Mikrotik DHCP option

RouterOS General
1

Hi,

I need to add a specific DHCP option to my DHCP server (On RouterOS). I need to add this (linux example):

option root-path "10.0.1.4:/var/tmp/rootfs";

I’ve done this:

/ip dhcp-server option
add code=17 name=root-path value="'10.0.1.4:/var/tmp/rootfs'"

and added this dhcp-option=root-path to my network configuration.

Tried to capture traffic on the same network using wireshark but this option 17 is not recorded in wireshark trace. All other DHCP parameters are decoded by wireshark (they are in trace).
Not sure how can make sure this option is really sent by dhcp server. Any idea why is this option not captured by wireshark?
Does dhcp client need to request this option first and only then the dhcp server will send this option to client? I am using windows 10 pc to test this and i don’t think it is even requesting this option.
Any other idea?

2

Hi

I remember having issues with Android & iphone devices when adding dhcp options forcefully to the offer.
Apparently in latest impl, these have to be explicitly requested first, for them to be accepted by client.

3

Because it is either not present in the packet at all or it is there but in a wrong format so Wireshark doesn’t recognize it as such. But in the latter case, most Wireshark protocol dissectors report “malformed packet”.

Does dhcp client need to request this option first and only then the dhcp server will send this option to client?

Yes, exactly. The server must not send any option which the client has not asked for.

I am using windows 10 pc to test this and i don’t think it is even requesting this option.

Wireshark will also show you the list of requested options in the Discovery and Request messages sent by the client.