VTP Updates over 802.1q on Ubuntu
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Author:  nokem [ Thu Jun 27, 2013 10:46 pm ]
Post subject:  VTP Updates over 802.1q on Ubuntu

I have 3 real Cisco Switches, a 3550 and 2x 2950t

One of the 2950T's (S1) is connected on port fa0/8 to one of the ethernet ports of my Ubuntu (eth1).

On my Ubuntu box I did modprobe 8021q and I set the MTU to 1536 to be sure it could carry the extra 4 tagged bits.

Now over in GNS3 setup a cloud for gen_eth1 and point it as a 3725 with a 16 port switch card in it.

Configuring trunking on the connected ports on either side of the cloud. I can ping the management VLAN of the real switch. I created a new VLAN and gave it an IP on the real switch and did the same on the GNS3 switch and gave them IP's in the same subnet and once again it happily pings.

The problem is that it will not update VTP. Similar to the MicroNugget with Keith Barker on 802.1q trunking on a MAC ( ), I was hoping that once the trunk was set up, my GNS3 "switch" would pick up VTP updates from the real switch. Even after setting the correct vtp domain, this is not the case.

My overall goal, since I do not own a physical router was to do router on a stick within GNS3 to take care of inter VLAN routing for the real switches.

Is there anything obvious I may have forgotten that anyone can think of? I can post configs, but I figured if it was something obvious or someone could link me a good guide on this, it might save time before trawling configs.

All help much appreciated.


Author:  grossmj [ Fri Jun 28, 2013 1:27 am ]
Post subject:  Re: VTP Updates over 802.1q on Ubuntu


Do you see any CDP neighbors? I would also capture on your host interface to see if VTP gets there.

Author:  nokem [ Fri Jun 28, 2013 1:58 am ]
Post subject:  Re: VTP Updates over 802.1q on Ubuntu

Thanks for your reply.

Yes the physical and virtual switches can see each other on sh cdp neighbors.

I can't run a capture right now since I am in the middle of another lab but I will try to fix it a bit later.

Author:  brezular [ Sun Jun 30, 2013 5:45 pm ]
Post subject:  Re: VTP Updates over 802.1q on Ubuntu

if trunking isn't working the problem could be misconfigured VTP. Could you please plug another 2950 to Fa0/8 and check if VTP updates are working between two real switches?

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