MPLS Forwarding Flags

[Evan Roggenkamp]

Is there a reference to determine the meaning of the values in red below? I cannot seem to find any documentation that indicates how to interpret this output. Thanks!

RP/0/RSP0/CPU0:ASR9001-Aggr1#sh mpls forwarding prefix 10.252.255.1/32 detail        
Tue Jun 23 16:11:26.744 UTC
Local  Outgoing    Prefix             Outgoing     Next Hop        Bytes       
Label  Label       or ID              Interface                    Switched    
------ ----------- ------------------ ------------ --------------- ------------
24269  24269       10.252.255.1/32    Te0/0/2/1    10.144.254.38   1655547518  
     Updated Jun 22 13:59:03.055
     Path Flags: 0x400 [ BKUP-IDX:0 (0x9e1536b0) ]
     Version: 41190, Priority: 3
     MAC/Encaps: 14/18, MTU: 9086
     Label Stack (Top -> Bottom): { 24269 }
     NHID: 0x3
     Packets Switched: 20098378

       24008       10.252.255.1/32    Te0/0/2/0    10.144.254.33   0           
     Updated Jun 22 13:59:03.055
     Path Flags: 0x300 [ IDX:0 BKUP, NoFwd ]
     Version: 41190, Priority: 3
     MAC/Encaps: 14/22, MTU: 9086
     Label Stack (Top -> Bottom): { 24008 24268 }
     NHID: 0x2
     Packets Switched: 0

[Vinit Jain]

Hello Evan

The above output means that there are two paths to reach the prefix. one is primary and other is backup. for the primary path, the label stack is shown from Top -> Bottom. The MTU value you can notice. A NHID is either 16 or 24 or 32 bits in size. The NHID is carried in packet header from ingress card to the egress card. NHID lookup on the egress card fetches the packet header-rewrite on the egress. This is generally used for hardware forwarding. These values are only helpful when troubleshooting hardware forwarding issues. I dont think there will be much documentation for the same.

Hope this helps.

Vinit