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rfc:rfc4277

Network Working Group D. McPherson Request for Comments: 4277 Arbor Networks Category: Informational K. Patel

                                                         Cisco Systems
                                                          January 2006
                 Experience with the BGP-4 Protocol

Status of This Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2006).

Abstract

 The purpose of this memo is to document how the requirements for
 publication of a routing protocol as an Internet Draft Standard have
 been satisfied by Border Gateway Protocol version 4 (BGP-4).
 This report satisfies the requirement for "the second report", as
 described in Section 6.0 of RFC 1264.  In order to fulfill the
 requirement, this report augments RFC 1773 and describes additional
 knowledge and understanding gained in the time between when the
 protocol was made a Draft Standard and when it was submitted for
 Standard.

McPherson & Patel Informational [Page 1] RFC 4277 Experience with the BGP-4 Protocol January 2006

Table of Contents

 1.  Introduction .................................................  3
 2.  BGP-4 Overview ...............................................  3
     2.1.  A Border Gateway Protocol ..............................  3
 3.  Management Information Base (MIB) ............................  3
 4.  Implementation Information ...................................  4
 5.  Operational Experience .......................................  4
 6.  TCP Awareness ................................................  5
 7.  Metrics ......................................................  5
     7.1.  MULTI_EXIT_DISC (MED) ..................................  5
           7.1.1.  MEDs and Potatoes ..............................  6
           7.1.2.  Sending MEDs to BGP Peers ......................  7
           7.1.3.  MED of Zero Versus No MED ......................  7
           7.1.4.  MEDs and Temporal Route Selection ..............  7
 8.  Local Preference .............................................  8
 9.  Internal BGP In Large Autonomous Systems .....................  9
 10. Internet Dynamics ............................................  9
 11. BGP Routing Information Bases (RIBs) ......................... 10
 12. Update Packing ............................................... 10
 13. Limit Rate Updates ........................................... 11
     13.1. Consideration of TCP Characteristics ................... 11
 14. Ordering of Path Attributes .................................. 12
 15. AS_SET Sorting ............................................... 12
 16. Control Over Version Negotiation ............................. 13
 17. Security Considerations ...................................... 13
     17.1. TCP MD5 Signature Option ............................... 13
     17.2. BGP Over IPsec ......................................... 14
     17.3. Miscellaneous .......................................... 14
 18. PTOMAINE and GROW ............................................ 14
 19. Internet Routing Registries (IRRs) ........................... 15
 20. Regional Internet Registries (RIRs) and IRRs, A Bit
     of History ................................................... 15
 21. Acknowledgements ............................................. 16
 22. References ................................................... 17
     22.1. Normative References ................................... 17
     22.2. Informative References ................................. 17

McPherson & Patel Informational [Page 2] RFC 4277 Experience with the BGP-4 Protocol January 2006

1. Introduction

 The purpose of this memo is to document how the requirements for
 publication of a routing protocol as an Internet Draft Standard have
 been satisfied by Border Gateway Protocol version 4 (BGP-4).
 This report satisfies the requirement for "the second report", as
 described in Section 6.0 of [RFC1264].  In order to fulfill the
 requirement, this report augments [RFC1773] and describes additional
 knowledge and understanding gained in the time between when the
 protocol was made a Draft Standard and when it was submitted for
 Standard.

2. BGP-4 Overview

 BGP is an inter-autonomous system routing protocol designed for
 TCP/IP internets.  The primary function of a BGP speaking system is
 to exchange network reachability information with other BGP systems.
 This network reachability information includes information on the
 list of Autonomous Systems (ASes) that reachability information
 traverses.  This information is sufficient to construct a graph of AS
 connectivity for this reachability, from which routing loops may be
 pruned and some policy decisions, at the AS level, may be enforced.
 The initial version of the BGP protocol was published in [RFC1105].
 Since then, BGP Versions 2, 3, and 4 have been developed and are
 specified in [RFC1163], [RFC1267], and [RFC1771], respectively.
 Changes to BGP-4 after it went to Draft Standard [RFC1771] are listed
 in Appendix N of [RFC4271].

2.1. A Border Gateway Protocol

 The initial version of the BGP protocol was published in [RFC1105].
 BGP version 2 is defined in [RFC1163].  BGP version 3 is defined in
 [RFC1267].  BGP version 4 is defined in [RFC1771] and [RFC4271].
 Appendices A, B, C, and D of [RFC4271] provide summaries of the
 changes between each iteration of the BGP specification.

3. Management Information Base (MIB)

 The BGP-4 Management Information Base (MIB) has been published
 [BGP-MIB].  The MIB was updated from previous versions, which are
 documented in [RFC1657] and [RFC1269], respectively.
 Apart from a few system variables, the BGP MIB is broken into two
 tables: the BGP Peer Table and the BGP Received Path Attribute Table.

McPherson & Patel Informational [Page 3] RFC 4277 Experience with the BGP-4 Protocol January 2006

 The Peer Table reflects information about BGP peer connections, such
 as their state and current activity.  The Received Path Attribute
 Table contains all attributes received from all peers before local
 routing policy has been applied.  The actual attributes used in
 determining a route are a subset of the received attribute table.

4. Implementation Information

 There are numerous independent interoperable implementations of BGP
 currently available.  Although the previous version of this report
 provided an overview of the implementations currently used in the
 operational Internet, at that time it has been suggested that a
 separate BGP Implementation Report [RFC4276] be generated.
 It should be noted that implementation experience with Cisco's BGP-4
 implementation was documented as part of [RFC1656].
 For all additional implementation information please reference
 [RFC4276].

5. Operational Experience

 This section discusses operational experience with BGP and BGP-4.
 BGP has been used in the production environment since 1989; BGP-4 has
 been used since 1993.  Production use of BGP includes utilization of
 all significant features of the protocol.  The present production
 environment, where BGP is used as the inter-autonomous system routing
 protocol, is highly heterogeneous.  In terms of link bandwidth, it
 varies from 56 Kbps to 10 Gbps.  In terms of the actual routers that
 run BGP, they range from relatively slow performance, general purpose
 CPUs to very high performance RISC network processors, and include
 both special purpose routers and the general purpose workstations
 that run various UNIX derivatives and other operating systems.
 In terms of the actual topologies, it varies from very sparse to
 quite dense.  The requirement for full-mesh IBGP topologies has been
 largely remedied by BGP Route Reflection, Autonomous System
 Confederations for BGP, and often some mix of the two.  BGP Route
 Reflection was initially defined in [RFC1966] and was updated in
 [RFC2796].  Autonomous System Confederations for BGP were initially
 defined in [RFC1965] and were updated in [RFC3065].
 At the time of this writing, BGP-4 is used as an inter-autonomous
 system routing protocol between all Internet-attached autonomous
 systems, with nearly 21k active autonomous systems in the global
 Internet routing table.

McPherson & Patel Informational [Page 4] RFC 4277 Experience with the BGP-4 Protocol January 2006

 BGP is used both for the exchange of routing information between a
 transit and a stub autonomous system, and for the exchange of routing
 information between multiple transit autonomous systems.  There is no
 protocol distinction between sites historically considered
 "backbones" versus "regional" or "edge" networks.
 The full set of exterior routes carried by BGP is well over 170,000
 aggregate entries, representing several times that number of
 connected networks.  The number of active paths in some service
 provider core routers exceeds 2.5 million.  Native AS path lengths
 are as long as 10 for some routes, and "padded" path lengths of 25 or
 more autonomous systems exist.

6. TCP Awareness

 BGP employs TCP [RFC793] as it's Transport Layer protocol.  As such,
 all characteristics inherent to TCP are inherited by BGP.
 For example, due to TCP's behavior, bandwidth capabilities may not be
 realized because of TCP's slow start algorithms and slow-start
 restarts of connections, etc.

7. Metrics

 This section discusses different metrics used within the BGP
 protocol.  BGP has a separate metric parameter for IBGP and EBGP.
 This allows policy-based metrics to overwrite the distance-based
 metrics; this allows each autonomous system to define its independent
 policies in Intra-AS, as well as Inter-AS.  BGP Multi Exit
 Discriminator (MED) is used as a metric by EBGP peers (i.e., inter-
 domain), while Local Preference (LOCAL_PREF) is used by IBGP peers
 (i.e., intra-domain).

7.1. MULTI_EXIT_DISC (MED)

 BGP version 4 re-defined the old INTER-AS metric as a MULTI_EXIT_DISC
 (MED).  This value may be used in the tie-breaking process when
 selecting a preferred path to a given address space, and provides BGP
 speakers with the capability of conveying the optimal entry point
 into the local AS to a peer AS.
 Although the MED was meant to only be used when comparing paths
 received from different external peers in the same AS, many
 implementations provide the capability to compare MEDs between
 different autonomous systems.
 Though this may seem a fine idea for some configurations, care must
 be taken when comparing MEDs of different autonomous systems.  BGP

McPherson & Patel Informational [Page 5] RFC 4277 Experience with the BGP-4 Protocol January 2006

 speakers often derive MED values by obtaining the IGP metric
 associated with reaching a given BGP NEXT_HOP within the local AS.
 This allows MEDs to reasonably reflect IGP topologies when
 advertising routes to peers.  While this is fine when comparing MEDs
 of multiple paths learned from a single adjacent AS, it can result in
 potentially bad decisions when comparing MEDs of different autonomous
 systems.  This is most typically the case when the autonomous systems
 use different mechanisms to derive IGP metrics, BGP MEDs, or perhaps
 even use different IGP protocols with vastly contrasting metric
 spaces.
 Another MED deployment consideration involves the impact of the
 aggregation of BGP routing information on MEDs.  Aggregates are often
 generated from multiple locations in an AS to accommodate stability,
 redundancy, and other network design goals.  When MEDs are derived
 from IGP metrics associated with said aggregates, the MED value
 advertised to peers can result in very suboptimal routing.
 The MED was purposely designed to be a "weak" metric that would only
 be used late in the best-path decision process.  The BGP working
 group was concerned that any metric specified by a remote operator
 would only affect routing in a local AS if no other preference was
 specified.  A paramount goal of the design of the MED was to ensure
 that peers could not "shed" or "absorb" traffic for networks they
 advertise.

7.1.1. MEDs and Potatoes

 Where traffic flows between a pair of destinations, each is connected
 to two transit networks, each of the transit networks has the choice
 of sending the traffic to the peering closest to another transit
 provider or passing traffic to the peering that advertises the least
 cost through the other provider.  The former method is called "hot
 potato routing" because, like a hot potato held in bare hands,
 whoever has it tries to get rid of it quickly.  Hot potato routing is
 accomplished by not passing the EBGP-learned MED into the IBGP.  This
 minimizes transit traffic for the provider routing the traffic.  Far
 less common is "cold potato routing", where the transit provider uses
 its own transit capacity to get the traffic to the point in the
 adjacent transit provider advertised as being closest to the
 destination.  Cold potato routing is accomplished by passing the
 EBGP-learned MED into IBGP.
 If one transit provider uses hot potato routing and another uses cold
 potato routing, traffic between the two tends to be symmetric.
 Depending on the business relationships, if one provider has more
 capacity or a significantly less congested transit network, then that
 provider may use cold potato routing.  The NSF-funded NSFNET backbone

McPherson & Patel Informational [Page 6] RFC 4277 Experience with the BGP-4 Protocol January 2006

 and NSF-funded regional networks are examples of widespread use of
 cold potato routing in the mid 1990s.
 In some cases, a provider may use hot potato routing for some
 destinations for a given peer AS, and cold potato routing for others.
 The different treatment of commercial and research traffic in the
 NSFNET in the mid 1990s is an example of this.  However, this might
 best be described as 'mashed potato routing', a term that reflects
 the complexity of router configurations in use at the time.
 Seemingly more intuitive references, which fall outside the vegetable
 kingdom, refer to cold potato routing as "best exit routing", and hot
 potato routing as "closest exit routing".

7.1.2. Sending MEDs to BGP Peers

 [RFC4271] allows MEDs received from any EBGP peers by a BGP speaker
 to be passed to its IBGP peers.  Although advertising MEDs to IBGP
 peers is not a required behavior, it is a common default.  MEDs
 received from EBGP peers by a BGP speaker SHOULD NOT be sent to other
 EBGP peers.
 Note that many implementations provide a mechanism to derive MED
 values from IGP metrics to allow BGP MED information to reflect the
 IGP topologies and metrics of the network when propagating
 information to adjacent autonomous systems.

7.1.3. MED of Zero Versus No MED

 [RFC4271] requires an implementation to provide a mechanism that
 allows MED to be removed.  Previously, implementations did not
 consider a missing MED value the same as a MED of zero.  [RFC4271]
 now requires that no MED value be equal to zero.
 Note that many implementations provide a mechanism to explicitly
 define a missing MED value as "worst", or less preferable than zero
 or larger values.

