tcpdump csak ennyit látok, mikor csatlakozni szeretnék:
Ebből az abc.host.hu a mi szerverünk és a hablaty.fixip.t-online.hu az övéké :D
sudo tcpdump -v -i any host a.b.c.d
tcpdump: data link type LINUX_SLL2
tcpdump: listening on any, link-type LINUX_SLL2 (Linux cooked v2), snapshot length 262144 bytes
17:02:50.996393 enp5s0f3 Out IP (tos 0x10, ttl 64, id 55446, offset 0, flags [DF], proto TCP (6), length 60)
abc.host.hu.54770 > hablaty.fixip.t-online.hu.8822: Flags [S], cksum 0x9a55 (incorrect -> 0xd502), seq 1740129444, win 64240, options [mss 1460,sackOK,TS val 2576916359 ecr 0,nop,wscale 7], length 0
17:02:50.998977 enp5s0f3 In IP (tos 0x0, ttl 122, id 16068, offset 0, flags [DF], proto TCP (6), length 60)
hablaty.fixip.t-online.hu.8822 > abc.host.hu.54770: Flags [S.], cksum 0x2120 (correct), seq 1744668184, ack 1740129445, win 65535, options [mss 1380,nop,wscale 3,sackOK,TS val 3806912023 ecr 2576916359], length 0
17:02:50.999014 enp5s0f3 Out IP (tos 0x10, ttl 64, id 55447, offset 0, flags [DF], proto TCP (6), length 52)
abc.host.hu.54770 > hablaty.fixip.t-online.hu.8822: Flags [.], cksum 0x9a4d (incorrect -> 0x4d9f), ack 1, win 502, options [nop,nop,TS val 2576916362 ecr 3806912023], length 0
17:02:50.999398 enp5s0f3 Out IP (tos 0x10, ttl 64, id 55448, offset 0, flags [DF], proto TCP (6), length 92)
abc.host.hu.54770 > hablaty.fixip.t-online.hu.8822: Flags [P.], cksum 0x9a75 (incorrect -> 0xe89d), seq 1:41, ack 1, win 502, options [nop,nop,TS val 2576916362 ecr 3806912023], length 40
17:02:51.002076 enp5s0f3 In IP (tos 0x0, ttl 122, id 16069, offset 0, flags [DF], proto TCP (6), length 52)
hablaty.fixip.t-online.hu.8822 > abc.host.hu.54770: Flags [F.], cksum 0xcf90 (correct), seq 1, ack 1, win 32768, options [nop,nop,TS val 3806912026 ecr 2576916362], length 0
17:02:51.002076 enp5s0f3 In IP (tos 0x0, ttl 122, id 16070, offset 0, flags [DF], proto TCP (6), length 40)
hablaty.fixip.t-online.hu.8822 > abc.host.hu.54770: Flags [R.], cksum 0x82a3 (correct), seq 2, ack 41, win 0, length 0
^C
6 packets captured
7 packets received by filter
0 packets dropped by kernel