Capture between two hosts

BPF filter: traffic between exactly two endpoints

tcpdump -i eth0 'host 10.0.0.1 and host 10.0.0.2'
tool
tcpdump18 commands
tags
tcpdumpnetworklinux

More tcpdump commands

  • Verbose with packet content
    tcpdump -i eth0 -vvv -A -s 0 port 5432

    Full verbose output with ASCII packet content for PostgreSQL

  • Limit capture count
    tcpdump -i eth0 -c 100 -w capture.pcap

    Stop after capturing 100 packets

  • Capture only TCP SYN packets
    tcpdump -nn 'tcp[tcpflags] & (tcp-syn|tcp-ack) == tcp-syn'

    Catch only connection-initiating SYNs (no SYN-ACK) to spot scans or backlog floods

  • Capture SYN and FIN flags
    tcpdump -nn 'tcp[tcpflags] & (tcp-syn|tcp-fin) != 0'

    Show only connection open/close packets to trace short-lived churning sessions

  • Host filter excluding SSH noise
    tcpdump -nn -i any host <ip> and not port 22

    Watch traffic to/from a host while dropping your own SSH session noise

all 18 tcpdump commands