Understanding Conditional Route Advertising in a Chassis Cluster

Route advertisement over redundant Ethernet interfaces in a chassis cluster is complicated by the fact that the active node in the cluster can change dynamically. Conditional route advertisement enables you to advertise routes in such a way that incoming traffic from the core network is attracted to the Border Gateway Protocol (BGP) interface that exists on the same node as the currently active redundant Ethernet interface. In this way, traffic is processed by the active node and does not traverse the fabric interface between nodes. You do this by manipulating the BGP attribute at the time routes are advertised by BGP.

Before You Begin

For background information, read Understanding Chassis Cluster Formation

The goal of conditional route advertisement in a chassis cluster is to ensure that incoming traffic from the upstream network arrives on the node that is on the currently active redundant Ethernet interface. To understand how this works, bear in mind that in a chassis cluster, each node has its own set of interfaces. Figure 84 shows a typical scenario, with a redundant Ethernet interface connecting the corporate LAN, through a chassis cluster, to an external network segment.

Figure 84: Conditional Route Advertising

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