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I have a Linksys RV042 router, hooked up in a fairly standard configuration (only using one WAN port - hooked to a cable modem). DNS lookups from systems on the LAN are failing intermittently. This happens even if the computers are manually configured to use specific name servers (not using a proxy on the RV042), it happens with different name servers (comcast, opendns), and it happens with Linux and Windows boxes.

I did some experimenting with tcpdump and wireshark, and it looks like the responses from the DNS server are sometimes coming back with an incorrect port number - using a port (at least sometimes) from a previous DNS request. That is, I can see all of the DNS requests going out as expected, and most of the time the response comes back correctly, but maybe 1 out of 20 times, the response comes back to a port number that's different from the one used in the request.

Is there a known problem with the NAT implementation in the RV042 that would cause problems with incoming UDP responses? Or is there some sort of configuration problem that I can fix?

I've seen a bunch of similar inquiries on various forums, but no useful answers so far...

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We seem to have almost the same problem. What firmware are you running? Ours is 1.3.12.19-tm and when we tried to upgrade to 4.0.0.07-tm-20100819 but it just locked up. Might try a factory upgrade then reset next. –  matschaffer Mar 28 '11 at 12:56
    
Are the clients asking the router for DNS lookups which is forwarding them or is it providing clients an external server to use for lookups? Try setting a client manually to google DNS (8.8.8.8) –  SpacemanSpiff Dec 22 '11 at 15:33
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2 Answers

I am having a related problem with Policy Violations and resulting blocked connections due to mangled DNS responses... I've heard that it is most noticeable on Mac OS X and that the work-around is to downgrade to 1.3.12.6-tm firmware.

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I have 4 RV042's which I have not had problems with, I have my DHCP in the router assigning my internal DC/DNS server IP addresses to the clients, so the clients get the names from the internal network, the DNS servers then get it from OpenDNS servers. I haven't noticed any issues with DNS lookups from the DC's

How is the DNS IP assigned to the clients? Are they pointing to the RV042 as the DNS server or some other servers?

I'm on the latest 1.x firmare. I could never get the 4.x to work.

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