Bridging with 1600 series, IP range?

[harryburnham]

We have to implement a straightforward bridge between two sites. The original site uses ip addresses 197.0.0.1 to 197.0.0.50 (which we can't change as it is under the control of another supplier) with subnet mask of 255.255.255.0. We are re-deploying two 1600 routers from another site and wish to bridge to the new site using IP numbers 197.0.0.100 to 197.0.0.150 with subnet mask 255.255.255.0 so that all PCs on both sites can see each other. The document :-http://www.cisco.com/warp/public/779/smbiz/service/configs/leasedline/ll_bridge.htm shows the settings for bridging but uses different subnets at each end. Putting these settings into our routers, but using our IP numbers does not work. The leased line shows as up and the HDLC protocol is up but we can not ping between the sites, it as if they are not connected. Is it not going to be possible to achieve this?

[konigl]

The Cisco document you reference shows a different IP address for the Boston router in the picture than it uses in the configuration text below, which is a mistake; but the subnet masking is correct in that it puts all the IP addresses in the 10.whatever subnet, for management purposes.

Key commands to this bridging-only configuration are that "no ip routing" be present at the global level of the config, and that each interface in a particular router is part of the same bridge group, in this case "bridge-group 1". Also, at the global level "bridge 1 protocol ieee" for Spanning Tree.

Regardless of the IP address inconsistency noted above, this configuration should work for bridging. (I am going to simulate the Cisco document's setup later tonight with two 2500-series routers, and two external T1 CSU/DSUs in a back-to-back connection, to confirm this.)

What kind of leased line do you have? Your router may show line up/protocol up to the central office, but your service provider might have to flip a switch or change a config parameter on their gear to let traffic flow between the two. If I were a betting man, I would wager that the problem is at their end.

Most times when I've pulled my hair out with a non-functioning leased line configuration, and double-, triple- and quadruple-checked my configurations, and even questioned my own competency as an engineer, the problem has ultimately turned out to be an issue at the leased line service provider's end.

Hope this helps.

[harryburnham]

Hi, Thanks for the input. I don't believe that there is a problem with the line, it's a BT kilostream (128KBps) and I can ping between the IP numbers assigned to the serial ports on the routers and I can Telnet from one to the other. I assume that this means the line is working OK.

I am assuming that the problem lies in the IP set-up, in that the routers don't like having the same Class C subnet at both ends (I noted that Config-Maker won't let you assign addresses in this way, and the router config commands object to the same range being assigned to both interfaces (i.e. the ethernet and the serial).

Any further comments gratefully appreciated.

Harry

[konigl]

Just following up with the results of my test last night. Bridging worked as outlined in the Cisco document. From my laptop, I was able to ping and telnet each device in the equipment stack below via its IP address. Also was able to access the GUI on the routers and switches using my web browser. None of the devices had a default gateway specified.

Compaq laptop (IP address 10.20.30.40, mask 255.0.0.0) to

3Com 1100 switch (IP address 10.1.1.10, mask 255.0.0.0) to

Cisco 2514 router "Atlanta" (IP address 10.1.1.1, mask 255.0.0.0) to

ADC Kentrox CSU/DSU (IP address 10.30.0.2, mask 255.0.0.0) to

T1-crossover block to

ADC Kentrox CSU/DSU (IP address 10.20.0.2, mask 255.0.0.0) to

Cisco 2514 router "Boston" (IP address 10.2.2.2, mask 255.0.0.0) to

3Com 1100 switch (IP address 10.1.1.20, mask 255.0.0.0)

If you can get your routers in the same room together, you could do a similar test to verify that the equipment and configurations are bridging properly. When you know your gear works, then you can be sure you have a leased line service provider problem.

Hope this helps.

[konigl]

Harry,

Telnet OK from one router to the other rules out the line.

If the router is objecting to the same IP subnet being assigned to both interfaces, that tells me IP routing is enabled. You must get the router to stop trying to route IP; then it will let you put the same IP address on each interface. Use these commands (and substitute your IP address and mask):

config terminal

no ip routing

interface Ethernet0

ip address 10.1.1.1 255.0.0.0

bridge-group 1

interface Serial0

ip address 10.1.1.1 255.0.0.0

bridge-group 1

exit

bridge 1 protocol ieee

end

write memory

Make sure that each router's interfaces belong to the same bridge group number. This number is locally significant; it is not communicated across the serial link to the other router. That doesn't mean they can't be the same, though.

This should take care of it.

-Larry

[harryburnham]

Thanks to all for the interest and advice. I have been away for a few days hence the lateness of this post. I finally got it working, cleared all the settings out of both ends and put them all in again and this time it worked; I suppose it will remain one of those mysteries that never gets solved. Anyway Thanks Again,

Harry