INTERNET-DRAFT                                      D. Meyer
draft-ietf-idr-bgp-analysis-05.txt
draft-ietf-idr-bgp-analysis-06.txt                  K. Patel
Category                                       Informational
Expires: December 2004                             June February 2005                           August 2004

                        BGP-4 Protocol Analysis
                  <draft-ietf-idr-bgp-analysis-05.txt>
                  <draft-ietf-idr-bgp-analysis-06.txt>

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   Status of this Document Memo

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Copyright Notice

   Copyright (C) The Internet Society (2004). All Rights Reserved.

Abstract

   The purpose of this report is to document how the requirements for
   advancing a routing protocol from Draft Standard to full 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 [RFC1774] and summarizes the key
   features of BGP-4 protocol, and analyzes the protocol with respect to
   scaling and performance.

                           Table of Contents

   1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . .   4
   2. Key Features and algorithms of the BGP protocol. . . . . . . .   4
    2.1. Key Features. . . . . . . . . . . . . . . . . . . . . . . .   4
    2.2. BGP Algorithms. . . . . . . . . . . . . . . . . . . . . . .   5
    2.3. BGP Finite State Machine (FSM). . . . . . . . . . . . . . .   6
   3. BGP Capabilities . . . . . . . . . . . . . . . . . . . . . . .   7
   4. BGP Persistent Peer Oscillations . . . . . . . . . . . . . . .   7
   5. Implementation Guidelines. . . . . . . . . . . . . . . . . . .   7
   6. BGP Performance characteristics and Scalability. . . . . . . .   8
    6.1. Link bandwidth and CPU utilization. . . . . . . . . . . . .   8
     6.1.1. CPU utilization. . . . . . . . . . . . . . . . . . . . .   9
     6.1.2. Memory requirements. . . . . . . . . . . . . . . . . . .  10
   7. BGP Policy Expressiveness and its Implications . . . . . . . .  11
    7.1. Existence of Unique Stable Routings . . . . . . . . . . . .  12
    7.2. Existence of Stable Routings. . . . . . . . . . . . . . . .  13
   8. Applicability. . . . . . . . . . . . . . . . . . . . . . . . .  14
   9. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . .  15
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  16
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
   12. References. . . . . . . . . . . . . . . . . . . . . . . . . .  17
    12.1. Informative Normative References . . . . . . . . . . . . . . . . . . .  17
   13. Author's Addresses.
    12.2. Informative References . . . . . . . . . . . . . . . . . .  18
   13. Author's Addresses. . . .  19
   14. Full Copyright Statement. . . . . . . . . . . . . . . . . . .  19
   15. Intellectual Property . . . . . . . . . . . . . . . . . . . .  20
   16. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .  20

1.  Introduction

   BGP-4 is an inter-autonomous system routing protocol designed for
   TCP/IP internets. Version 1 of the BGP-4 protocol was published in
   [RFC1105]. Since then BGP versions 2, 3, and 4 have been developed.
   Version 2 was documented in [RFC1163]. Version 3 is documented in
   [RFC1267]. Version 4 is documented in the [BGP4] (version 4 of BGP
   will hereafter be referred to as BGP). The changes between versions
   are explained in Appendix A of [BGP4]. Possible applications of BGP
   in the Internet are documented in [RFC1772].

   BGP introduced support for Classless InterDomain Routing [CIDR].
   Since earlier versions of BGP lacked the support for CIDR, they are
   considered obsolete and unusable in today's Internet.

2.  Key Features and algorithms of the BGP protocol

   This section summarizes the key features and algorithms of the BGP
   protocol. BGP is an inter-autonomous system routing protocol; it is
   designed to be used between multiple autonomous systems. BGP assumes
   that routing within an autonomous system is done by an intra-
   autonomous system routing protocol. BGP also assumes that data
   packets are routed from source towards destination independent of the
   source. BGP does not make any assumptions about intra-autonomous
   system routing protocols deployed within the various autonomous
   systems. Specifically, BGP does not require all autonomous systems to
   run the same intra-autonomous system routing protocol (i.e., interior
   gateway protocol or IGP).

