Gateway confusion

Discussion in 'Network Routers' started by twlllmxxx, Feb 13, 2013.

  1. twlllmxxx

    twlllmxxx Guest

    I've got 3 or 4 computers on a LAN. From all computers and either
    browser (FF or IE), I get the same result: DNS can't find google.com.
    If I type in an IP address for google, I can get right to it. If I
    bypass the router and go directly to the cable modem, I can type in
    google.com and get right to it.

    Sounds like a router problem. The strange thing is this problem only
    exists for google.com. As far as I know, all other URLs are recognized
    by the DNS.

    So I'm trying to figure out what can go wrong with a router that it
    only malfunctions on one single URL, google.com. But my knowledge in
    these matters is limited.

    Trying to research it out, I come to this mystery: ipconfig says my
    default gateway is one thing, and my router status page says it's
    something else.

    What on earth is going on?
    This is a signature line.
     
    twlllmxxx, Feb 13, 2013
    #1
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  2. twlllmxxx

    Char Jackson Guest

    What I assume from that is that each of your computers is configured to use
    DHCP to acquire its IP address and Netmask, DNS server IP, and Gateway IP.
    While each computer will have a different IP address, (naturally), all of
    them will share the same values for Netmask, DNS server, and Gateway IP.
    Further, the DNS server IP and the Gateway IP (and the DHCP server IP) will
    all be the same, and will all be the LAN IP of your router. So far, so good.
    The first thing to check is the router - what is it using for a DNS server
    IP? Can you change it? If the router allows that value to be changed, try an
    open DNS server such as the ones from OpenDNS, Google, etc. For testing,
    since they are easy to remember, I use Google (8.8.8.8) and Level 3 (4.2.2.1
    thru 4.2.2.6). In your case, I would try Google's DNS because it would be
    ironic indeed if their own DNS couldn't find the Google domain.

    If your router doesn't allow you to change the DNS IP's, consider changing
    them on your computers. Your computers don't have to use your router's IP as
    their DNS server IP; you can enter actual DNS server IP's in those fields.
    On each of your computers, the default gateway is the LAN IP of your router.
    On the router, the default gateway IP belongs to your ISP and is your
    gateway (pun intended) into their network and from there to the Internet.
     
    Char Jackson, Feb 13, 2013
    #2
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  3. twlllmxxx

    twlllmxxx Guest

    That's right. They're configured to use DHCP. I'm not able to change
    the DNS server IP on the router, but if I change it on the computer
    (to 8.8.8.8) I am indeed able to get google.com.

    On 2 of 3 computers I checked, DNS never works on google.com unless I
    change the DNS IP on the computer. On the third computer the default
    DNS works sometimes and sometimes not. That's the kind of behavior I
    expect in dying hardware. I don't understand why the problem only
    shows on google.com.

    I'm sure it's a router hardware problem. I've bought a new router but
    haven't installed it yet because I want to understand what the old
    router is doing. It's just so bizarre that only google.com is
    affected.

    I'm trying to understand how this stuff works. For each of my
    computers, the default gateway is the LAN IP of my router. So one of
    my browsers sends a URL to the LAN IP of my router, and the router
    sends it on to the DNS IP given it by my ISP. And there it is resolved
    into an IP address that is the correct destination.

    So the DNS address listed in ipconfig is what the computer thinks it
    is, and the DNS listed on the status page of my router is what the ISP
    gave it. That would explain why ipconfig says my default gateway is
    one thing, and my router status page says it's something else.

    Am I beginning to approach an understanding?
     
    twlllmxxx, Feb 14, 2013
    #3
  4. twlllmxxx

    Char Jackson Guest

    Google is a very common destination, so it sort of makes sense that an issue
    would rear its head there first. There might be many other sites similarly
    affected, but if you don't visit them, you'd never know.
    I would say yes, you're on the right track, but be careful not to mix DNS
    server IPs with Gateway IP's when you're thinking about this stuff. Within
    your LAN, both of those will typically be the same IP because those
    functions are handled in the same piece of hardware, your router, but beyond
    your LAN they will almost certainly not be the same hardware or the same IP
    address. You can probably see that by looking at the router's admin pages.
    Likewise for DHCP. Within your LAN, it's likely that same router that's
    handling DNS and Gateway duties, but beyond your LAN it will be different.
     
    Char Jackson, Feb 14, 2013
    #4
  5. twlllmxxx

    twlllmxxx Guest

    ipconfig says

    IP Address = 192.168.123.101
    Subnet Mask = 255.255.255.0
    Default Gateway = 192.168.123.254
    DHCP Server = 192.168.123.254
    DNS Servers = originally 192.168.123.254, but using that when I ask FF
    for google.com, FF tells me "Firefox can't find the server at
    www.google.com." So I manually change the DNS Server IP on the
    computer to 8.8.8.8, and then FF can find google.com.

