controlling DHCP

[James R. Van Zandt]

David Kramer <david at thekramers.net> wrote:
>   James R. Van Zandt wrote:
>   > David Rosenstrauch <darose at darose.net> wrote:
>   >>   ... a better solution to the problem is this:  run an 
>   >>   internal DNS server on your LAN, and your problem is solved.
>   > 
>   > Right.  Simple job for a Linux box, though I've been trying to leave
>   > mine off to save power & wear and tear.  However, my router (Linksys
>   > WRT54GS, firmware v2.07.1) is *already* a Linux box.  I guess I have
>   > to install third party firmware to get DNS running there.  Anybody
>   > have experience with this?
>
>   I'm sorry if I missed anything from not having watched this thread
>   closely enough, but your WRT54GS already serves DNS internally.  The
>   initial problem seemed to be the way it was configured (the expiration,
>   IIRC).  Why is this insufficient?

The WRT54GS serves DHCP.  It also does dynamic DNS (which, as I
understand it, means that when the cable company changes my IP, the
router will notify dyndns, so the "jrv.homeip.net" will still point
here).  However, I can't find anything in the WRT54GS user manual
about its serving DNS.  

After surfing a bit, I see that HyperWRT and DD-WRT third party
firmware implement DNSMasq which is a DNS server.  However I'm
somewhat reluctant to risk goofing up a working piece of hardware.

>   > By the way, the other reason to leave local machines DHCP rather than
>   > static, is that when the cable company moves their DNS servers, your
>   > machines get reconfigured automatically.
>
>   Again, apologies if I miss anything, but why would you need to change
>   internal IP addresses just because your external IP address
>   changed? 

It's not my own IP I'm thinking of here, but the IP of the DNS server.
Each of my machines has to be configured to point to one or more DNS
servers.  The machines using DHCP get their DNS servers and netmasks
automatically.  For the ones with static IP, I have configured their
DNS servers manually in /etc/resolv.conf:
  search comcast.net
  nameserver 68.87.71.226
  nameserver 68.87.73.242
i.e. the ones Comcast provides*.  When those servers move to different
IPs (as they did within the last few days), my networking breaks, and
I have to diagnose the problem and update that file.

* Maybe I would be better off adding one reliable DNS somewhere else.

                - Jim Van Zandt