   Finally, note that BGP is a real inter-autonomous system routing
   protocol, and as such it imposes no constraints on the underlying
   interconnect topology of the autonomous systems. The information
   exchanged via BGP is sufficient to construct a graph of autonomous
   systems connectivity from which routing loops may be pruned and many
   routing policy decisions at the autonomous system level may be
   enforced.

2.1.  Key Features

   The key features of the protocol are the notion of path attributes
   and aggregation of network layer reachability information (NLRI).

   Path attributes provide BGP with flexibility and extensibility. Path
   attributes are partitioned into well-known and optional. The
   provision for optional attributes allows experimentation that may
   involve a group of BGP routers without affecting the rest of the
   Internet. New optional attributes can be added to the protocol in
   much the same way that new options are added to, say, the Telnet
   protocol [RFC854].

   One of the most important path attributes is the Autonomous System
   Path, or AS_PATH. Autonomous System's (AS) As the reachability information traverses the
   Internet, this (AS_PATH) information is augmented by the list of
   autonomous systems that have been traversed thus far, forming the
   AS_PATH. The AS_PATH allows straightforward suppression of the
   looping of routing information. In addition, the AS_PATH serves as a
   powerful and versatile mechanism for policy-based routing.

   BGP enhances the AS_PATH attribute to include sets of autonomous
   systems as well as lists via the AS_SET attribute. This extended
   format allows generated aggregate routes to carry path information
   from the more specific routes used to generate the aggregate. It
   should be noted however, that as of this writing, AS_SETs are rarely
   used in the Internet [ROUTEVIEWS].

2.2.  BGP Algorithms

   BGP uses an algorithm that is neither a pure distance vector
   algorithm or a pure link state algorithm. It is instead a modified
   distance vector algorithm referred to as a "Path Vector" algorithm
   that uses path information to avoid traditional distance vector
   problems. Each route within BGP pairs destination with path
   information to that destination. Path information (also known as
   AS_PATH information) is stored within the AS_PATH attribute in BGP.
   The path information assist BGP in detecting AS loops thereby
   allowing BGP speakers select loop free routes.

   BGP uses an incremental update strategy in order to conserve
   bandwidth and processing power. That is, after initial exchange of
   complete routing information, a pair of BGP routers exchanges only
   changes to that information. Such an incremental update design
   requires reliable transport between a pair of BGP routers to function
   correctly. BGP solves this problem by using TCP for reliable
   transport. TCP further assist BGP in limiting congestion to the
   advertised window limits.

   In addition to incremental updates, BGP has added the concept of
   route aggregation so that information about groups of destinations
   that use hierarchical address assignment (e.g., CIDR) may be
   aggregated and sent as a single Network Layer Reachability (NLRI).

   Finally, note that BGP is a self-contained protocol. That is, BGP
   specifies how routing information is exchanged both between BGP
   speakers in different autonomous systems, and between BGP speakers
   within a single autonomous system.

2.3.  BGP Finite State Machine (FSM)

   The BGP FSM is a set of rules that are applied to a BGP speaker's set
   of configured peers for the BGP operation. A BGP implementation
   requires that a BGP speaker must connect to and listen on TCP port
   179 for accepting any new BGP connections from its peers. The BGP
   Finite State Machine, or FSM, must be initiated and maintained for
   each new incoming and outgoing peer connections. However, in steady
   state operation, there will be only one BGP FSM per connection per
   peer.

   There may exist a temporary period where in a BGP peer may have
   separate incoming and outgoing connections resulting into two
   different BGP FSMs for a peer (instead of one). This can be resolved
   following BGP connection collision rules defined in the [BGP4].

   Following are different states of BGP FSM for its peers:

   IDLE:           State when BGP peer refuses any incoming
                   connections.

   CONNECT:        State in which BGP peer is waiting for
                   its TCP connection to be completed.

   ACTIVE:         State in which BGP peer is trying to acquire a
                   peer by listening and accepting TCP connection.

   OPENSENT:       BGP peer is waiting for OPEN message from its
                   peer.

   OPENCONFIRM:    BGP peer is waiting for KEEPALIVE or NOTIFICATION
                   message from its peer.

