Information Technology Reference
In-Depth Information
Build temporary BGP sessions in advance so that routing information is still available
during the migration process. These sessions can be removed after the migration. This
approach is the most complex of all but might be useful when the router under migra-
tion cannot be removed from the forwarding path, such as in the cases that the path
via the router is the only path or that the redundant paths via other routers are
overloaded.
Traffic loss caused by routing information black holes occurs only during configuration
changes and thus is temporary and short. The following case studies demonstrate in detail
how to prevent or minimize traffic loss during migration.
Case Study 1: iBGP Full Mesh to Route Reflection
Migration
This case study presents detailed procedures on how to migrate an iBGP fully meshed
network to a route reflection-based architecture. The starting topology is as shown in
Figure 8-1. The final topology after the migration is shown in Figure 8-2.
Starting Configurations and RIBs
This section shows BGP and IGP configurations before the migration. Examples 8-1
through 8-7 show the configurations for R1 through R7, respectively. All BGP speakers in
AS 100 are fully meshed. A peer group called Internal is used for all the iBGP sessions.
There are three ways to make R8 reachable in AS 100: setting next-hop-self on R1, making
the link between R1 and R8 part of the IGP domain in AS 100, or using a route map on R1
to reset the next hop to R1. In this case study, the BGP next hop on R1 is reset for all internal
sessions using next-hop-self .
Relevant Configurations on R1
Example 8-1
router isis
net 49.0001.1921.6810.0001.00
is-type level-2-only
!
router bgp 100
no synchronization
bgp router-id 192.168.100.1
bgp log-neighbor-changes
neighbor Internal peer-group
neighbor Internal remote-as 100
neighbor Internal update-source Loopback0
neighbor Internal next-hop-self
neighbor 192.168.18.8 remote-as 200
neighbor 192.168.100.2 peer-group Internal
neighbor 192.168.100.3 peer-group Internal
neighbor 192.168.100.4 peer-group Internal
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