= 2012-05-29 =

== hadoop.nchc.org.tw ==

 * 錯誤訊息：nf_conntrack: table full, dropping packet.
{{{
~$ dmesg | grep 
[1146203.787306] nf_conntrack: table full, dropping packet.
[1146203.787880] nf_conntrack: table full, dropping packet.
[1146203.790825] nf_conntrack: table full, dropping packet.
[1146203.791307] nf_conntrack: table full, dropping packet.
[1146203.791503] nf_conntrack: table full, dropping packet.
[1146203.791818] nf_conntrack: table full, dropping packet.
[1146203.791987] nf_conntrack: table full, dropping packet.
[1146208.785365] nf_conntrack: table full, dropping packet.
[1146208.785635] nf_conntrack: table full, dropping packet.
[1146208.786510] nf_conntrack: table full, dropping packet.
}}}
 * [參考] [http://www.pc-freak.net/blog/resolving-nf_conntrack-table-full-dropping-packet-flood-message-in-dmesg-linux-kernel-log/ Resolving “nf_conntrack: table full, dropping packet.” flood message in dmesg Linux kernel log]
 * [原因] 阻斷攻擊（DDoS）
 * [解法] 修改 /etc/sysctl.conf 增加 ip_conntrack_max 、降低 ip_conntrack_generic_timeout
{{{
net.ipv4.netfilter.ip_conntrack_max=16384
net.ipv4.conf.default.arp_ignore=1
net.ipv4.conf.all.arp_ignore=1
net.ipv4.ip_forward=1
net.ipv4.icmp_echo_ignore_broadcasts=1
net.ipv4.icmp_ignore_bogus_error_responses=1
net.ipv4.tcp_ecn=1
net.ipv4.tcp_fin_timeout=30
net.ipv4.tcp_keepalive_time=120
net.ipv4.tcp_syncookies=1
net.ipv4.tcp_timestamps=0
net.ipv4.netfilter.ip_conntrack_tcp_timeout_established=300
net.ipv4.netfilter.ip_conntrack_udp_timeout=60
net.ipv4.netfilter.ip_conntrack_udp_timeout_stream=180
net.ipv4.netfilter.ip_conntrack_generic_timeout = 120
net.ipv4.netfilter.ip_conntrack_tcp_timeout_established = 54000
}}}