    The router is a rather old U.S.Robotics (Model # 8004, 1.1101). Its
    Status page says

    IP Address = 68.98.59.228
    Subnet Mask = 255.255.248.0
    Gateway = 68.98.56.1
    Domain Name Server = 68.105.28.12, 68.105.29.12

    The ISP is Cox.

    I guess I'm looking for evidence of a hardware failure (stuck bit or
    something) that is misdirecting my request for google.com. (But why
    only for google.com?)
     
    twlllmxxx, Feb 14, 2013
    #5
  6. twlllmxxx

    twlllmxxx Guest

    Indeed other sites may be affected, but I haven't run across any. Only
    google.

    I assume the data packet that the computer sends to the router
    contains other information that tells the router whether this should
    go to the gateway or to a DNS server. I don't know what the format of
    these data packets is.

    I'm pretty good at digging information out of books, but I can't find
    anything useful on routers. Everything is either too basic, directed
    at people who have to have it explained what a binary number is, or
    too advanced, directed at a system administrator for a large
    corporation. Nothing for somebody with a modest home system who just
    wants to know what's going on.
     
    twlllmxxx, Feb 14, 2013
    #6
  7. twlllmxxx

    twlllmxxx Guest

    That's an interesting suggestion. I assume if the ISP's DNS server
    were misconfigured it would have been called to their attention and
    fixed by now. In fact I initially suspected that somebody hacked into
    my router and replaced some addresses. Like maybe somebody wanting to
    sabotage google's market.
    Yeah, that alleviates the symptom, but doesn't tell me what the actual
    problem was.
     
    twlllmxxx, Feb 14, 2013
    #7
  8. twlllmxxx

    Char Jackson Guest

    Have you ever done a factory reset on that router? If not, it might be time
    to do it so you can start from scratch.
     
    Char Jackson, Feb 15, 2013
    #8
  9. twlllmxxx

    Char Jackson Guest

    I think you said earlier that bypassing your router results in success,
    making me think that the ISP's DNS server is OK.

    It still looks like a problem with your router. Don't just reboot it, do a
    factory reset on it, however that's accomplished for that model. Then set it
    up again, from scratch, and test it. Depending on the test results, go from
    there.
     
    Char Jackson, Feb 15, 2013
    #9
  10. twlllmxxx

    twlllmxxx Guest

    Good suggestion. I should have thought of it. So I did a factory
    reset. Twice, just to be sure. No change. Same problem.
     
    twlllmxxx, Feb 18, 2013
    #10
  11. twlllmxxx

    twlllmxxx Guest

    twlllmxxx, Feb 18, 2013
    #11
  12. twlllmxxx

    twlllmxxx Guest

    Remote administration is not enabled. As far as I know, it never was.
    There's nobody around here to do it behind my back.
    Cox is all about marketing. Their technical work is done by
    contractors. They are who first told me it must be a router problem.
    Yeah, using 8.8.8.8 for the DNS server works. So does bypassing the
    router and using Cox's DNS server. NOT bypassing the router, but
    typing Cox's DNS into the TCP/IP properties dialog results in not
    being able to find google.com. That router can not find google using
    Cox's DNS, but can using Google's DNS.

    Indeed.
     
    twlllmxxx, Feb 18, 2013
    #12
  13. twlllmxxx

    Char Jackson Guest

    It was worth a shot.
    Did you notice whether the same DNS server was being used in both cases? It
    would be interesting to know if Cox is assigning one DNS server when you
    connect directly and another (broken) server when you connect via the
    router.
    I'm inclined to think it's a misconfigured DNS server, which is why I
    wondered if they assign you the same one whether you connect directly or via
    the router.
    Good luck with it.
     
    Char Jackson, Feb 18, 2013
    #13
  14. twlllmxxx

    twlllmxxx Guest

    When I connect through the router, ipconfig lists two DNS servers:
    68.105.28.12 and 68.105.29.12. When I connect directly to the cable
    modem, ipconfig lists three: the two already listed plus one at
    68.105.28.11.

    To see if that last one is the only one that actually works, I typed
    that one into the TCP/IP properties dialog as preferred DNS server.
    Then, connected through the router, in response to a request for
    google.com, I again get "Server not found".
     
    twlllmxxx, Feb 19, 2013
    #14
  15. twlllmxxx

    twlllmxxx Guest

    Sorry, I misspoke. When I connect throuth the router, the router lists
    two DNS servers...

    When I connect directly to the cable modem, ipconfig lists three...

    I try to word things right, but I often screw up. Sorry.
     
    twlllmxxx, Feb 19, 2013
    #15
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