docs/156689: stf output-only documentation gives bad configuration advice

[Mark Andrews]

>Number:         156689
>Category:       docs
>Synopsis:       stf output-only documentation gives bad configuration advice
>Confidential:   no
>Severity:       non-critical
>Priority:       high
>Responsible:    freebsd-doc
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          doc-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu Apr 28 07:00:21 UTC 2011
>Closed-Date:
>Last-Modified:
>Originator:     Mark Andrews
>Release:        FreeBSD 8.2-STABLE i386
>Organization:
ISC
>Environment:
System: FreeBSD sex.dv.isc.org 8.2-STABLE FreeBSD 8.2-STABLE #10: Sat Feb 26 18:02:12 EST 2011 marka at sex.dv.isc.org:/usr/obj/usr/src/sys/DEBUG i386

>Description:

The stf documentation suggests the following configuration.  This
will result in traffic originating from the 6to4 address for which
reply traffic will not be accepted.

     # ifconfig ne0 inet 133.4.5.6 netmask 0xffffff00
     # ifconfig stf0 inet6 2002:8504:0506:0000:a00:5aff:fe38:6f86 \
             prefixlen 16 alias deprecated link0
     # route add -inet6 2002:: -prefixlen 16 ::1
     # route change -inet6 2002:: -prefixlen 16 ::1 -ifp stf0

>How-To-Repeat:

Configure the system as above and try to talk to any a machine with
a 6to4 address.  You can observe the traffic with tcpdump.

e.g. "tcpdump -i ne0 -n -p not udp and not tcp and not arp" will
remove most of the extranious packets.

>Fix:

Use "anycast" rather than "deprecated" so that the kernel will
choose a different IPv6 source address.

     # ifconfig ne0 inet 133.4.5.6 netmask 0xffffff00
     # ifconfig stf0 inet6 2002:8504:0506:: prefixlen 16 alias anycast link0
     # route add -inet6 2002:: -prefixlen 16 ::1
     # route change -inet6 2002:: -prefixlen 16 ::1 -ifp stf0

I tested this on a FreeBSD 4.11 box but I don't believe this part of the
stack has changed much since then.  The above documentation is from
FreeBSD 8.


>Release-Note:
>Audit-Trail:
>Unformatted: