why include an answer in the query?
Kent Tong
kent at cpttm.org.mo
Wed Apr 19 07:02:37 UTC 2006
Hi,
We have a local DNS server that uses the ISP's DNS server
as a forwarder. Usually it is working fine. But recently
we find that it can't resolve www.yahoo.com (but yahoo.com
is OK), because the ISP's DNS server is not responding to
the query on www.yahoo.com (but does respond to a queries
on yahoo.com). However, using the "host" command to query
the ISP's DNS server directly works fine for both domain
names. So Yahoo is working and the ISP's DNS server is also
working fine.
Using tcpdump we find that if the query is for www.yahoo.com,
our local DNS server will include an answer in the query
to the ISP's DNS server (tcpdump shows the [1au] flag for
the DNS packet), while for yahoo.com it won't:
[root at cladmr003 root]# tcpdump -A -i eth2 port 53
tcpdump: verbose output suppressed, use -v or -vv for full
protocol decode listening on eth2, link-type EN10MB (Ethernet),
capture size 96 bytes
14:54:55.723957 IP n8z108l98.broadband.ctm.net.1751 >
macau.ctm.net.domain: 34796+ [1au] A? www.yahoo.akadns.net. (49)
E..M.. at .@.5...lb.......5.9...............www.yahoo.akadns.net...
....)........
Do you think it is this answer that is causing the ISP's DNS
server to reject the query? If no, what else could be causing
this behavior?
Thanks!
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