mpls ldp explicit-null

初期設定

全I/FでOSPFとLDPを起動

Before

Hub#sh mpls for
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop
Label      Label      or Tunnel Id     Switched      interface
16         Pop Label  172.16.1.0/24    0             Gi0/0      192.168.0.10

iosv-4#sh mpls fo
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop
Label      Label      or Tunnel Id     Switched      interface
16         16         192.168.1.0/24   0             Gi0/0      172.16.1.1
17         17         192.168.2.0/24   0             Gi0/0      172.16.1.1
18         Pop Label  192.168.0.0/24   0             Gi0/0      172.16.1.1  

mpls ldp explicit-null

iosv-3#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
iosv-3(config)#mpls label protocol ldp
iosv-3(config)#mpls ldp explicit-null

After

Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop
Label      Label      or Tunnel Id     Switched      interface
16         explicit-n 172.16.1.0/24    0             Gi0/0      192.168.0.10

iosv-4#sh mpls fo
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop
Label      Label      or Tunnel Id     Switched      interface
16         16         192.168.1.0/24   0             Gi0/0      172.16.1.1
17         17         192.168.2.0/24   0             Gi0/0      172.16.1.1
18         explicit-n 192.168.0.0/24   0             Gi0/0      172.16.1.1  

CCOによれば、ラベルと一緒にQoSも剝がれてしまうときに使うらしい。