Subject: Route-IPv6-Information Attribute

From: Bernard Aboba <[email-masked]>
Date: Sun, 10 Apr 2011 11:53:41 -0700

At IETF-80 we discussed the differences between the Framed-IPv6-Prefix, Framed-IPv6-Route and Route-IPv6-Information attributes.  The differences appear to be as follows:

Framed-IPv6-Prefix:  Configures an IPv6 prefix (and route) for the user on the NAS and results in the prefix being advertised in an RA from the NAS. 

Framed-IPv6-Route:  Configures additional routes on the NAS.  These additional routes may be advertised by an IGP,
depending on the value of Framed-Routing. 

Route-IPv6-Information:  Configures additional routes on the NAS.  These additional routes will be advertised within the RA via the Route Information Option described in RFC 4191 Section 2.3. 

In comparing RFC 4191 Section 2.3 with the format of the Route-IPv6-Information Attribute, there appear to be some differences in the information included.  The Route-IPv6-Information Attribute does not include the Route Preference or the Route Lifetime within the Route Information Option.  Also the definition of the Prefix Length and Prefix appears to be different.  Is there a reason for this? 

Assuming that it is desirable to utilize the same format for the Attribute and the Option, potential replacement text for Section 3.3 would be as follows:

3.3. Route-IPv6-Information

   This Attribute specifies a prefix (and corresponding route) for the
   user on the NAS, which is to be announced using the Route Information
   Option defined in "Default Router Preferences and More Specific
   Routes" [RFC4191] Section 2.3.   It is used in the Access-Accept 
   packet and can appear multiple times.  It may also be
   used in the Access-Request packet as hint to the server.

   A summary of the Route-IPv6-Information attribute format is shown
   below.

      0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |    Length     | Prefix Length |Resvd|Prf|Resvd|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Route Lifetime                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Prefix (Variable Length)                    |
      .                                                               .
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      TBA3 for Route-IPv6-Information

   Length

      Length in bytes.  At least 4 and no larger than 20; typically 12
      or less.

   Prefix Length
               8-bit unsigned integer.  The number of leading bits in
               the Prefix that are valid.  The value ranges from 0 to
               128.  The Prefix field is 0, 8, or 16 octets depending on
               Length.

   Prf (Route Preference)
               2-bit signed integer.  The Route Preference indicates
               whether to prefer the router associated with this prefix
               over others, when multiple identical prefixes (for
               different routers) have been received. 

   Resvd (Reserved)
               Two 3-bit unused fields.  They MUST be initialized to
               zero.

   Route Lifetime
               32-bit unsigned integer.  The length of time in seconds
               (relative to the time the packet is sent) that the prefix
               is valid for route determination.  A value of all one
               bits (0xffffffff) represents infinity.

   Prefix      Variable-length field containing an IP address or a
               prefix of an IP address.  The Prefix Length field
               contains the number of valid leading bits in the prefix.
               The bits in the prefix after the prefix length (if any)
               are reserved and MUST be initialized to zero.

Does this make sense?