-----Original Message----- From: netfilter-admin@xxxxxxxxxxxxxxxxxxx [mailto:netfilter-admin@xxxxxxxxxxxxxxxxxxx] On Behalf Of Pawel Pilat Sent: Tuesday, June 22, 2004 1:34 AM To: netfilter@xxxxxxxxxxxxxxxxxxx Subject: ECN problem? > -----Original Message----- > From: netfilter-admin@xxxxxxxxxxxxxxxxxxx > [mailto:netfilter-admin@xxxxxxxxxxxxxxxxxxx] On Behalf Of Pawel Pilat > Sent: Monday, June 21, 2004 1:59 AM > To: netfilter@xxxxxxxxxxxxxxxxxxx > Subject: ECN problem? > > Hello everyone, > it's my first post on this list so plese understanding ... > I think that i have problem with ECN , this is my > situation: > > IN--->R--->ISP > > where: > IN - my internal net > R - my linux router (2.4.25, ipt-1.2.9) ISP - my ISP > > so when i trying to connect from internal net to Internet i > expirencing very slow transfers (500 - 700 > bps) but from router everything is ok (transfer rate 50 - 60 kbps) > when i used tcpdump on external interfece on router i realized that my > ISP sends to me in every TCP packet TOS field set to 0x03 (ECN-CT > + ECN-CE) i think that > is the problem > > i tried using: > > iptables -t mangle -A PREROUTING -i $EXTIF -j TOS --set-tos 0x00 but > without any result > > my question is: > 1.it is possible to set linux box to ignore this fields in packets? > 2. there is another way to solve the problem? > > thank for advices > best regards > > POSTER PL > > > > > __________________________________ > Do you Yahoo!? > Take Yahoo! Mail with you! Get it on your mobile phone. > http://mobile.yahoo.com/maildemo > > Most ISP have ECN enabled on their routers today, so this is not > unusual. If the packets you are receiving from your ISP have > Cx=1 (0x03) then this means > it is indeed experiencing congestion, and if your box is also ECN > enabled, then the congestion windows on both devices are probably > being cut in half. > This needs to be confirmed before you do anything. > To confirm this, I would > suggest that you first check and see if you box is ECN enabled by > checking your kernel config for CONFIG_INET_ECN=y. If it is, check the > two high-order bits of bite 13 of the suspect TCP packet headers to > see if the congestion windows are being cut. If so, then this is > probably a correct assumption on your part. If so, the easiest > solution would be to disable ECN on your box. > You would need to recompile the kernel to that of course. However, it > would seem as though ECN is only doing its job and you may want to > explore that avenue. > > > > ######################################################## > This message has been scanned for viruses and dangerous content by > MailScanner, and is believed to be clean. > > postmaster@xxxxxxxxxxxxxxx > MailScanner at bandwidthco.com is for your absolute protection. > ######################################################## Thnx Mark my box isn't ECN enabled for sure to be completly sure I issued: echo "0" > /proc/sys/net/ipv4/tcp_ecn but this kind of behavior is strange for me or maybe my understanding of ECN isn't enough when i connect directly to ISP link non routing host everything seems to be OK (transfers rates) but EVERY returning packet in TCP sequence has TOS set to 0x03. it seems that every packet in connection from my hosts makes ISP router congested - I don't think so - both interfaces of router are ethernet 100 i set MTU on external if to 1460 also tried with lower values and iptables ..... -j TCPMSS ... also without results so my theories : 1. ISP sets TOS field to 0x03 on purpose on EVERY TCP packet directed to my host, but why? NAT preventing or sth ? 2. bad ECN implementation ? it is possible but affects only those people who share their connection. at this point i must say that i dont want to make war with my ISP - i have 3 PC and i want them all to be connected (network protocols and features test purposes) generally it's not forbidden by ISP i will examine those bytes just in case it's getting much interesting with each packet i captured ... :) i will be grateful for any advices best regards POSTER PL This is indeed an interesting problem, and it sounds like you have been investigating it for a while. You mentioned that the TOS target was not effective. Why not try the -m tos match, and send the 0x03 TOS packets to the ECN target for processing? This target allows you to selectively work around known ECN blackholes: -j ECN --ecn-tcp-remove. Apply this in the mangle table with -p tcp. Just out of curiosity, what type of NICs are in your box? ######################################################## This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. postmaster@xxxxxxxxxxxxxxx MailScanner at bandwidthco.com is for your absolute protection. ########################################################
