MPLS LDP Label Filtering
Table of Contents
Introduction
Label filtering can be used to minimize the number of prefixes in LIB and control which prefixes get advertised using LDP.
LDP Label Filtering
- One of the filtering capability of MPLS LDP is filtering which prefixes are accepted in from other LSRs.
- Another filtering capabilities of MPLS LDP is filtering which prefixes are advertised with out with LDP.
- Filtering prefix labels is beneficial with MPLS VPN, where LSPs to PE routers are only required and no core LSPs.
LDP Inbound Label Filtering
- Specifies which prefixes are allowed into the router.
- Filtering is accomplished per neighbor.
- Configuration startS with mpls ldp neighbor (ip) label accept ..
LDP Advertised Label Filtering
- Specifies which prefixes are advertised with labels using LDP.
- Optionally provides an ACL which allows to specify the filtering to a particular neighbors. This is referred to as a prefix acl, peer acl.
- Configuration start with mpls ldp advertised-labels…
- By default there is no implicit deny. REMEMBER: To configure all labels to be blocked that don't match any configured filters. Use the command no mpls ldp advertise-labels.
- If a multiple prefix, peer acl pairs match a prefix the first one wins.
- Does not work for LC-ATM, which use Downstream on Demand distribution method, uses "mpls ldp request-labels".
Relevant Commands
mpls ldp advertise-labels
Filters the prefix labels from being advertised from LSRs.
The no configures an explicit deny anything that does not match the above filters.
R1(config)# mpls ldp advertise-labels for (prefix acl) to (peer acl)
R1(config)# mpls ldp advertise-labels interface (int)
R1(config)# no mpls ldp advertise-labels
mpls ldp neighbor labels
Filters which prefix labels to accept coming in from a neighbor.
R1(config)# mpls ldp neighbor (ip) labels accept (acl)
debug mpls ldp advertise all
debug mpls ldp advertise all
show mpls forwarding-table
show mpls forwarding-table
show mpls ldp binding advertisement-acl
Shows which prefixes match the outbound filtering, but does not show if
show mpls ldp binding advertisement-acls