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FTOS Configuration Guide for the C-Series - Force10 Networks

FTOS Configuration Guide for the C-Series - Force10 Networks

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

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

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

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

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

• RFC 2519 (A Framework <strong>for</strong> 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 <strong>for</strong> BGP-4)<br />

• RFC 3065 (Autonomous System Confederations <strong>for</strong> 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 />

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

reachability in<strong>for</strong>mation with o<strong>the</strong>r 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 ano<strong>the</strong>r.<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 <strong>the</strong> BGP number.<br />

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

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

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

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

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

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

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

example of this is seen in Figure 335.<br />

460 Border Gateway Protocol (BGP)

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