   ESTABLISHED:    BGP peer connection is established and exchanges
                   UPDATE, NOTIFICATION, and KEEPALIVE messages with
                   its peer.

   There are different BGP events that operate on above mentioned states
   of BGP FSM for BGP peers. These BGP events are either mandatory or
   optional. They are triggered by the protocol logic as part of the BGP
   or using an operator intervention via a configuration interface to
   the BGP protocol.

   These BGP events are of following types: Optional events linked to
   Optional Session attributes, Administrative Events, Timer Events,
   TCP Connection based Events, and BGP Message-based Events. Both,
   the FSM and the BGP events are explained in details in [BGP4].

3.  BGP Capabilities

   The BGP Capability mechanism [RFC2842] provides an easy and flexible
   way to introduce new features within the protocol. In particular, the
   BGP capability mechanism allows a BGP speaker to advertise to its
   peers during startup various optional features supported by the
   speaker (and receive similar information from the peers). This allows
   the base BGP protocol to contain only essential functionality, while
   at the same time providing a flexible mechanism for signaling
   protocol extensions.

4.  BGP Persistent Peer Oscillations

   Ideally, whenever a BGP speaker detects an error in any peer
   connection, it shuts down the peer and changes its FSM state to IDLE.
   BGP speaker requires a Start event to re-initiate its idle peer
   connection. If the error remains persistent and BGP speaker generates
   Start event automatically then it may result in persistent peer
   flapping. However, although peer oscillation is found to be wide-
   spread in BGP implementations, methods for preventing persistent peer
   oscillations are outside the scope of base BGP protocol
   specification.

5.  Implementation Guidelines

   A robust BGP implementation is work conserving. This means that if
   the number of prefixes is bound, arbitrarily high levels of route
   change can be tolerated with bounded impact on route convergence for
   occasional changes in generally stable routes.

   A robust implementation of BGP should have the following
   characteristics:
         1.  It is able to operate in almost arbitrarily high levels
             of route flap without loosing peerings (failing to send
             keepalives) or loosing other protocol adjacencies as a
             result of BGP load.

         2.  Instability of a subset of routes should not affect the
             route advertisements or forwarding associated with the set
             of stable routes.

         3.  High levels of instability and peers of different CPU speed
             or load resulting in faster or slower processing of routes
             should not cause instability and should have a bounded
             impact on the convergence time for generally stable routes.

   Numerous robust BGP implementations exist.  Producing a robust
   implementation is not a trivial matter but clearly achievable.

6.  BGP Performance characteristics and Scalability

   In this section, we provide "order of magnitude" answers to the
   questions of how much link bandwidth, router memory and router CPU
   cycles the BGP protocol will consume under normal conditions.  In
   particular, we will address the scalability of BGP and its
   limitations.

6.1.  Link bandwidth and CPU utilization

   Immediately after the initial BGP connection setup, BGP peers
   exchange complete set of routing information.  If we denote the total
   number of routes in the Internet by N, the total path attributes (for
   all N routes) received from a peer as A, and assume that the networks
   are uniformly distributed among the autonomous systems, then the
   worst case amount of bandwidth consumed during the initial exchange
   between a pair of BGP speakers (P) is

           BW = O((N + A) * P)
   The following table illustrates the typical amount of bandwidth
   consumed during the initial exchange between a pair of BGP-4 speakers
   based on the above assumptions (ignoring bandwidth consumed by the
   BGP-4 Header).  For purposes of the estimates here, we will calculate
   BW = (((4 * N) + A) * P).
   BGP-4 was created specifically to reduce the size of the set of NLRI
   entries which have to be carried and exchanged by border routers.
   The aggregation scheme, defined in [RFC1519],describes [CIDR],describes the provider-
   based aggregation scheme in use in today's Internet.

   Due to the advantages of advertising a few large aggregate blocks
   instead of many smaller class-based individual networks, it is
   difficult to estimate the actual reduction in bandwidth and
   processing that BGP-4 has provided over BGP-3.  If we simply
   enumerate all aggregate blocks into their individual class-based
   networks, we would not take into account "dead" space that has been
   reserved for future expansion.  The best metric for determining the
   success of BGP's aggregation is to sample the number NLRI entries in
   the globally connected Internet today and compare it to projected
   growth rates before BGP was deployed.

