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7.8.1.0 - Force10 Networks

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FTOS supports Border Gateway Protocol (BGP) version 4, and implements BGP based on the following<br />

IETF documents:<br />

• RFC 1771 (BGPv4)<br />

• ID draft-ietf-idr-bgp4-15.txt (revision to BGPv4)<br />

• RFC 1772 (Application of BGP in the Internet)<br />

• RFC 1997 (BGP Communities Attribute)<br />

• RFC 1998 (Application of the BGP Community Attribute in Multi-home Routing)<br />

• RFC 2270 (Using a Dedicated AS for Sites Homed to a Single Provider)<br />

• RFC 2439 (BGP Route Flap Dampening)<br />

• RFC 2519 (A Framework for Inter-Domain Route Aggregation)<br />

• RFC 2796 (BGP Route Reflection - An Alternative to Full Mesh IBGP)<br />

• RFC 2842 (Capabilities Advertisement with BGP-4)<br />

• RFC 2918 (Route Refresh Capability for BGP-4)<br />

• RFC 3065 (Autonomous System Confederations for BGP)<br />

• RFC 2858 (MultiProtocol Border Gateway Protocol on BGPv4)<br />

• RFC 4360 (BGP Extended Communities Attribute)<br />

Protocol Overview<br />

Border Gateway Protocol (BGP) is an external gateway protocol that transmits interdomain routing<br />

information within and between Autonomous Systems (AS). Its primary function is to exchange network<br />

reachability information with other BGP systems. BGP generally operates with an Internal Gateway<br />

Protocol (IGP) such as OSPF or RIP, allowing you to communicate to external ASs smoothly. BGP adds<br />

reliability to network connections be having multiple paths from one router to another.<br />

Autonomous Systems (AS)<br />

BGP Autonomous Systems (ASs) are a collection of nodes under common administration, with common<br />

network routing policies. Each AS has a number, already assigned by an internet authority. You do not<br />

assign the BGP number.<br />

AS Numbers (ASNs) are important because the ASN uniquely identifies each network on the Internet. The<br />

IANA has reserved AS numbers 64512 through 65534 to be used for private purposes. The ASNs 0 and<br />

65535 are reserved by the IANA and should not be used in a live environment.<br />

Autonomous Systems can be grouped into three categories, defined by their connections and operation.<br />

A multihomed AS is one that maintains connections to more than one other AS. This allows the AS to<br />

remain connected to the internet in the event of a complete failure of one of their connections. However,<br />

this type of AS does not allow traffic from one AS to pass through on its way to another AS. A simple<br />

example of this is seen in Figure 74.<br />

126 Border Gateway Protocol

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