dhcp option

meliodas · 08-09-2022, 06:05 PM

Hi, this is related to both dhcp and dnsmasq. In dnsmasq.conf, I notice the following..for example:

dhcp-option=lan,3,192.168.0.1
dhcp-option=lan,15,domain.local
dhcp-option=lan,44,192.168.0.1

What do the bold numbers mean and where can I reference it that explains more about it ?

michaelk · 08-09-2022, 06:13 PM

Welcome to LinuxQuestions.

Those are option numbers the DHCP protocol uses to identify what data is being sent to the client. In your first example 3 is the gateway IP address.

https://www.iana.org/assignments/boo...rameters.xhtml

meliodas · 08-09-2022, 06:28 PM

Thanks for the welcome and the post.

michaelk · 08-09-2022, 06:47 PM

I guess the two most important options are 3 and 6. As posted 3 is the gateway IP address i.e. that tells a client where to send data outside of the LAN and 6, the DNS addresses. dnsmasq can be its own local DNS server which also forwards requests to network DNS servers like Google.

elgrandeperro · 08-10-2022, 08:14 AM

There should be macro substitutions that map the number to more readable names. I haven't found the full list, but here is
an example:

dhcp-option=option:router,192.168.10.1
dhcp-option=option:dns-server,192.168.10.1
dhcp-option=option:netmask,255.255.255.0

meliodas · 08-10-2022, 08:35 AM

Yeh with names it's easier but I'm dealing with mostly dnsmasq here since this is on a merlin-wrt router and it uses numbers mostly which can be confusing.

Another question, can dnsmasq handle
dhcp-pd to request an IPv6 prefix of your choice from the upstream ISP?

meliodas · 08-10-2022, 05:49 PM

I read that Android doesn't support stateful DHCPv6. DNSMASQ does SLACC however can it assign an IPv6 address of my choice to an Android device ?

I have this in dnsmasq.conf:

dhcp-option=android_hostname,192.168.0.100,[::abcd]

When I check the Android device it only get's assigned the IPv4 address correctly and the IPv6 address is random.