   At the time of this writing, the full set of exterior routes carried
   by BGP is approximately 120,000 134,000 network entries [ROUTEVIEWS].

6.1.1.  CPU utilization

   An important and fundamental feature of BGP is that BGP's CPU
   utilization depends only on the stability of its network which
   relates to BGP in terms of BGP UPDATE message announcments.  If the
   BGP network is stable: all the BGP routers within its network are in
   the steady state; then the only link bandwidth and router CPU cycles
   consumed by BGP are due to the exchange of the BGP KEEPALIVE
   messages.  The KEEPALIVE messages are exchanged only between peers.
   The suggested frequency of the exchange is 30 seconds.  The KEEPALIVE
   messages are quite short (19 octets), and require virtually no
   processing.  As a result, the bandwidth consumed by the KEEPALIVE
   messages is about 5 bits/sec.  Operational experience confirms that
   the overhead (in terms of bandwidth and CPU) associated with the
   KEEPALIVE messages should be viewed as negligible.

   During the periods of network instability, BGP routers within the
   network are generating routing updates that are exchanged using the
   BGP UPDATE messages.  The greatest overhead per UPDATE message occurs
   when each UPDATE message contains only a single network. It should be
   pointed out that in practice routing changes exhibit strong locality
   with respect to the route attributes.  That is, routes that change
   are likely to have common route attributes. In this case, multiple
   networks can be grouped into a single UPDATE message, thus
   significantly reducing the amount of bandwidth required (see also
   Appendix F.1 of [BGP4]).

6.1.2.  Memory requirements

   To quantify the worst case memory requirements for BGP, we denote the
   total number of networks in the Internet by N, the mean AS distance
   of the Internet by M (distance at the level of an autonomous system,
   expressed in terms of the number of autonomous systems), the total
   number of unique AS paths as A.  Then the worst case memory
   requirements (MR) can be expressed as

           MR = O(N + (M * A))

   Since a mean AS distance M is a slow moving function of the
   interconnectivity ("meshiness") of the Internet, for all practical
   purposes the worst case router memory requirements are on the order
   of the total number of networks in the Internet times the number of
   peers the local system is peering with.  We expect that the total
   number of networks in the Internet will grow much faster than the
   average number of peers per router.  As a result, BGP's memory
   scaling properties are linearly related to the total number of
   networks in the Internet.

   The following table illustrates typical memory requirements of a
   router running BGP.  We denote average number of routes advertised by
   each peer as N, the total number of unique AS paths as A, the mean AS
   distance of the Internet as M (distance at the level of an autonomous
   system, expressed in terms of the number of autonomous systems),
   number of bytes required to store a network as R, and number of bytes
   required to store one AS in an AS path as P.  It is assumed that each
   network is encoded as four bytes, each AS is encoded as two bytes,
   and each networks is reachable via some fraction of all of the peers
   (# BGP peers/per net).  For purposes of the estimates here, we will
   calculate MR = (((N * R) + (M * A) * P) * S).

   # Networks  Mean AS Distance # AS's # BGP peers/per net Memory Req
       (N)             (M)        (A)          (P)             (MR)
    ----------  ---------------- ------ ------------------- --------------
     100,000           20         3,000         20           10,400,000
     100,000           20        15,000         20           20,000,000
     120,000           10        15,000        100           78,000,000
     140,000           15        20,000        100           116,000,000

   In analyzing BGP's memory requirements, we focus on the size of the
   BGP RIB table (and ignoring implementation details).  In particular,
   we derive upper bounds for the size of the BGP RIB table.  For
   example, at the time of this writing, the BGP RIB tables of a typical
   backbone router carry on the order of 120,000 entries.  Given this
   number, one might ask whether it would be possible to have a
   functional router with a table that will have 1,000,000 entries.
   Clearly the answer to this question is more related to how BGP is
   implemented. A robust BGP implementation with a reasonable CPU and
   memory should not have issues scaling to such limits.

