2940 switch reverting to transparent mode

[antonios]

Hi ,

I would like to confirm that this behaviour on my 2940 is correct. I have a vtp server configured that is advertising about 10 vlans to the vtp clients of which the 2940 switch is one of these. What I see is that the trunk interface to my vtp server comes up and the 2940 is receiving these vtp advertisements but with a few seconds it has changed its mode to transparent from client.

Is this because it can only accomodate 4 vlans. I have read this in the configuration guide and I quote:

"When the network is configured with the maximum four VLANs, the switch automatically changes from VTP server or client mode to VTP transparent mode. The switch then operates with the VLAN configuration that preceded the one that sent it into transparent mode. "

Is this then the way the 2940 behaves when it learns more than 4 vlans from the VTP server.

Thanks

Tony

[Prashanth Krishnappa]

You are correct. It is because the switch can support only 4 VLANs. Once it gets a VTP update with more than 4 vlans, it changes to transparent mode and syslogs a message something like

SW_VLAN-6-VTP_MODE_CHANGE: VLAN manager changing device mode from CLIENT to TRANSPARENT.

or

SW_VLAN-6-VTP_MODE_CHANGE: VLAN manager changing device mode from SERVER to TRANSPARENT.

[cisco]

I have the same problem as discussed here. I have tried too created a new, small vtp-domain only for my 2940, and used one of them as server (with 4 vlan) and the rest of my 2940 as client. And hope that I would be able to distribute these 4 vlan. But so far no good. I have read the instruction and tried many times. What about vlan 1, 1002-1005? Do they count into the support of only 4 vlan?

Peder Sefland

[amitsin]

Hi Tony,

This behaviour is correct as the 2940 switch supports only 4 vlans STP instance. As the switch doesnot support more than 4 vlans so the switch will always revert to transparent mode. Please check the following link :

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2940/12120ea2/2940scg

/swvlan.htm#wp1353846

Hope this helps.

Amit Singh

[milan.kulik]

Don't you think this is a pretty STUPID feature?

Whatever the reason for 4 STP instances limit is (I suppose lack of memory in cheap 2940s), why the hell are not the ACTIVE VLANs (with ports assigned)only limited?

I can easily imagine that edge switch like 2940 could be limited to allow assigning ports into 4 VLANs only (including disabling other VLANs on uplink trunks).

But why can't be more VLANs present in the VLAN.dat database file (imported via VTP, e.g.)?

I typically use 2940s with 2 VLANs only: one for PCs, one for switch management. But any time I connect a new 2940 to my network I have to move it to VTP transparent mode and configure these 2 VLANs manually on it!

With the current 4-VLAN limit, wouldn't it be more comfortable to disable VTP completely?

BTW, I read somewhere this limit should be increased to 8, but can't find the article just now.

Regards,

Milan

[reuben.farrelly]

The limit was increased from 4 to 12 VLANs, in 12.1.22EA1 (-EA3 out today).

From the release notes: http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2940/12122ea1/ol554602.htm#wp638417

You can set up to 12 spanning-tree instances and 12 active VLANs. If more VLANs are defined in the VTP than there are spanning-tree instances, you can enable per-VLAN spanning-tree plus (PVST+) or rapid PVST+ on only 12 VLANs.

[milan.kulik]

Have you tested if the switch still moves to the transparent mode when more than 12 VLANs are defined in the VTP domain (even not active on the switch)?

Thanks,

Milan