show adjacency detail

[c.andrew]

On Ethernet links, with an 802.1q trunk, the long string of characters (below), indicate dest MAC, src MAC, 802.1q tag and the Ethertype.

sh adjacency fa1/0.200 det
Protocol Interface                 Address
IPV6     FastEthernet1/0.200       2001:200::4(5)
                                   1 packets, 114 bytes
                                   C4041FE80000C4001FE80010810000C8
                                   86DD
                                   IPv6 ND    never
                                   Epoch: 0

With a space between each section, these are the separate parts:

src MAC      dst MAC      802.1q   EtherType (IPv6)

C4041FE80000 C4001FE80010 810000C8 86DD

However - what's the significance of the leading 81 in the 802.1q portion?

Thanks,

Chris

[houtan haddadlarijani · Accepted solution]

It should be tag protoclol id (TPID) and is used to distinguish the frame from untagged frames.

If you look at 802.1q header, you find a 16-bit field (TPID) set to a value of 0x8100 in order to identify the frame as an IEEE 802.1Q-tagged frame.

[c.andrew]

Many Thanks. :-)