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Webcast-Catalyst9k
New Member

Subinterface & VLAN Issue

Hi All,

This is my first time using this so be easy on me!

I have setup two Subinterfaces on a FastEthernet interface on a 2801 router. Both are tagged with different VLan's and the interface is physially connected into a 2980 switch port which is trunked. Ok so far.

The problem the arises. On the 2980 switch, I assign a port into one Vlan and it works fine. However anything connected to the other Vlan can't be ping'ed. I can ping the gateway address of both but just can't get to any device on one of the Vlans.

I have this set up on another site and it works fine.

Need any more info please reply!

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Re: Subinterface & VLAN Issue

Hi Friend,

Yes that is the issue. You can configure native vlan on your subinterface fa0/0.2 by just adding a native keyword after "encapsulation dot1q 2 native" or else you can change the native vlan 2 to 1 on trunk with a command "set vlan 1 2/29"

HTH

Ankur

13 REPLIES

Re: Subinterface & VLAN Issue

Hi,

What is the default-gateway that is being used on the hosts in the vlan. The default-gateway should be the sub-interface Ip of the router's interface in their respective vlans.

Please paste the router and switch config.

-amit singh

New Member

Re: Subinterface & VLAN Issue

Hi,

Thanks for the reply.

Please see attahced the Router and Switch config.

Hope you can see what the issue is as its been causing me hours of headache!

Rob.

Cisco Employee

Re: Subinterface & VLAN Issue

Hi Friend,

You have a policy map configured on your sub interface fa0/0.4 and which calls for route map which further calls for access list 99 which specifies the source ip subnet address for your subinterface fa0/0.4 subnet.

Now anything which comes on your subinterface fa0/0.4 from its subnet it will pass the policy and will be fwded as per the route set in your route map overriding the routing table.

So can you change you access list 99 with extended access list with source and destination ip address so that when traffic from your fa0/0.4 hits the subinterface if it is only for specific destinations it will follow the route condition of route map else will follow normal routing table.

HTH

Ankur

*Pls rate all helpfull post

Re: Subinterface & VLAN Issue

Hi,

I agree with Ankur on this. Probably this is the catch. All the Traffic from Vlan 4 is being directly policy routed over the GRE tunnel 1 and is not cmojng back to the vlan2. Use the Extended ACL as suggested by Ankur and you should be good to go.

HTH,

-amit singh

New Member

Re: Subinterface & VLAN Issue

Hi,

Thanks for this but the issue is with the other subInterface. The fa0/0.2 is the one that is causing the problem. By making access-list 99 extended, will this fix the problem? Thanks a million if so. I'll rate it as solved.

Cisco Employee

Re: Subinterface & VLAN Issue

Hi Friend,

As you stated in your original post "just can't get to any device on one of the Vlans" can you confirm from where you can't get to it?

I believe you are not able to get to subinterface fa0/0.2 from your fa0/0.4 subinterface or vice versa? If its intefvlan related yes extended ACL will resolve the issue.

Ankur

New Member

Re: Subinterface & VLAN Issue

Hi,

I can't access any device on fa0/0.2 from any location. I can ping the gateway but thats all.

So you suggest i create an extended ACL for fa0/0.4 - with source ip 10.250.5.0 and destination 192.168..7.137 which is the next hop set out by the route map?

Sorry If i'm confusing the issue.

Cisco Employee

Re: Subinterface & VLAN Issue

Hi Friend,

Before changing the ACL, I will recommend you to remove the policy map from the subinterface fa0/0.4 if possible and see if that resolves the issue.

If yes then a plan is required as what is the intention for putting a route map and ACL can be planned accordingly.

HTH

Ankur

New Member

Re: Subinterface & VLAN Issue

Hi,

I've removed the route-map from this interface as you requested but I still can't ping 172.17.11.251 - a device on the Vlan 2.

Could the issue not reside on the switch?

I have this set up on another router and switch in a different site and it seems to work ok.

Re: Subinterface & VLAN Issue

Hi,

Cna you put " show trunk " output from the switch.

-amit singh

New Member

Re: Subinterface & VLAN Issue

Sure - please see attached:

i see that port 2/29 was in the native vlan 2? can this be changed?

Cisco Employee

Re: Subinterface & VLAN Issue

Hi Friend,

Yes that is the issue. You can configure native vlan on your subinterface fa0/0.2 by just adding a native keyword after "encapsulation dot1q 2 native" or else you can change the native vlan 2 to 1 on trunk with a command "set vlan 1 2/29"

HTH

Ankur

New Member

Re: Subinterface & VLAN Issue

Yes - that fixed it.

Nice one - Thanks for your help.

I'll definatley be using this site alot over the coming weeks\months\years!!!!

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