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 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 ? 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? > 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
