my smtp server is very slow to accept connections today

[Paul Howarth]

Don Russell wrote:
> On 4/4/2006 4:29 AM, Paul Howarth wrote:
>> Don Russell wrote:
>>> I'm using FC5 and have the "nightly yum update" turned on.
>>> My FC5 box runs a mail server.
>>> Yesterday, there were no problems.
>>> Today, I can't send mail from PCs on the network... the Thunderbird 
> client
>>> says "Connected to 10...." and eventuaally times out.
>>>> From external machines I can telnet to port 25 and it takes anywhere 
> from
>>> 40-80 seconds to get a reply from the server.
>>> If I'm on the same machine as the server, the connection is immediate.
> That tells me it is not smtp that's slow, but something relating to
> external connections.
>>> I have not changed any configurations... but with the nightly updates,
> what could account for introducing such a delay?
>>> I'm thinking somethin like it's trying to a reverse dns look up to
> check
>>> the address connecting, and that's taking a long time?
>>> Any ideas/suggestions?
>> Check that your nsswitch.conf has an appropriate hosts entry.
> 
> hmmm, I don't know what's "appropriate". :-(
> The nsswitch.conf file looks pretty generic... the "hosts" line says:
> hosts: files dns

That looks OK.

> Guessing, I changed that to
> hosts: files dns [NOTFOUND=return]
> 
> then "service network restart"
> but that had no effect...
> 
> hmmm, do I need to have my PCs listed in /etc/hosts ?

No. Sendmail needs to look up MX records, which it can't get from a 
hosts file anyway.

> If so, that means something changed because this was all working fine the
> other day... could a "nightly yum" have wiped out my /etc/hosts file?

Which new packages were installed on the night in question? (check 
/var/log/yum.log)

>> Check that /etc/resolv.conf points to nameservers that are working.
>>
>> Try using "dig" to check them out, e.g.
>>
>> $ dig @first.name.server -x 212.56.100.58
>>
>> See how long the lookups take.
> 
> 
> I tried several times with the two dns addresses in /etc/resolv.conf and
>   the longest query time was 180mSec, the shortest was 25mSec.
> 
> However, I also tried dig @dns-server - x 10.10.10.13
> (the 10. address is my PC that tries to connect to my mail server at
> 10.10.10.250)
> 
> That timed out after 15 seconds.... expected, but far short of the delay I
> see when I "telnet 10.10.10.250 25" from 10.10.10.13

Doesn't really sound like a DNS issue then.

Paul.