Configuring LDP IPv4 FEC Filtering
By default, when a targeted LDP session is established, the Junos OS always exchanges both the IPv4 forwarding equivalence classes (FECs) and the Layer 2 circuit FECs over the targeted LDP session. For an LDP session to an indirectly connected neighbor, you might only want to export Layer 2 circuit FECs to the neighbor if the session was specifically configured to support Layer 2 circuits or VPLS.
In a mixed vendor network where all non-BGP prefixes are advertised into LDP, the LDP database can become large. For this type of environment, it can be useful to prevent the advertisement of IPv4 FECs over LDP sessions formed because of Layer 2 circuit or LDP VPLS configuration. Similarly, it can be useful to filter any IPv4 FECs received in this sort of environment.
If all the LDP neighbors associated with an LDP session are Layer 2 only, you can configure the Junos OS to advertise only Layer 2 circuit FECs by configuring the l2-smart-policy statement. This feature also automatically filters out the IPv4 FECs received on this session. If you have configured an explicit export or import policy, this feature is disabled.
If one of the LDP session’s neighbors is formed because of a discovered adjacency or if the adjacency is formed because of an LDP tunneling configuration on one or more RSVP LSPs, the IPv4 FECs are advertised and received using the default behavior.
To prevent LDP from exporting IPv4 FECs over LDP sessions with Layer 2 neighbors only and to filter out IPv4 FECs received over such sessions, include the l2-smart-policy statement:
For a list of hierarchy levels at which you can configure this statement, see the statement summary for this statement.
