Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?

 

Understanding the Default BGP Routing Policy on Packet Transport Routers (PTX Series)

 

On PTX Series Packet Transport Routers, the default BGP routing policy differs from that of other Junos OS routing devices.

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.

The default behavior for load balancing and BGP routes on PTX Series routers is as follows. It has the following desirable characteristics:

  • 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

The default routing policy on the PTX Series routers is as follows:

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.

user@host> show policy junos-ptx-series-default
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.