misc/152458: rtadvd neetds to allow RA without a prefix info option

[Steinar Haug]

>Number:         152458
>Category:       misc
>Synopsis:       rtadvd neetds to allow RA without a prefix info option
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sun Nov 21 19:40:11 UTC 2010
>Closed-Date:
>Last-Modified:
>Originator:     Steinar Haug
>Release:        7.3-STABLE
>Organization:
Nethelp Consulting
>Environment:
FreeBSD dhcp1.noc.ventelo.net 7.3-STABLE FreeBSD 7.3-STABLE #8: Sun Nov 14 21:36:26 CET 2010     sthaug at dhcp1.noc.ventelo.net:/usr/src/sys/i386/compile/DHCP1  i386

>Description:
In IPv6 it should be possible to generate a Router Advertisement which
contains no prefix info option (the idea being that I want a host on the
LAN to populate its default router list but nothing else). However, I
cannot seem to get rtadvd to do this.

My Juniper routers can do this without any problem.

If I start rtadvd with no /etc/rtadvd.conf file, it sends RAs with a
prefix info option corresponding to the IPv6 address of the interface.
In the /etc/rtadvd.conf I can explicitly specify prefixes ("addr"),
but I can't find any way to specify that no prefix info option should
be sent.

If I start rtadvd with the -s option, it still sends RAs with a prefix
info option corresponding to the IPv6 address of the interface.

If I start rtadvd with a config file which specifies a prefix using
the "addr" option, I can get rtadvd to send RAs without the "auto"
flag - thus the prefix won't be used for SLAAC. E.g.:

em1:raflags="m":pinfoflags="l":addr="2001:8c0:8500:3::"

gives me a RA like the following (tcpdump output):


20:26:15.469184 IP6 (hlim 255, next-header ICMPv6 (58) payload length: 56) fe80::214:22ff:fe1a:8439 > ff02::1: [icmp6 sum ok] ICMP6, router advertisement, length 56
        hop limit 64, Flags [managed], pref medium, router lifetime 1800s, reachable time 0s, retrans time 0s
          source link-address option (1), length 8 (1): 00:14:22:1a:84:39
          prefix info option (3), length 32 (4): 2001:8c0:8500:3::/64, Flags [onlink], valid time 2592000s, pref. time 604800s


But this is not quite the same as not announcing a prefix.

It's possible we simply have some missing functionality here.
>How-To-Repeat:
Start rtadvd. Observe using tcpdump or similar that a prefix info option is
always included in the RAs transmitted on the interface.

>Fix:


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