I'm confused about the T flag for an IPv6 multicast address with a
permanent group ID and would like to solicit clarification...
According to Section 4.2 of RFC3307:
Permanent group IDs are allocated on an Expert Review basis, in the
range 0x40000000 to 0x7FFFFFFF. These permanent group IDs are meant
to be used in IPv6 multicast addresses, defined in [UNIMCAST].
(UNIMCAST=RFC3306)
I interpret this as the corresponding IPv6 multicast address being
based on a unicast network prefix as defined in RFC3306. Thus the P
flag of the 4-bit flags field must be 1, and then the T flag must also
be 1 as specified in RFC3306:
o If P = 1, T MUST be set to 1, otherwise the setting of the T
bit is defined in Section 2.7 of [ADDRARCH].
Meanwhile, Section 4.3 of RFC3307 reads:
It
should be noted that the high-order bit of the Group ID will be the
same value as the T flag.
Doesn't this contradict the relationship between the T flag and
permanent group IDs? In fact, the high-order bit of a permanent group
ID is 0 while the T flag must be 1 as I explained above.
Or am I missing something?
JINMEI, Tatuya
Communication Platform Lab.
Corporate R&D Center, Toshiba Corp.
[EMAIL PROTECTED]
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