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Need ideas for connecting 2 same networks across a T-1

Ok, I'm a moron. What is the best/most efficient way to connect two like/same networks across a T-1? I have tried bridging, but I'm looking for another answer. I have use of a 3620 with a serial port on the "home" network end and a 2620 with a serial port on the "remote" end. I'm lazy and I don't want to re-IP/subnet 1,000+ computers to create a subnetted network for the "remote" site. What are my options.

Thanks,

D

2 REPLIES
Gold

Re: Need ideas for connecting 2 same networks across a T-1

There's no easy answer, because there are a number of factors that come into play.

If you don't bridge, you might be able to do something with NAT and static mappings to server resources. But that would be more trouble than it's worth, I think. And there's always the possibility of a duplicate IP address (one on each site) causing you problems in either case.

Why not bridge, and also set up a secondary IP address on the LAN interface of the router on your home network? Bridging will tie the two networks together for now (and assuming they are the same IP subnet), and you can convert the machines on your home network at your own pace. Eventually, your home network will be a unique subnet, then you can do away with the bridging and just route. That way you won't be wasting WAN bandwidth with broadcasts.

You'll still have the duplicate IP address issue to contend with, initially. So know what IP addresses are in use on each LAN before you bridge them, and eliminate the conflicts ahead of time.

If you're doing DHCP at each site, the bridged configuration will have address requests from either side heard on both sides. So in your "home" network, set up a DHCP scope for the new IP subnet, and set up address reservations using MAC addresses of your local machines. That way, when local machines broadcast for an IP address, both the local DHCP and remote DHCP servers will hear it; but the local one will probably be the one whose reply is heard by the client first, and that address reservation will be the one served up. Client almost always finishes the address negotiations with the first server to respond to it. (Or you can just assign new static IP addresses locally.)

DNS or WINS name resolution will also be an issue, especially with Microsoft Windows Networking over TCP/IP. Broadcast name resolution will work as long as the two networks are bridged; but DNS and/or WINS will be needed as Layer 3 separation creeps into the picture.

And master browser elections will take place, per protocol, on the bridged Microsoft networks. So a network with clients that have IP, NWLink IPX/SPX, and especially NetBEUI loaded, will be electing a master browser for each. And NetBEUI will be going nuts with broadcasts of browser elections if you have more than 255 nodes, because that's the maximum it can support (and it's non-routable). Best bet is to eliminate any and all unnecessary desktop protocols, and standardize on IP if you can. This means on network-attached printers, too. Macintoshes using AppleTalk and the default cable range network number will also run into problems beyond 255 nodes.

Of course, another issue might be the size of the IP subnet itself that you're using. For example, if both nets use the same subnet number and mask, but the number of machines on both networks totals more than that subnet can support, then you're going to have to start renumbering locally first, before you join the two networks.

I think you're going to be renumbering anyway, one way or another, so get used to the idea.

For what it's worth, Cisco's design guidelines call for no more than 500 IP machines per broadcast domain (bridged or switched network, VLAN, or whatever you want to call it). And that recommended maximum number drops to 200 if multimedia or multiple desktop protocols (IPX, AppleTalk, DECnet, other) are involved. Excessive network broadcasting by desktop clients may already be impacting performance of your network-attached computers; if so, joining the two networks together will only make it worse. You may want to VLAN things locally first with a Layer 3 switch providing routing service between VLANs. Then connect to the other site. Probably should break the remote site into multiple VLANs, too.

Without more details, I can only talk in generalities here. Hope this helps anyway.

Bronze

Re: Need ideas for connecting 2 same networks across a T-1

It is done with NAT and is documented here

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr_c/ipcprt1/1cfipadr.htm#1002518

Heres is a summary of what it does. Ignore the illegite and legit comments and focus on the last sentence.

Translating Overlapping Addresses

The NAT overview discusses translating IP addresses, which could occur because your IP addresses are not legal, officially assigned IP addresses. Perhaps you chose IP addresses that officially belong to another network. The case of an address used both illegally and legally is called overlapping. You can use NAT to translate inside addresses that overlap with outside addresses. *** Use this feature if your IP addresses in the stub network are legitimate IP addresses belonging to another network, and you want to communicate with those hosts or routers***

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