VLAN questions

dbarboza27 · ‎06-18-2010

Hi,

I have a couple of questions about VLAN.

1. Based in the following scenario:

Switch A ---Trunk---- Switch B ----Trunk------ Switch C

If I create a VLAN in swithes A and C (for reference VLAN 100), but I dont create it in Switch B, is it possible to communicate the hosts connected on Switch A in vlan 100 with the hosts connected to Vlan 100 in Switch B ?????

2. I know that the ethernet interfaces are broadcast. I supose that the VLAN interface are too, but I would like a second opinion about that.

Thanks for your comments,

Jon Marshall · ‎06-18-2010

dbarboza27 wrote:

Hi,

I have a couple of questions about VLAN.

1. Based in the following scenario:

Switch A ---Trunk---- Switch B ----Trunk------ Switch C

If I create a VLAN in swithes A and C (for reference VLAN 100), but I dont create it in Switch B, is it possible to communicate the hosts connected on Switch A in vlan 100 with the hosts connected to Vlan 100 in Switch B ?????

2. I know that the ethernet interfaces are broadcast. I supose that the VLAN interface are too, but I would like a second opinion about that.

Thanks for your comments,

1. No they won't be able to communicate ie. you need vlan 100 on all 3 switches. I'm assuming your question was can hosts on switch A in vlan 100 communicate with hosts on switch C in vlan 100 which is not quite what you wrote.

2. Not sure what you mean. L3 SVI's are like routed ethernet interfaces in that they do indeed understand broadcasts but will not by default route those broadcasts to another subnet.

Jon

Dasuntha Dinesh · ‎06-19-2010

I also assume that you want hosts configured in vlan 100 in switch A needs to communicate with hosts in vlan 100 in Switch C.

No problem. They can communicate with each other without any problem.

No need to create vlan 100 in switch B.

Make sure the trunks are configured properly between switches.

Regards,

Dasuntha

Jon Marshall · ‎06-19-2010

Dasuntha_Dinesh wrote:

I also assume that you want hosts configured in vlan 100 in switch A needs to communicate with hosts in vlan 100 in Switch C.

No problem. They can communicate with each other without any problem.

No need to create vlan 100 in switch B.

Make sure the trunks are configured properly between switches.

Regards,

Dasuntha

Have you tested this ? If vlan 100 does not exist on switch B then you cannot get from switch A to switch C via L2 in vlan 100.

Jon

Dasuntha Dinesh · ‎06-19-2010

Jon,

I tested it & working fine.

And no need to configure vlan100 in switch B.

Only we need to configure trunk links properly.

Pls test. You'll also see it.

Regards,

Dasuntha

Jon Marshall · ‎06-19-2010

Dasuntha_Dinesh wrote:

Jon,

I tested it & working fine.

And no need to configure vlan100 in switch B.

Only we need to configure trunk links properly.

Pls test. You'll also see it.

Regards,

Dasuntha

Interesting. So when you say you need to configure the trunk links properly does that mean allowing vlan 100 on the trunk links ?

Jon

Dasuntha Dinesh · ‎06-19-2010

I didnt specify only vlan 100. I allowed all

I mean the trunk encapsulation should be properly configured.

I also had a doubt first, but I tested it & worked perfectly.

Jon Marshall · ‎06-19-2010

Dasuntha_Dinesh wrote:

I didnt specify only vlan 100. I allowed all

I mean the trunk encapsulation should be properly configured.

I also had a doubt first, but I tested it & worked perfectly.

So a "sh vlan brief" on switch B does not show vlan 100 ?

Sorry to ask so many questions but i didn't think this would work so it's news to me

Jon

Dasuntha Dinesh · ‎06-19-2010

yes. of course.

vlan 100 cant be in switch B. Coz i didnt created it in Switch B & I m not using VTP.

And in this question, we are not trying inter vlan communication.

And both hosts are in the same vlan & same ip subnet & switches carry the vlan information if the trunks are properly configured.

Jon Marshall · ‎06-19-2010

Dasuntha_Dinesh wrote:

yes. of course.

vlan 100 cant be in switch B. Coz i didnt created it in Switch B & I m not using VTP.

And in this question, we are not trying inter vlan communication.

And both hosts are in the same vlan & same ip subnet & switches carry the vlan information if the trunks are properly configured.

Then i stand corrected because i honestly thought that would not work. Thanks for the information and patience with my questions

Jon

Jon Marshall · ‎06-19-2010

One more question - how have you set the switches up with VTP ie. are they transparent or VTP server/client ?

Jon

Dasuntha Dinesh · ‎06-19-2010

I didnt configure VTP in any switch

Dasuntha Dinesh · ‎06-19-2010

I tested it both L2 & L3 switches.

its working fine in both L2 & L3 switches.

narendrakumar1987in · ‎06-20-2010

Dear Dasuntha,

Could you please post your configs.

Because as Jon says, it doesnt work for me either!!! I couldnt make this intra VLAN communication without creating the vlan 100 in the SW-B, regardless of what VTP domain i stay in.

The vlan i create in SW-A gets replicated to SW-C if i have SW-B in VTP mode transparent. But thats not the problem / question here.

The actual question is, Will the traffic from host A on SW-A's VLAN 100 reach SW-B's host B on vlan 100. ?

I would appreciate if you can post your configs. or atleast the output of "show vlan brief, show int trunk" in all three switches..

Happy Networking !!!!

Narendrakumar B

Do rate the helpful posts !!

thiruma.valavan · ‎06-20-2010

Switch A--- trunk link---- Switch B----trunk link ----Switch C

In example, you configured vlan 100 in Switch A and Switch c. But Switch B have configured in vlan 30 only

That time VTP help us to contact switch A(VTP SERVER MODE) and Switch C(VTP CLIENT MODE).

In Switch B has configured in VTP TRANSPARENT mode.