recursive queries fail with high load?

[Elias]

Hi Chris,

Do you get the timeouts if you try a 'dig @127.0.0.1 www.websudoku.com' too? 
We've encountered a similar instance where lookups against our interface's 
IP failed whereas against our own loopback was OK. The problem soon 
discovered was due to heavy loading on the machine. If it fails too, then 
probably you can try looking at your network (if its saturated or not).

There's also this very useful too found here - 
http://dns.measurement-factory.com/tools/dnstop/ which lets you see the top 
DNS talkers. Sometimes we do get customers sending hundreds if not thousands 
of recursive queries per second to our servers and once we blackhole them 
everything goes back to normal.



----- Original Message ----- 
From: "Chris Michels" <Chris.Michels at NAU.EDU>
To: <bind-users at isc.org>
Sent: Monday, February 26, 2007 1:31 PM
Subject: recursive queries fail with high load?


>
> I have 3 DNS servers running bind 9.3.2.  Two of them are failing to 
> resolve
> recursive queries.   Both of these servers have a higher load because they
> are used by our spam filtering software.  I have increased the
> recursive-clients option on both servers.  It seems like recursive queries
> are just taking a long time and timing out.   What is going on here or 
> where
> should I be looking for what is wrong?
>
> A dig of a random name returns:
>
> [root at ruby named]# dig www.websudoku.com[1] @ns2.nau.edu
>
> ; <<>>DiG 9.2.4 <<>>www.websudoku.com[2] @ns2.nau.edu
> ; (1 server found)
> ;; global options:  printcmd
> ;; connection timed out; no servers could be reached
>
> But if I set the timeout high it returns:
>
> [root at ruby named]# dig +time=240 www.websudoku.com[3] @ns2.nau.edu
>
> ; <<>>DiG 9.2.4 <<>>+time=240 www.websudoku.com[4] @ns2.nau.edu
> ; (1 server found)
> ;; global options:  printcmd
> ;; Got answer:
> ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 50071
> ;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 2, ADDITIONAL: 0
>
> ;; QUESTION SECTION:
> ;www.websudoku.com.             IN      A
>
> ;; ANSWER SECTION:
> www.websudoku.com[5].      3600    IN      CNAME   websudoku.com.
> websudoku.com.          3600    IN      A       66.39.22.227
>
> ;; AUTHORITY SECTION:
> websudoku.com.          3600    IN      NS      ns00.ns0.com.
> websudoku.com.          3600    IN      NS      ns97.pair.com.
>
> ;; Query time: 20270 msec
> ;; SERVER: 134.114.138.3#53(134.114.138.3)
> ;; WHEN: Sun Feb 25 22:27:40 2007
> ;; MSG SIZE  rcvd: 112
> rndc status shows:
>
> number of zones: 746
> debug level: 0
> xfers running: 0
> xfers deferred: 0
> soa queries in progress: 0
> query logging is OFF
> recursive clients: 1441/5000
> tcp clients: 0/1000
> server is up and running
>
> stats show a high percentage of failures
>
> +++ Statistics Dump +++ (1172467505)
> success 305925
> referral 114
> nxrrset 15781
> nxdomain 335350
> recursion 529820
> failure 303309
> --- Statistics Dump --- (1172467505)
>
>
>
> -- 
> Chris Michels -- Systems Programmer/Team Lead -- +1 928 523-6495
> Northern Arizona University -- Flagstaff, AZ
> PGP key: http://jan.ucc.nau.edu/~cvm[6] Team Info:
> http://www4.nau.edu/its/sia[7]
>
> "The significant problems we face cannot be solved at the same level of
> thinking we were at when we created them" -- Albert Einstein
>
>
>
> --- Links ---
>   1 http://www.websudoku.com
>   2 http://www.websudoku.com
>   3 http://www.websudoku.com
>   4 http://www.websudoku.com
>   5 http://www.websudoku.com
>   6 http://jan.ucc.nau.edu/%7Ecvm
>   7 http://www4.nau.edu/its/sia
>