How to keep a static IP and let DNS addresses be dynamically updated on Linksys WRT54GS ?

Correct.

True. If you set up your ISP's DNS servers in the Windoze client, and the ISP juggles DNS servers, then this will not work.

No. Your options are:

1. Use the cacheing DNS server in the WRT54G and point your clients DNS server to the WRT54G (192.168.1.1).

1. Use some other ISP's DNS servers. Many DNS servers allow public access from the internet. It's condidered good form to ask the other ISP if you can do this first, but everyone does this. I have the local university and a local very big corporation as my backup DNS servers. I suggest you download and play with Sam Spade 1.14:
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   use one of the numerous online DNS tools such as:
   formatting link
   find DNS servers and see if they are accessible.

2. Call your ISP's support people and ask them *WHY* they are juggling DNS servers. It might be that they have a flakey DNS server and are doing repairs.

1. If your ISP uses PPPoE or PPPoA, there *MIGHT* be a way for the ISP to update your setting from their end. I'm too lazy to read the RFC right now to check.

2. Use the WAN timeout feature to inititate a disconnect after perhaps 5 minutes of inactivity. You'll get a new IP/DNS/Gateway mess of IP's every time you disconnect. Unfortunately, you'll need to be idle for 5 minutes in order for this to work. It's a rather dumb way to do this, but it might work.

No. There is no feature or function of a DHCP server to prematurely expire a lease. I would love to have this feature to force everyone to renew their DHCP leases on command when I renumber a network.

You can try it yourself. Setup your router with a DHCP server using whatever address you find useful such as 192.168.1.1. Connect with a typical Windoze client which gets its IP address from the DHCP server in the router. Now, dive into the routers DHCP server configuration and change the /24 IP block to something like 192.168.111.1. This should probably be done with a 2nd computah, but it will work using just one machine. Now, do whatever you find entertaining on the router to get the client to expire the lease prematurely and get a new IP address in the correct /24 block. You can reboot, thrash, broadcast, curse, or whatever, the stupid Windoze DHCP client will just sit there on the wrong IP address until 50% of the lease time has expired. It will then try to renew the lease and get a DHCPNAK which will eventually convince it to ask for a new IP address. This is the same as: ipconfig /release ipconfig /renew My point is that the renewal has to be initiated by the client, not by the DHCP server.

Methinks that PPPoE can force an update without also forcing a disconnect. I know it can force a disconnect which automatically requires that the PPPoE client get new IP/DNS/Gateway addresses. I can see that on SBC dynamic DSL accounts where the IP address may change several times a day for no obvious reason. However, I've also noticed that the two DNS servers delivered never change.

Yeah. That's what I'm thinking. There's no obvious benefit to juggling DNS server IP's. It will drive most client computahs nuts. It would be nice to know what problem the OP is trying to solve.

Well, I lied a bit. If your Windoze client has the "detect network connections" check box set, rebooting the router will cause the ethernet connection to disconnect. This signals Windoze clear the DHCP assigned IP values and get a new set of IP/DNS/Gateway IP addresses. This is the same effect as rebooting the router to get a new set from the ISP. So, if we eliminated rebooting the router or rebooting client as an option, the above DHCP test is still valid.

Not even with the sveasoft firmware? It's a pretty basic function of DHCP servers, I would have thought there'd be a way.

I think he should do that in any case - DNS servers really shouldn't change that much. I can see a round-robin system where they want to balance load among a half-dozen or so servers, but _all_ (or at least most) of them should still be available.

snipped-for-privacy@laposte.net wrote in news:1124897681.541809.170210 @g44g2000cwa.googlegroups.com:

You know this for a fact? I myself don't have this problem with the ISP in using static IP on the router. However, I am not sure about it because the DNS IP(s) never change. However, you gave valid static DNS IP(s) that belong to servers on the NIC setup and I don't see why the machines couldn't continue to use those static DNS IP(s) to do name resolution to IP while the router obtained different DNS IP(s). I am not for sure but may be that will only come into play with the dynamic DNS IP(s) for the DHCP server on the router in using its DHCP features to assign IP(s). Again, I am not sure about it.

It's called the DHCP table. Once a table entry has been added to it associating the MAC of the NIC to the DHCP IP assigned by the DHCP server on the router, the router will issues the same DHCP IP to the NIC. On a small LAN, the machines will get the same DHCP IP(s) assigned to the NIC (s) and you could consider it to be static for what it's worth. Of course, one could delete an entry out of the DHCP table and add more computers and possibly get different IP for the machine that had the entry deleted, because of the new machines being added. It's kind of like a first come first served kind of thing.

Duane :)

Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:

I was not sure about it and it seems like it will not work. However, if one could use static IP(s) that the ISP provided, one could configure the router to use the static IP(s) from the ISP and not have the router obtain DHCP IP(s) from the ISP. I know AT&T once gave me static IP information and I configured the router to use those IP(s). So, with that kind of setup, one could use static IP(s) on the router I would think and not be bothered with what the OP is going through, if I am in the ball park.

