[Dnsmasq-discuss] problems resolving *.yahoo.com

Simon Kelley simon@thekelleys.org.uk
Sun, 05 Dec 2004 09:15:36 +0000

Charles Hastings wrote:
> Lately, I've been experiencing a intermittant problem when looking up
> hostnames from yahoo.com.  Sometimes, when querying *.yahoo.com through
> dnsmasq, a "server error" is returned.  Querying the name server that
> dnsmasq relays to works as expected.
> The problem is resolved by waiting a while, or restarting dnsmasq.
> Here's what happens when I try to look up www.yahoo.com:
> root@fw:~# host www.yahoo.com localhost
> Using domain server:
> Name: localhost
> Address:
> Aliases:
> Host www.yahoo.com not found: 2(SERVFAIL)

The only circumstance under which dnsmasq will itself generate the 
SERVFAIL return code is overflow of its internal tables. If that happens 
  then the query would never be forwarded to the upstream server, so 
it's not the case here. The SERVFAIL is really coming from the upstream 
nameserver, as shown by the tcpdump.

Since dnsmasq forwards the original query bit-for-bit unchanged except 
for the query-id, it's unlikely that dnsmasq is taking a valid query and 
rendering it invalid somehow (though it's theoretically possible).

My guess is that there is a problem upstream, maybe with the servers for 
the yahoo.com domain, or attbi's connection to them, such the the attbi 
servers don't get an answer from the yahoo.com servers in time and 
return the error code. When you then retry the query direct, the delayed 
reply from yahoo will have arrived a attbi, and the query works. (Or you 
hit another machine in their DNS cluster.) Doing the query again through 
dnsmasq would also work.

If, on the other hand, it's really the case that queries fail _only_ 
when relayed via dnsmasq then something very strange it happening.