Encoding and decoding Encapsulated DHCP options (RFC 2132)

Posted on Fri 19 October 2012 in Python

Vendor specific DHCP options may be provided encapsulated in DHCP option 43.
With this little script you can encode and decode vendor encapsulated option according to RFC 2132.

For example with this command you can tunnel options 66 (TFTP Server), 67 (TFTP Path), 132 (VLAN ID) and 133 (VLAN QOS):

$ ./dhcp-encapsulated-options.py encode 66 http://provisionig.example.com 67 settings.xml 132 33 133 6
Encoding part 1: http://provisionig.example.com
 Option ID: 66
 Option length: 30
 Encoded Option part: 42:1E:68:74:74:70:3A:2F:2F:70:72:6F:76:69:73:69:6F:6E:69:67:2E:65:78:61:6D:70:6C:65:2E:63:6F:6D

Encoding part 2: settings.xml
 Option ID: 67
 Option length: 12
 Encoded Option part: 43:0C:73:65:74:74:69:6E:67:73:2E:78:6D:6C

Encoding part 3: 33
 Option ID: 132
 Option length: 2
 Encoded Option part: 84:02:33:33

Encoding part 4: 6
 Option ID: 133
 Option length: 1
 Encoded Option part: 85:01:36

Full encoded options: 42:1E:68:74:74:70:3A:2F:2F:70:72:6F:76:69:73:69:6F:6E:69:67:2E:65:78:61:6D:70:6C:65:2E:63:6F:6D:43:0C:73:65:74:74:69:6E:67:73:2E:78:6D:6C:84:02:33:33:85:01:36

And then you can add the encoded options in you dhcpd config file:

host device.labo.local {  
    hardware ethernet 01:04:23:3b:d0:21;  
    fixed-address 172.16.18.30;  
    option vendor-encapsulated-options
    42:1E:68:74:74:70:3A:2F:2F:70:72:6F:76:69:73:69:6F:6E:69:67:2E:65:78:61:6D:70:6C:65:2E:63:6F:6D:43:0C:73:65:74:74:69:6E:67:73:2E:78:6D:6C:84:02:33:33:85:01:36;  
}

And viceversa you can decode an encapsulated option:

$ ./dhcp-encapsulated-options.py decode 42:1E:68:74:74:70:3A:2F:2F:70:72:6F:76:69:73:69:6F:6E:69:67:2E:65:78:61:6D:70:6C:65:2E:63:6F:6D:43:0C:73:65:74:74:69:6E:67:73:2E:78:6D:6C
Decoding part 1: 42:1E:68:74:74:70:3A:2F:2F:70:72:6F:76:69:73:69:6F:6E:69:67:2E:65:78:61:6D:70:6C:65:2E:63:6F:6D
 Option ID: 66
 Option lenght: 30
 Option value: "http://provisionig.example.com"

Decoding part 2: 43:0C:73:65:74:74:69:6E:67:73:2E:78:6D:6C
 Option ID: 67
 Option lenght: 12
 Option value: "settings.xml"

End of encoded options

decoding dhcp encapsulated options encoding python rfc2132