I’ve already discussed IPv6 multicast addresses within my previous article that IPv6 multicast addresses work much like IPv4 multicast addresses. The IPv6 enabled devices can join and listen for multicast traffic with an IPv6 multicast address.
The multicast address consists of an 8-bit address, 4-bit flag, 4-bit scope, and 112-bit group ID fields. An IPv6 multicast address can identify multiple network interfaces. In IPv6 multicasting, IPv6 datagram packets addressed to some multicast address are sent to all interfaces which are recognized by the address. The figure below illustrates the multicast address.
Format Prefix (FP)
The very first eight items of IPv6 multicast address is ever “1111 1111”. It’s known as the “Format Prefix”. The prefix from the multicast group is comparable to a hyperlink-local address.
Flags
Flags field has four bits. The 4 reserved bits may be used to indicate the character of certain multicast addresses. Presently, the very first three bits are not being used, there all first three bits are going to zero. The 4th bits is “T” (Transit) bit.
If the need for T field is zero, this marks the multicast address like a permanently-assigned, and “well-known” multicast address. If set to 1, what this means is this isn’t permanently assigned a multicast address.
Scope ID
Scope ID is four items of fields defining the scope from the multicast address. The need for scope ID is 16 different possible values from to fifteen. Based on the value is illustrates within the following image.
Group ID
It’s 112 bits lengthy and accustomed to find out the multicast group inside the given scope.
Assigned IPv6 Multicast Address
Using multicast address we are able to send just one packet to a number of destinations. The multicast IPv6 address Prefix is FF00::/8. Multicast addresses are only able to be destination addresses. There’s two kinds of IPv6 multicast addresses:
- Assigned multicast
- Solicited-node multicast
A designated multicast address is really a single address to achieve several devices managing a common service. It’s used in times with specific protocols for example DHCPv6.Two common IPv6 assigned multicast groups would be the following:
All-nodes multicast group
All-nodes multicast group can join all IPv6-enabled devices. The ff002::1 IPv6 address is restricted to this group. A packet delivered to this group should receive and processed by all IPv6 interfaces within the group. RA message towards the all-nodes multicast group may be the illustration of All-nodes multicast group.
When an IPv6 router transmits Internet Control Message Protocol version 6 (ICMPv6) RA message towards the all-nodes multicast group. It informs all IPv6-enabled devices around the network about IPv6 prefix, prefix length, default gateway and all sorts of various other information.
All-routers multicast group
All-routers multicast group can join all routers around the local network segment. The IPv6 address FF02::2 is restricted to the all-routers multicast group. A nearby router can join and becomes part of the all-routers multicast group if this enabled being an IPv6 router using the “ipv6 unicast-routing” command. The “ipv6 unicast-routing” may be the command of worldwide Configuration Mode.
All IPv6 enabled routers on the local network will get and process a packet delivered to this group. IPv6-enabled devices send ICMPv6 Router Solicitation (RS) messages for an all-routers multicast address. The Router Solicitation (RS) message demands a Router Advertisement (RA) message in the IPv6 router to help the unit in the address configuration.
Solicited-Node IPv6 Multicast Addresses
A solicited-node multicast address is much like towards the all-nodes multicast address. We are able to map the solicited-node multicast address to some special Ethernet multicast address. This enables the Ethernet NIC to filter the frame by analyzing the destination MAC address without delivering it towards the IPv6 process to find out if the unit may be the deliberate target from the IPv6 packet.
The Solicited-node multicast is really a flooding optimization. If sufficient information had been recognized to support unicast operation there could be no reason. When there’s no information to aid unicast operation, the solicited-node multicast can be used. The solicited-node enables for that flooded visitors to achieve all nodes like broadcast.
Solicited-node multicast addresses can make instantly utilizing a special mapping from the device’s unicast address using the solicited-node multicast prefix that is ff02:::::1:ff00::/104. It may be produced instantly for each unicast address on the device.
Reserved IPv6 Multicast Addresses
Address Description
ff02::1 All nodes around the local network
ff02::2 All routers around the local network
Ff02::4 The all-Distance Vector Multicast Routing Protocol address.
ff02::9 Routing Information Protocol (RIP) routers
ff02::a EIGRP routers
ff02::d Protocol Independent Multicast routers
ff02::e Resource Reservation Protocol (RSVP)
ff02::1:2 All Dynamic Host Configuration Protocol servers and relay agents around the local network site
ff02::1:3 Link-local multicast name resolution