7.1.4. MEDs and Temporal Route Selection

 Some implementations have hooks to apply temporal behavior in MED-
 based best path selection.  That is, all things being equal up to MED
 consideration, preference would be applied to the "oldest" path,
 without preference for the lower MED value.  The reasoning for this
 is that "older" paths are presumably more stable, and thus
 preferable.  However, temporal behavior in route selection results in
 non-deterministic behavior, and as such, may often be undesirable.

McPherson & Patel Informational [Page 7] RFC 4277 Experience with the BGP-4 Protocol January 2006

8. Local Preference

 The LOCAL_PREF attribute was added to enable a network operator to
 easily configure a policy that overrides the standard best path
 determination mechanism without independently configuring local
 preference policy on each router.
 One shortcoming in the BGP-4 specification was the suggestion that a
 default value of LOCAL_PREF be assumed if none was provided.
 Defaults of zero or the maximum value each have range limitations, so
 a common default would aid in the interoperation of multi-vendor
 routers in the same AS (since LOCAL_PREF is a local administration
 attribute, there is no interoperability drawback across AS
 boundaries).
 [RFC4271] requires that LOCAL_PREF be sent to IBGP Peers and not to
 EBGP Peers.  Although no default value for LOCAL_PREF is defined, the
 common default value is 100.
 Another area where exploration is required is a method whereby an
 originating AS may influence the best path selection process.  For
 example, a dual-connected site may select one AS as a primary transit
 service provider and have one as a backup.
                   /---- transit B ----\
       end-customer                     transit A----
                   /---- transit C ----\
 In a topology where the two transit service providers connect to a
 third provider, the real decision is performed by the third provider.
 There is no mechanism to indicate a preference should the third
 provider wish to respect that preference.
 A general purpose suggestion has been the possibility of carrying an
 optional vector, corresponding to the AS_PATH, where each transit AS
 may indicate a preference value for a given route.  Cooperating
 autonomous systems may then choose traffic based upon comparison of
 "interesting" portions of this vector, according to routing policy.
 While protecting a given autonomous systems routing policy is of
 paramount concern, avoiding extensive hand configuration of routing
 policies needs to be examined more carefully in future BGP-like
 protocols.

McPherson & Patel Informational [Page 8] RFC 4277 Experience with the BGP-4 Protocol January 2006

9. Internal BGP In Large Autonomous Systems

 While not strictly a protocol issue, another concern has been raised
 by network operators who need to maintain autonomous systems with a
 large number of peers.  Each speaker peering with an external router
 is responsible for propagating reachability and path information to
 all other transit and border routers within that AS.  This is
 typically done by establishing internal BGP connections to all
 transit and border routers in the local AS.
 Note that the number of BGP peers that can be fully meshed depends on
 a number of factors, including the number of prefixes in the routing
 system, the number of unique paths, stability of the system, and,
 perhaps most importantly, implementation efficiency.  As a result,
 although it's difficult to define "a large number of peers", there is
 always some practical limit.
 In a large AS, this leads to a full mesh of TCP connections
 (n * (n-1)) and some method of configuring and maintaining those
 connections.  BGP does not specify how this information is to be
 propagated.  Therefore, alternatives, such as injecting BGP routing
 information into the local IGP, have been attempted, but turned out
 to be non-practical alternatives (to say the least).
 To alleviate the need for "full mesh" IBGP, several alternatives have
 been defined, including BGP Route Reflection [RFC2796] and AS
 Confederations for BGP [RFC3065].

10. Internet Dynamics

 As discussed in [RFC4274], the driving force in CPU and bandwidth
 utilization is the dynamic nature of routing in the Internet.  As the
 Internet has grown, the frequency of route changes per second has
 increased.
 We automatically get some level of damping when more specific NLRI is
 aggregated into larger blocks; however, this is not sufficient.  In
 Appendix F of [RFC4271], there are descriptions of damping techniques
 that should be applied to advertisements.  In future specifications
 of BGP-like protocols, damping methods should be considered for
 mandatory inclusion in compliant implementations.
 BGP Route Flap Damping is defined in [RFC2439].  BGP Route Flap
 Damping defines a mechanism to help reduce the amount of routing
 information passed between BGP peers, which reduces the load on these
 peers without adversely affecting route convergence time for
 relatively stable routes.

