DNS lookup in FC2 still slow.

[Yang Xiao]

On Tue, 03 Aug 2004 20:14:25 -0400, Ben Vitale <bsvitale at comcast.net> wrote:
> Jack Bowling wrote:
> 
> >On Mon, Aug 02, 2004 at 08:53:58PM -0400, Ben Vitale wrote:
> >
> >
> >>Hi,
> >>   Yes, I realize this is an often asked question, and for that I
> >>apologize.  I have the two lines..
> >>
> >>alias net-pf-10 off
> >>alias ipv6 off
> >>
> >>   ..in my /etc/modprobe.conf, and I have restarted several times since
> >>they were put in place.  They have had no effect, and I don't think IPv6
> >>is the culprit anyway.. my ifconfig shows all regular IP addresses.
> >>   I checked the ping times of my nameservers, and the one at the top
> >>of /etc/resolv.conf has the best times - on average, 8.5ms.  I would
> >>assume this is just a Comcast provider problem, but this was not an
> >>issue until I upgraded to FC2.
> >>
> >>
> >
> >Ben - I wonder if it is a problem with ECN on the nameserver or somewhere
> >on the route? First check to see if you have ECN turned on in your kernel:
> >
> >cat /proc/sys/net/ipv4/tcp_ecn
> >
> >If you get a 1 back, it is turned on. As a test, turn it off by:
> >
> >echo 0 > /proc/sys/net/ipv4/tcp_ecn
> >
> >and see if the slow ping still happens.
> >
> >BTW, Ian Gulliver wrote a useful program called ecncheck which tests ECN
> >along a route. There is also a companion program called ecnmx which
> >compiles from the same tarball that does the same for mailservers. Look for
> >it on freshmeat.net
> >
> >
> >
> >
> Without any changes to kernel 2.6.6-1.435.2.3,
> 
> [bvitale at vandelay ~]$ cat /proc/sys/net/ipv4/tcp_ecn
> 0
> [bvitale at vandelay ~]$
> 
> [bvitale at vandelay ~/ecncheck]$ ecncheck 68.48.0.6 53
> With ECN:    Connection accepted by ns02.rtchrd01.md.comcast.net
> [68.48.0.6] at hop #7
> Without ECN: Connection accepted by ns02.rtchrd01.md.comcast.net
> [68.48.0.6] at hop #7
> WARNING: Host doesn't support ECN but fails gracefully
> [bvitale at vandelay ~/ecncheck]$
> 
> Not sure how to interpret that?
> 
> Also, do you think 8.5ms is "slow" for a DNS server ping?
> 
> Ben
> 
> 
> 
Hi
What's the dns query return time? what if you do a
dig @ns02.rtchrd01.md.comcast.net comcast.net.
also, have you tried to use a different dns server and see what the
performance is?
if it's under around 100 ms, then it's not the DNS server. I would use
a different server if it's above 500 ms.
You will get performance problems with DNS server of your ISPs from
time to time.

Yang