What is the address prefix in binary for multicast addresses?
A.
1111 1110 11
B.
1111 1111
C.
0000 010
D.
1111 1110 10
Explanation:
This question is confusing, since coding for Ipv4 is different than Ipv6. Lucily both encodings are
not listed as possible answers. Hopefully the question on the exam will be worded more clearly.
An IPv6 multicast address is an identifier for a group of nodes. A node may belong to any number
of multicast groups. Multicast addresses have the following format:
| 8 | 4 | 4 | 112 bits |
+—— -+—-+—-+———————————————+
|11111111|flgs|scop| group ID |
+——–+—-+—-+———————————————+
11111111 at the start of the address identifies the address as being a multicast address.
+-+-+-+-+
flgs is a set of 4 flags: |0|0|0|T|
+-+-+-+-+
The high-order 3 flags are reserved, and must be initialized to 0.
T = 0 indicates a permanently-assigned (“well-known”) multicast address, assigned by the global
internet numbering authority.
T = 1 indicates a non-permanently-assigned (“transient”) multicast address.
scop is a 4-bit multicast scope value used to limit the scope of the multicast group. The values are:
0 reserved 1 node-local scope 2 link-local scope 3 (unassigned) 4 (unassigned) 5 site-local scope
6 (unassigned) 7 (unassigned) 8 organization-local scope 9 (unassigned) A (unassigned) B
(unassigned) C (unassigned)
D (unassigned) E global scope F reserved
group ID identifies the multicast group, either permanent or transient, within the given scope.
Incorrect Answers:A: These bit configurations do not fit the prefix of multicast address.
C: These bit configurations do not fit the prefix of multicast address.
D: These bit configurations do not fit the prefix of multicast address.