Subject: [pim] PIM-SM RFC4601 Encoding questions

From: "James Courtier-Dutton" <[email-masked]>
Date: Mon, 30 Jun 2008 12:52:22 +0100

In Section 4.9.1
For: Encoded-Group Address:

Mask Len
        The Mask length field is 8 bits.  The value is the number of
        contiguous one bits that are left justified and used as a mask;
        when combined with the group address, it describes a range of
        groups.  It is less than or equal to the address length in bits
        for the given Address Family and Encoding Type.  If the message
        is sent for a single group, then the Mask length must equal the
        address length in bits for the given Address Family and Encoding
        Type (e.g., 32 for IPv4 native encoding, 128 for IPv6 native
        encoding).

For: Encoded-Source Address

Mask Len
        The mask length field is 8 bits.  The value is the number of
        contiguous one bits left justified used as a mask which,
        combined with the Source Address, describes a source subnet.
        The mask length MUST be equal to the mask length in bits for the
        given Address Family and Encoding Type (32 for IPv4 native and
        128 for IPv6 native).  A router SHOULD ignore any messages
        received with any other mask length.

So, for the Source address, Is the mask essentially not used for masking at all?

I would have thought that this would have been a useful feature, if
one wanted to join any source on a subnet for a particular group.
Why is it specifically rejected?

James
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