all other clients, a subset of clients, or none.
   This mechanism allows route server clients to instruct the route
   server to implement per-client export routing policies.

   As both standard BGP Communities and Extended Communities values are
   restricted to 6 octets or fewer, it is not possible for both the
   global and local administrator fields in the BGP Communities value to
   fit a 4-octet AS number.  Bearing this in mind, the route server
   operator SHOULD take care to ensure that the predefined BGP
   Communities values mechanism used on their route server is compatible
   with 4-octet AS numbers [RFC6793].

4.6.2.  Internet Routing Registries

   Internet Routing Registry databases (IRRDBs) may be used by route
   server operators to construct per-client routing policies.  "Routing
   Policy Specification Language (RPSL)" [RFC2622] provides a
   comprehensive grammar for describing interconnection relationships,
   and several toolsets exist that can be used to translate RPSL policy
   description into route server configurations.

4.6.3.  Client-Accessible Databases

   Should the route server operator not wish to use either BGP
   Communities or the public IRRDBs for implementing client export
   policies, they may implement their own routing policy database system
   for managing their clients' requirements.  A database of this form
   SHOULD allow a route server client operator to update their routing
   policy and provide a mechanism for allowing the client to specify
   whether they wish to exchange all their prefixes with any other route
   server client.  Optionally, the implementation may allow a client to
   specify unique routing policies for individual prefixes over which
   they have routing policy control.

4.7.  Layer 2 Reachability Problems

   Layer 2 reachability problems on an IXP can cause serious operational
   problems for IXP participants that depend on route servers for
   interconnection.  Ethernet switch forwarding bugs have occasionally
   been observed to cause non-transitive reachability.  For example,
   given a route server and two IXP participants, A and B, if the two
   participants can reach the route server but cannot reach each other,
   then traffic between the participants may be dropped until such time
   as the Layer 2 forwarding problem is resolved.  This situation does
   not tend to occur in bilateral interconnection arrangements, as the
   routing control path between the two hosts is usually (but not
   always, due to IXP inter-switch connectivity load-balancing
   algorithms) the same as the data path between them.

   Problems of this form can be partially mitigated by using
   Bidirectional Forwarding Detection (BFD) [RFC5881].  However, as this
   is a bilateral protocol configured between routers, and as there is
   currently no protocol to automatically configure BFD sessions between
   route server clients, BFD does not currently provide an optimal means
   of handling the problem.  Even if automatic BFD session configuration
   were possible, practical problems would remain.  If two IXP route
   server clients were configured to run BFD between each other and the
   protocol detected a non-transitive loss of reachability between them,
   each of those routers would internally mark the other's prefixes as
   unreachable via the BGP path announced by the route server.  As the
   route server only propagates a single best path to each client, this
   could cause either sub-optimal routing or complete connectivity loss
   if there were no alternative paths learned from other BGP sessions.

4.8.  BGP NEXT_HOP Hijacking

   Item 2 in Section 5.1.3 of [RFC4271] allows EBGP speakers to change
   the NEXT_HOP address of a received BGP route to be a different
   Internet address on the same subnet.  This is the mechanism that
   allows route servers to operate on a shared Layer 2 IXP network.
   However, the mechanism can be abused by route server clients to
   redirect traffic for their prefixes to other IXP participant routers.

                                   ____
                                  /    \
                                 | AS99 |
                                  \____/
                                   /  \
                                  /    \
                               __/      \__
                              /   \    /   \
                           ..| AS1 |..| AS2 |..
                          :   \___/    \___/   :
                          :      \      /      :
                          :       \    /       :
                          :        \__/        :
                          : IXP   /    \       :
                          :      |  RS  |      :
                          :       \____/       :
                          :                    :
                           ....................

           Figure 3: BGP NEXT_HOP Hijacking Using a Route Server

   For example, in Figure 3, if AS1 and AS2 both announce BGP routes for
   AS99 to the route server, AS1 could set the NEXT_HOP address for
   AS99's routes to be the address of AS2's router, thereby diverting
   traffic for AS99 via AS2.  This may override the routing policies of
   AS99 and AS2.

   Worse still, if the route server operator does not use inbound prefix
   filtering, AS1 could announce any arbitrary prefix to the route
   server with a NEXT_HOP address of any other IXP participant.  This
   could be used as a denial-of-service mechanism against either the
   users of the address space being announced by illicitly diverting
   their traffic or the other IXP participant by overloading their
   network with traffic that would not normally be sent there.

   This problem is not specific to route servers, and it can also be
   implemented using bilateral BGP sessions.  However, the potential
   damage is amplified by route servers because a single BGP session can
   be used to affect many networks simultaneously.

