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DNS problem when static DHCP is used

Discussion in 'HyperWRT Firmware' started by mmisnan, Feb 9, 2006.

  1. mmisnan

    mmisnan Network Guru Member

    I've just flashed my wrt54gs with thibor13c, replacing it from dd-wrtv23. Last night I was thinkering with the static DHCP assignment but doing so, it led to a DNS problem on all devices connected to the router either wired or wireless. Out of the sudden, all DNS requests were failed... but adding DNS servers manually on my PC solved this. I resetted my router but it won't do any good and at last, I deleted all static DHCP assignments that I had and everything back to normal. Is there any know issue between DNS and static DHCP assignments? Thanks for any help.
     
  2. Thibor

    Thibor Super Moderator Staff Member Member

    i'm using static dhcp myself and haven't seen any issues whilst using it. i'll have a play with it though and see if anything turns up. did you reboot your router after setting it up?
    what are your dns options(which checkboxes are selected)?
    are your dns fields in your router filled in?
     
  3. howardp6

    howardp6 Network Guru Member

    If you set a static IP Address on your NIC you have to enter the DNS server addresses from you rrouter status page otherwise the URL you enter into your browser is not resolved into IP Addresses. If you have a DNS server on your LAN, it can resolve URLs otherwise you you have to enter the DNS servers addresses.
     
  4. mmisnan

    mmisnan Network Guru Member

    Hi Thibor,

    I will try reproduce it again tonight .. settings that I had before:

    Basic setup: Use Dnsmasq for DNS (ticked), no static DNS defined
    Static DHCP: Using Device List screen, add MACs to Static DHCP list, save setting.

    It is reproducable .. and guess what, here is my /etc/resolve.conf on my Fedora machine:

    Code:
    [root@wiraone init.d]# cat /etc/resolv.conf
    ; generated by /sbin/dhclient-script
    search localdomain
    nameserver 172.16.126.1
    
     
  5. mmisnan

    mmisnan Network Guru Member

    Hi Howard,

    Nope, I didn't set a static IP address on my PC .. I defined it at the router level under Static DHCP. I'm getting the correct IP address as per the one I defined on the router, it just that the DNS sent by the router doesn't seem to point to the router itself. This happened not only on my Linux PC, but the other 3 Win XP PCs that I have.
     
  6. prowler1968

    prowler1968 Network Guru Member

    mmisnan:

    I have a mixed network with Win9x and XP machines all connected to the WRT with 13c firmware. I have both DHCP server enabled and about 6 machines with the STATIC DHCP assignments. All machines are obtaining the IP and DNS assignments correctly.

    A possibility that maybe your STATIC DHCP is in the same range as the DHCP server? I'm set to give DHCP on address 192.168.0.5 ~ 192.168.0.70. My STATIC DHCP assignments are 192.168.0.100 and above. I've read this could be a problem when the ranges overlap, at least when I used DD-WRT.

    With HyperWRT, I have had no issues with what you are seeing.

    One last thought - at least on the XP machines, there is a tick box for Obtain an IP address Automatically AND Obtain a DNS automatically. Are both ticked, or perhaps the DNS is using an old value?
     
  7. Thibor

    Thibor Super Moderator Staff Member Member

    it looks like you have the "use static entries and isp entries" box checked otherwise the only dns server you'd get would be the router
     
  8. mmisnan

    mmisnan Network Guru Member

    I can confirm that the "use static entries and isp entries" is not checked. Here is the basic setup I have ..

    [​IMG]
    [​IMG]
     
  9. mmisnan

    mmisnan Network Guru Member

    Well, it is not a big lost since I can live with dynamic DNS .. I was just stumped yesterday since I thought, hey .. may be I can have a static IP address for all PCs that I have and no worry about IP conflict when some of the PC went asleep and the lease expired.. After I set the static DHCP, went out .. and when I got back .. my kids and my wife started screaming saying that the internet was down .. :)

    Anyway, further information .. I've WRT54GS-UK/v4.0 and as some of you may have expected .. from PC World £49.90 combo :)
     
  10. prowler1968

    prowler1968 Network Guru Member

    mmisnan:

    Did you go to the Administration.asp/Factory defaults and select Clear NVRAM and then reboot?

    How about when you flashed from DD-WRT to HyperWRT? Did you press reset for 30 seconds to clear DD-WRT settings before flashing to HyperWRT?

    From my typical usage, press and hold reset 30 seconds. Go to Administration/Factory Defaults and select clear NVRAM and Reboot. Flash HyperWRT again. After successfully updated, press reset AGAIN for 30 seconds, go to Administration/Factory Defaults and Clear NVRAM and reboot AGAIN. Now, enter your setup. It may not always be necessary, but I always go through this routine, even if upgrading from 13 to 13a to 13b to 13c.
     
  11. mmisnan

    mmisnan Network Guru Member

    Prowler: thanks, will do this tonight and see if this solve the problem.
     
  12. mmisnan

    mmisnan Network Guru Member

    Just an update, its all sorted out now. Thanks to Prowler, I did the Clear NVRAM thingy (without reflashing) and it works now. Most probably some DD-WRT settings were left in the NVRAM.
     
  13. prowler1968

    prowler1968 Network Guru Member

    Hey, glad to hear that it worked. It takes a little extra time to properly clear the router between upgrades, but the stability is worth the trouble.
     
  14. dvaskelis

    dvaskelis Network Guru Member

    If the problem returns you should try moving your static IP addresses (the one you showed was .7) outside of the range of the dynamic IP addresses (the range you showed was .6 through .15).
     
  15. mmisnan

    mmisnan Network Guru Member

    Suggestion noted .. will do that when I got back home.
     

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