Bridging with Two Routers 1

[PinkLips]

I have 2 Cisco routers (2621) and 2 remote locations.
I want both locations to have the same LAN subnet.
How can I do that? What type of routing protocol should I used? Can you post a sample config.

10.10.2.x/24 RtrA s0/0<---------->s0/0 RtrB 10.10.2.x/24






Thanks,
Nicole

 

[nedbert9]

This is a very interesting question. Thanks!

I'm only a CCNA, but I can see there would be an ARP broadcast issue, as well as any other broadcast based protocol like NetBios, DHCP etc.

I hope someone comes along to better define and explain the pro's and con's.

Before any subnet to subnet communication can occur the source host would have to learn the destination MAC. Since the source would assume the destination is on the same subnet and the router blocks broadcasts by default the source would never learn the MAC address of the destination. However, you can enable ARP broadcast forwarding on each router in effect creating a bridge using the following command in global config mode.

ip forward-protocol any-local-broadcast

This will take the broadcasts from each Ethernet subnet and forward out other interfaces, your serial links.

Good luck and don't break anything

nedbert9
A+, CCNA, CNE 3-5, MCSE NT4, MCP 2003
A leisurely lifestyle is a sign of wisdom and maturity - Aristotle

 

[nedbert9]

Also, in order to get specific configs you need to provide information on the type of WAN connections you will be using.

nedbert9
A+, CCNA, CNE 3-5, MCSE NT4, MCP 2003
A leisurely lifestyle is a sign of wisdom and maturity - Aristotle

 

[PinkLips]

PPP/T1

Example of why I need this maybe a server cluster. One server at each remote location replicating data back and forth.

10.10.2.x/24 RtrA s0/0<---------->s0/0 RtrB 10.10.2.x/24
server1 10.10.2.1 server2 10.10.2.2

Thanks,
Nicole

 

[nedbert9]

I understand. Does the clustering software you will be using require that the servers be on the same subnet? That seems a bit odd to me. Most I know of either have heartbeat links or are fully IP enabled.

After spending some time thinking about it this would work fine if you just needed communication between these two subnets. However, let's say someone sent data from a completely different network to location1, location1's router would drop that data on to the local interface for the subnet. If the true destination is a host at location2 it would not work. Even though location2 is receiving broadcasts originating from location1, it will not receive directed traffic originating from any other network because location1 thinks it's local interface is the end point.

Someone more experienced will need to give you a more definitive answer. Sorry.

nedbert9
A+, CCNA, CNE 3-5, MCSE NT4, MCP 2003
A leisurely lifestyle is a sign of wisdom and maturity - Aristotle

 

[rmstar]

Hi Nicole,

Sorry for a long post.

I have implemented bridging at my company because of our legacy HP 3000 systems, the servers are at one location (hub) while the terminals are at the remote location. If memory serves me, they don't have a default gateway capability (from the remote side) so we have to bridge between the sites.

I set up the following on the remote site:

bridge 1 protocol ieee
interface Ethernet0/0
no ip address
bridge-group 1

From the hub site:

bridge 1 protocol ieee
interface Serial2/1
no ip address
bridge-group 1

You can setup IP addresses on both sides of the link if you want but in that case, you will be routing IP but bridging all other traffic. This is probably not what you want, I'm guessing.

You have other options, which I would recommend you research a bit, they are CRB and IRB. I am also using IRB for another site. It will allow you to route IP as well as bridge it. If you implemented IRB you would be using a virtual interface called the BVI to which you assign an IP address, you must remove the IP address from the router(s)physical interface.

A sample config would be as such:
At hub site:

bridge irb
bridge 1 protocol ieee
bridge 1 route ip
interface Serial2/1 <--link to remote site
no ip address
bridge-group 1

interface BVI1
ip address 10.10.2.X 255.255.255.0

You would probably setup the remote site in a similar fashion. Bear in mind the BVI1 ip address is now your default gateway address for that site.


Not sure if any of this will help, hopefully it will point you in the right direction or prompt others to comment.

take care and good luck!

Mark

 

[rmstar]

Oops, I just reread my last post, forgot to include the following:
*add*
For remote site:
interface serial0/0
no ip address
bridge-group 1

From the hub site:
interface Ethernet0/0
no ip address
bridge-group 1

 

[nedbert9]

RMSTAR, thank you for making us aware of this bridging method.

nedbert9
A+, CCNA, CNE 3-5, MCSE NT4, MCP 2003
A leisurely lifestyle is a sign of wisdom and maturity - Aristotle

 

[nedbert9]

This should help you solidify the idea.

http://searchnetworking.techtarget.com/searchNetworking/Downloads/DSLch6.pdf

Pages 182-183 in the manual.

nedbert9
A+, CCNA, CNE 3-5, MCSE NT4, MCP 2003
A leisurely lifestyle is a sign of wisdom and maturity - Aristotle

 

[PinkLips]

Thanks guys. I'm new to routing and it will take me some time to digest the information Kisses to all.

Thanks,
Nicole

 

[rmstar]

To nebert9 and Pinklips, you're both very welcome. Glad to be able to contribute.

If you don't already own it, I would highly recommend the following book: CISCO IOS IN A NUTSHELL, O'reilly Press, author: James Boney, First Edition. It's like a cookbook covering many areas of the Cisco IOS, it's been very helpful in getting a handle on the less known (to me anyway ) router configurations that I've come across, namely, the bridging concepts I have mentioned. The only downside (possibly), it's IP based only.

Take care

Mark

 

[rmstar]

It's nedbert9 not nebert9, lol, sorry about that.