Re: Unusable DNS, 10.4 Tiger
Re: Unusable DNS, 10.4 Tiger
- Subject: Re: Unusable DNS, 10.4 Tiger
- From: email@hidden
- Date: Thu, 1 Dec 2005 11:36:46 -0700
On Nov 30, 2005, at 7:03 PM, Peter Sichel wrote:
On 11/30/05, email@hidden wrote:
For whatever reason,
any DNS lookup on my computer takes 5-7 seconds. If I try the query
again, it takes a fraction of a second, but sometimes reverts to the
full time.
Hi Zack,
I don't know the solution to your problem, but I do have a few
troubleshooting ideas that might help. As you may know, I'm the
developer of a network troubleshooting utility called IPNetMonitorX.
You can download and try it free for 21 days. Ideas:
(1) Does it help to flush the DNR cache?
(Flush Cache in IPNetMonitorX Lookup tool)
Nope
(2) Can you isolate the problem to the local DNR (Domain Name
Resolver)
versus querying the corresponding name server directly? IPNetMonitorX
has both a "Lookup" tool that uses the local DNR and a "NS Query" tool
that allows you to query the corresponding name server directly.
How do
the results compare?
They both are taking about 6-15 seconds today. I may have used NS
Query incorrectly, I entered Qwest's DNS of 205.171.3.65 and tried
nslookup and got:
nslookup://65.3.171.205.in-addr.arpa;querytype=A;server=205.171.3.65
name server
Default server: 205.171.3.65
Address: 205.171.3.65#53
Server: 205.171.3.65
Address: 205.171.3.65#53
Non-authoritative answer:
*** Can't find 65.3.171.205.in-addr.arpa: No answer
----------------[End of response]----------------
The query took about 6 seconds.
(3) Use the TCP Dump tool with options "-n -p udp port 53" to watch
DNS
queries on the wire. Is the query being sent to the expected server
promptly, or trying some other servers first? Does the response (if
any) arrive promptly?
Here is a dump for:
curl hotmail.com
tcpdump://en0@localhost;options=-n -p udp port 53
11:23:34.523781 IP 192.168.0.50.50424 > 205.171.3.65.53: 39700+ A?
hotmail.com. (29)
11:23:42.025238 IP 192.168.0.50.50427 > 205.171.2.65.53: 39700+ A?
hotmail.com. (29)
11:23:42.112253 IP 205.171.2.65.53 > 192.168.0.50.50427: 39700 2/0/0
A 64.4.33.7, (61)
----------------[End of response]----------------
The 11:23:34.523781 line appears instantly, then an 8 second delay
until the 11:23:42.025238 line appears, then 11:23:42.112253 is
instant after that. I don't quite know if I am reading this right
but, doesn't it look like the first query never comes back, so it
times out and tries sending it again, at which point it gets a
response back immediately? Any idea why this would always happen?
Could I shorten that timeout to say half a second?
(4) What Name Servers did you actually get back from the DHCP
Server on
your LAN if any? You can view these in the DHCP Lease tool.
Right now DHCP is off and I am using manual. If we get this working,
I'll turn it on and make sure everything still works.
I'm guessing there might be some problem with the configured name
servers, or some conflict related to DNR caching. I haven't seen this
particular behavior in my own experience, but I have noticed Tiger can
sometimes lose its router information when switching between Ethernet
and AirPort configurations with a short or interrupted sleep in
between. The IP reconfiguration process appears susceptible to
awkwardly timed interruptions. When this happens, I just turn AirPort
off and back on to force the IP stack to reconfigure.
Hmmm I could see that, although this is my primary computer and
always on en0. Just out of curiosity, could I tell it to send 2 dns
requests in quick succession, so the second reply comes faster? I
just wonder if this is something related to my wireless hub and
router, like, maybe the first response is blocked somehow. I just
can't imagine that though. I will try running this on my ibook since
I think it is running a lot better than my imac. Is there anything I
can adjust on my imac, like the DNR thing, or have we ruled that out
now? Also, is port 53 special in the router? Could I open it so it
skips NAT for that port somehow? Thanx,
------------------------------------------------------------------------
Zack Morris Z Sculpt Entertainment This Space
email@hidden http://www.zsculpt.com For Rent
------------------------------------------------------------------------
If the doors of perception were cleansed, everything would appear to man
as it is, infinite. -William Blake, The Marriage of Heaven and Hell
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