3550 and 2950 VTP/trunk interoperability

Netstudent · July 2007

Okay so I just got home from school and I instructed a lab on VTP and VLANS. I brought my 2950 and 2924 to school and used the school's 2 3550's. So I don't have any configs to post but I could not for the life of me get the VLANS from the VTP server which was on the 2950 to propogate to the 3550. The 2950 was connected to the 2924 and one of the 3550's. I setup the vtp domain and got the vlans to propogate to the 2924 but no the 3550. I also setup trunks between the swicthes and all trunks were dot1Q. IS there a limitation to dot1Q and vtp propogation? What needs to be configured on a 3550 BUT NOT on a 2924 to get VTP to communicate?

I set the 3550 up just like the 2924. The only thing I did differently on the 3550 was set the encapsulation to NEGOTIATE. The ports are automatically set to AUTO for trunking and I couldn;t turn that off untill I set an encapsulation. I didn;t know order of operation would become an issue, but I guess it is. Anyone have any ideas on what I missed or any VTP configs that are 3550 specific????

IF anyone needs anymore info on the setup, it's all in my head so just ask.

peterd51 · July 2007

Hi,

I vaguely recall that the 3500 switches default to ISL not 802.1q like the other switches do.

I have a lot of problems with 3500's...they seem to have a few things different to other switches.

Regards
Peter

MACattack · July 2007

Hi, check the vtp version if vtp 1 or 2 some switches has a default value of vtp 1 some are vtp 2.

Also there is a big difference between vtp version and vtp v 2 mode when you issue show vtp status.

VTP version : 2 <<< if vtp version 2 is available. Sometimes version 1 or 2 depends on the platform. In your case 2950 and 3550 is differenet check on cisco website.
VTP v2 mode : disabled (default) it is not currently running as version 2.

If I could remember by default also 3550 set it's port as layer 3 port issue no switchport.

What more... could be the possble problem?

Netstudent · July 2007

That may have been the problem. I didn't even think to check the versions. I thought that maybe it had something to do with the trunk setup or trunk encapsulation. The trunks were operational because I did a show int trunk on the 3550 and it showed that I had the trunk ports I setup. Bad thing is, by the time I get the rack back at school, it will have already been erased by another class. We only have 2 or 3 racks floating around campus. I have setup vtp and vlans more times than I can count and never had a problem untill i tried it on 3550's in front of my whole class.

But it's all good, they don't ask me to instruct the labs for nothing. Unfortunately my professor is handicap and can't walk, so he knows I can instruct the labs just as good as anyone.

Is there any correlation at all between trunk encap and vtp propagation? Or are those two entities completely independent???

If I could remember by default also 3550 set it's port as layer 3 port issue no switchport

Well the switch was giving me messages saying the port defaults to AUTO for trunking. Everytime I issued the switchport mode trunk command, it would come back saying something about it already being set to AUTO. The other end of the link was a 2950 and it was set to trunk so the 3550's side of the link should have trunked and it did. I did a show run several times and I don;t recall seeing "no switchport" under the interface fields.

dtlokee · July 2007

To set the switchport to trunk on the 3550 you also need to set the encapsulation first or it will give you an error.

SW1(config-if)#switch mode trunk
Command rejected: An interface whose trunk encapsulation is "Auto" can not be configured to "trunk" mode.

now if you set the encapsulation first it works:

SW1(config-if)#switch trunk enc dot1q
SW1(config-if)#switch mode trunk     
SW1(config-if)#

Now keep in mind the 2950 only supports 802.1q encapsulation and the 3550 will support both ISL and 802.1q

As far as VTP, the switches all defaul to vtp version 1 even if they support version 2. Things to check would be the vtp domain name and password (caps count) and make sure the mode is server or client, and ensure the revision number is the same on all switches. If you have one set to transparent it will ignore the updtes.

Netstudent · July 2007

I checked the domain name and client/server options several times. I did not setup a vtp password as I didn;t think that was required. And yes I noticed the order of operation with trunk encapsulation. I figured that out, but couldn;t figure out why the 3550 wouldn't exchange VTP with the 2950. 2950 being the server.

When I did a show vtp stat on the 3550, it was a client, it was in the correct vtp domain, the revision number was 0 and at the bottom of the output, the source of vtp updates was 0.0.0.0 as if it were the server. So this tells me that there was absolutely no VTP communication going on.

Actually now that I think about it, are VLAN interfaces with IP's required to exchange VTP mesages? Because now I remember on my home setup, the source of VTP info at the bottom of the show vtp status output on a client displayed the server's VLAN interface IP. But then again I didn't setup a vlan int ip on the 2924 and it got the updated VTP info just fine.

SO at this point I guess it's going to be difficult for anyone to give a definitive answer because i have no configs to post. O well maybe I can set it up again next week.

3550 and 2950 VTP/trunk interoperability

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