iBGP Configuration with a Loopback Address In the configuration above, R1-AGS router belongs to AS 300 while R6-2500 router belongs to AS 400. If they are not directly connected, the neighbor ebgp-multihop ( registered customers only) command must be used and a path through an IGP or static route to reach the peer must exist in order for the routers to establish neighbor relationship. Peers must be directly connected when using eBGP. !- Specifies a neighbor 10.10.10.2 !- in the remote AS 400, making !- this an eBGP connection. Router bgp 300 !- Enables BGP for the autonomous !- system 300. In this configuration, the router R1-AGS is in AS 300 and Router R6-2500 is in AS 400. !- Specifies a neighbor 10.10.10.2 !- in the remote AS 400, making !- this an iBGP connection. Router bgp 400 !- Enables BGP for the autonomous !- system 400. In this configuration, both routers are in AS 400. Note: To find additional information on the commands used in this document, use the Command Lookup Tool ( registered customers only). In this section, you are presented with the information to configure the features described in this document. IBGP Configuration with a Loopback AddressĮBGP Configuration with a Loopback Address This section contains the following configuration examples: Conventionsįor more information on document conventions, refer to Cisco Technical Tips Conventions.
#LOOPBACK TUTORIAL SERIES#
The command outputs shown in this document were taken from the 2500 Series Routers running IOS ® version 12.2(24a).
#LOOPBACK TUTORIAL SOFTWARE#
This document is not restricted to specific software and hardware versions. Prerequisites Requirementsīefore you attempt this configuration, ensure that you meet this requirement: Refer to Using the Border Gateway Protocol for Interdomain Routing for more complex configurations. Note: You can use these configurations for establishing neighbor relationship.
The sample configurations in this document are for iBGP and eBGP, both with and without a loopback addresses. In addition to that, it also allows the routers running BGP with multiple links between them to load balance over the available paths.
This method of peering using a loopback interface is useful since it will not bring down the BGP session when there are multiple paths between the BGP peers, which would otherwise result in tearing down the BGP session if the physical interface used for establishing the session goes down. However, using the neighbor update-source ( registered customers only) command, any operational interface, including the loopback interface, can be specified to be used for establishing TCP connections. A BGP session between two BGP peers is said to be an internal BGP (iBGP) session if the BGP peers are in the same autonomous systems.īy default, the peer relationship is established using the IP address of the interface closest to the peer router. The BGP session between two BGP peers is said to be an external BGP (eBGP) session if the BGP peers are in different autonomous systems (AS). A BGP router needs to establish a connection (on TCP port 179) to each of it's BGP peers before BGP updates can be exchanged. BGP is an exterior gateway protocol (EGP), used to perform interdomain routing in TCP/IP networks.
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