
Configuring BGP Services
117356-B Rev. 00
8-3
Bay Networks supports BGP-3 and BGP-4:
• BGP-3 assumes that each advertised network is a natural class network (A, B,
or C) based on its high-order bits. BGP-3 cannot advertise subnets or
supernets.
• BGP-4 has no concept of address classes. Each network listed in the Network
Layer Reachability Information (NLRI) portion of an update message
contains a prefix length field, which describes the length of the mask
associated with the network. This allows for both supernet and subnet
advertisement. The supernet advertisement is what makes classless
interdomain routing (CIDR) possible.
This section covers the following topics:
Peer-to-Peer Sessions
A BGP router employs a BGP speaker, which is an entity within the router that
transmits and receives BGP messages and acts upon them. A BGP speaker forms
a neighbor relationship with another BGP speaker by establishing a
peer-to-peer
session
. For instructions, see “Establishing a Peer-to-Peer Session” on page 8-35.
An autonomous system can include one or more BGP speakers that provide
external route information for the networks within the AS. An AS containing a
single BGP speaker that establishes a peer-to-peer session with a single external
BGP speaker is a
stub AS.
The BGP speaker provides external route information
for the networks contained within its AS only.
Topic Page
Peer-to-Peer Sessions
8-3
Interior BGP Routing 8-4
IBGP Route Server 8-5
BGP Updates 8-12
BGP Implementation Notes 8-15
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