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how to connect two subnets together?

On Networking » Networking

6,301 words with 10 Comments; publish: Sat, 17 Nov 2007 00:30:00 GMT; (450187.50, « »)

This is only theoretical, but it will happen next month, where I will be responsible for connecting two LANs together. this is the most involving network job I've tackled. So I'd like to hear what you think my options are.

Both LANs will be in the same building so they will be connected via CAT5.

Each LAN will have a different subnet so we are talking Subnet A and B.

Security is not and issue, it is a trusted network.

Performance is an issue.

I Hear you can put two NICs in one computer and plug in both LANs and configure each NIC for a specific subnet? And then is IPForwarding what I need to setup in order for a computer on SubnetA to connect to SubnetB?

correct me if I'm wrong but this is called a gateway?

Is a router a device that can do this as well?

Are there any other options?

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    • You need a router. You can do this using a Linux box wiht multiple network cards, but be sure your addressing won't conflict, etc.
      #1; Sat, 17 Nov 2007 18:06:00 GMT
    • A router will do the job, be it a dedicated hardware router or a computer you set up as a router (depending on your exact setup, a simple bridge might do as well).

      Technically, the main difference between a router and a gateway is that a gateway performs the functions of a router, but can also join two networks which speak different protocols, or have different physical architectures. The distinctions between the two tend to blur in real-life usage of the terms, though.

      Here's a link (http://www.tldp.org/HOWTO/Adv-Routing-HOWTO/index.html) with in-depth information concerning using a Linux box as your router.

      #2; Sat, 17 Nov 2007 18:07:00 GMT
    • In order for the computers to talk to each other, you'll have to tell each system how to find the other subnet.

      You just have to tell the computer about the gateway IP address for that machine. IP forwarding isn't really a good idea for two-way communication, but routing works out great, as each machine can call the other machine's IP address directly.

      #3; Sat, 17 Nov 2007 18:08:00 GMT
    • u need a bridge , u can buy a sinmple one that is easy to configure , and this is its job to connect the two networks like a bridge.
      #4; Sat, 17 Nov 2007 18:09:00 GMT
    • === Original Words ===


      u need a bridge , u can buy a sinmple one that is easy to configure , and this is its job to connect the two networks like a bridge.

      That's only if you're connecting two physical LAN segments and intend to use the same logical subnet on those two segments. Then, a bridge would do just fine.

      But, if you have two LAN segments using two different subnetting schemes, you'd need a router, as if you used a bridge, the machines still wouldn't be able to talk to each other-- even though they're on the same physical (OSI Layer 1) network, they're not on the same logical (OSI Layer 3) network.

      #5; Sat, 17 Nov 2007 18:10:00 GMT
    • Nothing against a Linux router, but I would rather use a actual router in any kind of a business environment ( I assume that is what your doing).. The Cisco 2514 router has 2 ethernet and 2 serial ports on it so that should work fine. You can pick them up for about $250 off Ebay the last time I checked. There is a ton of good documentation out there for setting these up, and its really not that had once you get the basics of IOS.
      #6; Sat, 17 Nov 2007 18:11:00 GMT
    • OK, good stuff,

      these two networks will be on different subnets so it sounds like a bridge won't work for me. And yes it will be done in a buisness environment.

      So it sounds like I want a router, lets say, for example cisco 2514 that Gertrude mentioned, it has 2 ethernet ports. I suppose I would plug in each network into it and be able to somehow logon to it to configure the two networks to see each other? will I have to change the configurations of the client computers (say for example, put in a gateway address?)

      Is the process of going through a router, noticable (performance wise?)

      Thanks for the link DMR , I'll go through it tonight.

      #7; Sat, 17 Nov 2007 18:12:00 GMT
    • I believe with a router, the performance will not change within a network, but will be slower between networks proportional to the number of computers accessing the other network (both ways). If the ethernet port on the router is a 100Mb/s port, that bandwidth is shared with the entire subnet. This may not be a problem, depending on the intended usage, and the number of computers. The more computers you are using, the less bandwidth they can all use.
      #8; Sat, 17 Nov 2007 18:13:00 GMT
    • I wouldn't recommend buying a bridge (if you can even buy them anymore). They are rather antiquated. Most switches you can buy today that are managed have layer three functionality built in anymore. So in relation to performance, a Switch will offer you the most in my opinion, rather than a router. You will be able to create seperate VLANs within the switch for different groups and manage your LAN much much better. And even if security isn't a issue, having full duplex wire speed connections most likely will be. And a switch usually costs less than a router. But I don't know how many ports you need. Perhaps a switch with all of this functionality is overkill. With a semi modern managed switch, you will be able to assign IPs to the switch interfaces and the switch will take care of the routing for you. Really, as always, it boils down to how much money you want to spend. You can pick up some decent switches at CompUSA.

      For example check this out:


      You see, I actually build networks like these for a living. Gigabit Ethernet metro rings, Sonet rings...etc...thus the name :D

      PS...switches usually break down a lot less than routers.

      I bet you would be real happy with a managed switch! Now if you don't mind spending a little more money, the Cisco Catalyst 3550 series is real nice.

      #9; Sat, 17 Nov 2007 18:14:00 GMT
    • Yes, you'll need each client's default gateway entry to point to the router (unless you're using DHCP, in which case the DCP server will take care of that).

      As far as the router configuration, that's usually done via a management port on the router; configuration is done via a PC connected to that port. Some routers also have a web-based cofiguration utility, which you access over the network via your Web browser.

      #10; Sat, 17 Nov 2007 18:15:00 GMT