Issue: Clarification of Framed-IPv6-Prefix in RFC 3162

["Bernard Aboba" <bernard_aboba@hotmail.com>]

Issue:  Clarification of Framed-IPv6-Prefix in RFC 3162
Submitter name: Bernard Aboba
Submitter email address: aboba@internaut.com
Date first submitted: November 4, 2005
Reference:
Document: Issues & Fixes -01
Comment type: T
Priority: S
Section: New
Rationale/Explanation of issue:

Section 2.3 of RFC 3162 states:

     This Attribute indicates an IPv6 prefix (and corresponding route)
     to be configured for the user.  It MAY be used in Access-Accept
     packets, and can appear multiple times.  It MAY be used in an
     Access-Request packet as a hint by the NAS to the server that it
     would prefer these prefix(es), but the server is not required to
     honor the hint.  Since it is assumed that the NAS will plumb a
     route corresponding to the prefix, it is not necessary for the
     server to also send a Framed-IPv6-Route attribute for the same
     prefix.

This raises several issues:

a.  What is the expected behavior of the NAS on receiving 
Framed-IPv6-Prefix?   Is the NAS expected to use the prefix only on the link 
between itself and the CPE?

b. Does the receipt of a Framed-IPv6-Prefix imply that the NAS is supposed 
to announce the prefix using RS?  Or does this require allocation of a new 
value of Framed-Routing?

c. Since the prefix length can be between 0 and 128, can Framed-IPv6-Prefix 
be used to send a /128?  What does the NAS do in that case?  What if the NAS 
also receives a Framed-Interface-Id attribute?

Here are my (strawman) answers:

a. The NAS plumbs a route for the prefix.  It also advertises the prefix via 
RS/RA.  The NAS does not do anything else unless it is explicitly told to do 
so (e.g. in Framed-Routing).

b. Yes.  A new value of Framed-Routing is not required to cause the prefix 
to be announced via RS.  Framed-Routing is intended to be used only with 
routing protocols (primarily RIPv2), rather than with RS/RA or Prefix 
Delegation.

c. Framed-IPv6-Prefix can be used to send a /128.  If received, the NAS will 
plumb a route for the prefix.  However, it will not announce the /128 via 
RS, only the /64.  If the NAS also receives a Framed-Interface-ID attribute 
it will use it if the protocol involved requires an Interface-ID (e.g. PPP). 
 Otherwise, it will ignore the attribute.



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