7.  BGP Policy Expressiveness and its Implications

   BGP is unique among deployed IP routing protocols in that routing is
   determined using semantically rich routing policies.  Although
   routing policies are usually the first thing that comes to a network
   operator's mind concerning BGP, it is important to note that the
   languages and techniques for specifying BGP routing policies are not
   actually a part of the protocol specification ([RFC2622] for an
   example of such a policy language).  In addition, the BGP
   specification contains few restrictions, either explicitly or
   implicitly, on routing policy languages.  These languages have
   typically been developed by vendors and have evolved through
   interactions with network engineers in an environment lacking vendor-
   independent standards.

   The complexity of typical BGP configurations, at least in provider
   networks, has been steadily increasing.  Router vendors typically
   provided hundreds of special commands for use in the configuration of
   BGP, and this command set is continually expanding.  For example, BGP
   communities [RFC1997] allow policy writers to selectively attach tags
   to routes and use these to signal policy information to other BGP-
   speaking routers.  Many providers allow customers, and sometimes
   peers, to send communities that determine the scope and preference of
   their routes.  These developments have more and more given the task
   of writing BGP configurations aspects associated with open-ended
   programming.  This has allowed network operators to encode complex
   policies in order to address many unforeseen situations, and has
   opened the door for a great deal of creativity and experimentation in
   routing policies.  This policy flexibility is one of the main reasons
   why BGP is so well suited to the commercial environment of the
   current Internet.

   However, this rich policy expressiveness has come with a cost that is
   often not recognized.  In particular, it is possible to construct
   locally defined routing policies that can lead to unexpected global
   routing anomalies such as (unintended) nondeterminism and to protocol
   divergence.  If the interacting policies causing such anomalies are
   defined in different autonomous systems, then these problems can be
   very difficult to debug and correct.  In the following sections, we
   describe two such cases relating to the existence (or lack thereof)
   of stable routings.

7.1.  Existence of Unique Stable Routings

   One can easily construct sets of policies for which BGP can not
   guarantee that stable routings are unique.  This can be illustrated
   by the following simple example.  Consider the example of four
   Autonomous Systems, AS1, AS2, AS3, and AS4.  AS1 and AS2 are peers,
   and they provide transit for AS3 and AS4 respectively, Suppose
   further that AS3 provides transit for AS4 (in this case AS3 is a
   customer of AS1, and AS4 is  a multihomed customer of both AS3 and
   AS2).  AS4 may want to use the link to AS3 as a "backup" link, and
   sends AS3 a community value that AS3 has configured to lower the
   preference of AS4's routes to a level below that of its upstream
   provider, AS1.  The intended "backup routing" to AS4 is illustrated
   here:

           AS1 ------> AS2
           /|\          |
            |           |
            |           |
            |          \|/
           AS3 ------- AS4
   That is, the AS3-AS4 link is intended to be used only when the
   AS2-AS4 link is down (for outbound traffic, AS4 simply gives routes
   from AS2 a higher local preference).  This is a common scenario in
   today's Internet.  But note that this configuration has another
   stable solution:

           AS1 ------- AS2
            |           |
            |           |
            |           |
           \|/         \|/
           AS3 ------> AS4

   In this case, AS3 does not translate the "depref my route" community
   received from AS4 into a "depref my route" community for AS1, and so
   if AS1 hears the route to AS4 that transits AS3 it will prefer that
   route (since AS3 is a customer).  This state could be reached, for
   example, by starting in the "correct" backup routing shown first,
   bringing down the AS2-AS4 BGP session, and then bringing it back up.
   In general, BGP has no way to prefer the "intended" solution over the
   anomalous one, and which is picked will depend on the unpredictable
   order of BGP messages.

   While this example is relatively simple, many operators may fail to
   recognize that the true source of the problem is that the BGP
   policies of ASes can interact in unexpected ways, and that these
   interactions can result in multiple stable routings.  One can imagine
   that the interactions could be much more complex in the real
   Internet.  We suspect that such anomalies will only become more
   common as BGP continues to evolve with richer policy expressiveness.
   For example, extended communities provide an even more flexible means
   of signaling information within and between autonomous systems than
   is possible with [RFC1997] communities.  At the same time,
   applications of communities by network operators are evolving to
   address complex issues of inter-domain traffic engineering.

