Route IP and Bridge Other Protocols

[mwkirk]

I have a setup where there are currently 2 Cisco routers connected via T-1 and they are routing IP. What I am being asked to do is leave the IP routing in place and selectively bridge other traffic. The situation is these guys have 3Com NBX phone switch and they have remote phones on the other side of this link. The phones have IPs and work but there is some type of issue with the Call Center software that my guy who knows the NBX stuff is hoping will be corrected by running the phones at Layer-2 which is the way the NBX phones work by default. I have looked over the IRB functionality thinking that might play into it but this is something I haven't had to deal with. I guess what I need is for the router to do is a fallback-bridge type of setup like I have done on a 3500 series. I know that is not a feature in an IOS router but that is basically how I need it to work. Any Ideas?

[Richard Burts · Accepted solution]

Mike

I think that there is a solution that is less complicated. If you are routing IP and want to bridge non-IP traffic then it should work if you configure bridging on the LAN and on the serial interfaces. A config would look something like this:

bridge 1 protocol ieee

interface FastEthernet0/0

bridge-group 1

interface Serial1/0

bridge-group 1

This will route IP and will take non-IP traffic from the LAN and bridge it over the serial. Configuration of IRB would allow you to route IP on some interfaces and to bridge IP on other interfaces. As long as you want to route IP on all interfaces and to bridge non-IP traffic then IRB is overkill.

There is a general caveat about bridging over serial links. Bridging will transport broadcast traffic over the serial and it may consume bandwidth and impact performance. But if you are being told that you need to do it, there is an implementation that will do what you describe.

HTH

Rick

[dgahm]

What protocol do the phones use? Sounds like IP.

It is going to be pretty hard to bridge IP to the phones and route all other IP traffic. IRB might work, but you are going to need to separate the traffic on different interfaces.

I would want to investigate the specifics of the issue. Perhaps you could do a packet capture to determine what layer 2 traffic needs to traverse the link. It may be a broadcast that can be forwarded via the UDP broadcast forwarding function of the router.

[mwkirk]

By default, the 3Com NBX phones operate at Layer-2 and do not even need an IP address. I am stretching my NBX knowledge here but for routed environments you purchase a license for "IP On the Fly" I think it is called. The customer has this and I think my NBX guy has worked through this with 3Com and is looking to take the IPs off the phones and have them become layer-2 devices. The phones work as it stands now but when calls are routed through a call-center package they are running there are issues.

I understand the issues with broadcast traffic and such but they are wanting to give this a shot to see if it helps or hinders things any.

MK

[Richard Burts]

Mike

As long as you recognize the potential downside of doing it, I believe that all you have to do is to enable bridging. You would need to do it on the routers on both sides of the serial link (would it be a correct assumption to believe that the phone is connected on a LAN on one side of the serial link and the phone switch is on the LAN on the other side?).

HTH

Rick