Filtering Outbound LDP Label Bindings
You can configure export policies to filter LDP outbound labels. You can filter outbound label bindings by applying routing policies to block bindings from being advertised to neighboring routers or switches. To configure outbound label filtering, include the export statement:
For a list of hierarchy levels at which you can include this statement, see the statement summary section for this statement.
The named export policy (configured at the [edit policy-options] hierarchy level) is applied to all label bindings transmitted to all LDP neighbors. The only from operator that applies to LDP outbound label filtering is route-filter, which matches bindings with the specified prefix. The only to operators that apply to outbound label filtering are the operators in Table 1.
Table 1: to Operators for LDP Outbound-Label Filtering
to Operator | Description |
|---|---|
interface | Matches on bindings sent to a neighbor that is adjacent over the specified interface |
neighbor | Matches on bindings sent to the specified LDP router ID |
next-hop | Matches on bindings sent to a neighbor advertising the specified interface address |
If a binding is filtered, the binding is not advertised to the neighboring router or switch, but it can be installed as part of an LSP on the local router or switch. You can apply policies in LDP to block the establishment of LSPs, but not to control their routing. The path an LSP follows is determined by unicast routing, not by LDP.
LDP sessions are not bound to interfaces or interface addresses. LDP advertises only per-router or per-switch (not per-interface) labels. If multiple parallel links exist between two routers or switches, only one LDP session is established, and it is not bound to a single interface.
Do not use the next-hop and interface operators when a router or switch has multiple adjacencies to the same neighbor.
Filtered labels are marked in the database:
user@host> show ldp database Input label database, 10.10.255.1:0-10.10.255.3:0 Label Prefix 100007 10.10.255.2/32 3 10.10.255.3/32 Output label database, 10.10.255.1:0-10.10.255.3:0 Label Prefix 3 10.10.255.1/32 100001 10.10.255.6/32 (Filtered)
For more information about how to configure policies for LDP, see the Routing Policy Configuration Guide.
Examples: Filtering Outbound LDP Label Bindings
Block transmission of the route for 10.10.255.6/32 to any neighbors:
Send only 131.108/16 or longer to router ID 10.10.255.2, and send all prefixes to all other routers or switches:
