tcpdump:
[root@bespinwerks ~] # tcpdump -i eth0 port 80
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
12:23:39.478997 IP dw135-198-237-222.dhcpw.sest.example.com.3364 > bespinwerks.http: Flags [S], seq 388975608, win 65535, options [mss 1260,nop,wscale 1,nop,nop,sackOK], length 0
12:23:39.479043 IP bespinwerks.http > dw135-198-237-222.dhcpw.sest.example.com.3364: Flags [S.], seq 3273086762, ack 388975609, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 6], length 0
12:23:39.479982 IP dw135-198-237-222.dhcpw.sest.example.com.3364 > bespinwerks.http: Flags [.], ack 1, win 32768, length 0
12:23:39.480543 IP dw135-198-237-222.dhcpw.sest.example.com.3364 > bespinwerks.http: Flags [P.], seq 1:595, ack 1, win 32768, length 594
12:23:39.480564 IP bespinwerks.http > dw135-198-237-222.dhcpw.sest.example.com.3364: Flags [.], ack 595, win 110, length 0
12:23:39.542350 IP bespinwerks.http > dw135-198-237-222.dhcpw.sest.example.com.3364: Flags [.], seq 1:3781, ack 595, win 110, length 3780
12:23:39.543976 IP dw135-198-237-222.dhcpw.sest.example.com.3364 > bespinwerks.http: Flags [.], ack 2521, win 32768, length 0
12:23:39.544007 IP bespinwerks.http > dw135-198-237-222.dhcpw.sest.example.com.3364: Flags [.], seq 3781:7561, ack 595, win 110, length 3780
12:23:39.544884 IP dw135-198-237-222.dhcpw.sest.example.com.3364 > bespinwerks.http: Flags [.], ack 3781, win 32768, length 0
EDIT: Depois de reler sua pergunta, iftop pode ser uma opção melhor:
12.5Kb 25.0Kb 37.5Kb 50.0Kb 62.5Kb
+----------------------------+-----------------------------+-----------------------------+-----------------------------+-----------------------------
bespinwerks:ssh => dw135-198-237-222.dhcpw.sest.example.com:dj-ilm 1.48Kb 1.88Kb 2.08Kb
<= 160b 160b 177b
192.168.1.255:netbios-dgm => STATION:netbios-dgm 0b 0b 0b
<= 0b 194b 51b
192.168.1.255:17500 => rm-macbook:17500 0b 0b 0b
<= 0b 109b 57b
255.255.255.255:17500 => rm-macbook:17500 0b 0b 0b
<= 0b 109b 57b
255.255.255.255:17500 => GACDTL05RX7322:17500 0b 0b 0b
<= 0b 0b 116b
bespinwerks:41307 => bespin:domain 0b 0b 16b
<= 0b 0b 36b
bespinwerks:39407 => bespin:domain 0b 0b 15b
<= 0b 0b 21b
bespinwerks:44091 => bespin:domain 0b 0b 15b
<= 0b 0b 20b
bespinwerks:44738 => bespin:domain 0b 0b 15b
<= 0b 0b 19b
bespinwerks:59540 => bespin:domain 0b 0b 16b
<= 0b 0b 16b
bespinwerks:49364 => bespin:domain 0b 0b 15b
<= 0b 0b 15b
192.168.1.255:17500 => STATION:17500 0b 0b 0b
<= 0b 0b 29b