All About Multicast IP Range

Happy Tuesday!!

In this post, we will discuss IP addressing for multicast applications. Multicast applications use an address range that falls under the category of class D and ranges from 224.0.0.0 to 239.255.255.255. We all know that IP addresses are categorized into five classes: class A, B, C for LANs and WANs, and class D for multicasting, class E use by research organization.

You must use this class D range if you want to host any multicast services or multicast servers. The multicast address represents a multicast application, and it's usually called a group address.

Let us take an example, say a server sends multicast streaming to a selected set of receivers. During multicast streaming, it will not send to the exact IP addresses of the receivers. Let's say the IP addresses are 10.14.5.6 and 10.14.5.7, but instead it will send to the group address. Now the group address will be the multicast address and the destination address will be something like 224.0.0.5. By using this address, we will be able to identify a group and identify which users want to receive multicast traffic. These users will join the group and receive the multicast service. When multicast traffic is sent, the destination address will always be the multicast address, so class D addresses are used. \

In other words, it will never be the receiver's address, it will always be the multicast address range, or group address, as I mentioned earlier.

Multicast address ranges are categorized according to IANA as 224-239 and further classified into different categories as follows:

• Permanent multicast group
• Source-Specific multicast group
• Private multicast address

Permanent Multicast Group

We have two different ranges for this multicast group, one for non-routed purpose and one for routed purpose, within the range 224.0.0.0 -224.0.1.255.

The addresses between 224.0.0.x and 255 are reserved for network protocols on the same local segment.  Since these addresses are on the same local segment, they will not be forwarded to the next router, and the default TTL value is 1. Within this range, these packets are not forwarded by the router. Imagine you have an address 224.0.0.1 used by the multicast-capable host. Suppose you have a multicast-capable PC or host in your LAN and you want to check the connectivity and get a reply from all the hosts running multicast traffic in the LAN. There is a good chance you will receive a response when you ping to this. 

Multicast-enabled hosts listen to 224.0.0.1, while multicast-enabled routers listen to 224.0.0.2.        

• Address 224.0.01 identifies the all-host group.
• This group must be joined by every multicast-capable host.
• ICMP echo requests sent to this address will be answered by all multicast capable hosts on the network.

ping 224.0.0.1

Type escape sequence to abort.

Sending 1, 100-byte ICMP Echos to 224.0.0.1, timeout is 2 seconds:

Reply to request 0 from 10.12.9.240, 4 ms

Reply to request 0 from 10.12.10.79, 44 ms

Reply to request 0 from 10.12.10.82, 44 ms

Reply to request 0 from 10.12.10.78, 44 ms

        

• Address 224.0.0.2 identifies all-routers-group
• Routers that support multicast join this group on all multicast-enabled interfaces.
• The router will not forward this address range to the other routers since these two addresses work only one hop apart.

We also have some other multicast address ranges, such as

• 224.0.0.5 , 224.0.0.6 used by the OSPF to exchange link-state information.
• 224.0.0.9--All RIPV2 routers
• 224.0.0.13-- All PIM routers
• 224.0.0.10--EIGRP

The address is reserved for some protocols which operate within the same local segment and require less than one hop.

There are now protocols reserved for the routed permanent multicast address range, and those protocols will be forwarded throughout the entire network. Therefore, routers with this particular group address will be forwarded to the next address.

• 224.0.1.39 - 224.0.1.40 are reserved for PIM RP messages

Source Specific Multicast (SSM)

The entire range of 232.0.0.0-232.255.255.255 is reserved for source-specific multicast. IGMP version 3 uses this.

Private Multicast addresses (239.0.0.0-239.255.255.255)

You can use this address range within your company if you want to run any multicast application more like a private IP address.