On Wed, May 28, 2025 at 5:52 AM ying chen <yc1082463@xxxxxxxxx> wrote: > > Hello all, > > I encountered an "nf_conntrack: table full" warning on Linux 6.15-rc4. > Running cat /proc/net/nf_conntrack showed a large number of > connections in the SYN_SENT state. > As is well known, if we attempt to connect to a non-existent port, the > system will respond with an RST and then delete the conntrack entry. > However, when we frequently connect to non-existent ports, the > conntrack entries are not deleted, eventually causing the nf_conntrack > table to fill up. > > The problem can be reproduced using the following command: > hping3 -S -V -p 9007 --flood xx.x.xxx.xxx > > ~$ cat /proc/net/nf_conntrack > ipv4 2 tcp 6 112 SYN_SENT src=xx.x.xxx.xxx dst=xx.xx.xx.xx > sport=2642 dport=9007 src=xx.xx.xx.xx dst=xx.x.xxx.xxx sport=9007 > dport=2642 mark=0 zone=0 use=2 > ipv4 2 tcp 6 111 SYN_SENT src=xx.x.xxx.xxx dst=xx.xx.xx.xx > sport=11510 dport=9007 src=xx.xx.xx.xx dst=xx.x.xxx.xxx sport=9007 > dport=11510 mark=0 zone=0 use=2 > ipv4 2 tcp 6 111 SYN_SENT src=xx.x.xxx.xxx dst=xx.xx.xx.xx > sport=28611 dport=9007 src=xx.xx.xx.xx dst=xx.x.xxx.xxx sport=9007 > dport=28611 mark=0 zone=0 use=2 > ipv4 2 tcp 6 112 SYN_SENT src=xx.x.xxx.xxx dst=xx.xx.xx.xx > sport=62849 dport=9007 src=xx.xx.xx.xx dst=xx.x.xxx.xxx sport=9007 > dport=62849 mark=0 zone=0 use=2 > ipv4 2 tcp 6 111 SYN_SENT src=xx.x.xxx.xxx dst=xx.xx.xx.xx > sport=3410 dport=9007 src=xx.xx.xx.xx dst=xx.x.xxx.xxx sport=9007 > dport=3410 mark=0 zone=0 use=2 > ipv4 2 tcp 6 111 SYN_SENT src=xx.x.xxx.xxx dst=xx.xx.xx.xx > sport=44185 dport=9007 [UNREPLIED] src=xx.xx.xx.xx dst=xx.x.xxx.xxx > sport=9007 dport=44185 mark=0 zone=0 use=2 > ipv4 2 tcp 6 111 SYN_SENT src=xx.x.xxx.xxx dst=xx.xx.xx.xx > sport=51099 dport=9007 src=xx.xx.xx.xx dst=xx.x.xxx.xxx sport=9007 > dport=51099 mark=0 zone=0 use=2 > ipv4 2 tcp 6 112 SYN_SENT src=xx.x.xxx.xxx dst=xx.xx.xx.xx > sport=23609 dport=9007 src=xx.xx.xx.xx dst=xx.x.xxx.xxx sport=9007 > dport=23609 mark=0 zone=0 use=2 The default timeout is 120 seconds. /proc/sys/net/netfilter/nf_conntrack_tcp_timeout_syn_sent
