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Example: Overriding the Default BGP Routing Policy on PTX Series Packet Transport Routers

Understanding the Default BGP Routing Policy on Packet Transport Routers

The PTX Series routers are MPLS transit platforms that do IP forwarding, typically using interior gateway protocol (IGP) routes. The PTX Series Packet Forwarding Engine can accommodate a relatively small number of variable-length prefixes.

Note: A PTX Series router can support full BGP routes in the control plane so that it can be used as a route reflector (RR). It can do exact-length lookup multicast forwarding and can build the multicast forwarding plane for use by the unicast control plane (for example. to perform a reverse-path forwarding lookup for multicast).

Given the PFE limitation, the default routing policy for PTX Series routers is for BGP routes not to be installed in the forwarding table. You can override the default routing policy and select certain BGP routes to install in the forwarding table.

• Allows you to override the default behavior without needing to alter the default policy directly

• Reduces the chance of accidental changes that nullify the defaults
• Sets no flow-control actions, such as accept and reject

As shown here, the junos-ptx-series-default policy is defined in [edit policy-options]. The policy is applied in [edit routing-options forwarding-table], using the default-export statement. You can view these default configurations by using the | display inheritance flag.

Also, you can use the show policy command to view the default policy.

Policy junos-ptx-series-default:
    Term t1:
        from proto BGP
         inet.0
        then install-to-fib no
    Term t2:
        from proto BGP
         inet6.0
        then install-to-fib no
    Term t3:
        then load-balance per-packet

Caution: We strongly recommend that you do not alter the junos-ptx-series-default routing policy directly.

Junos OS chains the junos-ptx-series-default policy and any user-configured export policy. Because the junos-ptx-series-default policy does not use flow-control actions, any export policy that you configure is executed (by way of the implicit next-policy action) for every route. Thus you can override any actions set by the junos-ptx-series-default policy. If you do not configure an export policy, the actions set by junos-ptx-series-default policy are the only actions.

You can use the policy action install-to-fib to override the no-install-to-fib action.

Similarly, you can set the load-balance per-prefix action to override the load-balance per-packet action.

Example: Overriding the Default BGP Routing Policy on PTX Series Packet Transport Routers

This example shows how to override the default routing policy on packet transport routers, such as the PTX Series Packet Transport Routers.

• Requirements
• Overview
• Configuration
• Verification

Requirements

This example requires Junos OS Release 12.1 or later.

Overview

By default, the PTX Series routers do not install BGP routes in the forwarding table.

For PTX Series routers, the configuration of the from protocols bgp condition with the then accept action does not have the usual result that it has on other Junos OS routing devices. With the following routing policy on PTX Series routers, BGP routes do not get installed in the forwarding table.

Routing table: default.inet
Internet:
Destination        Type RtRef Next hop           Type Index NhRef Netif
default            perm     0                    rjct    36     2

No BGP routes are installed in the forwarding table. This is the expected behavior.

This example shows how to use the then install-to-fib action to effectively override the default BGP routing policy.

Configuration

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

Installing Selected BGP Routes in the Forwarding Table

Step-by-Step Procedure

1. Configure a list of prefixes to install in the forwarding table.
   [edit policy-options prefix-list install-bgp]

   user@host# set 66.0.0.1/32
2. Configure the routing policy, applying the prefix list as a condition.
   [edit policy-options policy-statement override-ptx-series-default term 1]

   user@host# set from prefix-list install-bgp

   user@host# set then install-to-fib

   user@host# set then load-balance per-prefix
3. Apply the routing policy to the forwarding table.
   [edit routing-options forwarding-table]

   user@host# set export override-ptx-series-default

Results

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

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

Verification

Confirm that the configuration is working properly.

Verifying That the Selected Route Is Installed in the Forwarding Table

Purpose

Make sure that the configured policy overrides the default policy.

Action

From operational mode, enter the show route forwarding-table command.

Internet:
Destination        Type RtRef Next hop           Type Index NhRef Netif
66.0.0.1/32        user     0                    indr 2097159     3
                                                 ulst 2097156     2
                              5.1.0.2            ucst   574     1 et-6/0/0.1
                              5.2.0.2            ucst   575     1 et-6/0/0.2

Meaning

This output shows that the route to 66.0.0.1/32 is installed in the forwarding table.