Duane :)

That's called "static DHCP" where the MAC address of a client is reserved for only that client. That works just fine for insuring that the IP address does not change. However, it does NOT reserve the gateway IP address, or the DNS IP addresses which are the current problem. In other words, it would do nothing to solve the moving DNS servers IP's.

Yep. That's the problem. He could dive into the Sveasoft Alchemy firmware in the WRT54G and write a script that checks for valid DNS servers. All the tools are there. Something like:

#(@) dns-renew.sh # Checks for valid DNS servers and renews the lease if invalid. # Run from cron. # # Check if

can be resolved. nslookup should ignore # the local DNS cache. If not, there's probably an option to do # fresh lookup. # Nameserver is not specified so that it uses the DNS # servers in the router. if [ nslookup ] do # do nothing. the dns servers are valid. sleep 60 # wait a minute and do it again. else # DNS lookup fails. Time to renew from ISP. ifdown vlan1 # disconnect. sleep 10 # snooze for 10 seconds. ifup vlan1 # reconnect and renew. done

I haven't tested this so use it at your own risk. With my miserable programming abilities, it's probably buggy. My WRT54G reports the WAN interfeace as vlan1 for some odd reason. This might be an artifact of some of my tinkering. Run: ifconfig to get the real WAN interface name. Good luck.

Not what I was suggesting. All DHCP servers I have used have an option to offer IP "X" to MAC address "Y" - if the DHCP server in the Linksys could do that (either with or without 3rd party firmware), then it would solve his problem.

Agreed. I was just going over dhclient documentation a couple of days ago, and there was a note that some dhcp servers can ask you to give up your lease, but they can't force it.

Yeah, I agree. I didn't invent the term. It's still better than SBC's mutation of static IP over PPPTP called "sticky static IP". There's also the misuse of NAT which really should be called PAT (port address translation). Then there's the total confusion between the various types of bridges, client adapters, game adapters, workgroup bridges, and other CPE equipment. Probably more but I don't wanna think about it.

Customer: I think SBC switched me to a static IP account. Me: Huh? How can you tell? Customer: I can hear static on the phone. Me: Put the microfilter back on where it belongs.

Please go up one paragraph where he wrote: "My problem is my provider updates the DNS addresses several time a day so I need them to be updated automatically or I will sometimes lose the name resolution."

What you quoted was his proposed solution to the moving DNS servers supplied by his ISP. That solution (static DHCP) will not do anything for the moving DNS server problem. Note that one of my proposed solutions is to simply ignore the shifting DNS servers and find a different DNS server that doesn't change. That should best be done in the WRT54G WAN config, but could also be setup in the client PC's.

Incidentally, this is a great example of why I wanna know what the problem that the OP is trying to solve, and not the place where the OP thinks they are stuck.

You can certainly do that with the sveasoft option, it's generally called a reservation. Don't know about the standard Linksys firmware as I haven't used it in ages.

David.

That didn't sound like the > Is there a way to fix the address on the router using a table which

He wanted to give his local machines fixed (or at least predictable) IPS. Seems to me that this would do the job - along with your previous suggestion to set the local computers' DNS server to the router.

First, he said:

So the soluti> problem : under XP, if I choose a static IP, I also need to fix the DNS > addresses.

which is resolved by simply fixing the DNS address as the address of the router (I'm not certain that even matters, because I would think _that's_ the address the DHCP server is going to give the clients).

Implicit in the whole problem is that allowing DHCP to issue dynamic address to the XP systems never resulted in problems - so the router should be _at least_ as capable as an XP system of handling the odd situation at the ISP's end.

You _don't_ always need to understand a whole problem to solve it. Solve the bits you know, and most of the time the rest falls into place.

Oxymoron that one, Static Dynamic Host Configuration Protocol. :)

Thanks Jeff, Derek, David and Duane for your posts.

I react to all your articles :

First of all, I wanted to give you more details about my ISP : He does not provide us a standard DSL modem but a modem called "Freebox" which is specific to Free (the ISP) => I know that Free build the internal hardware itself. On the input, we plug the phone line and on the ouput, we plug the VoIP phone, the TV and the Internet (RJ45). This is called triple-play and I suppose you have the same kind of modem in the US. Thanks to this system, I suppose that Free can manage the DNS entries as it likes and eventually does not respect DHCP standards. Two years ago, I tried using a standard DSL modem (a DSL PCI card) configured with DHCP and I always had name resolution problems => I had to reload the configuration like I do with the WRT54GS.

It seems to be a very good idea. I will try it this evening.

Jeff, I post a request about DNS servers in the other thread I initiated in this forum so just forget it.

I do not believe they will do something but I will try posting a request to them.

I suppose that the DHCP table is not implemented in the WRT54GS router Linksys firmware and should be run on a DHCP server computer (like they do in big companies) As far as I am concerned, I won't do this because this is a lot of administration's job ! Anyway, perhaps there is a more recent Linksys firmware which manages DHCP tables => I have a look.

OK, I will try running Sveasoft because everybody here seems to think it's much better than the Linksys one. Anyway, if Sveasoft implements DHCP tables, it would be excellent !