Re: Question regarding RFC 2461

[Roy Brabson <rbrabson@us.ibm.com>]

> I have a question about whether a NA sent to all-nodes multicast address
> with the solicited bit ON is valid or invalid.  Here are excerpts from 
the
> RFC.
> 
> For destination address in a NA:   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
> 
> This makes it sound like a NA could be sent to the all nodes multicast
> address and have the solicited bit ON.
> 
> However, here is what is says under the solicited bit:  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.
> 
> This states the solicited bit MUST NOT be set if the NA is destined for 
a
> multicast address.
> 
> Can you please clarify if a NA sent to all-nodes multicast address with
> solicited bit ON is considered valid or invalid.  Thanks!

This is covered in section 7.2.4:

   If the source of the solicitation is the unspecified address, the
   node MUST set the Solicited flag to zero and multicast the
   advertisement to the all-nodes address.  Otherwise, the node MUST set
   the Solicited flag to one and unicast the advertisement to the Source
   Address of the solicitation.

Roy

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