Understanding the output of show mpls forwarding-table a.b.c.d detail ...

[jerrytozhang]

Hi,there:

I don't understand the meaning of the number 0001400000012000 below, can anybody help me out? more details.

Thanks,

---

lactometer#show mpls forwarding-table 10.200.254.4 detail

Local Outgoing Prefix Bytes tag Outgoing Next Hop

tag tag or VC or Tunnel Id switched interface

20 18 10.200.254.4/32 0 Tu1 point2point

MAC/Encaps=14/22, MRU=1504, Tag Stack{20 18}, via Et0/0/0

00604700881D00024A4008008847 0001400000012000

No output feature configured

---

[mheusing · Accepted solution]

Hi,

your label stack is {20 18} and a label is 4 Bytes with

20 Bits label,

3 cos bits

1 Bottom of stack bit

8 TTL bits.

So 0001400000012000 can be read as 00014000 00012000.

Hex 0x00014000 = binary 00000000000000010100 000 0 00000000 = label 20 cos 0 S 0 TTL 0

Hex 0x00012000 = binary 00000000000000010010 000 0 00000000 = label 18 cos 0 S 0 TTL 0

Be aware that exp/cos bits, s and TTL are set when getting the IP packet and thus will not be 0 on outgoing labeled packets. The 0 is just a placeholder.

Hope this helps! Please use the rating system.

Regards, Martin

[Webdotsingh3678]

First of all, thanks for label stack information discussion.

Can you confirm which one is top label out of these. I think label 16 is top label but not confirmed.

And

what "00604700881D00024A4008008847" value means.

MAC/Encaps=14/22, MRU=1496, Tag Stack{20 16}, via Et0/0/0
00604700881D00024A4008008847 0001400000010000

Regards,

Shammi Singh

[Giuseppe Larosa]

Hello Webdotsinght3678,

in the output

MAC/Encaps=14/22, MRU=1496, Tag Stack{20 16}, via Et0/0/0
00604700881D00024A4008008847 0001400000010000

The inner label is 16 that is 10 in hex. The outer label is 20.

The hexadecimal sequence that you see is how the packet rewrite is performed before sending on wire so:

00604700881D    destination MAC address

00024A400800      source MAC address

8847     Ethertype for MPLS frames over ethernet

Hope to help

Giuseppe