VTP domain change

[michal.grzelak]

Hi,

Our network runs in one VTP domain. All switches are Cat6500 (ISO) sup2 or sup720. All is working in Layer 2.

We are using vlans above 1000 which cannot be propagated by VTP and needs to be configured by hand on every switch. We changed the VTP domain so every 6500 switch was its own VTP domain and then trouble started ... something strange occured. The MAC addresses were not propagated to other switches in vlan (layer 2 only vlan). Putting static entries did not solve the problem. The MAC addresses in the same VLAN were only propagated from access1(VTP access1) to core1(VTP core1),but not to the access2 (VTP access2). Same thing the other way.

On switches that we didnt change vtp, everything worked fine. After couple of hours trying to solve the problem, I changed back to same VTP domain for all switches and MACs starts propagate.

What was cousing this problem ?

Thanks and regards:

Michal

[m.benhassine]

VTP doesn't know propagate advertisements outside the vtp domain. It, rather maintains information consistency between the switches in the same vtp domain through the trunk links.

Configuring different vtp domain is the same as isolating each switch in a domain.

PS:

"You can use VTP to manage VLANs 1 to 1005 in your network. (Note that VTP does not support

VLANs 1025 to 4094.)

When you make a change to the VLAN configuration on a VTP server, the change is propagated to all

switches in the VTP domain. VTP advertisements are transmitted out all trunk connections, including

Inter-Switch Link (ISL), IEEE 802.1Q, IEEE 802.10, and ATM LAN Emulation (LANE).

VTP servers advertise their VLAN configuration to other switches in the same VTP domain and

synchronize their VLAN configuration with other switches based on advertisements received over

trunk links. VTP server is the default mode.

Each switch in the VTP domain sends periodic advertisements out each trunk port to a reserved multicast

address. VTP advertisements are received by neighboring switches (in the same domain), which update their VTP and VLAN

configurations as necessary.

The following global configuration information is distributed in VTP advertisements:

• VLAN IDs (ISL and 802.1Q)

• Emulated LAN names (for ATM LANE)

• 802.10 SAID values (FDDI)

• VTP domain name

• VTP configuration revision number

• VLAN configuration, including the maximum transmission unit (MTU) size for each VLAN

• Frame format

"

Please rate if it helps

Regards

M. BEN HASSINE

[michal.grzelak]

Hi, Thanks for an replay. But there is something more strange about it. After a change most vlans did talk to each other even if they were in different domains, but only one did not work,layer 2 Vlan. We have 3 switches connected. SwitchA(vtp domain A)-SwitchB(vtp domain B)-SwitchC(vtp domain C). MACs from switchA went to switch B but could not appear on switch C. All are connected by trunks 802.1q, all vlans allowed,VTP version 2. Any ideas ?

[m.benhassine]

The VTP does not limit the communication between VLANs (using layer 3). It limits rather the adverstisements to the switches in the VTP domain. VTP handles information about VLANs in the VTP domain and ensure VLAN database consistency between the different switches IN THE SAME VTP DOMAIN.

Since you've VLANs configured on the different switches, it is a good idea to verify if you have configured the same VLAN (Layer 2) on the three switches and if that the ... MAC adresses belong to the same VLAN... since the broadcast domain is limited to the VLAN and the MAC adresses will be propagated only to the ports belonging to the same VLAN in the different switches through the trun links.

...But please notice that these are two different issues.

[michal.grzelak]

Hi m.benhassine,

Thx for replay.Situation here is slitly different, cause all switches were in the same VTP domain before the change, and all have the same VLAN database. After a change of a VTP domain (each switch was its own VTP domain, but has the same VLANs learned from old VTP domain as client) only one VLAN 901 - layer 2 only had a problem. Other VLANs worked well. Maybe its becouse there was no routing running between them ? But then, those VLANs are the same, same names, so what stops learnig of the MAC addresses in the same layer 2 VLAN ?? Anyone has any idea ?

Thanks

Michal