Nelluri,
You are correct in your thinking about only having one server in
a VTP domain. It's the default of 5500's to use "server" mode when vtp is
configured. What you've noticed would seem to be correct in that VTP
announcements/messages only traverse a trunk link between directly connected
switched devices. In your post you mentioned that the both switches were
connected over a trunk on port(s) 1/2, but that the port was logically
disabled. Since the other two trunk ports are connected to routers(do not
participate in vtp messages) there isn't any way for the VTP advertisements
to pass between the 5500's.
Kennedy Clarke's book - LAN Switching, Chp 12, gives some clear definitions
of VTP, the modes, and mechanisms. A really good text for switching. Also,
Sean Odom's - switching black book has some good info on the topic as well.
HTH
Nigel..
----- Original Message -----
From: Nelluri Reddy
To:
Sent: Sunday, July 08, 2001 12:37 PM
Subject: Cisco 5505 switch puzzle [7:11335]
> I hope that some one can explain the behavior of VTP on Cisco 5505
> switches.
>
> I have two Cisco 5505 switches, S1 running version 4.2.2 and S2 running
> 4.5.4. All ports on S1 assigned to VLAN 10, except ports 1/2 and 2/23
> which are trunk ports. All ports on S2 are assigned to VLAN 11, except
> ports 1/2 and 2/23 which are trunk ports. The two trunk ports 2/23 on
> both switches are connected to two 2621 routers. The two two trunk ports
> 1/2 on both switches are interconnected by MMF cable, but the port on S1
> is logically disabled so that the two switches can not communicate with
> each other.
>
> set vtp domain xyz
> set vtp mode server
>
> have been configured on both switches.
>
> All the four trunk ports are configured for ISL with VLANS 1,10 and 11
> only. However when I do a "sh trunk" on S1 it says that the trunk on
> port 2/23 has VLANS 1,10-11 available, but only VLANS 1 and 10 are
> active. When I execute the same command on S2, it says that VLANS 1 and
> 11 are active and available on trunk for port 2/23.
>
> Basically S1 did not know anything about VLAN 11 and S2 did not know
> anything about VLAN 10.
>
> The idea is to run HSRP between the two routers so that if any one
> router fails, all devices attached to both switches will be able to
> communicate to the outside via the remaining router.
>
> This requires that traffic should flow between the two switches and each
> switch must be aware of both VLANs 10 and 11.
>
> After making sure that the VTP version number was zero on both switches,
> on a fateful morning, at 4 am, I enabled remotely the trunk on 1/2 port
> on S1 so that the link between the two switches became active. To my
> utter dismay, S2 promptly and completely shut itself down and I could
> not communicate with it. I drove to my office to pick up my laptop and
> drove to the remote location to find out what had happened.
>
> All non-trunked ports were in an "inactive" state in S2. Apparently when
> S2 received the VTP advertisement from S1 and did not see VLAN 11 in it,
> S2 rendered inactive all ports assigned to VLAN 11. But both S1 and S2
> are in "server" mode! Why did this happen? This behavior is typical when
> there is a revision level mis-match and a "client" mode switch receives
> an update with a higher revision number and missing VLAN definitions.
>
> Cisco TAC says that there should be only one server in any VTP domain. I
> don't believe that.
>
> TAC also said that a better method would be to configure both switches
> in transparent VTP mode.
>
> Any ideas?
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