Re: my smtp server is very slow to accept connections today

On 4/6/2006 5:28 PM, Les Mikesell wrote:
On Thu, 2006-04-06 at 18:43, Don Russell wrote:

I've been using this address range for years, and never noticed any problems. Just recently I notice it takes a long time to get a response when connecting from 10.10.10.253 to 10.10.10.250 using ssh.

Telnet 10.10.10.250 25 (smtp) from 10.10.10.253 takes a very long time (a minute or more sometimes) to get a response... My Thunderbird mail clients time out trying to send mail to 10.10.10.250 when last week they had no problems at all.

I also tried telnet from "outside" and it takes a while for a response too... it used to be much quicker...

If you're curious... try telnet drussell dnsalias com 25 (with dots in all the right places) and see how long it takes for you to get a response...

Maybe you're right... maybe my ISP was providing the necessary lookups and now that's broken on their end...

I got a connection immediately - the response close to a minute
later. Do you perhaps have 2 nameservers listed in your
resolv.conf with the 1 one not responding?

Yes... that's the symptom.. connects, then waits ...

login as: don
don@xxxxxxxxxxxx's password:
Last login: Thu Apr 6 14:59:28 2006 from 10.10.10.253
[don@boris ~]$ cat < /etc/resolv.conf
; generated by /sbin/dhclient-script
search san.rr.com
nameserver 66.75.164.90
nameserver 66.75.164.89
[don@boris ~]$


I just tried two digs which replied right away..
dig @66.75.164.89 ibm.com ---> replied in 27 mSec
dig @66.75.164.90 ibm.com ---> replied in 26 mSec

That tells me the two dns servers defined there are responsive...

and looking back through my Cisco router firewall logs, I see tons of udp 66.75.164.90 port 1078 denials... before and after my digs... :-(



The other thing that happens during a connection is that
sendmail will try an IDENT query on the socket to identify
the user if the other end is unix-like. Normally you get
a quick ICMP response if nothing is listening on port 113
at the other end, but if you have a firewall configured to
silently drop packets you'll have to wait for the timeout,
probably 30 seconds.


And does the ssh server do that sort of thing too?

I don't think it tries IDENT, but it will do the reverse
dns to log the hostname from the inbound connection.


hmmm, with the same symptom... quick to connect, slow to reply...

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