Interface index hack in IP_ADD_MEMBERSHIP

[Bruce M Simpson]

Eugene Grosbein wrote:
>
> I recall that routed and ripd used to utilize something similar
> long time ago. I'm not sure if they have switched to another API.
>   
You're right -- this would break routed on point-to-point interfaces.

They didn't, unless it was updated at the upstream, i.e. rhyolite.com.

This means that the RFC1724 hack can't be safely deprecated without 
breaking this use case, until routed is updated to use the RFC 3678 
protocol-independent ASM API.

Linux uses a slightly different technique to work-around this; ip_mreq 
is expanded to ip_mreqn internally, and the interface index is 
explicitly passed around in the kernel.

The blocker in the FreeBSD case which prevents us simply adopting this 
is the source interface selection logic in ip_output().

Regards,
BMS