Odd Network Problem with FC5+

Albert Graham agraham at g-b.net
Fri Nov 16 01:31:02 UTC 2007


I thought this was one of your servers and you had access to it ?

My guess now is the server is overloaded most probably it has a 
completely overloaded mailq and is probably swapping like made, as the 
same problems appear on their web server (which is the same host).

You have to wait until the Admin wakes up :(


Blake Hudson wrote:
> Thanks for the feedback, unfortunately I don't control
> mail.jococourthouse.com. I'm just trying to get my users' e-mail there.
> I'm glad (i guess) to see RHEL is also affected. I thought this may be
> limited to Fedora, but it looks like probably a larger compatibility
> issue with whatever jococourthouse.com is doing on their end. Just wish
> I knew what it was and how to work around it.
> I initially suspected an ident/rdns issue too, but I don't think it is.
> As the firewall settings on all boxes are similar (allow all ports out,
> block all but used ports in) and wireshark didn't show anything but the
> smtp traffic coming from the remote. Turning iptables off had no affect,
> if it matters.
> I'm still thinking this is something more fundamental to IP/TCP.
> Unfortunately, this is a bit out of my area of expertise. Still hoping
> to get some input from an IP guru. Luckily, this issue seems to be
> easily repeatable.
> -Blake
> Albert Graham wrote:
>> Blake,
>> Is there some feature on your firewall that does some "intelligent"
>> content filtering on port 23 ? which is skipped for your intranet ?,
>> if so disable that feature and re-test.
>> (I assume the machine is not under any load and the mail queue is
>> empty - mailq)
>> I tried to connect from FC5, FC6 and RHEL 3 with the same results as
>> you, and from 3 countries so I'm pretty sure its a local problem and
>> not specific FC5 in anyway.
>> Al.
>> ps. I have a mail cluster sending 1m+ mails per day without any
>> problems using FC5.
>> blake at ispn.net wrote:
>>> I seem to be having trouble sending mail from an FC5 server to
>>> mail.jococourthouse.com.
>>> The problem manifests itself as extreme slowness, which eventually leads
>>> to a timeout before I can even receive a full welcome prompt from the
>>> remote side.
>>> I have tested on ~ 10 boxes (different hardware) around the US ranging
>>> from FC5 through FC8 and NONE can telnet to this mx while RH, FC3 RH4,
>>> windows, and cisco gear on the same networks can ALL telnet without a
>>> problem.
>>> wireshark on the FC5 boxes show that the TCP handshake occurs as normal,
>>> however from then on all I receive from the remote side are 60 byte
>>> frames
>>> labeled 'TCP segment of a reassembled PDU' until I eventually receive an
>>> RST from the remote. - A capture on the working boxes looks normal.
>>> I suspect the problem is related to an IP/TCP change in the kernel or
>>> FC5+, however I have no idea what change could have occurred. Any
>>> insight
>>> or recommendations for resolving this problem would be appreciated.
>>> Thanks,
>>> -Blake

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