The IP Multicast Deployment

In the deployment of IP multicasting the essentional and key component is designing and documenting the appropriate Multicast addressing scheme [1].

Some of the common problems that customers face during the IP multicast deployment are [1]

  • Keeping administration and troubleshooting of IP multicast as simple as possible. [1]
  • Controlling the distribution and the use of IP multicast group addresses within an organization, for instance, between Business Units. [1]
  • Controlling the distribution and scope of multicast application data within an organization. [1]
  • Locating Rendezvous Points with Protocol Independent Multicast (PIM) Sparse mode and which IP multicast groups each will serve. [1]
  • Controlling IP multicast traffic on WAN links so that high rate groups cannot saturate low speed links. [1]
  • Linking to the Internet for multicast. [1]
  • Allowing for future requirements and expansion so that readdressing is unnecessary at a later date. [1]

Proper Multicast addressing policy is needed to solve these issues. Without proper planning of addressing these problems increase the administrative work and less control on network.

IP Multicast Addresses

Ethernet MAC Address Mapping

The IANA owns a block of Ethernet MAC addresses that start with 01:00:5E in hexadecimal. Half of this block is allocated for multicast addresses. This creates the range of available Ethernet MAC addresses to be 0100.5e00.0000 through 0100.5e7f.ffff. [2]

This allocation allows for 23 bits in the Ethernet address to correspond to the IP multicast group address. The mapping places the lower 23 bits of the IP multicast group address into these available 23 bits in the Ethernet address. [2]

Performance Impact of Address Mapping

IP address is a 32 bit number and MAC address is consisting of 48 bits. First 4 bits in multicast IP address are reserved and remaining bits are 28, while first 25 bits are reserved in multicast MAC address and remaining bits are 23. When IP address is mapped with MAC address only 23 bits are mapped, and 5 bits of IP address are lost in mapping process. So the 32:1 address ambiguity comes, this means 32 different IP multicast addresses can be represented with single MAC address. If any of these 31 other groups are also active on the local LAN, the host CPU will receive interrupts when a frame is received for any of these other groups.[1]

IP Version 6 Multicast Addressing

An IPv6 multicast address is an identifier for a group of nodes. A node may belong to any number of multicast groups. Multicast addresses have the following format. [3]

References

  1. http://www.cisco.com/warp/public/cc/techno/tity/prodlit/ipmlt_wp.pdf [2010 Feb 18]
  2. http://www.cisco.com/en/US/docs/internetworking/technology/handbook/IP-Multi.html#wp1020617 [2010 Feb 18]
  3. http://www.ietf.org/rfc/rfc2373.txt [2010 Feb 19]
  4. http://www.net130.com/CMS/Files/Uploadimages/art7.gif [2010 Feb 23]
  5. http://www.h3c.com/portal/res/200706/01/20070601_109034_image006_201278_57_0.gif [2010 Feb 23]

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