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Sécurité, Système, Réseau

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Tcpdump is sometimes the only way to capture and analyse packets. Here is a little cheatsheets. <note> This cheatsheets will be WIP for a while. Stay tuned!! </note>

Simple packet capture with terminal output

tcpdump -nvv

Packet capture with output in a file (pcap format)

tcpdump  -nvv  -s 0 -w /tmp/srv.pcap -s 0


w <file> Output packet in a file instead of the standard output 
s <size> (snaplen)Maximal payload data size to output in the file

Read pcap file in a shell using tcpdump

tcpdump -vvvvr test.pcap

<note> The -r switch must be followed by the pcap file name</note>

Capture filter by net / host / protocol

tcpdump -nvvv net mask 
tcpdump -nvvv src
tcpdump -nvvv host
tcpdump -nvv  dst port 80 
tcpdump -nvv  port 80

All theses options can be mix with and or or keywords ….

Capture everything except certain protocol

To capture everything except SSH (port 22)

tcpdump -nv not port 22

IPv6 packet capture

tcpdump  -nvvv ip6 host 2001:41d0:2:5006::1

Here, we keep only IPv6 packet from or to 2001:41d0:2:5006::1.

Useful Filters

eth.addr / eth.src / eth.dst ==> filter on Mac Address
ip.addr / ip.src / ip.dst    ==> Filter by IP addresse
tcp.port / tcp.dstport / tcp.srcport ==> TCP filter
tcp.window_size ==> useful for  //zero windows// search
vlan.id ==> filter on vlan id


tcpdump.txt · Dernière modification: 2018/02/18 16:01 (modification externe)