VLAN / VTP Troubles.

robert.bahr · ‎05-17-2008

I'm having a bit of a problem, I'll try and explain the best I can without posting configs.

I have recently taken charge of administering a network. Our LAN consists of 15 Catalyst switches; the models vary. We have some 2950's, 3750's, and 3750G's. Our core switch is a 3750, and we have two pop switches, one of them a 2950 (named POP1), and a 3750G (POP2).

We have a VTP domain setup across all the switches. I have checked all of them, they all have the right domain, POP2 is the only VTP server, and all of the VTP revision # is the same across all 15 switches. Also, all of our switch to switch links are trunked and encapsulated DOT1Q (which I have manually checked).

We have VLAN 109 setup across our network, that connects to another link. This VLAN uplinks through POP2 (VTP Svr) to a Cisco SOHO 91. The port on POP2 is not trunked, it's on VLAN 109. Across the network, there are a handful of ports that don't have access to the network on VLAN 109; they can't pull DHCP. The DHCP server is directly connected to the SOHO. I can pull an IP and surf when I connect a client directly into the SOHO. Curveball; I can do the same thing when I connect a client into POP1 on VLAN 109. Everyone else can't on any other switch. The only thing I can't explain is that on POP1 and POP2, VLAN 109 shows up/up when I do a "show ip int vlan 109". On any switch that is beyond that, it shows as admin down/down. A no shut does not fix this, and I'm trying to stay out of vlan database. I shouldn't have to go in there anyways since they are VTP clients.

There is a port that I desperately need up on VLAN 109, connected to UserSw1 (Catalyst 3750). VLAN 109 is admin down/down on this switch, and the connections switch to switch are trunked. UserSw1 is directly connected with POP2. UserSw1 is running 12.0, POP2 is running 12.2.

Please let me know how to further troubleshoot this problem, or if you need more info. I'm out of ideas, and the evidence from troubleshooting this has me running in circles.

glen.grant · ‎05-17-2008

It kind of depends on who is actually doing the routing in this network. If you can see vlan 109 across the network and the vtp revisions match then the layer 2 portion is working correctly. Is the core switch doing routing ? on the SOHO is the dhcp server on 109 or is on another segment on the SOHO . If so then you may have to add ip helper statements to the interface on the core pointing the segment the dhcp server is on . Whats the address on the dhcp server ? Does it fall into the 109 address range ? You may need to add a ip helper address on the core?? (assuming he is doing the routing pointing to the dhcp server address.

robert.bahr · ‎05-17-2008

VLAN 109 is being routed by an iDirect Satellite Rtr, which has a DHCP server built in. That's connected to the SOHO, which is connected to the POP switchport that is on 109.

All other VLAN's are being routed by the Core Switch, but that should be completely transparent to 109. All the hardware is auto configured and serviced by someone else; I should mention that VLAN is for an Internet Cafe.

robert.bahr · ‎05-20-2008

We still have this problem.

robert.bahr · ‎05-23-2008

Still having this problem. Any help? I put in a ip helper statement on the VTP Server switch, which is connected to the SOHO, no effect.

Kevin Dorrell · ‎05-23-2008

There is something that puzzles me a bit about this. You say you do a show int vlan 109 on all the switches, and the POP switches show up/up, but all the other switches show down/down. Does that mean you have an SVI on VLAN 109 on every switch? That is a bit unusual for a VLAN, which, after all, is actually a layer-2 construct as far as VTP is concerned.

Normally, I would expect you to have only a couple of SVIs on the VLAN, with perhaps HSRP running between them so they present a single virtual router address to the VLAN, and for the rest of the switches to be running layer-2 only for that VLAN.

How many of these switches are doing layer-3 on VLAN 109?

The way to check the connectivity of VLAN 109 at layer-2 is rather show spanning-tree vlan 109, and check they all agree on who is root.

BTW, your 2950 will only allow one VLAN interface up at a time, and that is for management. But that does not matter so long as it is part of the Spanning-Tree for VLAN 109.

Kevin Dorrell

Luxembourg