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Date: Mon, 05 Feb 2007 16:56:49 -0800
From: "Eugene M. Kim" <freebsd.org@ab.ote.we.lv>
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Subject: rtadvd(8) and deprecated prefixes
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Greetings,

Unless disabled with -s flag, rtadvd(8) automatically picks up on-link
prefixes from the routing table and includes them in RA messages.  In
doing so, rtadvd does not seem to distinguish preferred prefixes
(preferred lifetime > 0) from distinguished ones (pltime = 0), but
simply advertises both kinds using the default pltime set in
rtadvd.conf(5) for fresh, preferred prefixes.  As a result, deprecated
prefixes end up being advertised as valid (i.e. pltime > 0),
demonstrated in the following two ifconfig(8) outputs (the first on the
router, the second on a host that receives RA from the router):

home 16:37:24 ~ $ 5 /sbin/ifconfig fxp0 inet6
fxp0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        options=8<VLAN_MTU>
        inet6 fe80::2a0:c9ff:feaa:106%fxp0 prefixlen 64 scopeid 0x1
        inet6 2001:470:1f00:3605:2a0:c9ff:feaa:106 prefixlen 64
        inet6 2001:470:1f00:3605:: prefixlen 64 anycast
        inet6 2001:470:1f01:3222:: prefixlen 64 anycast deprecated

seerajeane 16:39:13 ~ $ 3 /sbin/ifconfig em0 inet6
em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        options=19b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,TSO4>
        inet6 fe80::2e0:81ff:fe51:1e73%em0 prefixlen 64 scopeid 0x1
        inet6 2001:470:1f00:3605:2e0:81ff:fe51:1e73 prefixlen 64 autoconf
        inet6 2001:470:1f01:3222:2e0:81ff:fe51:1e73 prefixlen 64 autoconf

Note that the two automatically configured addresses on em0 are still
preferred, while the prefix 2001:470:1f01:3222::/64 is deprecated on the
router.

I believe rtadvd(8) should advertise deprecated on-link prefixes with
pltime of 0, but I still wanted to know what other people think about
this before working on actual code.  So, here is the question: Is this
really something to be fixed?

Regards,
Eugene