Re: how to debug a DNS resolution problem ?

[Roger "Peņa" Escobio <orkcu yahoo com>]

--- Waleed Harbi <waleed harbi gmail com> wrote:

> try use also nslookup,host,ping, commands, and
> disconnect the Internet when
> you test this task
> 
>
http://www.adminschoice.com/docs/dns_trouble_shooting.htm
>
http://networking.ringofsaturn.com/Unix/dnstroubleshooting.php
> 
thanks for the links Waleed, that help me find the d2
option for nslookup, I use it and found at least the
reason why dig was saying "Couldn't find server
'ns1.sld.cu': Name or service not known", it is a
timeout problem

look at the nslookup debug trace:
> sld.cu.
addlookup()
make_empty_lookup()
looking up sld.cu.
start_lookup()
setup_lookup(0x9cf54a0)
resetting lookup counter.
cloning server list
clone_server_list()
make_server(200.55.135.114)   <----- this is my server
using root origin
recursive query
add_question()
starting to render the message
done rendering
create query 0x9cf4328 linked to lookup 0x9cf54a0
do_lookup()
send_udp(0x9cf4328)
bringup_timer()
have local timeout of 10
working on lookup 0x9cf54a0, query 0x9cf4328
get_address()
sockcount=1
recving with lookup=0x9cf54a0, query=0x9cf4328,
sock=0x9cf6608
recvcount=1
sending a request
lock_lookup dighost.c:1466
success
send_done()
sendcount=0
check_if_done()
list empty
unlock_lookup dighost.c:1475
connect_timeout()    <---- I got a timeout
lock_lookup dighost.c:1706
success
;; connection timed out; no servers could be reached
cancel_lookup()

so, I got a timeout but with whom !!!???
I have connectivity with the network sld.cu., I can
reach its IP and even I can request to its ns servers
directly, look another nslookup debug trace:

> sld.cu.
addlookup()
make_empty_lookup()
looking up sld.cu.
start_lookup()
setup_lookup(0x85d04a0)
resetting lookup counter.
cloning server list
clone_server_list()
make_server(196.1.112.25)  <--- sld.cu nameserver
using root origin
recursive query
add_question()
starting to render the message
done rendering
create query 0x85cf328 linked to lookup 0x85d04a0
do_lookup()
send_udp(0x85cf328)
bringup_timer()
have local timeout of 10
working on lookup 0x85d04a0, query 0x85cf328
get_address()
sockcount=1
recving with lookup=0x85d04a0, query=0x85cf328,
sock=0x85d1608
recvcount=1
sending a request
lock_lookup dighost.c:1466
success
send_done()
sendcount=0
check_if_done()
list empty
unlock_lookup dighost.c:1475
recv_done() <-- here is where it should get a timeout
lock_lookup dighost.c:2142
success

so, there is something between get the info from the
cu. nameservers and send the query to the sld.cu
nameservers that is making a timeout, but I can't
imagine what can be that :-(

does anybody knows how to know _to where_ is sending
the dns query ?

any strace trick ? any oscure option in dig or
nslookup to print the IP to where is sending the
_last_ query in a recursive one?

thanks
roger

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