Behavior of Default Route Handling in RFC 3442 (Classless Static Routes) vs. Router Option

[sikkandarsikkandar8-maker]

According to RFC 3442,

“If the DHCP server returns both a Classless Static Routes option and a Router option, the DHCP client MUST ignore the Router option.”

In the latest version, when the DHCP server does not include a default route (0.0.0.0/0) in the Classless Static Routes (CSR) option, the client falls back to using the Router option (Option 3) to configure the default gateway.

However, in the older version (e.g., v6.9.2), if the CSR option does not include a default route, the client does not use the Router option. Instead, the default route must be explicitly set in the CSR table on the DHCP server for the device to install it.

This raises the question: Which is the correct behavior — should the client ignore the Router option entirely when CSR is present, or should it fall back to the Router option if no default route is defined in CSR?