McPherson & Patel Informational [Page 9] RFC 4277 Experience with the BGP-4 Protocol January 2006

 None of the current implementations of BGP Route Flap Damping store
 route history by unique NRLI or AS Path, although RFC 2439 lists this
 as mandatory.  A potential result of failure to consider each AS Path
 separately is an overly aggressive suppression of destinations in a
 densely meshed network, with the most severe consequence being
 suppression of a destination after a single failure.  Because the top
 tier autonomous systems in the Internet are densely meshed, these
 adverse consequences are observed.
 Route changes are announced using BGP UPDATE messages.  The greatest
 overhead in advertising UPDATE messages happens whenever route
 changes to be announced are inefficiently packed.  Announcing routing
 changes that share common attributes in a single BGP UPDATE message
 helps save considerable bandwidth and reduces processing overhead, as
 discussed in Section 12, Update Packing.
 Persistent BGP errors may cause BGP peers to flap persistently if
 peer dampening is not implemented, resulting in significant CPU
 utilization.  Implementors may find it useful to implement peer
 dampening to avoid such persistent peer flapping [RFC4271].

11. BGP Routing Information Bases (RIBs)

 [RFC4271] states "Any local policy which results in routes being
 added to an Adj-RIB-Out without also being added to the local BGP
 speaker's forwarding table, is outside the scope of this document".
 However, several well-known implementations do not confirm that
 Loc-RIB entries were used to populate the forwarding table before
 installing them in the Adj-RIB-Out.  The most common occurrence of
 this is when routes for a given prefix are presented by more than one
 protocol, and the preferences for the BGP-learned route is lower than
 that of another protocol.  As such, the route learned via the other
 protocol is used to populate the forwarding table.
 It may be desirable for an implementation to provide a knob that
 permits advertisement of "inactive" BGP routes.
 It may be also desirable for an implementation to provide a knob that
 allows a BGP speaker to advertise BGP routes that were not selected
 in the decision process.

12. Update Packing

 Multiple unfeasible routes can be advertised in a single BGP Update
 message.  In addition, one or more feasible routes can be advertised
 in a single Update message, as long as all prefixes share a common
 attribute set.

McPherson & Patel Informational [Page 10] RFC 4277 Experience with the BGP-4 Protocol January 2006

 The BGP4 protocol permits advertisement of multiple prefixes with a
 common set of path attributes in a single update message, which is
 commonly referred to as "update packing".  When possible, update
 packing is recommended, as it provides a mechanism for more efficient
 behavior in a number of areas, including:
    o Reduction in system overhead due to generation or receipt of
      fewer Update messages.
    o Reduction in network overhead as a result of less packets and
      lower bandwidth consumption.
    o Reduction in frequency of processing path attributes and looking
      for matching sets in the AS_PATH database (if you have one).
      Consistent ordering of the path attributes allows for ease of
      matching in the database, as different representations of the
      same data do not exist.
 The BGP protocol suggests that withdrawal information should be
 packed in the beginning of an Update message, followed by information
 about reachable routes in a single UPDATE message.  This helps
 alleviate excessive route flapping in BGP.

13. Limit Rate Updates

 The BGP protocol defines different mechanisms to rate limit Update
 advertisement.  The BGP protocol defines a
 MinRouteAdvertisementInterval parameter that determines the minimum
 time that must elapse between the advertisement of routes to a
 particular destination from a single BGP speaker.  This value is set
 on a per-BGP-peer basis.
 Because BGP relies on TCP as the Transport protocol, TCP can prevent
 transmission of data due to empty windows.  As a result, multiple
 updates may be spaced closer together than was originally queued.
 Although it is not common, implementations should be aware of this
 occurrence.

13.1. Consideration of TCP Characteristics

 If either a TCP receiver is processing input more slowly than the
 sender, or if the TCP connection rate is the limiting factor, a form
 of backpressure is observed by the TCP sending application.  When the
 TCP buffer fills, the sending application will either block on the
 write or receive an error on the write.  In early implementations or
 naive new implementations, setting options to block on the write or
 setting options for non-blocking writes are common errors.  Such
 implementations treat full buffer related errors as fatal.

McPherson & Patel Informational [Page 11] RFC 4277 Experience with the BGP-4 Protocol January 2006

 Having recognized that full write buffers are to be expected,
 additional implementation pitfalls exist.  The application should not
 attempt to store the TCP stream within the application itself.  If
 the receiver or the TCP connection is persistently slow, then the
 buffer can grow until memory is exhausted.  A BGP implementation is
 required to send changes to all peers for which the TCP connection is
 not blocked, and is required to send those changes to the remaining
 peers when the connection becomes unblocked.
 If the preferred route for a given NLRI changes multiple times while
 writes to one or more peers are blocked, only the most recent best
 route needs to be sent.  In this way, BGP is work conserving
 [RFC4274].  In cases of extremely high route change, a higher volume
 of route change is sent to those peers that are able to process it
 more quickly; a lower volume of route change is sent to those peers
 that are not able to process the changes as quickly.
 For implementations that handle differing peer capacities to absorb
 route change well, if the majority of route change is contributed by
 a subset of unstable NRLI, the only impact on relatively stable NRLI
 that makes an isolated route change is a slower convergence, for
 which convergence time remains bounded, regardless of the amount of
 instability.

