Thread: DHCP & Router

  1. #1
    int x = *((int *) NULL); Cactus_Hugger's Avatar
    Join Date
    Jul 2003
    Banks of the River Styx

    DHCP & Router

    A friend of mine purchased a new router to replace an old router & wireless access point. The new router is replacing two pieces of equipment, and will hopefully provide a better signal that the tiny AP they have now.

    She hooked everything up, and it didn't work. I took a look at it, the setup was fine. The computers on the LAN talked to the router, the computers on the wireless LAN talk to the router, but nothing has internet. The router shows a light on its internet symbol, indicating the link is ok, but accessing the routers configuration page shows that it can't aquire an IP address.

    Moving the ethernet cable connecting router & WAN from the new router to the old one, reassociating with the appropriate wireless AP, and I have internet. Move the cable, reass., only LAN.

    I connected my laptop directly to the WAN, and attempted DHCP. This failed -- no response after the DHCP Discover. I started a wireshark capture, this shows exactly that. However, I see ARP requests and other DHCP traffic (so the link is connected) but my own DHCP discovers go unanswered.

    I tried changing my cards MAC address to that of the old router, and repeating the DHCP request -- no luck.

    Any ideas? Best I could come up with is that the old router is holding a lease, and isn't reaquiring it when the link comes back (is this proper?), but would fail if the lease expired.
    long time; /* know C? */
    Unprecedented performance: Nothing ever ran this slow before.
    Any sufficiently advanced bug is indistinguishable from a feature.
    Real Programmers confuse Halloween and Christmas, because dec 25 == oct 31.
    The best way to accelerate an IBM is at 9.8 m/s/s.
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  2. #2
    Guest Sebastiani's Avatar
    Join Date
    Aug 2001
    Waterloo, Texas
    Just a shot in the dark (I'm no network expert) but are you sure that the computers are configured to detect the IP address automatically? It's possible that your friend set up the old router with a static address.
    #include <cmath>
    #include <complex>
    bool euler_flip(bool value)
        return std::pow
            std::complex<float>(0, 1) 
            * std::complex<float>(std::atan(1.0)
            *(1 << (value + 2)))
        ).real() < 0;

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