Re: Future use??
The reasons routers would drop packets with a 240/4 destination address is for compliance with RFC 1812, s5.3.7 which says:
> An IP destination address is invalid if it is among those defined as
> illegal destinations in 4.2.3.1, or is a Class E address (except
> 255.255.255.255).
> A router SHOULD NOT forward any packet that has an invalid IP
> destination address or a destination address on network 0.
And this was the justification for needing to implement this in IOS CEF when I worked at Cisco in the CEF team (and a customer request for compliance with this part of the RFC).
Destination address checks in any non-trivial packet forwarding implementation are essentially free, even in software, due to use of optimised forwarding lookups like mtries/Patricia tries. Source address checks cost cycles, but even then it was deemed acceptable to spend them on other s5.3.7 provisions for source addresses.
Biting the hand that feeds IT
