Re: Talk between 2 VTP domain - Page 2

cisco · ‎03-27-2006

Hi,

How to make 2 different VTP domain talk to each other .Both domain are in same building .

Thanks

CD

ankurbhasin · ‎05-10-2006

Hi Neo,

VTP domain is not at all concerned with communication between same vlans on multiple switches.

VTP as you know is just to get rid of manual vlan creation on multiple switches in big network.

But if you aready have vlan created like vlan 13 on switch with VTP Domain A and on switch with VTP domain B they can talk to each other if you have trunk between the 2 switches or even if you have an access port between 2 switches but the access port is configured for vlan 13.

Now because User A and User B are in same vlan they are in same broadcast domain so they do not need any layer 3 device and mac address of user B will be learned on switch who is in VTP domain A via trunk port and now when User A waan a talk to User B on other switch the frame will have the destination mac address of user B and when the farme from user A will enter switch which is in vtp domain A it will know that it has to move out of trunk port where the mac address is leraned and in this way it will reach switch who is in vtp domain B and vice versa will happen.

Hope I am clear with my explaination.

Pleas rate the post if it helped.

Regards,

Ankur

cisco · ‎05-10-2006

Hi Ankur !,

Thanks for your long reply.Now my next question is just guess that already VLAN_13 (10.X.X.X)is created in my VTP_Domain_A and now if VTP_Domain_B comes in picture with same name VLAN_13 (192.168.X.X) ? now how the VLAN info will be tagged ?

regards

Neo

ankurbhasin · ‎05-10-2006

Hi Neo,

Now here is the trick, VLAN info will be tagged the same way because on top of IP packet there is always a layer 2 frame encapsulation so no matter whatever IP you give to machines vlan information will be tagged the same way on trunk.

But because the 2 machines are on different network they will not talk to each other on layer 3 but yes layer 2 communication will work fine by which I mean machine B will reply to machine A for layer 2 broadcats ARP request. But if you try to ping machine B from machine A you will not get a reply because they are in different network.

HTH, if yes please rate the post.

Ankur

cisco · ‎05-10-2006

Hi Ankur,

AFAIK VLANs are created when a single broadcast is broken into multiple broadcast domain .So how will ARP will get the reply if these 2 machines are in different broadcast domain or You mean to say , as the name of the VLAN is same broadcast will travel from User_A which is in VLAN_13 on VTP_Domain_A to User_B which is in VLAN_13 on VTP_Domain_B , considering the fact ip addressing of both the VLANs are different ?

regards

Neo

cisco · ‎05-11-2006

Hi,

any thoughts...

regards

Neo

ankurbhasin · ‎05-11-2006

Hi Neo,

Considering the fact machine B and machine A has different ip address but still they are in same vlan.

Any layer 2 broadcast will reach machine B as when any traffic move out from machine A on switch A and hits the interface it will get a PVID of vlan 13 and it will broadcast the ARP request to all the ports in VLAN 13 which will also reach machine B because it is also in vlan 13 on switch B.

But when machine A will try to ping then it will check the boolean algorithem and will come to know machine b is in different network and will not get a reply.

HTH, if yes please rate the post.

Ankur

devang_etcom · ‎05-11-2006

hello Mr. Ankur,

now here as we are talking about different IP address right??? now is it possible to establish communication using any layer 3 functionality...

regards

Devang

pciaccio · ‎05-11-2006

With the VTP domain issue pushed aside for now. to make the VLAN subnet communicate via a trunk . This will work if you use Dot1Q trunking and set the Vlans in question to the native vlan's. Dot1Q will not tag the native VLAN. so if you have say vlan 1 on one switch set for native and the other switch is set for vlan 10 as native. If you Dot1Q trunk between them the VLAN subnet will communicate.Do not allow other VLAN's to go across the trunk.Since your VTP domain are not sync'd you will see different subnets on any similiar VLAN's numbers....Hope this helps....