enquiry on validation of dhcp offered addres

[sthaug at nethelp.no]

> Current scripts seems no validation at all. They "trust" everything from DHCP.

This is indeed how DHCP is designed to work. If your DHCP server is
untrustworthy, it can do a *lot* of damage. And the client cannot
protect against all such damage, because it cannot (in general) know
whether a DHCP lease is correct or not - it has to trust the server.

> I have several ideas in mind:
> 1. dhcp validation on dhclient - reject ipv4 class A,B,C private addresses and ipv6 ULA prefix
>       - i think it is the most "clean" way
> 2. validation on network config scripts - reject ipv4 class A,B,C private addresses and ipv6 ULA prefix
>        - it is quite hard for me, i do not know how to manipulate ipv4 subnet and ipv6 prefix in shell script

Rejecting IPv4 private addresses and IPv6 ULA addresses may be correct
in *your* configuration - and should be correct in general for Internet
connected hosts. It will obviously not be correct in all configurations
and therefore cannot be a standard part of dhclient.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no