FEC Filtering Configuration Example

Consider three MPLS router system devices with an ID 10.66 with the transit device between them.

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Inbound FEC filtering example

The following configuration configures the prefix list to allow all /32 addresses, the prefix list to allow 172.16.0.0/16 ge 24 le 24, prefix list to allow172.16.0.0/16 ge 24 le 28, and a prefix list to allow all of the previous FECs.

device(config)# ip prefix filter172_24 permit 172.16.09.0/16 ge 24 le 24
device(config)# ip prefix filter172_24 permit 172.16.09.0/16 ge 24 le 24
device(config)# ip prefix-list filter172_28 permit 172.16.0.0/16 ge 24 le 28
device(config)# ip prefix-list filterAll permit 0.0.0.0/0 ge 32 
device(config)# ip prefix-list filterAll permit 172.16.0.0/16 ge 24 le 28

Verify the configuration by using the show mpls ldp command.

device(config)# exit
device# show mpls ldp
Label Distribution Protocol version 1
  LSR ID: 10.44.44.44, using Loopback 1 (deleting stops LDP)
  Hello interval: Link 5 sec, Targeted 15 sec
  Hold time value sent in Hellos: Link 15 sec, Targeted 45 sec
  Keepalive interval: 6 sec, Hold time multiple: 6 intervals
  Load sharing: 1
  Tunnel metric: 0
  FEC used for auto discovered peers: current 129, configured 129
  Graceful restart: disabled
device(config)# do show mpls ldp database
Session 10.44.44.44:0 - 10.14.14.14:0
 Downstream label database:
   Label        Prefix            State               
   3            10.14.14.14/32    Installed
   1024         172.16.8.0/24     Installed
   1025         172.16.16.0/24    Installed
   1026         172.16.32.0/24    Installed
   1027         172.16.64.0/24    Installed
   1028         172.16.8.0/28     Installed
   1029         172.16.8.16/28    Installed
   1030         172.16.8.32/28    Installed
   1031         172.16.8.64/28    Installed
 Upstream label database:
   Label        Prefix              
   3            10.44.44.44/32
   1033         10.66.66.66/32
Session 10.44.44.44:0 - 10.66.66.66:0
 Downstream label database:
   Label        Prefix            State               
   3            10.66.66.66/32    Installed
 Upstream label database:
   Label        Prefix              
   3            10.44.44.44/32
   1024         172.16.8.0/24
   1025         172.16.16.0/24
   1026         172.16.32.0/24
   1027         172.16.64.0/24
   1028         172.16.8.0/28
   1029         172.16.8.16/28
   1030         172.16.8.32/28
   1031         172.16.8.64/28
   1032         10.14.14.14/32