tcpdump -pnvvvvvi re0 host 172.16.3.23 and port 23
tcpdump: listening on re0, link-type EN10MB (Ethernet), capture size 96 bytes
1	13:47:02.177817 IP (tos 0x0, ttl 64, id 38048, offset 0, flags [DF], proto TCP (6), length 60, bad cksum 0 (->507e)!)
    213.108.209.9.38137 > 172.16.3.23.23: Flags [S], cksum 0x55cc (incorrect -> 0x29d3), seq 764150625, win 65535, options [mss 1460,nop,wscale 3,sackOK,TS val 2271509297 ecr 0], length 0
2	13:47:02.181163 IP (tos 0x0, ttl 61, id 60828, offset 0, flags [none], proto TCP (6), length 60)
    172.16.3.23.23 > 213.108.209.9.38137: Flags [S.], cksum 0x2e45 (correct), seq 4022548164, ack 764150626, win 8192, options [mss 1460,nop,wscale 0,nop,nop,TS val 178166 ecr 2271509297], length 0
3	13:47:02.181191 IP (tos 0x0, ttl 64, id 38050, offset 0, flags [DF], proto TCP (6), length 52, bad cksum 0 (->5084)!)
    213.108.209.9.38137 > 172.16.3.23.23: Flags [.], cksum 0x55c4 (incorrect -> 0x597f), seq 1, ack 1, win 8326, options [nop,nop,TS val 2271509301 ecr 178166], length 0
4	13:47:02.190146 IP (tos 0x0, ttl 61, id 60830, offset 0, flags [none], proto TCP (6), length 55)
    172.16.3.23.23 > 213.108.209.9.38137: Flags [P.], cksum 0x41fc (correct), seq 1:4, ack 1, win 8192, options [nop,nop,TS val 178166 ecr 2271509301], length 3 [telnet DO TERMINAL TYPE]
5	13:47:02.293308 IP (tos 0x0, ttl 64, id 38066, offset 0, flags [DF], proto TCP (6), length 52, bad cksum 0 (->5074)!)
    213.108.209.9.38137 > 172.16.3.23.23: Flags [.], cksum 0x55c4 (incorrect -> 0x5910), seq 1, ack 4, win 8326, options [nop,nop,TS val 2271509409 ecr 178166], length 0