Information Technology Reference
In-Depth Information
Example 5-49
Final Configuration for R13 (Continued)
no synchronization
bgp log-neighbor-changes
neighbor 10.1.1.4 remote-as 65100
neighbor 10.1.1.4 default-originate
no auto-summary
bgp bestpath compare-routerid
!
As discussed in the section “Defining the Problem,” the root cause of the problem should
be addressed. After the network has been migrated to a BGP core, the underlying issue of
address assignment and prefix summarization should be resolved.
The number of prefixes involved in this case study made the use of
network
statements
unfeasible, requiring direct redistribution. After the addressing and prefix summarization
issue has been resolved, the BGP configurations on the border routers should be changed
to inject prefixes using
network
statements, and the redistribution should be removed. This
does not include the remote site aggregation, because of the issue of black-holing traffic,
unless a physical circuit directly connects the hub routers and iBGP connectivity is
established between the hub routers.
Summary
This chapter provided an overview of when to use BGP in an enterprise core network.
It was stressed that BGP should not be used as a patch to solve a problem without also
addressing the problem's root cause. This is most often seen in networks where BGP is used
to resolve address assignment issues that prevent summarization. The deployment of BGP
achieves better scalability at the price of increased convergence times.
Three common BGP core architectures were presented, and each was examined in depth.
The internal-only BGP core architecture and the external-only BGP core architecture
are most commonly seen in small- to medium-sized networks. They become increasingly
difficult to manage as the network grows. The internal/external BGP core architecture is the
most common architecture and is very well-suited to scale as the network expands.
Finally, a case study was provided to examine how to migrate from an IGP-only network
to a BGP network core. The network requirements were complex and realistic, providing a
real-world scenario. The steps in the migration were detailed, and extensive configuration
information was provided.
