Subject: [mobile-ip] Mipv6 issue #147: Inconsistent RA&prefix rules

From: Jari Arkko <[email-masked]>
Date: Sun, 27 Oct 2002 17:20:37 +0200

Section 7.2 has the following text:

    In a solicited Router Advertisement, a home agent MUST, and all other
    routers SHOULD, include at least one Prefix Information option with
    the Router Address (R) bit set.  Neighbor Discovery specifies that,
    if including all options in a Router Advertisement causes the size of
    the Advertisement to exceed the link MTU, multiple Advertisements can
    be sent, each containing a subset of the options [12].  In this case,
    at least one of these multiple Advertisements being sent instead
    of a single larger solicited Advertisement, MUST include a Prefix
    Information option with the Router Address (R) bit set.

    All routers SHOULD include at least one Prefix Information option
    with the Router Address (R) bit set, in each unsolicited multicast
    Router Advertisement that they send.  If multiple Advertisements
    are being sent instead of a single larger unsolicited multicast
    Advertisement, at least one of these multiple Advertisements SHOULD
    include a Prefix Information option with the Router Address (R) bit
    set.

I'm curious as to why this was originally written like this. In
particular,

- Wouldn't a MAY be more appropriate for non-HA routers? I fail
   to see why DHAAD or the mobile node needs to know the global
   address of non-HAs. It is possible that the non-HA router knows
   the addresses of some HAs, so the addresses can be sometimes
   included but SHOULD may be an overkill. Or is there something
   I'm missing?

- The first paragraph seems to say that for non-HA routers,
   if the RA fits one packet then (R) bit is a SHOULD. If
   the RA does not fit then the (R) bit is a MUST?!

- The rules for unsolicited and solicited RAs are different.
   Why don't we require HAs to include the bit in all unsolicited
   RAs as well?

Ok, so I may have missed something. If not, I suggest the following
text:

    In a Router Advertisement, a home agent MUST, and all other
    routers MAY, include at least one Prefix Information option with
    the Router Address (R) bit set. Neighbor Discovery specifies that,
    if including all options in a Router Advertisement causes the size of
    the Advertisement to exceed the link MTU, multiple Advertisements can
    be sent, each containing a subset of the options [12]. In this case,
    at least one (not all) of these multiple Advertisements being sent
    needs to satisfy the above requirement.

And corresponding modifications in the requirements-for-all-routers
section.

Jari