tcpdump

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some common tcpdump usages

some common tcpdump cli

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# Reading / Writing Captures to a File
tcpdump port 80 -w capture_file

# read PCAP files by using the -r switch
tcpdump -r capture_file

# port 2000 of any nic
tcpdump -i any port 2000 –nn

# Everything on an interface
tcpdump -i eth0

# Find Traffic by IP
# One of the most common queries, using host, you can see traffic that’s going to or from 1.1.1.1.
tcpdump host 1.1.1.1

# Filtering by Source and/or Destination
tcpdump src 1.1.1.1
tcpdump dst 1.0.0.1

# Finding Packets by Network
tcpdump net 1.2.3.0/24

# Get Packet Contents with Hex Output
tcpdump -c 1 -X icmp

# Show Traffic Related to a Specific Port
tcpdump port 3389
tcpdump src port 1025

# Show Traffic of One Protocol
tcpdump icmp

# Show only IP6 Traffic
tcpdump ip6

# Find Traffic Using Port Ranges
tcpdump portrange 21-23

# Find Traffic Based on Packet Size
tcpdump less 32
tcpdump greater 64
tcpdump <= 128

# ==================================

# It’s All About the Combinations

# ========= AND =========
# and or &&

# ========= OR =========
# or or ||

# ========= EXCEPT =========
# not or !

# From specific IP and destined for a specific Port
# Let’s find all traffic from 10.5.2.3 going to any host on port 3389.
tcpdump -nnvvS src 10.5.2.3 and dst port 3389

# From One Network to Another
# Let’s look for all traffic coming from 192.168.x.x and going to the 10.x or 172.16.x.x networks
# and we’re showing hex output with no hostname resolution and one level of extra verbosity.
tcpdump -nvX src net 192.168.0.0/16 and dst net 10.0.0.0/8 or 172.16.0.0/16

# Non ICMP Traffic Going to a Specific IP
# This will show us all traffic going to 192.168.0.2 that is not ICMP.
tcpdump dst 192.168.0.2 && src ! icmp
tcpdump dst 192.168.0.2 and src not icmp

# catch packages from(to) eth0 or eth1
tcpdump -vi eth0 || eth1 -w tmp.pcap

Advanced

match MAC address & VLAN

  • ether host - capture packets sent from and to
  • ether src - capture packets sent from
  • ether dst - capture packets sent to
  • vlan - match

match protocol

Match protocols in L3 header:

  • ip proto - PROTO: icmp, icmp6, igmp, igrp, pim, ah, esp, vrrp, udp, or tcp

Follow are abbreviations:

  • icmp = proto icmp
  • tcp = proto tcp
  • udp = proto udp

Match protocols in L2 header:

  • ether proto - PROTO: ip, ip6, arp, rarp, atalk, aarp, decnet, sca, lat, mopdl, moprc, iso, stp, ipx, or netbeui

Follow are abbreviations:

  • ip = ether proto ip
  • ip6 = ether proto ip6
  • arp = ether proto arp
  • rarp = ether proto rarp
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tcpdump -i eth0 arp
tcpdump -i eth0 icmp