rfc1970.txt

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Narten, Nordmark & Simpson  Standards Track                    [Page 21]

RFC 1970       Neighbor Discovery for IP Version 6 (IPv6)    August 1996


   Priority       15

   Authentication Header
                  If a Security Association for the IP Authentication
                  Header exists between the sender and the destination
                  address, then the sender SHOULD include this header.

ICMP Fields:

   Type           135

   Code           0

   Checksum       The ICMP checksum.  See [ICMPv6].

   Reserved       This field is unused.  It MUST be initialized to zero
                  by the sender and MUST be ignored by the receiver.

   Target Address
                  The IP address of the target of the solicitation.  It
                  MUST NOT be a multicast address.

Possible options:

   Source link-layer address
                  The link-layer address for the sender.  On link layers
                  that have addresses this option MUST be included in
                  multicast solicitations and SHOULD be included in
                  unicast solicitations.

   Future versions of this protocol may define new option types.
   Receivers MUST silently ignore any options they do not recognize and
   continue processing the message.


















Narten, Nordmark & Simpson  Standards Track                    [Page 22]

RFC 1970       Neighbor Discovery for IP Version 6 (IPv6)    August 1996


4.4.  Neighbor Advertisement Message Format

   A node sends Neighbor Advertisements in response to Neighbor
   Solicitations and sends unsolicited Neighbor Advertisements in order
   to (unreliably) propagate new information quickly.

      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      |     Code      |          Checksum             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |R|S|O|                     Reserved                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                                                               +
     |                                                               |
     +                       Target Address                          +
     |                                                               |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Options ...
     +-+-+-+-+-+-+-+-+-+-+-+-

IP Fields:

   Source Address
                  An address assigned to the interface from which the
                  advertisement is sent.

   Destination Address
                  For solicited advertisements, the Source Address of an
                  invoking Neighbor Solicitation or, if the
                  solicitation's Source Address is the unspecified
                  address, the all-nodes multicast address.

                  For unsolicited advertisements typically the all-nodes
                  multicast address.

   Hop Limit      255

   Priority       15

   Authentication Header
                  If a Security Association for the IP Authentication
                  Header exists between the sender and the destination
                  address, then the sender SHOULD include this header.




Narten, Nordmark & Simpson  Standards Track                    [Page 23]

RFC 1970       Neighbor Discovery for IP Version 6 (IPv6)    August 1996


ICMP Fields:

   Type           136

   Code           0

   Checksum       The ICMP checksum.  See [ICMPv6].

   R              Router flag.  When set, the R-bit indicates that the
                  sender is a router.  The R-bit is used by Neighbor
                  Unreachability Detection to detect a router that
                  changes to a host.

   S              Solicited flag.  When set, the S-bit indicates that
                  the advertisement was sent in response to a Neighbor
                  Solicitation from the Destination address.  The S-bit
                  is used as a reachability confirmation for Neighbor
                  Unreachability Detection.  It MUST NOT be set in
                  multicast advertisements or in unsolicited unicast
                  advertisements.

   O              Override flag.  When set, the O-bit indicates that the
                  advertisement should override an existing cache entry
                  and update the cached link-layer address.  When it is
                  not set the advertisement will not update a cached
                  link-layer address though it will update an existing
                  Neighbor Cache entry for which no link-layer address
                  is known.  It SHOULD NOT be set in solicited
                  advertisements for anycast addresses and in solicited
                  proxy advertisements.  It SHOULD be set in other
                  solicited advertisements and in unsolicited
                  advertisements.

   Reserved       29-bit unused field.  It MUST be initialized to zero
                  by the sender and MUST be ignored by the receiver.

   Target Address
                  For solicited advertisements, the Target Address field
                  in the Neighbor Solicitation message that prompted
                  this advertisement.  For an unsolicited advertisement,
                  the address whose link-layer address has changed.  The
                  Target Address MUST NOT be a multicast address.









Narten, Nordmark & Simpson  Standards Track                    [Page 24]

RFC 1970       Neighbor Discovery for IP Version 6 (IPv6)    August 1996


Possible options:

   Target link-layer address
                  The link-layer address for the target, i.e., the
                  sender of the advertisement.  MUST be included on link
                  layers that have addresses.

   Future versions of this protocol may define new option types.
   Receivers MUST silently ignore any options they do not recognize and
   continue processing the message.

4.5.  Redirect Message Format

   Routers send Redirect packets to inform a host of a better first-hop
   node on the path to a destination.  Hosts can be redirected to a
   better first-hop router but can also be informed by a redirect that
   the destination is in fact a neighbor.  The latter is accomplished by
   setting the ICMP Target Address equal to the ICMP Destination
   Address.

      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      |     Code      |          Checksum             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Reserved                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                                                               +
     |                                                               |
     +                       Target Address                          +
     |                                                               |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                                                               +
     |                                                               |
     +                     Destination Address                       +
     |                                                               |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Options ...
     +-+-+-+-+-+-+-+-+-+-+-+-






Narten, Nordmark & Simpson  Standards Track                    [Page 25]

RFC 1970       Neighbor Discovery for IP Version 6 (IPv6)    August 1996


IP Fields:

   Source Address
                  MUST be the link-local address assigned to the
                  interface from which this message is sent.

   Destination Address
                  The Source Address of the packet that triggered the
                  redirect.

   Hop Limit      255

   Priority       15

   Authentication Header
                  If a Security Association for the IP Authentication
                  Header exists between the sender and the destination
                  address, then the sender SHOULD include this header.

ICMP Fields:

   Type           137

   Code           0

   Checksum       The ICMP checksum.  See [ICMPv6].

   Reserved       This field is unused.  It MUST be initialized to zero
                  by the sender and MUST be ignored by the receiver.

   Target Address An IP address that is a better first hop to use for
                  the ICMP Destination Address.  When the target is the
                  actual endpoint of communication, i.e., the
                  destination is a neighbor, the Target Address field
                  MUST contain the same value as the ICMP Destination
                  Address field.  Otherwise the target is a better
                  first-hop router and the Target Address MUST be the
                  router's link-local address so that hosts can uniquely
                  identify routers.

   Destination Address
                  The IP address of the destination which is redirected
                  to the target.








Narten, Nordmark & Simpson  Standards Track                    [Page 26]

RFC 1970       Neighbor Discovery for IP Version 6 (IPv6)    August 1996


Possible options:

   Target link-layer address
                  The link-layer address for the target.  It SHOULD be
                  included (if known).  Note that on NBMA links, hosts