IBM RackSwitch G8000, Application Manual

Page: 249 / 362

© Copyright IBM Corp. 2011 Chapter 21. Border Gateway Protocol
247
Loopback Interfaces
In many networks, multiple connections may exist between network devices. In
such environments, it may be useful to employ a loopback interface for a common
BGP router address, rather than peering the switch to each individual interface.
When a loopback interface is created for BGP, the switch automatically uses the
loopback interface as the BGP peer ID, instead of the switch’s local IP interface
address.
Note: To ensure that the loopback interface is reachable from peer devices, it must
be advertised using an interior routing protocol (such as OSPF), or a static
route must be configured on the peer.
To configure an existing loopback interface for BGP neighbor, use the following
commands:
What is a Route Map?
A route map is used to control and modify routing information. Route maps define
conditions for redistributing routes from one routing protocol to another or controlling
routing information when injecting it in and out of BGP. Route maps are used by
OSPF only for redistributing routes. For example, a route map is used to set a
preference value for a specific route from a peer router and another preference
value for all other routes learned via the same peer router. For example, the
following command is used to enter the Route Map mode for defining a route map:
A route map allows you to match attributes, such as metric, network address, and
AS number. It also allows users to overwrite the local preference metric and to
append the AS number in the AS route. See “BGP Failover Configuration” on
page 253 .
IBM N/OS allows you to configure 32 route maps. Each route map can have up to
eight access lists. Each access list consists of a network filter. A network filter
defines an IPv4 address and subnet mask of the network that you want to include in
the filter. Figure 23 illustrates the relationship between route maps, access lists, and
network filters.
RS G8000(config)#
router bgp
RS G8000(config-router-bgp)#
neighbor
<#>
update-source loopback
<1-5>
RS G8000(config-router-bgp)#
exit
RS G8000(config)#
route-map
<map number>(Select a route map)
RS G8000(config-route-map)#
?
(List available commands)