I am using a Linksys WRT54GS Wifi router under Windows XP SP2 and have the following problem :
My DSL provider modem works in DHCP => my IP address always stays the same but my provider DNS addresses can change several time a day (I suppose that my provider use a load balancing system which implies that the DNS addresses changes)
My router is also configured in DHCP. When I type "ipconfig /all", I can see that my IP address will be automatically renewed in 24 hours. Consequently, when my provider DNS addres changes, my router will not automatically update so name resolution fails on my computer.
Then, I have to manually connect on the router and request it to request the new DNS addresses in order to solve the problem. But I would the router to do this automatically.
Is there something I miss in the router configuration ? Otherwise, is there a way to push the new DNS entries from my DSL modem to the router ?
Are you sure about that? Such a system might not work even with a directly connected PC. The way DHCP works is that the client is responsible for obtaining the IP/DNS/Gateway addresses. There's no way for the DHCP server to "force" the client to change IP's. (Exception: Methinks PPPoE and PPPoA can force a change by initiating a disconnect, but I'm not sure). The key is the lease time. The client and the router will issue a DHCP lease renewal in half the lease time. The minimum lease time is 1 hour, so your ISP can theoretically juggle DNS servers every 30 minutes.
Wrong. The lease time displayed by your Windoze machine is the lease time of the DHCP server in the WRT54G router, not that of the ISP's DHCP server. In addition, the WRT54G has a nifty DNS cacheing server built in. The DNS server IP on your Windoze machine should be the IP address of the router (192.168.1.1) and should not change. What's important is the lease time on the status page of the WRT54G, not the Windoze client.
Questions:
Are you sure your ISP juggles DNS servers? I don't know of any ISP that does this. The load on DNS servers is rarely high enough to justify a load balancing scheme.
Who is your ISP? I wanna try nslookup on their servers and see what they're really doing.
Are you sure that you're using DHCP and not PPPoE or PPPoA? These handle IP updates differently from DHCP.
Thanks for all your explanations. Here are my replies to your questions.
Jeff Liebermann a =E9crit :
I am pretty sure they do it. This morning, I looked at the router status page and saw the 2 DNS IP entries. This afternoon, my computer was unable to resolve any host name. In order to solve the problem, I forced the router to get the configuration again from the DSL modem and I noticed that the second DNS entry changed (and I was able to resolve the host names)
This is Free (a French ISP) and the Web site is "
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"
I double-checked this and I am sure that I am using DHCP.
I did not find the lease information on the router status page. Perhaps I should upgrade the BIOS ?
OK. I guess they really are juggling DNS addresses. That's a first for me. I wonder if this is some kind of scheme to keep free users from staying connected and idle for too long?
Nice mess. Their backup nameserver (freens1-l.free.fr) can't even resolve their own domain (free.fr). At least the primary nameserver works correctly.
NSLookup shows only two authoritative nameservers for free.fr: freens1-a.free.fr A (Address) 213.228.0.82 (main) freens1-l.free.fr A (Address) 213.228.0.198 (backup) I've been pounding on these most of the last 4 hours and they are not changing. However, free.fr may have other nameservers hidden behind their firewall for their own customers. Lookups show a 7 day expire so there's no way they are juggling the public nameservers with that long a DNS cache.
I'm using Sveasoft Alchemy firmware which gives me a command line interface for the unerlying Linux operating system. I can see the file: /tmp/udhcpd.leases but it's cryptic garbage. I can't seem to figure out how to display the current DCHP cache with lease times. Since I have a static IP on the WAN side, I don't think dumping my file will show anything. I'll do some digging to see if I can extract the values.
Meanwhile, methinks just using some other ISP's DNS server may be the only way to work around the problem.
Do you mean that I can statically define these 2 nameservers in my router configuration. If so, it would solve my problems !
Do you know any reliable DNS public server ?
I have heard of this firmware and it sounds good. You say you are getting a command line interface in Linux. I know that the firmware is supposed to be run by the router : since I am running Windows XP SP2, can you just confirm that it will be OK for me (I will get the command line interface as well under XP)
No. That would be so nice, but the stock firmware for the WRT54G can't do it. I just tried it.
2nd best is the Sveasoft firmware has provisions for adding a "Local DNS" nameserver but that apparently has to be on the LAN side, not the WAN. It's on the "Basic Setup" page. I just shoved another local nameserver into the "Local DNS" field. The "Status" page set this nameserver as the primary DNS server, leaving the other two DNS servers to be set via DHCP. This will work if Linksys has the same feature.
3rd best is to setup your Windoze machines for DHCP or static IP addresses, and just set your DNS server to the two free.fr server IP's. Unlike the WRT54G, Windoze allows you to use DHCP for the IP address, but static (manually set) IP's for the DNS fields. This bypasses the DNS cache in the router, but you probably won't notice the difference.
Do I have to do ALL the work? You should find a DNS server that is physically close to your location. I'm not familiar with France or French geography and therefore cannot offer a guaranteed solution.
Find another local French ISP. Then, to to:
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plug their domain name into the "DNS Lookup" box on the upper right. (Try it with free.fr first). Select "NS" for nameserver. Then go down to the "Click here to check that all DNS servers are reporting the same results" and look at the latency in msec. For cable or DSL, it should be less than about 50msec to be considered useful. I'm getting about 110msec from France to California which is NOT fast.
Recommended:
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may want to spend $20 and get Talisman, which I'm told is better. I haven't had time to try it.
Yes, using Alchemy, not the stock Linksys firmware. You telnet or use SSH2 to connect to the router from your Windoze box and you get the Linux (Bash) shell prompt. If you're not familiar with running Linux from the command line, this may be a learning experience.
Any computer or operating system that can run telnet or some SSH client such as Putty will work. However, I can see that you need to do some studying and get some experience with Linux before you try Learning by Destroying(tm). I suggest you download or borrow one of the Linux "Live CD" distributions. This lets you boot Linux on your desktop without actually installing anything on the hard disk. There are also versions that boot from a floppy disk such as Trinux. When you're comfortable with the shell command line, then you can safely destroy your router.
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