CDP "punch-through"

[Paulen]

All,

I have this setup:

[HP2626](25)-------[HP5304]------(26)[HP2626]

From the rightmost 2626 I do a 'sho cdp nei det' and get this result:

CDP neighbors information

Port : 26
Device ID : 00 14 38 6a 0a 00
Address Type : IP
Address : 10.20.15.30
Platform : HP J4850A ProCurve Switch 5304XL, revision E.10.37, ROM ...
Capability : Switch
Device Port : 28
Version : HP J4850A ProCurve Switch 5304XL, revision E.10.37, ROM ...

------------------------------------------------------------------------------

Port : 26
Device ID : h05renas1(000f20-16e3c0)
Address Type : IP
Address : 10.20.15.11
Platform : Revision H.08.53 /sw/code/build/fish(f04)HP 2626
Capability : Switch
Device Port : 25
Version : Revision H.08.53 /sw/code/build/fish(f04)HP 2626



i.e I see the CDP info from the other 2626 through the 5304. Thus, the 5304 both replies to CDP and is transparent. I can't seem to remember having seen this before. Anyone have clue here?

[Matt Hobbs]

Since CDP is no longer supported on the newer firmware releases I'm not too surprised that the 5300 is simply forwarding them.

If possible I'd recommend you update all of the switches and use LLDP instead.

[Paulen]

Actually I have seen this on/through another switch as well; but that was a Cisco of rather obscure character.

But - if CDP is no longer supported on the E.10.37 - why will it respond to requests at all?

[Richard Brodie_1]

"But - if CDP is no longer supported on the E.10.37 - why will it respond to requests at all?"

LLDP packets are used to populate the CDP neighbour information. I think it's sending LLDP and is transparent to CDP.

Some switches have readonly (rather than no) CDP support, with later firmware. I think that applies to the rightmost 2626.

I don't think that CDP packets update the LLDP MIBS however, so "show lldp info remote" probably will show only the 5304. You could also turn CDP off with "no cdp run".