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New Member

Trunk link on a router

How to configure a router interface to be a trunk link and route VLAN, VTP packets to different networks?

7 REPLIES
Purple

Re: Trunk link on a router

Routers do not run VTP.

However, you can configure a router ethernet interface to be a trunk using config like the following:

interface FastEthernet0

no ip address

!

interface FastEthernet0.10

ip address 10.1.1.1 255.255.255.0

encapsulation dot1q 10

!

interface FastEthernet0.20

ip address 10.2.1.1 255.255.255.0

encapsulation dot1q 20

!

Paresh

New Member

Re: Trunk link on a router

Hi,

I am trying to do similar thing.

How to configure router interfaces to support multiple vlan on same ip subnet.

In other words, we want vlan 10 and 20 to use same ip address of router.

Thanks,

Re: Trunk link on a router

Hi,

you cannot have a same subnet IP to a multiple vlans, while creating vlans, each vlan should be on different subnet, may be i think you wanted to do VLSM(Variable Length Subnet Mask) in which where you can use a single network with multiple subnet.

eg.

interface FastEthernet0/0

no ip address

interface FastEthernet0/0.1

ip address 10.1.1.1 255.255.255.240

encapsulation dot1q 1

interface FastEthernet0/0.2

ip address 10.1.1.17 255.255.255.224

encapsulation dot1q 2

refer to this site for more understand about VLSM.

http://en.wikipedia.org/wiki/VLSM

hope this helps.

rate this post if ur cleared.

New Member

Re: Trunk link on a router

Thanks for your help.

But it is not convenient for us to redo VLSM.

Or maybe my question is not clear.

Please take a look example in the thread. Assume we already configured router and switch with two vlan and used subinterface on router to trunk.

Later, we want to create another vlan(let us say 40) on switch and allow users on 40 to be on the same subnet as 20. How we should do?

Forgive my english. I can send you a diagram if you need.

Thanks,

Re: Trunk link on a router

Yeah it would be better if you could send me the diagram to make a clear understanding

Re: Trunk link on a router

Hi

As u say that u want the same sunbet as vlan 20 why do u want to create vlan 40 just assign the specified ports in vlan 20 as they will have the same subnet.i think u r confused abt vlans and subnets.

vlan is broadcast domain.and each broadcast domain has its own subnet.

Thanks

Mahmood

New Member

Re: Trunk link on a router

Mahmood wrote:

"vlan is broadcast domain.and each broadcast domain has its own subnet".

Thanks Mahood. You are right!

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