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Tcpdump

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Important flags

  • -n to disable (per-packet blocking) DNS lookups
  • -s snaplen to capture more than the default snapshot length. 0 for no limit.
  • -e to show link-layer information

Recipes

  • Capture all arp: tcpdump arp
  • Capture packets to or from a MAC address M: tcpdump ether host M

Gotchas

  • tcpdump will not function on a DPDK interface once a DPDK application has bound the interface
  • A filter matching L4 fields (including TCP/UDP port) will not match any fragments save the first. Watch for [+] to indicate more fragments.