Designs That Avoid a Fully Meshed IBGP4 Network

The problem presented by a fully meshed IBGP-4 network can be solved by design. If a hub-and-spoke network were developed, this would streamline the TCP connections. This is a good thing, but it does require some additional design and configuration. The solution is the implementation of route reflectors and the network design that they support.

The design can become quite complicated with multiple route reflectors that afford redundancy, which is always reassuring. Multiple levels of route reflector can even be configured, creating a hierarchical design.

Nonroute reflector routers are not affected by the change in design and routing update propagation. Indeed, they are blissfully unaware of any changes because they still receive the updates that they need. The updates are also unchanged because no changes are made to the attribute values. This makes migration to a network design incorporating route reflectors very straightforward.

The only design requirement is that the IBGP-4 route reflectors must be fully meshed to ensure the correct propagation of updates. This is illustrated in Figure 9-4.

The benefits of route reflectors include these:

• The capability to scale the network, given the other characteristics

• A strong hierarchical design

• A reduction of traffic on the network

• A reduction in the memory and CPU to maintain TCP sessions on the client IBGP-4 peers

• Faster convergence because synchronization is not needed

• Faster convergence and a simpler network because two routing protocols are implemented:

— IBGP-4 for external routing information traversing the autonomous system

— IGP for routes internal to the autonomous system

The solution provided by route reflectors is used in large IBGP-4 environments such as ISP networks, where a fully meshed IBGP-4 network could result in a large number of TCP sessions.

Figure 9-4 Design of IBGP-4 Network Using Route Reflectors

IBGP

after the configuration of route reflectors

Client RR Client Client

Figure 9-4 Design of IBGP-4 Network Using Route Reflectors

IBGP

after the configuration of route reflectors

Client RR Client Client

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