At 10:44 PM -0600 11/14/07, blake@xxxxxxxx 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. TCP Window Scaling, introduced about that time, and a bad router? At 5:57 PM +0200 7/24/06, Alexander Dalloz wrote: >Stefan Kuhlemann schrieb: > >> even more strange - today around 10:00 o'clock the sendmail started to >> work normal until 16:00 o'clock. (with nothing changed since sunday >> 22:00) >> >> My feelings tell me that the reason might be some strange 'ill-broken' >> firewall network stack or some weird netwok communication issues (like >> the 'fun' with the ECN-flag some years ago) >> I'm tomorrow 'on-site'...... >> >> Stefan > >Try following kernel parameter change > >sysctl -w net.ipv4.tcp_window_scaling=0 > >and see if that helps. TCP window scaling behaviour changed with kernel >2.6.17 to be again more aggressive[1]. Some other systems are just >broken in this regard. > >Alexander -- ____________________________________________________________________ TonyN.:' <mailto:tonynelson@xxxxxxxxxxxxxxxxx> ' <http://www.georgeanelson.com/>
