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Question about VTP

T

tontod

Diamond Member
We have a core switch that was already configured as a VTP server, and had another switched connected to it as a VTP client. They were both up and running fine. I needed to add a 3rd switch, so before connecting it to anything, I set it (new switch) up as a VTP client, gave it the same domain and password as the other 2 switches, configured it for trunking on 2 ports, then connected those 2 ports to the core switch. It seemed like they negotiated, then soon after, all the lights on the core switch turned to orange. I found out that the core switch had lost all its VLANs and VTP was disabled (no domain). Any ideas why this might happen?

After that happened, I immediately disconnected the connections from the core switch to the new switch, re-enabled VTP server on the core switch, went to the switch that was originally configured as a VTP client, re-configured VTP on it. After all this, the core switch lost all its VLAN info again. So, I'm not running with VTP on the core switch now. Scratching my head as to what could have caused this. The only thing I can think of is that both the core switch and the switch that was already working had a "VTP V2 Mode", whereas the new switch did not have the line when I did a "show vtp status". But, I made sure I set the new switch to VTP version 2 like the other switches.
 
drebo said:
VTP mode transparent: the only valid VTP mode.
Click to expand...

Yep. The client had a higher revision number and the server believed it. It's a common problem and why you always, always, always disable vtp or set it to transparent before connecting.

Way back in the day it had it's uses and you still had to be careful of it. Today? Completely worthless and to be avoided.
 
My opinion is that if you have too many VLANs to manually add to the switches, you have too many vlans. And if you have to add too many VLANs to each switch, you have bad network design. VTP = not useful in a well-designed network.
 
drebo said:
My opinion is that if you have too many VLANs to manually add to the switches, you have too many vlans. And if you have to add too many VLANs to each switch, you have bad network design. VTP = not useful in a well-designed network.
Click to expand...

Data center design and L2 everywher is changing that. Fun times.

But in late 90s and early 2000s you were still in vlans trunked everywhere.

Still. The point remains. Avoid vtp at all costs in a modern network. It's time is long gone.
 
Interesting outlook. We've never, ever had an issue such as that unless it involved switches as servers (only happened once that I'm aware of a good 10 years ago). The only time we use transparent is when configuring "extended" VLANs. Else, client/server works perfectly well. We make it a point to reset the revision number (if not taken care of by a domain name change).

And depending on your environment, it's not a bad design to have multiple VLANs spanning across some number of switches. All depends on your environment I suppose.
 
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There's only a small # of VLANs, and the network isnt that big, so VTP isnt really needed. I'll just keep it turned off, dont have time to play around with it. Guess I should have connected the 2 switches 1st, then turned on VTP.
 
Ok, now I have an issue passing VLANs with trunking. It seems I can only ping the core switch if the corresponding VLAN on the new switch has an IP associated with it. Just having the VLAN defined and a "no ip address" isnt sufficient. I made sure that when I do a "sh vlan", all the VLANs I created do show up.

I have 2 ports set up on the core and the new switch for trunking (dot1q), but only connected each port on the switches. Would that cause an issue?
 
tontod said:
Ok, now I have an issue passing VLANs with trunking. It seems I can only ping the core switch if the corresponding VLAN on the new switch has an IP associated with it. Just having the VLAN defined and a "no ip address" isnt sufficient. I made sure that when I do a "sh vlan", all the VLANs I created do show up.

I have 2 ports set up on the core and the new switch for trunking (dot1q), but only connected each port on the switches. Would that cause an issue?
Click to expand...

That's normal if you're pinging from the switch. If it has no SVI/vlan interface with an IP then it has no address to source the ping with and no route to it.
 
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