Multicast addresses are identified by the pattern “1110” in the first four bits, which corresponds to a first octet of 224 to 239 (1110 0000 ~ 1110 1111). So, the full range of multicast addresses is from 224.0.0.0 to 239.255.255.255. Since multicast addresses represent a group of IP devices (sometimes called a host group) they can only be used as the destination of a datagram; never the source.
The multicast addresses are in the range 224.0.0.0 through 239.255.255.255.
The range of addresses between 224.0.0.0 and 224.0.0.255, inclusive,
is reserved for the use of routing protocols and other low-level
topology discovery or maintenance protocols, such as gateway discovery
and group membership reporting. Multicast routers should not forward
any multicast datagram with destination addresses in this range,
regardless of its TTL.
- Local Network Control Block (224.0.0.0 - 224.0.0.255 (224.0.0/24))
- Internetwork Control Block (224.0.1.0 - 224.0.1.255 (224.0.1/24))
- AD-HOC Block I (224.0.2.0 - 224.0.255.255)
- RESERVED (224.1.0.0-224.1.255.255 (224.1/16))
- SDP/SAP Block (224.2.0.0-224.2.255.255 (224.2/16))
- AD-HOC Block II (224.3.0.0-224.4.255.255 (224.3/16, 224.4/16))
- RESERVED (224.5.0.0-224.251.255.255 (251 /16s))
- DIS Transient Groups 224.252.0.0-224.255.255.255 (224.252/14))
- RESERVED (225.0.0.0-231.255.255.255 (7 /8s))
- Source-Specific Multicast Block (232.0.0.0-232.255.255.255 (232/8))
- GLOP Block
- AD-HOC Block III (233.252.0.0-233.255.255.255 (233.252/14))
- Unicast-Prefix-based IPv4 Multicast Addresses (234.0.0.0-234.255.255.255)
- Scoped Multicast Ranges (235.0.0.0-238.255.255.255 Reserved) (239.0.0.0-239.255.255.255 Organization-Local Scope; multicast groups used within a private organization)
- The IPv4 Local Scope -- 239.255.0.0/16
- The Local Scope is the minimal enclosing scope, and hence is not further divisible (similar to private ip).
- Scope may grow downward from 239.255.0.0/16 into the reserved ranges 239.254.0.0/16 and 239.253.0.0/16. However, these ranges should not be utilized until the 239.255.0.0/16 space is no longer sufficient.
- The IPv4 Organization Local Scope -- 239.192.0.0/14
- 239.192.0.0/14 is defined to be the IPv4 Organization Local Scope, and is the space from which an organization should allocate sub-ranges when defining scopes for private use.
- The ranges 239.0.0.0/10, 239.64.0.0/10 and 239.128.0.0/10 are unassigned and available for expansion of this space.
- These ranges should be left unassigned until the 239.192.0.0/14 space is no longer sufficient.
- Expansion of the IPv4 Organization Local Scope
- The ranges 239.0.0.0/10, 239.64.0.0/10 and 239.128.0.0/10 are unassigned and available for expansion of this space.
sources:
http://www.iana.org/assignments/multicast-addresses/multicast-addresses.xhtml
http://www.tcpipguide.com/free/t_IPMulticastAddressing.htm
MAC address format
octet 0 : octet 1 : octet 2 : octet 3 : octet 4 : octet 5
xxxxxxx1 -> Multicast / broadcast bit
The 24-bit MAC address prefix 01-00-5E is reserved for layer 2 multicast.
01:00:5e:xx:xx:xx
This means we only have 23 bits of MAC address space to use for multicast.
(1 bit is reserved due to historical reason)
Multicast IP address = 4 octets = 32 bits - 4 bits (1110, reserved as Multicast IP) = 28 unique bits
So map 28 unique multicast IP address bits to 23 MAC address bits
We miss 5 bits of mapping information: 25 = 32. This means we will map 32 multicast IP addresses to 1 multicast MAC address.
We will take the following multicast MAC address and calculate what 32 multicast IP addresses map to it:
0 1 : 0 0 : 5 e : 0 b : 0 1 : 0 2
0000 0001 0000 0000 0101 1110 0000 1011 0000 0001 0000 0010
-----------------------------------------------------------------------------------------------------
Now we will take the lowest 23 bits of this MAC address:
000 1011 0000 0001 0000 0010
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Now we will take the class D multicast IP address range in binary:
1110 '0000 0'000 0000 0000 0000 0000 0000
The first 4 digits (1110) are the class D IP address in binary (224 in decimal).
the 5 bits followed by 1110 we lose because we have to map a 28 bits unique multicast IP address to a 23 multicast MAC
1110 '0000 0'000 0000 0000 0000 0000 0000
000 0000 0000 0000 1111 1011
244 0 0 251
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We will take the following multicast MAC address and calculate what 32 multicast IP addresses map to it:
0 1 : 0 0 : 5 e : 0 0 : 0 0 : f b
0000 0001 0000 0000 0101 1110 0000 0000 0000 0000 1111 1011
---------------------------------------------------------------------------------------------------------------
Now we will take the lowest 23 bits of this MAC address:
000 0000 0000 0000 1111 1011
-----------------------------------------------------------------------------------------------------
Now we will take the class D multicast IP address range in binary:
1110 '1111 1'111 1111 0000 0001 0000 0001
0 1 : 0 0 : 5 e : 7F : 01 : 01
0111 1111 0000 0001 0000 0001
7F 01 01
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