RFC1918 addresses to permit in for VPN?

I said:

>Nevertheless, the operational reality is that having a traceroute that
>shows RFC1918 addresses is more useful than a traceroute that shows
>* * *, and therefore I suspect most operators will continue to permit
>RFC1918 addresses into their networks as long as a few questionable
>individuals use them to source traffic.

i think it's only useful to show that (a) something's there

Yes, and that's sufficient justification for me. I don't particularly
like traffic filters.