How do I connect T1 to two DHCP routers, setup two networks

By iwish2too ยท 10 replies
Aug 26, 2011
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  1. I have a T1 backbone connected to a Linksys wireless 4 port N router running 2 hubs and 1 websmart POE switch. I need to bring in another network on the same T1 backbone, keeping it separated from my current network with it's own DHCP router. I'm thinking I need to go from the T1 to a hub uplink port, then out to the ethernet port on both routers. Keeping the current setting on #1 router and assigning an IP to the #2 Linksys router I'm not sure if this will work, but it seems right, right?
  2. Rick

    Rick TechSpot Staff Posts: 4,572   +65

    The T1 should be connected to your WAN port one way or another, otherwise your router cannot router Internet traffic. Nothing else should exist on the WAN port.

    In short, I don't think connecting your T1 to any ports on any of your hubs will work.

    Also, the "uplink" ports on hubs are usually just crossover (X) ports, but don't actually do any special routing or segregation. So whatever ports you choose shouldn't matter, aside from needing to have the right cable.

    The T1 should be connected to your Linksys's WAN port, where it will handle the routing. There should probably be no exception to this. However, if you connect the new network to any of your router or hub LAN ports, they will exist on the same network and you'll have two DHCP servers (a bad thing).

    With your current equipment, I see two ways around this:
    1. Connect the new network to yours using any LAN port you have available, use static IP address on all of the machines for at least one of the networks. Not a pretty solution and also a problem for "new" computers that hop on their network...
    2. Connect the new network to yours using any LAN port you have available, but do so from the secondary network's WAN port on the router. This will segregate the network from yours and their router will have to be configured to use your router as the WAN gateway.

    I think the second solution is pretty reasonable.

    Aside from DHCP trickery (Like a Linux server with some form of authoritative or segmented DHCP schema and MAC address bindings), I don't see any other way to solve this... I think the only "real" solution here would equipment that supports multiple VLANs, but such equipment is often very expensive and would require a holistic approach as all devices routing/switching traffic need to support QoS for VLAN'ing.
  3. iwish2too

    iwish2too TS Rookie Topic Starter

    Thanks Rick

    Thanks for your input Rick.
    Currently I do have the T1 in the WAN port of my Linksys wireless router. This is my network DHCP server and has been working great. We have a school moving into my church building and I'm trying to provide them with their own LAN and internet. I'm not going to spend the cash for VLAN stuff, not cost effective. So I guess I'll just have to give them a router with static IP routing and their IT guy will have to assign IP's to each of their machines. My Linksys router is managing about 20 user stations and 5/8 wireless each day. This leaves me about 20 IP avail for my network. I could easly manage the school's needs without another DHCP router, but I don't want them to see my shared folders on my network. The static solution is the only one I can think of. Plus I don't want to use up my IP's.
  4. jobeard

    jobeard TS Ambassador Posts: 11,122   +982

    Hmm; I think the simple daisy chaining of the routers
    should work correctly for you.

    Give the second router the address and let each router provide its own DHCP to the attached devices. For more connectivity, each router can have a switch attached to create the lan addresses.

    Devices on router#1 will always route to the uplink (ie the default gateway) and thus never see router#2 addresses.

    Devices on router#2 will route similary and also never see devices on router#1.

    This can be demonstrated by attempting
    • on #1: Ping
    • on #2: Ping

    Port Forwarding for either subset should not be allowed (ie it starves the other subnet for that port)
  5. iwish2too

    iwish2too TS Rookie Topic Starter

    Thanks Jobeard

    Thanks Jobeard for your input.
    But I'm thinking you have router#1 and #2 mixed up. Currently my T1 is plugged into the WAN port on my #1 router, which acts as my DHCP server and is also my wireless connection. I'm adding router#2 for the second network. I'm going to connect router#2 through one of my network hubs. I know two DHCP routers on the same network won't work, they will just continue to battle for IP's and the pc's will keep dropping connection. So are you saying if I connect router#2 to my network hub through the routers WAN port, it WON'T see router#1? Thus I can allow it to run with auto DHCP addressing, but I need to assign #2 router the IP?
  6. jobeard

    jobeard TS Ambassador Posts: 11,122   +982

    forget the hub idea. the only place you can use a hub is AFTER a router.

    Secondly, DHCP in a router only applies to devices connecting to that router, eg:

    r#1--->devA -->gets ip from r1.dhcp
    r#1--->devB --> gets ip from r1.dhcp
    and so does r#2 when you attach its WAN to a lan port on r#1

    r#1-->(wan side)r#2 so the WAN side address is something from r#1.dhcp - - and that's just fine.

    Now router#2 comes along and you configure it to have
    but that is from the view of those machines connected to it

    r#2-->devA-->gets ip from r2.dhcp ... and so on.

    all r#2.devX devices will get a gateway address of router#2 (
    and not interfere with router#1 at all.

    Try it - - it works :)
  7. iwish2too

    iwish2too TS Rookie Topic Starter

    Thanks Jobeard..a 2nd thought

    Gotchya, read my next please.....thx JB
  8. iwish2too

    iwish2too TS Rookie Topic Starter

    Jobeard a 3rd thought

    Thanks again.
    I'm going to install it today and I'll let you know how it goes.Thehub I'm using is after router#1. I have 4 hubs that are ported to r#1. When I was talking about the hub before the router in my first post..the hub would have been connected after the T1 router. But I snubbed that idea.
  9. jobeard

    jobeard TS Ambassador Posts: 11,122   +982

    the segmenting of dhcp range WILL work, but both routers need to be on the same subnet (a.b.c.x where a.b.c are identical) and that's NOT what you asked for.

    your issue is this concept

            +===>router1   <looks like [COLOR="Blue"]192.168.1[/COLOR].1
            +===>router2   <looks like [COLOR="Red"]192.168.2[/COLOR].1
    when you assign an IP address to a router, it is effective and ONLY seen from the lan side.

    Your conflict is on the WAN side where the T1 does the wan-side addressing for the router.

    I can't help you if you insist to stay with concepts that just don't work.
  10. iwish2too

    iwish2too TS Rookie Topic Starter

    JB...thx again

    Thx again. You are helping me ton's. I'm just tossing my thoughts at you so I can get a better understanding and correct my thinking. I'm clear on what you're saying and will set it up your way. Thx again for your help.
  11. iwish2too

    iwish2too TS Rookie Topic Starter

    JB....another thought

    So, this is what I've got so far, T1/Wan side of DHCP router#1/LAN port of r#1 to a network hub ported to the WAN port of router#2 DHCP and assigning IP addy.

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