14. Ordering of Path Attributes

 The BGP protocol suggests that BGP speakers sending multiple prefixes
 per an UPDATE message sort and order path attributes according to
 Type Codes.  This would help their peers quickly identify sets of
 attributes from different update messages that are semantically
 different.
 Implementers may find it useful to order path attributes according to
 Type Code, such that sets of attributes with identical semantics can
 be more quickly identified.

15. AS_SET Sorting

 AS_SETs are commonly used in BGP route aggregation.  They reduce the
 size of AS_PATH information by listing AS numbers only once,
 regardless of the number of times it might appear in the process of
 aggregation.  AS_SETs are usually sorted in increasing order to
 facilitate efficient lookups of AS numbers within them.  This
 optimization is optional.

McPherson & Patel Informational [Page 12] RFC 4277 Experience with the BGP-4 Protocol January 2006

16. Control Over Version Negotiation

 Because pre-BGP-4 route aggregation can't be supported by earlier
 versions of BGP, an implementation that supports versions in addition
 to BGP-4 should provide the version support on a per-peer basis.  At
 the time of this writing, all BGP speakers on the Internet are
 thought to be running BGP version 4.

17. Security Considerations

 BGP provides a flexible and extendable mechanism for authentication
 and security.  The mechanism allows support for schemes with various
 degrees of complexity.  BGP sessions are authenticated based on the
 IP address of a peer.  In addition, all BGP sessions are
 authenticated based on the autonomous system number advertised by a
 peer.
 Because BGP runs over TCP and IP, BGP's authentication scheme may be
 augmented by any authentication or security mechanism provided by
 either TCP or IP.

17.1. TCP MD5 Signature Option

 [RFC2385] defines a way in which the TCP MD5 signature option can be
 used to validate information transmitted between two peers.  This
 method prevents a third party from injecting information (e.g., a TCP
 Reset) into the datastream, or modifying the routing information
 carried between two BGP peers.
 At the moment, TCP MD5 is not ubiquitously deployed, especially in
 inter-domain scenarios, largely because of key distribution issues.
 Most key distribution mechanisms are considered to be too "heavy" at
 this point.
 Many have naively assumed that an attacker must correctly guess the
 exact TCP sequence number (along with the source and destination
 ports and IP addresses) to inject a data segment or reset a TCP
 transport connection between two BGP peers.  However, recent
 observation and open discussion show that the malicious data only
 needs to fall within the TCP receive window, which may be quite
 large, thereby significantly lowering the complexity of such an
 attack.
 As such, it is recommended that the MD5 TCP Signature Option be
 employed to protect BGP from session resets and malicious data
 injection.

McPherson & Patel Informational [Page 13] RFC 4277 Experience with the BGP-4 Protocol January 2006

17.2. BGP Over IPsec

 BGP can run over IPsec, either in a tunnel or in transport mode,
 where the TCP portion of the IP packet is encrypted.  This not only
 prevents random insertion of information into the data stream between
 two BGP peers, but also prevents an attacker from learning the data
 being exchanged between the peers.
 However, IPsec does offer several options for exchanging session
 keys, which may be useful on inter-domain configurations.  These
 options are being explored in many deployments, although no
 definitive solution has been reached on the issue of key exchange for
 BGP in IPsec.
 Because BGP runs over TCP and IP, it should be noted that BGP is
 vulnerable to the same denial of service and authentication attacks
 that are present in any TCP based protocol.

17.3. Miscellaneous

 Another routing protocol issue is providing evidence of the validity
 and authority of routing information carried within the routing
 system.  This is currently the focus of several efforts, including
 efforts to define threats that can be used against this routing
 information in BGP [BGPATTACK], and efforts to develop a means of
 providing validation and authority for routing information carried
 within BGP [SBGP] [soBGP].
 In addition, the Routing Protocol Security Requirements (RPSEC)
 working group has been chartered, within the Routing Area of the
 IETF, to discuss and assist in addressing issues surrounding routing
 protocol security.  Within RPSEC, this work is intended to result in
 feedback to BGP4 and future protocol enhancements.