7.2.  Existence of Stable Routings

   One can also construct a set of policies for which BGP can not
   guarantee that a stable routing exists (or worse, that a stable
   routing will ever be found).  For example, [RFC3345] documents
   several scenarios that lead to route oscillations associated with the
   use of the Multi-Exit Discriminator or MED, attribute.  Route
   oscillation will happen in BGP when a set of policies has no
   solution.  That is, when there is no stable routing that satisfies
   the constraints imposed by policy, then BGP has no choice by to keep
   trying.  In addition, BGP configurations can have a stable routing,
   yet the protocol may not be able to find it; BGP can "get trapped"
   down a blind alley that has no solution.

   Protocol divergence is not, however, a problem associated solely with
   use of the MED attribute.  This potential exists in BGP even without
   the use of the MED attribute.  Hence, like the unintended
   nondeterminism described in the previous section, this type of
   protocol divergence is an unintended consequence of the unconstrained
   nature of BGP policy languages.

8.  Applicability

   In this section we answer the question of which environments is BGP
   well suited, and for which environments it is not suitable.  This
   question is partially answered in Section 2 of BGP [BGP4], which
   states:

        "To characterize the set of policy decisions that can be enforced
        using BGP, one must focus on the rule that an AS advertises to its
        neighbor ASs only those routes that it itself uses.  This rule
        reflects the "hop-by-hop" routing paradigm generally used
        throughout the current Internet.  Note that some policies cannot
        be supported by the "hop-by-hop" routing paradigm and thus require
        techniques such as source routing to enforce.  For example, BGP
        does not enable one AS to send traffic to a neighbor AS intending
        that the traffic take a different route from that taken by traffic
        originating in the neighbor AS.  On the other hand, BGP can
        support any policy conforming to the "hop-by-hop" routing
        paradigm.  Since the current Internet uses only the "hop-by-hop"
        routing paradigm and since BGP can support any policy that
        conforms to that paradigm, BGP is highly applicable as an inter-AS
        routing protocol for the current Internet."

   One of the important points here is that the BGP protocol contains
   only the functionality that is essential, while at the same time
   providing a flexible mechanism within the protocol that allow us to
   extend its functionality.  For example, BGP capabilities provide an
   easy and flexible way to introduce new features within the protocol.
   Finally, since BGP was designed with flexibility and extensibility in
   mind, new and/or evolving requirements can be addressed via existing
   mechanisms.

   To summarize, BGP is well suitable as an inter-autonomous system
   routing protocol for any internet that is based on IP [RFC791] as the
   internet protocol and "hop-by-hop" routing paradigm.

9.  Acknowledgments

   We would like to thank Paul Traina for authoring previous versions of
   this document.  Tim Griffin, Randy Presuhn, Curtis Villamizar and
   Atanu Ghosh also provided many insightful comments on earlier
   versions of this document.

10.  Security Considerations

   BGP provides flexible mechanisms with varying levels of complexity
   for security purposes.  BGP sessions are authenticated using BGP
   session addresses and the assigned AS number.  Since BGP sessions use
   TCP (and IP) for reliable transport, BGP sessions are further
   authenticated and secured by any authentication and security
   mechanisms used by TCP and IP.

   BGP uses TCP MD5 option for validating data and protecting against
   spoofing of TCP segments exhanged between its sessions.  The usage of
   TCP MD5 option for BGP is described at length in [RFC 2385].  The TCP
   MD5 Key management is discussed in [RFC 3562]. BGP data encryption is
   provided using IPsec mechanism which encrypts the IP payload data
   (including TCP and BGP data).  The IPsec mechanism can be used in
   both, the transport mode as well as the tunnel mode. The IPsec
   mechanism is described in [RFC 2406]. Both, the TCP MD5 option and
   the IPsec mechanism are not widely deployed security mechanisms for
   BGP in today's Internet and hence it is difficult to guage their real
   performance impact when using with BGP.  However, since both the
   mechanisms are TCP and IP based security mechanisms, the Link
   Bandwidth, CPU utilization and router memory consumed by BGP protocol
   using it would be same as any other TCP and IP based protocols.

