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Community Member

Sub-Interfaces on an 1841 ISR

Hi All,

I'm trying to connect a few sites back to my office using sub-interfaces on an 1841 router. The only info the ISP gave my is the VLAN IDs of each site and the encapsulation type (dot1q). On the remote end of the connection is basically a layer 2 switch and a server. I can connect and ping when I configure the ip on the physical interface though, but not on the sub interfaces.. here's a sample of the config..

PHL_EDGE(config)#interface fa 0/1

PHL_EDGE(config-if)#no ip address

PHL_EDGE(config-if)#no shut

PHL_EDGE(config-if)#interface fa 0/1.1

PHL_EDGE(config-subif)#enca dot1q 320

PHL_EDGE(config-subif)#ip address 192.168.36.1 255.255.255.0

PHL_EDGE(config-subif)#no shut

any thoughts ??

3 REPLIES
Hall of Fame Super Gold

Re: Sub-Interfaces on an 1841 ISR

Donavan

If you can connect and ping when you configure the IP on the physical interface then either this is the native VLAN which sends untagged frames or the connection is not an 802.1q trunk.

You say that there are a few sites. If you put the IP address of a different site onto the physical interface can you connect and ping to that other site? If you can connect to several sites if you put the address of the site onto the physical interface then it suggests that the connection is not a trunk. If there is only a single site which works if you put its address onto the physical interface then it suggests that the VLAN for that site is the native VLAN (and you need to include the native keyword on that subinterface encapsulation command).

HTH

Rick

Community Member

Re: Sub-Interfaces on an 1841 ISR

Hi All,

There was a confi problem my ISP side.. I'm half way through having the sites up and running. I can connect using sub-interfaces now. The only problem is that i cannot browse the internet from remote locations. Internet is shared from the main office through the adsl interface to remote locations.I've attached my config for review..

Thks,

Donavan

Hall of Fame Super Gold

Re: Sub-Interfaces on an 1841 ISR

Donavan

I am glad to see that my analysis that this might be the native VLAN turned out to be correct. I have looked at the config that you posted and had several theories about what the problem might be - but most of them turned out to not be right.

To continue the investigation I have several questions which I hope you can provide answers.

- is the router able to access resources in the Internet? (can it ping Internet addresses?)

- are PCs on the subinterface able to ping the router subinterface address? (I would assume that they are able to ping the router subinterface address).

- are PCs on the subinterface able to ping the router dialer interface address?

- are PCs on the subinterface able to ping resources in the Internet using names to access?

- are PCs on the susinterface able to ping resources in the Internet using IP addresses for the destination?

HTH

Rick

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