BCMSN: Inter-vlan routing

Unanswered Question
Sep 16th, 2008

In interVLAN routing configuration to route traffic between different

VLANs that are configured on access layer switches.

If given two vlan IDs, say Vlan ID 10 and 20 and two ip addresses how would the ip address configured on each vlan interface be generated.

i.e. @

SW(if-config)#ip add . . .

I have this problem too.
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jcrussell Tue, 09/16/2008 - 16:33

Say you had the following:

Vlan 10 -

Vlan 20 -

To configure an IP address for them, you would create an SVI, or Switch Virtual Interface.

SW(config)# interface vlan10

SW(if-config)# ip address

SW(if-config)# no shut

SW(if-config)# exit

SW(config)# interface vlan20

SW(if-config)# ip address

SW(if-config)# no shut

SW(if-config)# exit


Is this what you were looking for?

Istvan_Rabai Tue, 09/16/2008 - 17:43

Just an addition to the previous post:

To be more specific, this configuration has to be applied on a layer3 switch, which is most often located in the distribution layer.

You probably have a layer2 switch in the access layer that cannot be configured for interVLAN routing.



covenant818 Wed, 09/17/2008 - 02:24

Thanks for the notes.

I thought the Vlan ID has to be part of the ip address i.e. one octet.

say for Vlan 20

and for Vlan 10

is there any rule that affects the first three octets or can it be anything. I saw a config where the first 3 octets were changed from the given ip address. Just wondering if it was right.

davehartburn Wed, 09/17/2008 - 04:26

The Vlan ID has nothing what so ever to do with the subnet range you use. Basically, pick a VLAN number and pick a range of IP addresses and off you go.

For a test lab, you can use any IP address you wish. In real life (or if connected to the internet), you will be given an IP address or range from your ISP. You either have to use IPs in that range or use NAT and use the range of 'private' IP addresses behind that NAT box. If you are doing CCNA, I think you get onto NAT afterwards.

Basically if the IP address starts with a 10, it is fine to use and put anything you want after that.


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