secdev
RFE: long DHCPv4 options (RFC 3396)
Brief description
Long DHCPv4 options longer than 255 bytes aren't supported out of the box. For example
raw(DHCP(options=[('captive-portal', 'a'*256)]))
fails with
error: While dissecting field 'options': ubyte format requires 0 <= number <= 255
but according to https://www.rfc-editor.org/rfc/rfc3396#section-1 it can be split and then it should be joined on the receiving side
when more than one option with a given type code appears in the DHCP packet, all such options should be concatenated together.
Wireshark started concatenating options according to that RFC a couple months ago: https://gitlab.com/wireshark/wireshark/-/merge_requests/18079
https://www.ietf.org/archive/id/draft-tojens-dhcp-option-concat-considerations-00.html was also mentioned there.
(It's possible to do all that manually. It's just something I noticed in the context of suboptions in https://github.com/NetworkConfiguration/dhcpcd/pull/404. It came up again when I took a look at https://github.com/secdev/scapy/pull/4638 and tried to stuff quite a few IP addresses into a reply :-))
Scapy version
7106b015379b621966f00667cf0bf3d4daec0262
Python version
Python 3.13.1
Operating system
Fedora 41
Additional environment information
No response
How to reproduce
raw(DHCP(options=[('captive-portal', 'a'*256)]))
and
DHCP(b'\x06\x02\x01\x02\x06\x02\x03\x04')
should be the same as
DHCP(b'\x06\x04\x01\x02\x03\x04')
Actual result
No response
Expected result
No response
Related resources
No response
