Hi,

My web server is currently under a DDOS attack I believe, the messages log is full of these kind of messages:

May 13 15:51:19 kernel: nf_conntrack: table full, dropping packet.
May 13 15:51:19 last message repeated 9 times
May 13 15:51:24 kernel: __ratelimit: 78 callbacks suppressed
May 13 15:51:24 kernel: nf_conntrack: table full, dropping packet.
May 13 15:52:06 kernel: possible SYN flooding on port 80. Sending cookies.

and a netstat has a huge amount of the following:

tcp 0 0 my.host.com:http bb176da0.virtua.com.br:4998 SYN_RECV
tcp 0 0 my.host.com:http 187.0.43.109:2694 SYN_RECV
tcp 0 0 my.host.com:http 109.229.4.145:1722 SYN_RECV
tcp 0 0 my.host.com:http 189-84-163-244.sodobr:63267 SYN_RECV
tcp 0 0 my.host.com:http bd66839d.virtua.com.br:3469 SYN_RECV
tcp 0 0 my.host.com:http 69.101.56.190.dsl.int:52552 SYN_RECV
tcp 0 0 my.host.com:http pc-62-230-47-190.cm.vt:2262 SYN_RECV
tcp 0 0 my.host.com:http 189-84-163-244.sodobr:63418 SYN_RECV
tcp 0 0 my.host.com:http pc-62-230-47-190.cm.vt:1741 SYN_RECV
tcp 0 0 my.host.com:http zaq3d739320.zaq.ne.jp:2141 SYN_RECV
tcp 0 0 my.host.com:http netacc-gpn-4-80-73.po:52676 SYN_RECV

tcpdump shows:

7:11:08.564510 IP 187-4-1xx-4.xxx.ipd.brasiltelecom.net.br.54821 > my.host.com.http: S 999692166:999692166(0) win 65535
17:11:08.566347 IP 114-44-171-67.dynamic.hinet.net.1129 > my.host.com.http: S 605369055:605369055(0) win 65535
17:11:08.570210 IP 200-101-13-130.pvoce300.ipd.brasiltelecom.net.br.5590 > my.host.com.http: S 2813379182:2813379182(0) win 16384
17:11:08.571290 IP dsl-189-143-30-99-dyn.prod-infinitum.com.mx.1615 > my.host.com.http: S 281542700:281542700(0) win 65535
17:11:08.583847 IP dsl-189-143-30-99-dyn.prod-infinitum.com.mx.1617 > my.host.com.http: S 499413892:499413892(0) win 65535
17:11:08.588680 IP 170.51.229.112.2569 > my.host.com.http: S 2195084898:2195084898(0) win 65535
17:11:08.588773 IP gw2-1.211.ru.3180 > my.host.com.http: F 2315901786:2315901786(0) ack 2620913033 win 64240
17:11:08.590656 IP 200-101-13-130.pvoce300.ipd.brasiltelecom.net.br.5614 > my.host.com.http: S 2813715032:2813715032(0) win 16384
17:11:08.591212 IP 203.82.82.54.15848 > my.host.com.http: S 4070423507:4070423507(0) win 16384
17:11:08.591254 IP 203.82.82.54.2545 > my.host.com.http: S 1790910784:1790910784(0) win 16384
17:11:08.591289 IP 203.82.82.54.28306 > my.host.com.http: S 578615626:578615626(0) win 16384
17:11:08.591591 IP gw2-1.211.ru.3191 > my.host.com.http: F 2316435991:2316435991(0) ack 2634205972 win 64240
17:11:08.591790 IP 200-101-13-130.pvoce300.ipd.brasiltelecom.net.br.5593 > my.host.com.http: S 2813659017:2813659017(0) win 16384
17:11:08.593691 IP gw2-1.211.ru.3203 > my.host.com.http: F 2316834420:2316834420(0) ack 2629074987 win 64240

I'm not sure what I can do to limit/mitigate this, currently no webpages are being served, any help gratefully appreciated.