Filter
Top Products
BGP and BGP4+ Introduction
Software Reference Supplement for SwitchBlade® x8112, x908, x900 and x610 Series Switches
1.6 AlliedWare Plus
TM
Operating System - Software Version 5.4.3-2.6 C613-50032-01 REV D
BGP is useful when you have at least two Internet connections. BGP is most useful when
you want to choose one outbound path over another path for particular destinations in
the Internet. Consider BGP when you have multiple Internet connections, where you want
to make some packets take one path and you want other packets to take another path.
External BGP (eBGP) Concepts
This section describes the basics of eBGP to configure, verify, and advertise eBGP routes:
■ External BGP (eBGP): describes connections, configuration and commands to verify
eBGP.
■ Verifying BGP: describes the contents of the BGP table, and routes learned with eBGP.
■ Advertising eBGP routes to ISPs: shows how to configure eBGP to advertise routes.
External BGP (eBGP)
BGP first forms a neighbor relationship with peers. BGP then learns information from its
neighbors, placing information in a table named the BGP table. BGP analyzes the BGP
table to choose the best route for each prefix in the BGP table, placing those routes into
the IP routing table.
This section discusses the configuration of eBGP peers (called neighbors), with settings
that may be needed for eBGP connections to result in working BGP neighborships, then
discusses the BGP table, listing the learned prefix/ length and path attributes (PA).
eBGP Neighbor Configuration
At a minimum, a router participating in BGP needs to configure the following settings:
■ The ASN for the router configured from a router bgp (BGP and BGP4+) command
from Global Configuration mode on the router to enter Router Configuration mode.
■ The IP address and ASN of each neighbor from a neighbor remote-as (BGP and
BGP4+) command from Router Configuration mode, once the ASN is configured with
the router bgp (BGP and BGP4+) command in the Global Configuration mode.
How Routers become eBGP Neighbors
Routers must meet several requirements to become BGP neighbors:
■ A local router’s ASN must match the reference from the neighboring router to that
ASN as specified from the router bgp (BGP and BGP4+) command.
■ The BGP router IDs of the two routers must not be the same.
■ Each router must establish a TCP connection with the other router.
The remote router’s IP address specified from the neighbor remote-as (BGP and
BGP4+) command and used in that TCP connection must match what the local router
configures from a router bgp (BGP and BGP4+) command.