Weird DNS routing problem (I think)

Posted on 2006-03-24
Last Modified: 2008-02-01
I recently installed a Netgear DG834G wireless ADSL modem/router for the office network here, replacing an antiquated setup consisting of one (Win98!) PC connected via a single DSL modem and running a software proxy server and firewall.

The router setup is pretty much 'vanilla' - it is acting as DHCP server for the LAN, it is automatically grabbing the DNS addresses from the ISP (BT Openworld).  It connects fine and for 95% of internet activity, it just works.

Anyway, it works really well, nearly all of the time, but there are certain websites that the LAN clients simply cannot browse to (the same sites are affected for all users).
I have checked all of the browser security and firewall settings on the client machines and tried a different browser on one machine.
The odd thing is that the client machines are able to resolve the IP of the inaccessible sites; for example PING returns:
Pinging [] with 32 bytes of data...
-It doesn't get any responses, but that's probably just because their system is set up to ignore ping requests.
Furthermore, TRACERT returns:
Tracing route to []
over a maximum of 30 hops:

  1    <1 ms    <1 ms    <1 ms []
  2    24 ms    23 ms    23 ms []
  3    24 ms    23 ms    24 ms
  4    26 ms    27 ms    26 ms
  5    26 ms    28 ms    25 ms
  6    27 ms    27 ms    26 ms
  7    26 ms    25 ms    43 ms
  8    25 ms    27 ms    29 ms
  9    26 ms    27 ms    26 ms
 10    26 ms    27 ms    25 ms
 11    27 ms    26 ms    27 ms []
 12    33 ms    26 ms    27 ms []
 13    29 ms    28 ms    28 ms []
 14    28 ms    27 ms    27 ms []
 15    28 ms    27 ms    26 ms []
 16    28 ms    27 ms    28 ms []
 17    29 ms    27 ms    27 ms []
 18    30 ms    29 ms    32 ms []
 19    31 ms    30 ms    30 ms

But pointing a web browser at just results in the standard 'Cannot find server or DNS Error' page.

Any suggestions here?  Could it just be that the router is knackered in some sort of subtle way?
Oh, BTW, I did also upgrade the router firmware to the latest version in trying to resolve this, but it didn't help.
Question by:Mangetout
    LVL 1

    Assisted Solution

    I think the DNS servers you are using are a little screwey.  My suggestion would be to try 2 well known Public DNS servers that should give you better results.  Put these in for
    your DNS servers..

    And then try to get to the page you are talking about.  

    LVL 31

    Expert Comment

    I would try a different browser.  Internet Explorer doesn't always do what it says on the tin.  I would recommend Netscape or Firefox.
    LVL 3

    Assisted Solution

    you may want to try to
    http://<actual ip address>
    and see if anything works...

    How about
    telnet 80
    get /

    and see if anything works...

    LVL 1

    Author Comment

    Thanks for the suggestions; I've tried Firefox (same results) and I've tried browsing straight to the IP address (same results).  I'll give it a try with different DNS server settings.

    I contacted BT Openworld Tech Support about this and they talked me through a number of things that I'd already tried (firewalls, security settings), then basically washed their hands of it, saying it couldn't possibly be their problem.
    LVL 31

    Accepted Solution

    >saying it couldn't possibly be their problem.
    How many times have I heard that from BT? !
    (1) Do you have a Proxy setup?  Disable it!
    (2) Firewall.  Disable it/them for testing purposes (you know the risks).
    (3) Make sure there is no Malware on your pc (do this in SafeMode)
    (4) type the following into a browser
    Do you get a website?
    (5) Don't use BT's DNS - try MarkMaloughney's - my experience with BT is that their DNS can be flaky.  Put this into the Router config..
    (6) Try assigning a Static IP address on the pc, and use the same DNS address in the settings on the pc
    LVL 3

    Expert Comment

    hmmm....tracert and ping works?   just some sites don't work?

    do the same consistently have a problem with some sites?
    While you're having a problem, does ping/traceroute work?
    Is it worth fixing? ;-)

    BTW, I just browsed to (with konqueror) and traceroute has a problem:

    16 (  101.114 ms (  88.045 ms (  96.817 ms
    17 (  102.263 ms (  106.178 ms *
    18  * * *
    19  * (  109.896 ms *
    20  * * *
    21  * * *
    22  * * *
    23  * * *

    This sometimes happens -- I haven't understood you have a machine running linux?

    Can you also directly connect a machine to the internet?  (I'd rather linux).
    Instead of through the router?
    LVL 1

    Author Comment

    >hmmm....tracert and ping works?   just some sites don't work?
    >do the same consistently have a problem with some sites?
    >While you're having a problem, does ping/traceroute work?
    Yes, it's consistently the same handful of sites; there doesn't appear to be anything special, content-wise about them.

    >Is it worth fixing? ;-)
    It MUST be fixed; one of the websites this company cannot access is Natwest Online Banking

    >This sometimes happens -- I haven't understood you have a machine running linux?
    I can boot my laptop into Ubuntu and try it.

    >Can you also directly connect a machine to the internet?  (I'd rather linux).
    >Instead of through the router?
    The router has the ADSL modem built into it; I may be able to find a spare standalone ADSL modem to test it.
    LVL 1

    Author Comment

    Oops, meant to say that yes, Ping and Tracert work consistently while browsing to the same sites fails consistently.
    LVL 3

    Assisted Solution

    I would say test the MTU settings on the client machines.
    Go here and try the ping test to see if it is an issue with MTU setting's.
    LVL 1

    Author Comment

    OK, I tried changing the DNS Server addresses in the router and it stopped working altogether; There must be some gateway setting or something that I have to change in conjunction with this, that I am missing or unaware of.

    I tried tweaking the MTU settings, but it didn't work and besides, the diagnostic process described at dslreports indicated that the current setting of 1458 was correct anyway. (I tried setting it lower and it made no difference).

    I tried browsing from a Linux machine (in fact I'm posting this from Mozilla under Ubuntu Linux), but the same selection of sites were inaccessible.  Traceroute, ping, etc work fine in Linux for the affected sites, as in Windows.

    I'm going to try swapping out the router next.
    LVL 1

    Expert Comment

    Why are you changing ANYTHING on the router?  The router should be set to get an IP and other network info via DHCP.  The router should pick up an address, gateway and DNS info and pass that to the clients.  Also set up your router as a DHCP server to dispense network info to your clients.  That should be it.  

    LVL 1

    Author Comment


    We have subnet of 16 static IPs associated with this broadband connection; the network address being x.x.x.0, user addresses (not actually in use) x.x.x.1 to x.x.x.13 and the router IP address is x.x.x.14, or it's supposed to be.  It was set to x.x.x.0.  Changed it to x.x.x.14 and it just *works* now.

    It is peculiar that it caused such a selective set of failures, whilst not adversely affecting 99.9% of sites.  Oh well.

    I am grateful for all your suggestions, so I'll split the points between everyone.

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