   Because route server clients cannot easily implement next-hop policy
   checks against route server BGP sessions, route server operators
   SHOULD check that the BGP NEXT_HOP attribute for BGP routes received
   from a route server client matches the interface address of the
   client.  If the route server receives a BGP route where these
   addresses are different and where the announcing route server client
   is in a different AS to the route server client that uses the next-
   hop address, the BGP route SHOULD be dropped.  Permitting next-hop
   rewriting for the same AS allows an organization with multiple
   connections into an IXP configured with different IP addresses to
   direct traffic off the IXP infrastructure through any of their
   connections for traffic engineering or other purposes.

4.9.  BGP Operations and Security

   BGP route servers SHOULD be configured and operated in compliance
   with [RFC7454] with the exception of Section 11, "BGP Community
   Scrubbing", which may not necessarily apply on a route server,
   depending on the route server operator policy.

5.  Security Considerations

   On route server installations that do not employ path-hiding
   mitigation techniques, the path-hiding problem outlined in
   Section 4.1 could be used by an IXP participant to prevent the route
   server from sending any BGP routes for a particular prefix to other
   route server clients, even if there was a valid path to that
   destination via another route server client.

   If the route server operator does not implement prefix leakage
   mitigation as described in Section 4.3, it is trivial for route
   server clients to implement denial-of-service attacks against
   arbitrary Internet networks by leaking BGP routes to a route server.

   Route server installations SHOULD be secured against BGP NEXT_HOP
   hijacking, as described in Section 4.8.

6.  References

6.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC7947]  Jasinska, E., Hilliard, N., Raszuk, R., and N. Bakker,
              "Internet Exchange BGP Route Server", RFC 7947,
              DOI 10.17487/RFC7947, September 2016,
              <http://www.rfc-editor.org/info/rfc7947>.

6.2.  Informative References

   [RFC1997]  Chandra, R., Traina, P., and T. Li, "BGP Communities
              Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,
              <http://www.rfc-editor.org/info/rfc1997>.

   [RFC2622]  Alaettinoglu, C., Villamizar, C., Gerich, E., Kessens, D.,
              Meyer, D., Bates, T., Karrenberg, D., and M. Terpstra,
              "Routing Policy Specification Language (RPSL)", RFC 2622,
              DOI 10.17487/RFC2622, June 1999,
              <http://www.rfc-editor.org/info/rfc2622>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <http://www.rfc-editor.org/info/rfc4271>.

   [RFC4360]  Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
              Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
              February 2006, <http://www.rfc-editor.org/info/rfc4360>.

   [RFC4456]  Bates, T., Chen, E., and R. Chandra, "BGP Route
              Reflection: An Alternative to Full Mesh Internal BGP
              (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
              <http://www.rfc-editor.org/info/rfc4456>.

   [RFC5291]  Chen, E. and Y. Rekhter, "Outbound Route Filtering
              Capability for BGP-4", RFC 5291, DOI 10.17487/RFC5291,
              August 2008, <http://www.rfc-editor.org/info/rfc5291>.

   [RFC5881]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
              DOI 10.17487/RFC5881, June 2010,
              <http://www.rfc-editor.org/info/rfc5881>.

   [RFC6793]  Vohra, Q. and E. Chen, "BGP Support for Four-Octet
              Autonomous System (AS) Number Space", RFC 6793,
              DOI 10.17487/RFC6793, December 2012,
              <http://www.rfc-editor.org/info/rfc6793>.

   [RFC7454]  Durand, J., Pepelnjak, I., and G. Doering, "BGP Operations
              and Security", BCP 194, RFC 7454, DOI 10.17487/RFC7454,
              February 2015, <http://www.rfc-editor.org/info/rfc7454>.

   [RS-ARCH]  Govindan, R., Alaettinoglu, C., Varadhan, K., and D.
              Estrin, "A Route Server Architecture for Inter-Domain
              Routing", 1995,
              <http://www.cs.usc.edu/assets/003/83191.pdf>.

Acknowledgments

   The authors would like to thank Chris Hall, Ryan Bickhart, Steven
   Bakker, and Eduardo Ascenco Reis for their valuable input.

Authors' Addresses

   Nick Hilliard
   INEX
   4027 Kingswood Road
   Dublin  24
   Ireland

   Email: nick@inex.ie


   Elisa Jasinska
   BigWave IT
   ul. Skawinska 27/7
   Krakow, MP  31-066
   Poland

   Email: elisa@bigwaveit.org


   Robert Raszuk
   Bloomberg LP
   731 Lexington Ave.
   New York, NY  10022
   United States of America

   Email: robert@raszuk.net


   Niels Bakker
   Akamai Technologies B.V.
   Kingsfordweg 151
   Amsterdam  1043 GR
   Netherlands

   Email: nbakker@akamai.com