DNS failure on ais.channel4.com

RouterOS General
1

Hi,

I’ve got a problem with my router board (RB2011L running v5.14).

I have been unable to watch catchup TV on Channel 4 here in the UK. The specific URL I’ve been using is ‘ps3.channel4.com’.

Using Wireshark I have tracked this down to a DNS problem. If using the router board DNS server the following domain name does not resolve ‘ais.channel4.com’.

Using Wireshark on the LAN side I can see that the client is sending a DNS request and the routerboard is responding to say there is no such domain.

If however I monitor the WAN side I can see the routerboard issuing the same request to my ISP DNS server and that server replying to the rouerboard with the correct information. - for some reason the routerboard is not relying to the original client with the information provided from the ISP server.

I have also tried using the ‘resolve ais.channel4.com’ on cli. This responds with ‘failure: dns server failure’

As a workaround I have added the ISP DNS server entry to the DHCP config which allows all lan hosts to resolve the URL.

I would be interested if any one has any thoughts on what the underlying issue is here?

Many Thanks

2

Open terminal and issue the following command:

/ip dns set max-udp-packet-size=4096

See if you can resolve that domain then. If it didn’t work, upgrade RouterOS to the latest stable version (v5.24 at the time of writing) . There had been some issues with DNS resolving that’s been fixed.

If you still had that problem after following those steps, report back.

3

Devil,

Thank you very much! All working now!

For the record - max-udp-packet-size was already at 4096 so I went ahead and updated to the latest (5.24) firmware which has sorted it out.

Thanks again