VLAN Connections between Switch and Router.

Unanswered Question
Feb 6th, 2008

Hi all,

I have the following setup:

HOST A - SWITCH B - SWITCH C - ROUTER D - SWITCH E - ROUTER F

Now, I understand (and it works) that the connections between the switches are in trunk mode.

So, with regard to above:

1. SWITCH B interface to the HOST A is in access mode.

2. The interfaces between SWITCH-B and SWITCH-C is in trunk mode (VLAN 100).

3. The interface between SWITCH-c & ROUTER-D is in access mode, on the same VLAN.

My questions are:

In what mode should the interface between ROUTER D and SWITCH E operate?

In what mode should the interface between SWITCH E and ROUTER F operate?

Basically HOST A should be able to ping ROUTER F.

And what is the logic? Should it be in access mode over the same VLAN 100? Different VLAN? Or in trunk mode?

Thanks a lot. Appreciate the insight.

Kind regards.

I have this problem too.
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bhupeshg@hcl.in Wed, 02/06/2008 - 06:20

In what mode should the interface between ROUTER D and SWITCH E operate? If you have more than 1 Vlan configured in your network than it should be in trunk mode.

In what mode should the interface between SWITCH E and ROUTER F operate? If you want a result to get a reply from router F for Host A, than you have to configure this link as trunk.

In this case if Vlan 100 is the dafult vlan for your network and also vlan 100 is configured as native vlan, than you can use the operation level based on access mode.

you need to check that if default vlan 1 is enable or disable and what is the native vlan no.

branfarm1 Wed, 02/06/2008 - 06:24

Hi. I think I can help answer this, but I make no guarantees ;)

Access mode ports are for connecting to end devices and this simply means that they are only carrying traffic for one VLAN.

Trunk ports allow ports between devices to carry traffic for multiple VLANs. This means, for example, that if you had 5 vlans, you could have two switches "trunked" together with one cable and have traffic from hosts in the same VLAN, on one switch, communicate with hosts on the other switch who are in the same VLAN. I would recommend reading the CCNA book or BCMSN book for detailed information.

Typically, if a port is trunked, it carries the traffic for all VLAN's configured on that switch. You can change that behavior, for example, by only allowing certain VLAN's on the trunk (switchport trunk allowed vlan xxx).

For your first question, given the setup above, I would say that you would want the interface between Router D and Switch E to be in access mode. The same goes for the second question -- access mode for the interface between Switch E and Router F. The interfaces on Switch E will have to be in the same vlan, and the router interfaces will have to be on the same network, for communication to occur.

For host A to ping Router F, you'll have to make sure that Router D has the correct routing information to get to Router F, and that Router F has the right routes setup to make it back t Host A.

Hope that helps!

s.arunkumar Wed, 02/06/2008 - 06:25

Hi

If ur router D has proper routing towards router F,then,

1.The interface between router D and switch E can be access or trunk.Its not mandatory that it should vlan 100.

2.Since the switch E is a layer 2,the link between switch E and router F can be

a.access port (but with same vlan as of between router D and switch E)

or

b.trunk (that allows vlan between router D and switch E)

arun

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Posted February 6, 2008 at 5:52 AM
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