kern/91665: [if_tun] Duplicate tun IP address

[Gleb Smirnoff]

Synopsis: [if_tun] Duplicate tun IP address

State-Changed-From-To: open->closed
State-Changed-By: glebius
State-Changed-When: Thu Jan 12 14:02:16 UTC 2006
State-Changed-Why: 
Actually the PPP software or RADIUS should take care about colliding
client IP addresses. Historically PPP software didn't do this relying
on the fact that kernel will refuse such configuration. Meanwhile
this configuration is valid and in some cases it is useful, and thus
since FreeBSD 5.4-RELEASE kernel doesn't refuse same IP addresses
on different interfaces.

To assist software that relies on the old behavior a helper sysctl
is available - net.inet.ip.same_prefix_carp_only. To get the old
behavior you need to add the following line to your /etc/sysctl.conf:

net.inet.ip.same_prefix_carp_only=1

http://www.freebsd.org/cgi/query-pr.cgi?pr=91665