Merging tagged subinterfaces in one vlan?

[joshhalley]

Hi,

This is a strange kinda question and has nothing to do with a good design but anyway. Does anybody know if there is a way of allowing the same vlan id on multiple sub interfaces on a trunk?

Ie:

interface fast 0/0.1

encap isl 10

ip vrf forwarding red

ip address 192.168.0.1 255.255.255.0

interface fast 0/0.2

encap isl 10

ip vrf fowarding green

ip address 192.168.0.2 255.255.255.0

interface fast 0/0.3

encap isl 10

ip vrf fowarding blue

ip address 192.168.0.3 255.255.255.0

If there is no possible way of doing this other than using seperate vlans, is there then a way of merging the vlans / subnets without the use of a IRB.

Any information would be greatly appreciated.

Kind Regards,

Josh

[ehirsel]

I do not believe that you can use the same vlan id for multiple sub-interfaces. This is because they are logical but there is only one physical connection, and the router appends the vlan id in the frame that it sends to the switch which uses that id to forward to the proper end stations.

Layer 2 swithes do not do vrf processing, so you will need to use seperate vlans.

Let me know if this helps.

[Kevin Dorrell]

I don't see how this could work. It might be OK for transmission, but what would it do with received packets? If they are tagged "10", which sub-interface would they be for?

OTOH, you can have multiple subnets on a single VLAN, simply by using secondary addresses.

Kevin Dorrell

Luxembourg

[joshhalley]

Hi Kevin,

Basically the requirement for vlan 10 being on all interfaces is to allow for static routes into different vrfs based on one transit subnet.

Hence meaning that from another router (192.168.0.5) in the above mentioned 192.168.0.0/24 segment the following routes into different vrfs could be achived.

ie:

From the other router in vlan 10 (192.168.0.5)

ip route 10.1.0.0/16 192.168.0.1

ip route 10.2.0.0/16 192.168.0.2

ip route 10.3.0.0/16 192.168.0.3.

Now if all of the interfaces on the router were to be physical interfaces terminating into vlan 10 there would be no problem with this working. However due to the vlan id limitation on a trunk interface this doesn't seem possible.

If you know of any way to overcome this issue, any information would be appreciated.

Kind Regards,

Josh