18. PTOMAINE and GROW

 The Prefix Taxonomy (PTOMAINE) working group, recently replaced by
 the Global Routing Operations (GROW) working group, is chartered to
 consider and measure the problem of routing table growth, the effects
 of the interactions between interior and exterior routing protocols,
 and the effect of address allocation policies and practices on the
 global routing system.  Finally, where appropriate, GROW will also
 document the operational aspects of measurement, policy, security,
 and VPN infrastructures.
 GROW is currently studying the effects of route aggregation, and also
 the inability to aggregate over multiple provider boundaries due to
 inadequate provider coordination.

McPherson & Patel Informational [Page 14] RFC 4277 Experience with the BGP-4 Protocol January 2006

 Within GROW, this work is intended to result in feedback to BGPv4 and
 future protocol enhancements.

19. Internet Routing Registries (IRRs)

 Many organizations register their routing policy and prefix
 origination in the various distributed databases of the Internet
 Routing Registry.  These databases provide access to information
 using the RPSL language, as defined in [RFC2622].  While registered
 information may be maintained and correct for certain providers, the
 lack of timely or correct data in the various IRR databases has
 prevented wide spread use of this resource.

20. Regional Internet Registries (RIRs) and IRRs, A Bit of History

 The NSFNET program used EGP, and then BGP, to provide external
 routing information.  It was the NSF policy of offering different
 prices and providing different levels of support to the Research and
 Education (RE) and the Commercial (CO) networks that led to BGP's
 initial policy requirements.  In addition to being charged more, CO
 networks were not able to use the NSFNET backbone to reach other CO
 networks.  The rationale for higher prices was that commercial users
 of the NSFNET within the business and research entities should
 subsidize the RE community.  Recognition that the Internet was
 evolving away from a hierarchical network to a mesh of peers led to
 changes away from EGP and BGP-1 that eliminated any assumptions of
 hierarchy.
 Enforcement of NSF policy was accomplished through maintenance of the
 NSF Policy Routing Database (PRDB).  The PRDB not only contained each
 networks designation as CO or RE, but also contained a list of the
 preferred exit points to the NSFNET to reach each network.  This was
 the basis for setting what would later be called BGP LOCAL_PREF on
 the NSFNET.  Tools provided with the PRDB generated complete router
 configurations for the NSFNET.
 Use of the PRDB had the fortunate consequence of greatly improving
 reliability of the NSFNET, relative to peer networks of the time.
 PRDB offered more optimal routing for those networks that were
 sufficiently knowledgeable and willing to keep their entries current.
 With the decommission of the NSFNET Backbone Network Service in 1995,
 it was recognized that the PRDB should be made less single provider
 centric, and its legacy contents, plus any further updates, should be
 made available to any provider willing to make use of it.  The
 European networking community had long seen the PRDB as too US-
 centric.  Through Reseaux IP Europeens (RIPE), the Europeans created
 an open format in RIPE-181 and maintained an open database used for

McPherson & Patel Informational [Page 15] RFC 4277 Experience with the BGP-4 Protocol January 2006

 address and AS registry more than policy.  The initial conversion of
 the PRDB was to RIPE-181 format, and tools were converted to make use
 of this format.  The collection of databases was termed the Internet
 Routing Registry (IRR), with the RIPE database and US NSF-funded
 Routing Arbitrator (RA) being the initial components of the IRR.
 A need to extend RIPE-181 was recognized and RIPE agreed to allow the
 extensions to be defined within the IETF in the RPS WG, resulting in
 the RPSL language.  Other work products of the RPS WG provided an
 authentication framework and a means to widely distribute the
 database in a controlled manner and synchronize the many
 repositories.  Freely available tools were provided, primarily by
 RIPE, Merit, and ISI, the most comprehensive set from ISI.  The
 efforts of the IRR participants has been severely hampered by
 providers unwilling to keep information in the IRR up to date.  The
 larger of these providers have been vocal, claiming that the database
 entry, simple as it may be, is an administrative burden, and some
 acknowledge that doing so provides an advantage to competitors that
 use the IRR.  The result has been an erosion of the usefulness of the
 IRR and an increase in vulnerability of the Internet to routing based
 attacks or accidental injection of faulty routing information.
 There have been a number of cases in which accidental disruption of
 Internet routing was avoided by providers using the IRR, but this was
 highly detrimental to non-users.  Filters have been forced to provide
 less complete coverage because of the erosion of the IRR; these types
 of disruptions continue to occur infrequently, but have an
 increasingly widespread impact.

