Request for Comments: 4274
BGP-4 Protocol Analysis
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 © The Internet Society (2006).
The purpose of this report 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 1774 and summarizes the key features of BGP-4, as well as analyzes the protocol with respect to scaling and performance.
Table of Contents
1. Introduction ....................................................2 2. Key Features and Algorithms of BGP ..............................3 2.1. Key Features ...............................................3 2.2. BGP Algorithms .............................................4 2.3. BGP Finite State Machine (FSM) .............................4 3. BGP Capabilities ................................................5 4. BGP Persistent Peer Oscillations ................................6 5. Implementation Guidelines .......................................6 6. BGP Performance Characteristics and Scalability .................6 6.1. Link Bandwidth and CPU Utilization .........................7 7. BGP Policy Expressiveness and its Implications ..................9 7.1. Existence of Unique Stable Routings .......................10 7.2. Existence of Stable Routings ..............................11 8. Applicability ..................................................12 9. Acknowledgements ...............................................12 10. Security Considerations .......................................12 11. References ....................................................13 11.1. Normative References ....................................13 11.2. Informative References ..................................14
BGP-4 is an inter-autonomous system routing protocol designed for TCP/IP internets. Version 1 of BGP-4 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 [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 Inter-Domain Routing (CIDR) [RFC1519]. Because earlier versions of BGP lacked the support for CIDR, they are considered obsolete and unusable in today's Internet.
The purpose of this report 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 [RFC1774] and summarizes the key features of BGP-4, as well as analyzes the protocol with respect to scaling and performance.
2. Key Features and Algorithms of BGP
This section summarizes the key features and algorithms of BGP. 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 either well-known or 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, for example, the Telnet protocol [RFC854].
One of the most important path attributes is the Autonomous System Path, or AS_PATH. 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. Instead, it uses a modified distance vector algorithm, referred to as a "Path Vector" algorithm. This algorithm uses path information to avoid traditional distance vector problems. Each route within BGP pairs information about the 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 assists BGP in detecting AS loops, thereby allowing BGP speakers to select loop-free routes.
BGP uses an incremental update strategy to conserve bandwidth and processing power. That is, after initial exchange of complete routing information, a pair of BGP routers exchanges only the changes to that information. Such an incremental update design requires reliable transport between a pair of BGP routers in order to function correctly. BGP solves this problem by using TCP for reliable transport.
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 is 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 connection. However, in steady state operation, there will be only one BGP FSM per connection per peer.
There may be a short period during which a BGP peer may have separate incoming and outgoing connections resulting in the creation of two different BGP FSMs relating to a peer (instead of one). This can be resolved by following the BGP connection collision rules defined in the [BGP4] specification.
The BGP FSM has the following states associated with each of 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 a number of BGP events that operate on the above mentioned states of the BGP FSM for BGP peers. Support of these BGP events is either mandatory or optional. These events are triggered by the protocol logic as part of the BGP or by 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 detail in [BGP4].
3. BGP Capabilities
The BGP capability mechanism [RFC3392] 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 to contain only essential functionality, while providing a flexible mechanism for signaling protocol extensions.
4. BGP Persistent Peer Oscillations
Whenever a BGP speaker detects an error in a peer connection, it shuts down the peer and changes its FSM state to IDLE. BGP speaker requires a Start event to re-initiate an idle peer connection. If the error remains persistent and BGP speaker generates a Start event automatically, then it may result in persistent peer flapping. 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 specification.
5. Implementation Guidelines
A robust BGP implementation is "work conserving". This means that if the number of prefixes is bounded, arbitrarily high levels of route change can be tolerated. High levels 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:
- It is able to operate in almost arbitrarily high levels of route flap without losing peerings (failing to send keepalives) or losing other protocol adjacencies as a result of BGP load.
- Instability of a subset of routes should not affect the route advertisements or forwarding associated with the set of stable routes.
- Instability should not be caused by peers with high levels of instability or with different CPU speed or load that result in faster or slower processing of routes. These instable peers 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 is 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 BGP 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 sets of routing information. If we denote the total number of routes in the Internet as 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)
BGP-4 was created specifically to reduce the size of the set of NLRI entries, which has to be carried and exchanged by border routers. The aggregation scheme, defined in [RFC1519], 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 growth rates that were projected before BGP was deployed.
