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Old 08-06-2012, 02:19 PM   #1
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2wire/AT&T router - LAN DNS table lookup error?

I have a Pace 2wire router with AT&T Internet service. It is a
3800HGV-B with software version

I believe this hardware/software to have a DNS lookup table error, but would be happy for someone to inform me otherwise. I am having problems with client/server programs such as Mythtv and BackupPC. Computers are turned off overnight, some unused for days. In summary, all computers have access to the Internet (ifconfig matches information from the 2wire). However the last computer booted always returns from the "host <computername>" command and "host" always returns the name of the last computer booted.

Computer names displayed in the router are picked up from each respective machine and LAN addresses are assigned via DHCP. When computers are shut down for 14 to 24 hours the 2wire's information on LAN computers clears (DNS TTL expires the tables?). I can jumble the boot order and the last machine booted always returns from the "host <computername>" command. I can boot a computer with a Linux Live OS and get the same results. All computers give results similar to below.

I believe the DNS tables created by the 2wire route for the LAN are flawed. Even if I had somehow misconfigured the 2wire, that still would not explain the localhost address jumping to the most recently booted computer. Using a Linux Live OS would seem to eliminate computer misconfigurations on my machines.

When you (perhaps) know more about the problem than tech support and your problem is not on their sheet, they are helpless to assist you. My best option seems to be to run my own DNS server, authoritative for my LAN.

I need help from the community. A total reset of the router is in order (but not until the Olympics are concluded, under threat of death) and I will report results.

**** Can someone tell where my reasoning is in error, and if so, where the true problem lies?

**** Is there anyone out there with a 2wire router willing to test? What does "host" return? Can you shut down computers until the "Home Network Devices" table on the router clears them, boot a machine, and see if "host <computername>" returns ? Boot another and does the previously booted computer now return a valid LAN address from "host <computername>" ?

If I am right and others can confirm, it will carry more weight. If I am wrong I will keep my head down and keep quiet.

Thank you for reading this too long post.

* 1) $ host laptop1 has address

2) $ host pcOK has address

2wire reports under Home->"Home Network Devices"
cisco (the AT&T box)

A) $ host domain name pointer laptop1

boot pc1 ----------------------

1a) $ host laptop1 has address

2a) $ host pcOK has address

* 3a) $ host pc1 has address

Aa) $ host domain name pointer pc1.

boot pc2 ---------------------

1b) $ host laptop1 has address

2b) $ host pcOK has address
Host not found: 4(NOTIMP)

3b) $ host pc1 has address

* 4b) $ host pc2 has address

Ab) $ host domain name pointer pc3.
Old 08-07-2012, 12:04 AM   #2
Registered: May 2009
Location: Fort Langley BC
Distribution: Kubuntu,Free BSD,OSX,Windows
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You don't mention what OS you are using, but most have a caching DNS server that you would surely be interested in. Set your own preferred upstream lookups, bypassing the 2wire.

DHCP gets its lookup table from the upstream host, so your 2Wire is getting its DNS info from your ISP as it too uses DHCP.

My philosopy is don't fight City Hall. It is much easier just to go around them. Use a caching DNS server, specify your preferred DNS provider ( google is ) and your off to watch Myth TV instead of getting grey hair.

It really is dead easy:
Old 08-07-2012, 03:32 PM   #3
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Your post is spot on. As I stated, I indeed will be running a DNS server and have begun the process. However it is an additional security risk to fix what should not be a problem in the first place (if my theory is correct). I really appreciate the link. Thanks for the prompt reply.

I am also crazy enough to care about Grandmother and Linux Newbie, new to GNU/Linux, perhaps finding it frustrating because something does not work which may not be the fault GNU/Linux. If someone could confirm my experience is not a solitary one, it would be great.

I am using Fedora, Linux Mint, and Mepis.
Old 02-08-2013, 03:19 PM   #4
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SOLVED - 2wire/AT&T router local network DNS resolution

Wanted to close this thread.

A hard reboot of the router fixed the problem, but of course blew away all the user settings.

It just went screwy on me again. I had computer "A" listed twice, once for wireless (.67) and once for wired (.72). when I did a 'host "A"' it returned an IP address of .71 which corresponds to no device/computer on the network. I had to clear the device list on the router and start over (no hard reboot). 99.99 percent of users probably have no problems. However if you run client/server programs, I recommend avoiding the 2wire/AT&T router until they allow you to turn off their local DNS resolution and run some real DNS software, or fix the local network DNS resolution. One man's opinion (and open to being told I am wrong). EOF
Old 08-27-2015, 03:23 PM   #5
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Final Solution:
Several of my LAN computers did not have an /etc/dhcp/dhclient.conf file. A one-liner in this file of: send dhcp-client-identifier = hardware;
fixed my problem for good (many months problem free). The above one-liner is surely too simple, but has cured all my problems with LAN IP address assignments via DHCP. If you have DHCP clients on your LAN, I strongly urge you to ensure all clients have a dhclient.conf file.


dns, hardware, lan, networking

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