UDP Peer Discovery
126.96.36.199 - 188.8.131.52 are the reserved multicast IP addresses, these are class D addresses.
Examples of Link Local Addresses
||All systems on this subnet
||All routers on this subnet
||OSPF designated routers
||Dynamic Host Configuration Protocol (DHCP) server/relay agent
- Servers are not bound to a specific interface, but instead we join the multicast group on a specific interface
- Clients aren’t bound to a specific interface, but start transmitting data to the multicast group.
Globally Scoped Addresses
Addresses in the range from 184.108.40.206 through 220.127.116.11 are called globally scoped addresses. These addresses are used to multicast data between organizations and across the Internet.
- The IP header of a multicast datagram includes a Time-to-Live (TTL) value that determines how far routers can forward a multicast datagram.
IP Multicasting Components
|Host (source or receiver)
||A host is any client or server on the network. A multicast-enabled host is configured to send and receive (or only send) multicast data.
||A multicast router is capable of handling host requests to join or leave a group and of forwarding multicast data to subnets that contain group members.
||A Class D IP address used for sending IP multicast data. An IP multicast source sends the data to a single multicast address. A specific IP multicast address is also known as a group address.
||A multicast group is the set of hosts that listen for a specific IP multicast address. A multicast group is also known as a host group.
||The Internet multicast backbone, or the portion of the Internet that supports multicast routing.
Unicast Routing Characteristics
- Unicast traffic is sent to a globally unique destination.
- Unicast routes in the routing table summarize ranges of globally unique destinations.
- Unicast routes are comparatively consistent, so the routing table needs to be updated only when the topology of the internetwork changes.
- Unicast routing protocols update the unicast routing table.
Multicast Routing Characteristics
- Multicast traffic is sent to an ambiguous group destination.
- Because group addresses represent different groups with different members, group addresses generally cannot be summarized in the IP multicast forwarding table.
- The location of group members is not consistent, so the IP multicast forwarding table might need to be updated whenever a group member joins or leaves a multicast group. Multicast routing protocols update the IP multicast forwarding table.
The set of hosts listening for a specific IP multicast address is
called a multicast group or a host group. Multicast groups have the
- Group membership is dynamic; hosts can join and leave the group at any time.
- Members of a group can be located anywhere on a multicast-enabled network.
- A host need not be a member of a multicast group to send data to the group’s IP multicast address.
- Group members can receive both unicast and multicast traffic.
- A host can be a member of any number of multicast groups.
- A multicast group has no size limits.
- Multicast groups can be either transient or permanent. Permanent
groups are assigned a well-known multicast address. For example,
multicast address 18.104.22.168 is a permanent address for the all-hosts
multicast group. Membership in a permanent group is transient; only the
address is permanent.