Is it possible to transparent bridge ethernet and serial on 1841 router?

[Ether]

Hi all,

We are trying to put an 1841 in the middle of a /30 subnet for the sole purpose of terminating the T1 from the ISP, with the LAN router being Viptela vEdge 100b. [vEdge >> 1841 >> ISP]

Is there a way to get the /30 IP to live on the vEdge and have the 1841 only transparent bridge it's serial and ethernet interfaces. Or any other solution would be welcome. We are trying to avoid having to create another subnet.

Thanks in advance

[Richard Burts]

There are solutions like Integrated Routing and Bridging that might do what you want. But the most simple approach would be to turn off ip routing and to enable bridging on both interfaces. It might look something like this:

no ip routing

bridge 1 protocol ieee

interface serial0/0

bridge-group 1

interface FastEth0/0

bridge-group 1

HTH

Rick

[Ether]

Hi Rich, thanks for your reply. The issue were having is the layer 2 mismatch between T1 (PPP encapsulation) and ethernet (MAC addressing). We've tried transparent bridging with no luck, without the BVI.

[Richard Burts]

Your original post asked a question about whether it is possible to do transparent bridging on an 1841 router. I answered that question. And I have seen that implementation work. Perhaps the real question is whether transparent bridging would solve your problem. Unfortunately I believe that the answer is that it would not solve your issue. When I have seen transparent bridging work over serial connections both sides were doing transparent bridging on the serial interface. If your ISP is running PPP and has assigned the IP address to the serial interface then I do not believe that transparent bridging on your side is going to accomplish what you want. I do not see much option other than having the /30 on the 1841  and a new subnet between the 1841 and your Edge.

HTH

Rick

[Ether]

Do you think there's anything else we can do on the router to get the T1 to ethernet handoff? Maybe bridging is not the right approach, possibly another method? Thank you for your thoughts on this so far.

[Richard Burts]

If the ISP connection is a T1 running PPP and if the ISP has put an IP address on their T1 interface then I do not see any viable alternative other than a router with a T1 and the IP address on the T1. You can create an Ethernet connection between the router and your vEdge and have an IP subnet on that connection and you can have the router forward traffic between vEdge and ISP. It does raise a question about whether NAT is being done, and if so would you move the NAT to the router? (I would think you would need to have the NAT on the router so it can translate to the public address from the ISP) Of is it possible that the ISP would use one subnet with public addressing for the router connection and provide a second subnet of IP addresses that you might use on vEdge?

HTH

Rick