tcpdump

List the interfaces

sudo tcpdump -D

Capture All traffic

tcpdump -i eth0
tcpdump -i wlan0

To a File

tcpdump -i eth0 -w capture.pcap
tcpdump -i any -w capture.pcap -nnn 'ip and port 80'

# Set Timeout
timeout 6m tcpdump -i eth0 -w capture.pcap

Read a file (.pcap)

-nn: Disable port and protocol name lookup. -r : Read capture data from the named file. -v : Display detailed packet data.

tcpdump -r capture.pcap
tcpdump -r capture.pcap -nnn -v 'ip and (port 80 or port 443)'

Filter

# Filter by Source IP
tcpdump src 192.168.0.1

# Filter by Destination IP
tcpdump dst 192.168.0.1

# Filter by Port
tcpdump port 80

# Filter by Protocol
tcpdump icmp

# Protocol and Port
tcpdump tcp port 443

# Source and Destination
tcpdump src 192.168.0.1 and dst 192.168.0.2

tcpdump -i any -w capture.pcap -n 'ip and port 80'

Display in ASCII

# Dispaly in ASCII
tcpdump -A

# Display in Hexadecimal
tcpdump -X

Specific Number of Packets

tcpdump -c 100

Display

# Capture and Display IPv6 Traffic
tcpdump -6

# Capture and Display Traffic in Timestamp Format
tcpdump -tttt

SSH Connections

# -l: real-time
# -e: including ethernet headers
tcpdump -i eth0 'tcp port 22' -l -e

HTTP Request and Response

tcpdump -i eth0 -s 0 -A -n 'tcp dst port 80'

IP Range and Protocol

tcpdump -i eth0 'net 192.168.0.0/24 and (tcp port 22 or icmp)'

DNS Traffic

tcpdump -i eth0 'udp port 53' -nnvvv

FTP Traffic

tcpdump -i eth0 -s 0 'tcp port 21'

遭受 DDos 攻擊時自動擷取封包

interface=ens1
dumpdir=/home/user/automatic-tcp-dump/
while /bin/true; do
  pkt_old=`grep $interface: /proc/net/dev | cut -d :  -f2 | awk '{ print $2 }'`
  sleep 1
  pkt_new=`grep $interface: /proc/net/dev | cut -d :  -f2 | awk '{ print $2 }'`
  pkt=$(( $pkt_new - $pkt_old ))
  echo -ne "\r$pkt packets/s\033[0K"
  if [ $pkt -gt 30000 ]; then
    echo -e "\n`date` Under Attack. Capturing Packets..."
    sudo  tcpdump -n -i $interface -s0 -c 20000 -w $dumpdir/dump.`date +"%Y%m%d-%H%M%S"`.pcap
    echo "`date` Packets Captured."
    sleep 300  && pkill -HUP -f /usr/sbin/tcpdump
  else
    sleep 1
  fi
done