At the time of this writing, the full set of exterior routes carried by BGP is approximately 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 announcements. If the BGP network is stable, all the BGP routers within its network are in the steady state. Thus, 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 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 as N, 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), 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))
Because 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 multiplied by the number of peers that 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 the 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), the number of octets required to store a network as R, and the 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 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 # ASes # 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 (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 containing 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 BGP issue that comes to a network operator's mind, it is important to note that the languages and techniques for specifying BGP routing policies are not part of the protocol specification (see [RFC2622] for an example of such a policy language). In addition, the BGP specification contains few restrictions, explicit or implicit, 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 provide 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 to 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. Due to these developments, the task of writing BGP configurations has increasingly more 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 protocol divergence and unexpected global routing anomalies such as (unintended) non- determinism. 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 cannot guarantee that stable routings are unique. This is illustrated by the following simple example. Consider four Autonomous Systems, AS1, AS2, AS3, and AS4. AS1 and AS2 are peers, and they provide transit for AS3 and AS4, respectively. Suppose 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. Therefore, if AS1 hears the route to AS4 that transits AS3, it will prefer that route (because 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. The solution 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 cannot 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 (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, BGP has no choice but to keep trying. In addition, even if BGP configurations can have a stable routing, 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.
In this section we identify the environments for which BGP is well suited, and the environments for which 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 ASes 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 BGP contains only essential functionality, while at the same time providing a flexible mechanism within the protocol that allows us to extend its functionality. For example, BGP capabilities provide an easy and flexible way to introduce new features within the protocol. Finally, because BGP was designed to be flexible and extensible, new and/or evolving requirements can be addressed via existing mechanisms.
To summarize, BGP is well suited as an inter-autonomous system routing protocol for any internet that is based on IP [RFC791] as the internet protocol and the "hop-by-hop" routing paradigm.
We would like to thank Paul Traina for authoring previous versions of this document. Elwyn Davies, 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. Because 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 exchanged between its sessions. The usage of TCP MD5 option for BGP is described at length in [RFC2385]. The TCP MD5 Key management is discussed in [RFC3562]. BGP data encryption is provided using the IPsec mechanism, which encrypts the IP payload data (including TCP and BGP data). The IPsec mechanism can be used in both the transport mode and the tunnel mode. The IPsec mechanism is described in [RFC2406]. Both the TCP MD5 option and the IPsec mechanism are not widely deployed security mechanisms for BGP in today's Internet. Hence, it is difficult to gauge their real performance impact when using with BGP. However, because both the mechanisms are TCP- and IP-based security mechanisms, the Link Bandwidth, CPU utilization and router memory consumed by BGP would be the same as any other TCP- and IP-based protocols.
BGP uses the IP TTL value to protect its External BGP (EBGP) sessions from any TCP- or IP-based CPU-intensive attacks. It is a simple mechanism that suggests the use of filtering BGP (TCP) segments, using the IP TTL value carried within the IP header of BGP (TCP) segments that are exchanged between the EBGP sessions. The BGP TTL mechanism is described in [RFC3682]. Usage of [RFC3682] impacts performance in a similar way as using any access control list (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-VULN] explains in depth about the BGP security vulnerability. 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; these efforts include [SBGP] and [SOBGP].
11.1. Normative References
[BGP4] Rekhter, Y., Li., T., and S. Hares, Eds., "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006. [RFC1519] 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] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. [RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities Attribute", RFC 1997, August 1996. [RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5 Signature Option", RFC 2385, August 1998. [RFC3345] McPherson, D., Gill, V., Walton, D., and A. Retana, "Border Gateway Protocol (BGP) Persistent Route Oscillation Condition", RFC 3345, August 2002. [RFC3562] Leech, M., "Key Management Considerations for the TCP MD5 Signature Option", RFC 3562, July 2003. [RFC3682] Gill, V., Heasley, J., and D. Meyer, "The Generalized TTL Security Mechanism (GTSM)", RFC 3682, February 2004. [RFC3392] Chandra, R. and J. Scudder, "Capabilities Advertisement with BGP-4", RFC 3392, November 2002. [BGP-VULN] Murphy, S., "BGP Security Vulnerabilities Analysis", RFC 4272, January 2006. [SBGP] Seo, K., S. Kent and C. Lynn, "Secure Border Gateway Protocol (Secure-BGP)", IEEE Journal on Selected Areas in Communications Vol. 18, No. 4, April 2000, pp. 582- 592.
11.2. Informative References
[RFC854] Postel, J. and J. Reynolds, "Telnet Protocol Specification", STD 8, RFC 854, May 1983. [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 Routing Protocol Standardization Criteria", RFC 1264, October 1991. [RFC1267] Lougheed, K. and Y. Rekhter, "Border Gateway Protocol 3 (BGP-3)", RFC 1267, October 1991. [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. [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. [RFC2406] Kent, S. and R. Atkinson, "IP Encapsulating Security Payload (ESP)", RFC 2406, November 1998. [ROUTEVIEWS] Meyer, D., "The Route Views Project", http://www.routeviews.org. [SOBGP] White, R., "Architecture and Deployment Considerations for Secure Origin BGP (soBGP)", Work in Progress, May 2005.
David Meyer EMail: email@example.com
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