21. Acknowledgements

 We would like to thank Paul Traina and Yakov Rekhter for authoring
 previous versions of this document and providing valuable input on
 this update.  We would also like to acknowledge Curtis Villamizar for
 providing both text and thorough reviews.  Thanks to Russ White,
 Jeffrey Haas, Sean Mentzer, Mitchell Erblich, and Jude Ballard for
 supplying their usual keen eyes.
 Finally, we'd like to think the IDR WG for general and specific input
 that contributed to this document.

McPherson & Patel Informational [Page 16] RFC 4277 Experience with the BGP-4 Protocol January 2006

22. References

22.1. Normative References

 [RFC1966]   Bates, T. and R. Chandra, "BGP Route Reflection An
             alternative to full mesh IBGP", RFC 1966, June 1996.
 [RFC2385]   Heffernan, A., "Protection of BGP Sessions via the TCP
             MD5 Signature Option", RFC 2385, August 1998.
 [RFC2439]   Villamizar, C., Chandra, R., and R. Govindan, "BGP Route
             Flap Damping", RFC 2439, November 1998.
 [RFC2796]   Bates, T., Chandra, R., and E. Chen, "BGP Route
             Reflection - An Alternative to Full Mesh IBGP", RFC 2796,
             April 2000.
 [RFC3065]   Traina, P., McPherson, D., and J. Scudder, "Autonomous
             System Confederations for BGP", RFC 3065, February 2001.
 [RFC4274]   Meyer, D. and K. Patel, "BGP-4 Protocol Analysis", RFC
             4274, January 2006.
 [RFC4276]   Hares, S. and A. Retana, "BGP 4 Implementation Report",
             RFC 4276, January 2006.
 [RFC4271]   Rekhter, Y., Li, T., and S. Hares, Eds., "A Border
             Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006.
 [RFC1657]   Willis, S., Burruss, J., Chu, J., "Definitions of Managed
             Objects for the Fourth Version of the Border Gateway
             Protocol (BGP-4) using SMIv2", RFC 1657, July 1994.
 [RFC793]    Postel, J., "Transmission Control Protocol", STD 7, RFC
             793, September 1981.

22.2. Informative References

 [RFC1105]   Lougheed, K. and Y. Rekhter, "Border Gateway Protocol
             (BGP)", RFC 1105, June 1989.
 [RFC1163]   Lougheed, K. and Y. Rekhter, "Border Gateway Protocol
             (BGP)", RFC 1163, June 1990.
 [RFC1264]   Hinden, R., "Internet Engineering Task Force Internet
             Routing Protocol Standardization Criteria", RFC 1264,
             October 1991.

McPherson & Patel Informational [Page 17] RFC 4277 Experience with the BGP-4 Protocol January 2006

 [RFC1267]   Lougheed, K. and Y. Rekhter, "Border Gateway Protocol 3
             (BGP-3)", RFC 1267, October 1991.
 [RFC1269]   Willis, S. and J. Burruss, "Definitions of Managed
             Objects for the Border Gateway Protocol: Version 3", RFC
             1269, October 1991.
 [RFC1656]   Traina, P., "BGP-4 Protocol Document Roadmap and
             Implementation Experience", RFC 1656, July 1994.
 [RFC1771]   Rekhter, Y. and T. Li, "A Border Gateway Protocol 4
             (BGP-4)", RFC 1771, March 1995.
 [RFC1773]   Traina, P., "Experience with the BGP-4 protocol", RFC
             1773, March 1995.
 [RFC1965]   Traina, P., "Autonomous System Confederations for BGP",
             RFC 1965, June 1996.
 [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, June 1999.
 [BGPATTACK] Convery, C., "An Attack Tree for the Border Gateway
             Protocol", Work in Progress.
 [SBGP]      "Secure BGP", Work in Progress.
 [soBGP]     "Secure Origin BGP", Work in Progress.

Authors' Addresses

 Danny McPherson
 Arbor Networks
 EMail: danny@arbor.net
 Keyur Patel
 Cisco Systems
 EMail: keyupate@cisco.com

McPherson & Patel Informational [Page 18] RFC 4277 Experience with the BGP-4 Protocol January 2006

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McPherson & Patel Informational [Page 19]

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