Linux 2.4.20 以后內(nèi)核的ECN問題

yaako

問題描述：
在安裝了2.4.20以后內(nèi)核的Linux，在連接如意通郵箱的smtp端口的時候，出現(xiàn)timeout的問題。在2.4.18內(nèi)核和其他操作系統(tǒng)上沒有這個問題。

Dec 14 17:10:58 mail1 postfix/smtp[5286]: D624020108F: to=, relay=none, delay=33, status=deferred (connect to smtp.ruyi.com[211.97.168.172]: Connection timed out)

cz:~# telnet smtp.ruyi.com 23
Trying 211.97.168.172...
telnet: Unable to connect to remote host: Connection timed out


問題原因：
在2.4.20以后的內(nèi)核里面，增加了一個 ECN 功能：
TCP Explicit Congestion Notification support
CONFIG_INET_ECN
Explicit Congestion Notification (ECN) allows routers to notify
clients about network congestion, resulting in fewer dropped packets
and increased network performance. This option adds ECN support to
the Linux kernel, as well as a sysctl (/proc/sys/net/ipv4/tcp_ecn)
which allows ECN support to be disabled at runtime.

Note that, on the Internet, there are many broken firewalls which
refuse connections from ECN-enabled machines, and it may be a while
before these firewalls are fixed. Until then, to access a site
behind such a firewall (some of which are major sites, at the time
of this writing) you will have to disable this option, either by
saying N now or by using the sysctl.

這個功能在和有些老的防火墻通訊的時候，會產(chǎn)生問題。


解決辦法：
1)
echo "0" >; /proc/sys/net/ipv4/tcp_ecn
2)
sysctl -w net.ipv4.tcp_ecn=0
3)編輯 /etc/sysctl.conf
net.ipv4.tcp_ecn=0
4)編譯內(nèi)核的時候，去掉 ECN 選項

相關(guān)鏈接：
http://lists.debian.org/debian-user/2003/debian-user-200304/msg02277.html
http://www.rfc-editor.org/rfc/rfc3168.txt

好好先生

是你自己總結(jié)的嗎?