Connection Lost change VTP Mode to transparent

[MarioLieb]

Hi All

i have a strange behavior, when i try to change the VTP Mode from Client to transparent. I have the following problem. In our network we use many "old" Cisco Catalyst 2950 and 3548XL. After i change my network and break it down in more small brodcastdomains (one Class B network i more Class C networks) i became the problem that the above mentioned switches only support 64 VLAN´s on PVSTP. When i configure more then 64 VLAN´s the config an the 3548 and 2950 show "no spanning tree vlan xxx" for the new vlan´s. Now i will change the vtp mode from Client to transparent at the 3548 and 2950. I tested this on a 3548. After i changed to vtp transparent i lost the connection to the switch. I conneted to the switch via consol-cable  to check the vlan database. All vlan´s stay in the vlandatabase. After i changed back to client mode. I can reached the switch. How can i change the vtp- mode without connection lost? Any ideas ?

Here the VTP- Server and Client config

VTP Version                     : 2
Configuration Revision          : 171
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 69
VTP Operating Mode              : Server
VTP Domain Name                 : XXX
VTP Pruning Mode                : Enabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0x10 0x5C 0xA3 0xF9 0x8A 0x3A 0xE2 0x6B
Configuration last modified by 172.25.0.201 at 6-9-10 07:20:25
Local updater ID is 172.25.0.201 on interface Vl1 (lowest numbered VLAN interfac
e found)

VTP Version                     : 2
Configuration Revision          : 171
Maximum VLANs supported locally : 254
Number of existing VLANs        : 69
VTP Operating Mode              : Client
VTP Domain Name                 : XXX
VTP Pruning Mode                : Enabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0x10 0x5C 0xA3 0xF9 0x8A 0x3A 0xE2 0x6B
Configuration last modified by 172.25.0.201 at 6-9-10 07:20:25

Thanks Mario

[Alexander Deems]

Have you tried changing it to transparent mode from the console? Then testing to see if you are able to access via telnet or ssh?

[Mohamed Sobair]

Alexandar,

You probabely lost connection because the Switch was learning those Vlan information from a server and you have change it to transparent . In VTP transparent Mode Switches doesnt accept VTP advertismnet but rather it forwards VTP advertisment as soon as it recieves it.

I suggest login to the switch by console and configure VTP transparnet with the required VLANs locally and then check.

HTH

Mohamed

[MarioLieb]

Hi Mohamen, hi Alexander

i need a easyer way. I must change the vtp- mode on 101 Switches!!! I original planed to change the vtp- mode via telnet. Also we are planning to replace these old switches with new one´s. But in the meantime i must change the vtp- mode because i need more VLAN´s and i would not have that there is no STP- Instance for these new VLAN´s.

Ok i tested to change the vtp- mode via telnet:

1. I loged in via telnet and change the vtp- mode from Client to tranparent

2. After a short time i lost the connection.

3. I loged in via console

4. checked the vlan- database, all my vlan´s stayed in the database

5. I switched back to Clint- Mode and than i became connection to the switch

I don´´t understand that behavior. I thought, when i change the vtp-- mode from Client to transparent, the only change is that the switch donßt become vtp- advertisements. And all vlan´s should stay at the vlan database. Is this right ? Why will i lost the connection ? When i change the vtp- mode via console will the atached Clients also lost the connection ?

Thanke

Mario

[thinakraj · Accepted solution]

In the transparent mode it does not originate advertisements or sysnchronize its database with any other switches.

It forwards VTP advertisements out its trunk links.

Plz check your trunk links.

If an switch receives a TC BPDU, it clears the MAC addresses

on that port and sets the TC bit on all BPDUs sent out its designated

and root ports until the TC timer expires, so that only your getting connection lost. …

[MarioLieb]

Hi all

@thinakraj

thanks for your explanation. I have to wait a few seconds and than the connection is back after i changed the vtp mode.

BUT

Now i have another problem.

After i change to transparent mode, there are some ports in a other VLAN as VLAN  1 for example VLAN 20. The clients on this port do not become a ip adress from the dhcp server. The vlan already exist on the switch and the vlan exists on my Layer 3 router and i have configured a ip helper. Some Clients become a IP some not.

Any idea´s ? If i pluged the client on a port of a switch which is a vtp client everything works fin.

Very strange

Thanks

Mario

[mahmoodmkl]

Hi,

I would suggest you that check all the switches are having the identical vlan info.

Also check the STP toplogy of all u r switches.

Thanks

Mahmood

[MarioLieb]

Hi mahmoodmkl

thanks for your answer. I think i had solve the problem ;-) The error was, that i used vtp pruning. So one Switch use vtp pruning and the over switch that is connected to the switch witch use vtp prunning. So i think that on the trunk the vlan will prunned out and so i cann´t get a connection on a accessport at the switch in tranparentmode for other vlan´s ;-). After i turned vtp prunning off, it works.

So i think that problem will we solved ;-)

Thanks

Mario

[Ha Dao]

Hi Mario, i am getting exactly the problem you got in 2010. I am also think about VTP pruning. Did you turn it off at VTP Server switch ? Is it safe ?

Can you share me more about your actions.

Tks so much

[MarioLieb]

Hi Dao

(hope that is your first namen ;-)) 2010 ufff that is a long time and problems ago ;-) Ok but what is know is. You can disable VTP- Prunning on your VTP- Server. This will not disturb your LAN. Maybe Spanningtree can try to come in a stable state per VLAN. But this should be so fast and your users will not have any outage. So you can disable VTP Prunning on the server. And after taht you can switch to transperant also without any outage.

Hope this will help 

Regard Mario