The 7705 SAR supports both inbound and outbound LDP label binding filtering.
Inbound filtering (import policy) allows the user to configure a policy to control the label bindings an LSR (Label Switch Router) accepts from its peers.
Import policy label bindings can be filtered based on the following:
neighbor — match on bindings received from the specified peer
prefix-list — match on bindings with the specified prefix/prefixes
The default import behavior is to accept all FECs received from peers.
Outbound filtering (export policy) allows the user to configure a policy to control the set of LDP label bindings advertised by the LSR (Label Switch Router).
Because the default behavior is to originate label bindings for the system IP address only, when a non-default loopback address is used as the transport address, the 7705 SAR does not advertise the loopback FEC automatically. With LDP export policy, the user is now able to explicitly export the loopback address to advertise the loopback address label and allow the node to be reached by other network elements.
Export policy label bindings can be filtered based on the following:
all — all local subnets by specifying ‟direct” as the match protocol
prefix-list — match on bindings with the specified prefix/prefixes
In order for the 7705 SAR to consider a received label to be active, there must be an exact match to the FEC advertised together with the label found in the routing table, or a longest prefix match (if the aggregate-prefix-match option is enabled; see Multi-area and Multi-instance Extensions to LDP). This can be achieved by configuring a static route pointing to the prefix encoded in the FEC.