   BGP uses IP TTL value to protect its EBGP sessions from any TCP (or
   IP) based CPU intensive attacks.  It is a simple mechanism which
   suggests the use of filtering BGP (TCP) segments using the IP TTL
   value carried within the IP header of BGP (TCP) segments exchanged
   between the EBGP sessions.  The BGP TTL mechanism is described in
   [BTSH]. Usage of [BTSH] impacts performance in a similar way as using
   any ACL policies for BGP.

   Such flexible TCP and IP based security mechanisms, allow BGP to
   prevent insertion/deletion/modification of BGP data, any snooping of
   the data, session stealing, etc.  However, BGP is vulnerable to the
   same security attacks that are present in TCP.  The [BGP-VUL]
   explains in depth about the BGP security vulneribility. At the time
   of this writing, several efforts are underway for creating and
   defining an appropriate security infrastructure within the BGP
   protocol to provide authentication and security for its routing
   information; some of which include [SBGP] and [SOBGP].

11.  IANA Considerations

   This document presents an analysis of the BGP protocol and hence
   presents no new IANA considerations.

12.  References

12.1.  Informative  Normative References

   [BGP4]          Rekhter, Y., T. Li., and S. Hares, Editors, "A
                   Border Gateway Protocol 4 (BGP-4)",
                   draft-ietf-idr-bgp4-20.txt. Work in progress.

   [CIDR]          Fuller, V., Li, T., Yu, J., and K. Varadhan,
                   "Classless Inter-Domain Routing (CIDR): an Address
                   Assignment and Aggregation Strategy", RFC 1519,
                   September, 1993.

   [RFC791]        "INTERNET PROTOCOL", DARPA INTERNET PROGRAM
                   PROTOCOL SPECIFICATION, RFC 791, September,
                   1981.

   [RFC854]        Postel, J. and J. Reynolds, "TELNET PROTOCOL
                   SPECIFICATION", RFC 854, May, 1983.

   [RFC1105]       Lougheed, K.,

   [RFC1997]       Chandra. R, and Y. Rekhter, "Border Gateway
                   Protocol BGP", T. Li, "BGP Communities
                   Attribute",  RFC 1105, June 1989.

   [RFC1163]       Lougheed, K., 1997, August, 1996.

   [RFC2842]       Chandra, R. and Rekhter, Y, "Border Gateway
                   Protocol BGP", RFC 1105, June 1990.

   [RFC1264]       Hinden, R., "Internet Routing Protocol
                   Standardization Criteria", J. Scudder, "Capabilities
                   Advertisement with BGP-4", RFC 1264, October 1991.

   [RFC1267]       Lougheed, K., 2842, May 2000.

   [RFC3345]       McPherson, D., Gill, V., Walton, D., and Rekhter, Y,
                   A. Retana, "Border Gateway Protocol 3 (BGP-3)", (BGP) Persistent
                   Route Oscillation Condition", RFC 1105, October 1991.

   [RFC1519]       Fuller, 3345,
                   August, 2002.

   [BTSH]          Gill, V., Li. T., Yu J., and K. Varadhan,
                   "Classless Inter-Domain Routing (CIDR): an
                   Address Assignment and Aggregation Strategy", RFC
                   1519, September 1993.

   [RFC1771]       Rekhter, Y., and T. Li, "A Border Gateway
                   Protocol 4 (BGP-4)", RFC 1771, March 1995.

   [RFC1772]       Rekhter, Y., and P. Gross, Editors, "Application
                   of the Border Gateway Protocol in the Internet",
                   RFC 1772, March 1995.

   [RFC1774]       Traina, P., "BGP-4 protocol analysis",
                   RFC 1774, March, 1995.

   [RFC1997]       Chandra. R, and T. Li, "BGP Communities
                   Attribute",  RFC 1997, August, 1996.

   [RFC2622]       Alaettinoglu, C., et. al., "Routing Policy
                   Specification Language (RPSL)" RFC 2622, May,
                   1998.

   [RFC2842]       Chandra, R. and J. Scudder, "Capabilities
                   Advertisement with BGP-4", RFC 2842, May 2000.

