Multicast address
41383
225785785
2008-07-15T11:44:16Z
58.20.71.63
/* IPv4 multicast addresses */
In [[computer network]]ing a '''multicast address''' is an identifier for a group of [[Server (computing)|host]]s that have joined a [[multicast]] group.
== IPv4 multicast addresses ==
Within [[Internet Protocol|IPv4]] it is historically known as a '''class D''' address, a type of [[IP address]]. It ranges from 224.0.0.0 to 239.255.255.255, or, equivalently, 224.0.0.0/4 (see [[Classless Inter-Domain Routing]]). Address assignments from within this range are specified in the [[internet engineering task force|IETF]] 'best current practice' [ftp://ftp.isi.edu/in-notes/bcp/bcp51.txt document] also known as RFC 3171.
The 224.0.0.0 to 224.0.0.255 range is assigned for multicasting on the local [[Local area network|LAN]] only. Well known examples are [[Routing Information Protocol|RIPv2]] which uses 224.0.0.9 and [[Open Shortest Path First|OSPF]] which uses the 224.0.0.5 address.
The following table is a partial list of well-known Class D addresses that are reserved for IP multicasting and registered with the [[Internet Assigned Numbers Authority]] (IANA).
{| class="wikitable"
|-
!IP multicast address
!Description
|-
|224.0.0.0
|Base address (reserved)
|-
|224.0.0.1
|The All Hosts multicast group that contains all systems on the same network segment
|-
|224.0.0.2
|The All Routers multicast group that contains all routers on the same network segment
|-
|224.0.0.5
|The Open Shortest Path First (OSPF) AllSPFRouters address. Used to send Hello packets to all OSPF routers on a network segment
|-
|224.0.0.6
|The OSPF AllDRouters address. Used to send OSPF routing information to OSPF designated routers on a network segment
|-
|224.0.0.9
|The RIP Version 2 group address. Used to send RIP routing information to all RIP v2 routers on a network segment
|-
|224.0.0.10
|EIGRP group address. Used to send EIGRP routing information to all EIGRP routers on a network segment
|-
|224.0.0.18
|[[Virtual Router Redundancy Protocol]]
|-
|224.0.0.22
|IGMP Version 3 ([[Internet Group Management Protocol]])
|-
|224.0.0.102
|[[Hot Standby Router Protocol]] Version 2
|-
|224.0.1.41
|[[H.323 Gatekeeper]] discovery address
|}
For a full and current listing of additional IP addresses that are reserved for multicasting, see the [http://www.iana.org/assignments/multicast-addresses Internet Multicast Addresses Web site].
The 233.0.0.0/8 range has been assigned by RFC 2770 as public multicast address space that is aligned along [[autonomous system (Internet)|autonomous system]] number allocations. Each byte of the AS number corresponds to the second and third [[octet (computing)|octet]]s of the multicast address.
The 239.0.0.0/8 range has been assigned by RFC 2365 as a locally administered address space with local or organizational scope.
For advice on choosing multicast addresses for use in your application, see [http://www.29west.com/docs/THPM/multicast-address-assignment.html this page on multicast address assignment].
== IPv6 multicast addresses ==
Multicast addresses in [[IPv6]] all have the prefix ff00::/8. Address assignments from within this range are specified in RFC 2373.
Bits 8 to 11 of the address (i.e., the third hexadecimal digit) are a set of flags, of which only the fourth is currently defined: 0 indicates an address permanently assigned by the [[Internet Assigned Numbers Authority|IANA]], and 1 indicates a non-permanently assigned or "transient" address. (In the addresses given below, an "x" indicates that the value of the digit in that position is unimportant in the current discussion.)
Similar to [[unicast]] addresses, IPv6 multicast addresses have different scopes depending on their prefix, though the range of possible scopes is different. The scope is indicated by bits 12 to 15:
*ffx0::/16 and ff0f::/16 are reserved.
*ffx1::/16 is interface-local, meaning packets with this destination address may not be sent over any network link, but must remain within the current node; this is the multicast equivalent of the unicast [[loopback address]].
*ffx2::/16 is link-local, meaning packets with this destination address may not be routed anywhere.
*ffx4::/16 is admin-local, i.e. "the smallest scope that must be administratively configured".
*ffx5::/16 is site-local, i.e. restricted to the local physical network.
*ffx8::/16 is organization-local, i.e. restricted to networks used by the organization administering the local network. (For example, these addresses might be used over [[VPN]]s; when packets for this group are routed over the public internet (where these addresses are not valid), they would have to be encapsulated in some other protocol.)
*ffxe::/16 is global scope, i.e. eligible to be routed over the public internet.
*Other scopes are unassigned.
These scopes are described in RFC 4291.
The "meaning" of a multicast address is unaffected by its scope; for example, if ff02::43 refers to all [[Network Time Protocol|NTP]] servers on the local network segment, then ff08::43 refers to all NTP servers in an organization's networks.
The following table is a partial list of well-known IPv6 multicast addresses that are registered with the [[Internet Assigned Numbers Authority]] (IANA).
{| class="wikitable"
! Address
! Description
|-
| ff02::1
| All nodes on the local network segment (equivalent to the IPv4 link-local broadcast address, 169.254.255.255)
|-
| ff02::2
| All routers on the local network segment
|-
| ff05::1
| All nodes on the local network site (roughly equivalent to the IPv4 local broadcast addresses 10.255.255.255 and 192.168.255.255)
|-
| ff0x::fb
| [[Zeroconf#Multicast_DNS_.28mDNS.29_and_DNS_Service_Discovery_.28DNS-SD.29|Multicast DNS]]
|-
| ff0x::108
| [[Network Information Service]]
|-
| ff0x::114
| Used for experiments
|-
| ff05::1:3
| All DHCP servers on the local network site (defined in RFC 3315)
|}
For a full and current listing of additional addresses that are allocated for multicasting, see the [http://www.iana.org/assignments/ipv6-multicast-addresses Internet Protocol Version 6 Multicast Addresses web site].
== Ethernet multicast addresses ==
Some well known [[Ethernet]] multicast addresses:
{| class="wikitable"
|-
!Ethernet multicast address
!Type Field
!Usage
|-
|01-00-0C-CC-CC-CC
|0x0802
|[[Cisco Discovery Protocol|CDP]] (Cisco Discovery Protocol), VTP (Virtual Trunking Protocol)
|-
|01-00-0C-CC-CC-CD
|0x0802
|Cisco Shared Spanning Tree Protocol Address
|-
|01-80-C2-00-00-00
|0x0802
|Spanning Tree Protocol (for bridges) [[IEEE 802.1D]]
|-
|01-00-5E-xx-xx-xx
|0x0800
|IPv4 [[Internet Group Management Protocol|IGMP]] Multicast Address
|-
|33-33-00-00-00-00
|0x86DD
|IPv6 Neighbor Discovery
|-
|33-33-xx-xx-xx-xx
|0x86DD
|IPv6 Multicast Address (RFC3307)
|}
Complete list: http://www.cavebear.com/archive/cavebear/Ethernet/multicast.html
== See also ==
*[[Broadcast address]]
[[Category:Network addressing]]