Help with dhcp options

[DVM]

I'm trying to setup a NAT with a DHCP server on the LAN side that will deliver a custom custom DHCP option to my victim. I have tried adding the dhcp_option list to dnsmasq

#!/bin/bash
# custom 

function setup() {
    # Show SETUP LED
    LED SETUP

    # Set the network mode to NAT
    NETMODE NAT
    sleep 5

    uci add_list dhcp.@dnsmasq[-1].dhcp_option='224,"my_payload_string"'

    # Restart dnsmasq with the new configuration
    /etc/init.d/dnsmasq restart	
}

function run() {
    # Show  ATTACK LED
    LED ATTACK
}

or replacing dnsmasq with lan

...
    #uci add_list dhcp.@dnsmasq[-1].dhcp_option='224,"my_payload_string"'
    uci add_list dhcp.lan.dhcp_option='224,"my_payload_string"'
...

Neither approach works as I don't see option 224 in the DHCP Ack

Can anyone help?

[kdodge]

just an idea, have you tried playing around with these yet:

https://openwrt.org/docs/guide-user/base-system/dhcp_configuration#dhcp_options ?

[DVM]

Thanks for the suggestion. I have read that and made another test:

dhcp.lan.dhcp_option='224,172.16.60.64' '42,172.16.60.64'

Now I see option 42 in the DHCP Ack message but not 224

 

[DVM]

I got it to sort-of work by adding this to /etc/dnsmasq.conf

dhcp-option-force=224,my_payload_string

Very strange but good enough for now. Thanks!

[kdodge]

Oh i see, option 224 is a "reserved" space. 

https://www.iana.org/assignments/bootp-dhcp-parameters/bootp-dhcp-parameters.xhtml

Its probably blocked normally, that's why you need to force it. I'm not sure how/if you can force something like that from uci, but I have not looked too deeply into that.

I'm kind of curious if you tried

uci add_list dhcp.lan.dhcp_option_force='224,"my_payload_string"'

what would happen, if part of the uci configure would work like that.

Edited July 4 by kdodge
new idea