   [RFC3345]       McPherson, D., Gill, V., Walton, D., and
                   A. Retana, "Border Gateway Protocol (BGP) Persistent
                   Route Oscillation Condition", RFC 3345,
                   August, 2002.

   [BTSH]          Gill, V., Heasley, Heasley, J., and D. Meyer, "The BGP TTL
                   Security Hack (BTSH)", draft-gill-btsh-02.txt.
                   Work in progress.

   [RFC2385]       Heffernan, A., "Protection of BGP Sessions via
                   the TCP MD5 Signature Option", RFC 2385,
                   August, 1998.

   [RFC3562]       Leech, M., "Key Management Considerations for
                   the TCP MD5 Signature Option", RFC 3562,
                   July, 2003.

   [RFC2406]       Kent, S., Atkinson, R., "IP Encapsulating Security
                   Payload (ESP)", RFC 2406, November, 1998.

   [ROUTEVIEWS]    Meyer, D., "The Route Views Project",
                   http://www.routeviews.org

   [SBGP]          Lynn, C., Mikkelson, J., and K. Seo, "Secure BGP S-BGP",
                   Internet-Draft, Work in Progress.

   [soBGP]         White, R., "Architecture and Deployment Considerations for
                   Secure Origin BGP (soBGP)", Internet-Draft, Work in Progress.

   [BGP_VULN]      Murphy, S., "BGP Security Vulnerabilities Analysis",
                   draft-ietf-idr-bgp-vuln-00.txt. work in progress

13.  Author's Addresses

   David Meyer
   Email: dmm@1-4-5.net

   Keyur Patel
   Cisco Systems
   Email: keyupate@cisco.com

14.  Full Copyright Statement

   Copyright (C) The Internet Society (2004). This document is subject
   to the rights, licenses

   [SBGP]          Lynn, C., Mikkelson, J., and restrictions contained K. Seo, "Secure BGP S-BGP",
                   Internet-Draft, Work in BCP 78 and
   except as set forth therein, the authors retain all their rights.

   This document and translations of it may be copied and furnished to
   others, Progress.

12.2.  Informative References

   [RFC854]        Postel, J. and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published J. Reynolds, "TELNET PROTOCOL
                   SPECIFICATION", RFC 854, May, 1983.

   [RFC1105]       Lougheed, K., and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice Y. Rekhter, "Border Gateway
                   Protocol BGP", RFC 1105, June 1989.

   [RFC1163]       Lougheed, K., and this paragraph are
   included on all such copies Rekhter, Y, "Border Gateway
                   Protocol BGP", RFC 1105, June 1990.

   [RFC1264]       Hinden, R., "Internet Routing Protocol
                   Standardization Criteria", RFC 1264, October 1991.

   [RFC1267]       Lougheed, K., and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual Rekhter, Y, "Border Gateway
                   Protocol 3 (BGP-3)", RFC 1105, October 1991.

   [RFC1771]       Rekhter, Y., and will not be
   revoked by the Internet Society or its successors or assigns.

   This document T. Li, "A Border Gateway
                   Protocol 4 (BGP-4)", RFC 1771, March 1995.

   [RFC1772]       Rekhter, Y., and P. Gross, Editors, "Application
                   of the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

15. Border Gateway Protocol in the Internet",
                   RFC 1772, March 1995.

   [RFC1774]       Traina, P., "BGP-4 protocol analysis",
                   RFC 1774, March, 1995.

   [RFC2622]       Alaettinoglu, C., et. al., "Routing Policy
                   Specification Language (RPSL)" RFC 2622, May,
                   1998.

   [RFC2406]       Kent, S., Atkinson, R., "IP Encapsulating Security
                   Payload (ESP)", RFC 2406, November, 1998.

   [ROUTEVIEWS]    Meyer, D., "The Route Views Project",
                   http://www.routeviews.org

13.  Author's Addresses

   David Meyer
   Email: dmm@1-4-5.net

   Keyur Patel
   Cisco Systems
   Email: keyupate@cisco.com

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16.  Acknowledgement
   ietf-ipr@ietf.org.

Disclaimer of Validity

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Copyright Statement

   Copyright (C) The Internet Society (2004).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.

Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.