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BGP and BGP4+ Introduction
Internal BGP (iBGP) Concepts
Routers that run BGP often run an IGP, such as OSPF, and have learned routes for the public range either as one route or with subset routes. If a single route exists for the public range, then you can add a redistribute (into BGP or BGP4+) (BGP and BGP4+) command to the BGP configuration to redistribute that route, and only that route, into BGP.
IGPs do not handle the public routing table. Internally peered BGP routers are capable of exchanging routing information without redistributing into an IGP. But an IGP can be used to connect two or more distant iBGP peers, and redistribution into an IGP may be used.
iBGP between Internet connected routers
When an organization uses more than one router to connect to the Internet, and those routers use BGP to exchange routing information with their ISPs, those same routers need to exchange BGP routes with each other as well. The BGP neighbor relationships occur inside that organization, making these routers iBGP peers.
iBGP with two Internet connected routers
Two
With an iBGP peer connection, each
Configuring iBGP
The most basic iBGP configuration differs only slightly compared to eBGP configuration. The configuration does not explicitly identify an eBGP versus an iBGP peer. Instead, for iBGP, the neighbor’s ASN listed on the neighbor
For eBGP, the neighbor
The configuration to use loopback interfaces as the update source mirrors configuration for eBGP peers, except that iBGP peers do not need to configure the neighbor ebgp- multihop (BGP and BGP4+) command.
For iBGP connections, only the following steps are required to make two iBGP peers use a loopback interface:
1.Configure an IP address on a loopback interface on each router.
2.Configure each router to use the loopback IP address as the source IP address, for the neighborship with the other router, using the neighbor
3.Configure the BGP neighbor
| Software Reference Supplement for SwitchBlade® x8112, x908, x900 and x610 Series Switches |
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AlliedWare PlusTM Operating System - Software Version | 1.9 |