dhcpdump1

Usage

Overview

This command parses the output of tcpdump to display the dhcp-packets for easier checking and debugging.

Usage

tcpdump -lenx -s 1500 port bootps or port bootpc | dhcpdump

If you want to filter a specific Client Hardware Address (CHADDR), then you can specifiy it as a regular expressions:

tcpdump -lenx -s 1500 port bootps or port bootpc | dhcpdump -h ^00:c0:4f

This will display only the packets with Client Hardware Addresses which start with 00:c0:4f.

Output

  TIME: 15:45:02.084272
    IP: 0.0.0.0.68 (0:c0:4f:82:ac:7f) > 255.255.255.255.67 (ff:ff:ff:ff:ff:ff)
    OP: 1 (BOOTPREQUEST)
 HTYPE: 1 (Ethernet)
  HLEN: 6
  HOPS: 0
   XID: 28f61b03
  SECS: 0
 FLAGS: 0
CIADDR: 0.0.0.0
YIADDR: 0.0.0.0
SIADDR: 0.0.0.0
GIADDR: 0.0.0.0
CHADDR: 00:c0:4f:82:ac:7f:00:00:00:00:00:00:00:00:00:00
 SNAME: .
 FNAME: .
OPTION:  53 (  1) DHCP message type         3 (DHCPREQUEST)
OPTION:  54 (  4) Server identifier         130.139.64.101
OPTION:  50 (  4) Request IP address        130.139.64.143
OPTION:  55 (  7) Parameter Request List      1 (Subnet mask)
                                              3 (Routers)
                                             58 (T1)
                                             59 (T2)

At the option field, the first field is the value of the option, the second one (between brackets) is the length of the option-datafield, the third field is the name of the option, the fourth field is the data of the option.

Return values

Always 0.

Notes

Privileged access is often needed for tcpdump.

Thanks to

Ralph Droms and Ted Lemons "The DHCP Handbook", ISBN 1-57870-137-6.

Peter Apian-Bennewitz <[email protected]> for his Client Hardware Address filtering