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Example: Configuring Conditional Route Advertising in a Chassis Cluster

Requirements

Before you begin, understand conditional route advertising in a chassis cluster. See Understanding Conditional Route Advertising in a Chassis Cluster.

Overview

As illustrated in Figure 1, routing prefixes learned from the redundant Ethernet interface through the IGP are advertised toward the network core using BGP. Two BGP sessions are maintained, one from interface t1-1/0/0 and one from t1-1/0/1 for BGP multihoming. All routing prefixes are advertised on both sessions. Thus, for a route advertised by BGP, learned over a redundant Ethernet interface, if the active redundant Ethernet interface is on the same node as the BGP session, you advertise the route with a “good” BGP attribute.

Figure 1: Conditional Route Advertising

To achieve this behavior, you apply a policy to BGP before exporting routes. An additional term in the policy match condition determines the current active redundant Ethernet interface child interface of the next hop before making the routing decision. When the active status of a child redundant Ethernet interface changes, BGP reevaluates the export policy for all routes affected.

The condition statement in this configuration works as follows. The command states that any routes evaluated against this condition will pass only if:

• The routes have a redundant Ethernet interface as their next-hop interface.
• The current child interface of the redundant Ethernet interface is active at node 0 (as specified by the route-active-on node0 keyword).
  {primary:node0}[edit]user@host# set policy-options condition reth-nh-active-on-0 route-active-on node0

Note that a route might have multiple equal-cost next hops, and those next hops might be redundant Ethernet interfaces, regular interfaces, or a combination of both. The route still satisfies the requirement that it has a redundant Ethernet interface as its next hop.

If you use the BGP export policy set for node 0 in the previous example command, only OSPF routes that satisfy the following requirements will be advertised through the session:

• The OSPF routes have a redundant Ethernet interface as their next hop.
• The current child interface of the redundant Ethernet interface is currently active at node 0.

You must also create and apply a separate policy statement for the other BGP session by using this same process.

In addition to the BGP MED attribute, you can define additional BGP attributes, such as origin-code, as-path, and community.

Configuration

CLI Quick Configuration

To quickly configure conditional route advertising, copy the following commands and paste them into the CLI:

Step-by-Step Procedure

1. Create the policies.
   {primary:node0}[edit]user@host# set policy-options policy-statement reth-nh-active-on-0 term ospf-on-0 from protocol ospf {primary:node0}[edit]user@host# set policy-options policy-statement reth-nh-active-on-0 term ospf-on-0 from condition reth-nh-active-on-0 {primary:node0}[edit]user@host# set policy-options policy-statement reth-nh-active-on-0 term ospf-on-0 then metric 10{primary:node0}[edit]user@host# set policy-options policy-statement reth-nh-active-on-0 term ospf-on-0 then accept {primary:node0}[edit]user@host# set policy-options condition reth-nh-active-on-0 route-active-on node0

Results

From configuration mode, confirm your configuration by entering the show policy-options command. If the output does not display the intended configuration, repeat the configuration instructions in this example to correct it.

If you are done configuring the device, enter commit from configuration mode.