Using DTP on a port-channel

[Jeremy Dubrulle]

Hi,

I have a simple question.

I've tried to configure a port-channel between two switches. But it seems that it's not possible to configure dtp on the port-channel.

The channel is well configured but I can't make the trunk working with "switchport mode dynamic auto" (or desirable) on the interface port-channel.

I mean I can enter the command but the channel doesn't transmit the frames and the channel doesn't work properly.

Is it normal?

Thanks.

[Peter Paluch]

Jeremy,

I would need to test this in a lab as I personally avoid DTP as much as possible - but that, of course, does not mean you should not try it out!

Before I do that, though, can you please answer the following questions for me?

1. Where exactly did you configure the switchport mode dynamic command - did you enter it on the physical ports or on the Port-channel virtual interface? It should be placed on both.
2. What does the show etherchannel summary command on both switches say? Does it show the Port-channel interface as SU (Switched, Up) with all physical ports marked with P (In Port-channel)?
3. What does the show interfaces trunk say? Especially if you configure at least one of the switches with switchport mode dynamic desirable, does the show int trunk show the Port-channel being treated as a trunk?

Best regards,
Peter

[Jeremy Dubrulle]

Thanks for your reply.

I try it with Packet Tracer and I think pkt is the problem.

It works perfectly when I put the trunk mode as "on". But it's completely bugging when using desirable on the port-channel and physical interfaces (interfaces shutting down, then upping, then trunking on/off, ...). And the trunk is not mounting when one side is desirable and the other auto.

So I think it's packet tracer, but thanks to tell me it could work.

NB : I know DTP shouldn't be used, but that's for my personal knowledge ;)

[Jeremy Dubrulle]

Seems that trunking mode has to be the same between etherchannel interfaces.

Look at the answer of a netacad quiz question I've done (on the attachment).

[glen.grant]

   No it should work.  One end should be auto and the other dynamic or both ends should be dynamic .  Maybe post your config.