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2 subnets / changed isp, then internet stopped working

Discussion in 'Networking Issues' started by philtrim, Nov 14, 2008.

  1. philtrim

    philtrim Addicted to LI Member

    Strange problem. (maybe not to an experienced IP guru)

    I have a client with 2 separate offices (2 subnets)

    Office 1 - DSL(Internet)--->Linksys--->Lan1
    Office 2 - T1-------------->Cisco----->Lan2

    I did not set this up originally. Office 1 shares their Internet
    connection with Office 2 (via the linksys rtr/gateway)

    Problem: Original ISP for Office 1, went out of
    business, so they went went a different provider (DSL)
    I came in, changed the config of the Linksys (just the PPOE setup)
    to get Office 1 back on the web. Office 1 Internet restored.
    I Did not change any settings (Router IP/LAN Range/DHCP on this Router)
    (The only thing that chaged was the WAN IP - dynamically from ISP)
    Also, there were No static routes setup on this router previously or
    at the time I looked at it/re-configured it.

    Office 2 then calls stating NO INTERNET from their side, went on-site to Office 2.
    No web sites would come up, although, I could ping the Router @ Office 1)
    from a workstation Office 2.

    I had another tech come in behind me, and he added a STATIC route
    on the Office 1 (Linksys Router) that included the Office 2 subnet,
    and this solved the problem.

    My question is. There was never a STATIC ROUTE in this Router before
    (when they had the other Internet provider) so how was Office 2 getting
    internet access, previously through this connection?
    THis really had me scratching my head.
    A static route entered my mind, but since I looked for one on the Router (when it was connected to the previous ISP) there was no Static Route listed.

    Do you think that it learned this previous ISP route dynamically? And, if this Static Route would have not been entered (by this other tech) do you think the router
    would have re-learned this other network on it's own (Dynamically with RIP, etc..?)

    I know this sounds confusing the way I described it, but I could not
    figure out why it worked (for Office 2) with the previous ISP and stopped working with the new ISP.

    But, maybe Static Routes are tied to the WAN IP address of the router, and when
    this is changed, maybe they get wiped out...??

  2. Stu22

    Stu22 Network Guru Member

    Are Office 1 & 2 on the same provider? Maybe it was a dynamic route and it died. For whatever reason the route wasn't restored. This is a little odd sounding :-P

    I'm not 100% sure of what your setup is, but I'm just gonna make a wild guess.

    Do you use Frame Relay through your T1 line to connect the two offices? If so, then maybe when it died, the PVC to the gateway got killed and it didn't know how to get there.

    Can you give me the output of "sh ip route" and "sh ip protocols" (if you can't and there are certain things that cannot be seen, then don't worry about it).

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