Speaking of MTU mismatches, don't forget that if you're using a PPPoE DSL line to adjust your MTU. Geoff Sent from my BlackBerry wireless handheld. -----Original Message----- From: "Ross S. W. Walker" <rwalker at medallion.com> Date: Mon, 10 Sep 2007 16:35:59 To:"CentOS mailing list" <centos at centos.org> Subject: RE: [CentOS] Performance of CentOS as a NAT gateway Bart Schaefer wrote: > > On 9/9/07, Barry Brimer <lists at brimer.org> wrote: > > Maybe it is time for some kernel networking tuning. > > After doing a bit of research: > > http://www.acc.umu.se/~maswan/linux-netperf.txt > http://wwwx.cs.unc.edu/~sparkst/howto/network_tuning.php > http://proj.sunet.se/E2E/tcptune.html > http://www.linuxguruz.com/iptables/howto/2.4routing-13.html > http://www-didc.lbl.gov/TCP-tuning/linux.html > > I ended up with this: > > net.core.rmem_default = 873800 > net.core.wmem_default = 655360 > net.core.rmem_max = 8738000 > net.core.wmem_max = 6553600 > net.ipv4.tcp_rmem = 8192 873800 8738000 > net.ipv4.tcp_wmem = 4096 655360 6553600 > net.ipv4.tcp_mem = 195584 873800 8738000 > > (The first number in tcp_mem is the original default.) > > Plus: > > ifconfig eth0 txqueuelen 1000 > ifconfig eth1 txqueuelen 1000 > > Unfortunately so far this doesn't seem to have made any difference. > We've had a load peak going since early this morning and the traffic > looks exactly like it did last week. The only way your going to know for absolute sure where the bottleneck exists is to do a wireshark/tcpdump trace simultaneously on both sides. Then with that information you will know where the bottleneck is and armed with that you can start exploring why there is a bottleneck there. Off the top of my head, there could be a IP MTU mismatch somewhere and with ICMP disabled this would cause a blackhole for some full packet traffic. -Ross ______________________________________________________________________ This e-mail, and any attachments thereto, is intended only for use by the addressee(s) named herein and may contain legally privileged and/or confidential information. If you are not the intended recipient of this e-mail, you are hereby notified that any dissemination, distribution or copying of this e-mail, and any attachments thereto, is strictly prohibited. If you have received this e-mail in error, please immediately notify the sender and permanently delete the original and any copy or printout thereof. _______________________________________________ CentOS mailing list CentOS at centos.org http://lists.centos.org/mailman/listinfo/centos