Chapter 6 LAN screens 95Nortel Business Secure Router 222 Configuration — BasicsBoth RIP-2B and RIP-2M send routing data in RIP-2 format; the differencebeing that RIP-2B uses subnet broadcasting while RIP-2M uses multicasting.Multicasting can reduce the load on nonrouter machines since they generally donot listen to the RIP multicast address and so do not receive the RIP packets.However, if one router uses multicasting, then all routers on your network mustuse multicasting, also.By default, RIP Direction is set to Both and RIP Version to RIP-1.MulticastTraditionally, IP packets are transmitted in one of two ways—Unicast (1 sender-1recipient) or Broadcast (1 sender-everybody on the network). Multicast deliversIP packets to a group of hosts on the network—not everybody and not just 1.IGMP (Internet Group Multicast Protocol) is a network layer protocol used toestablish membership in a Multicast group—it is not used to carry user data.IGMP version 2 (RFC 2236) is an improvement over version 1 (RFC 1112) butIGMP version 1 is still in wide use. If you want to read more detailed informationabout interoperability between IGMP version 2 and version 1, see sections 4 and 5of Internet Group Management Protocol (RFC 2236). The class D IP address isused to identify host groups and can be in the range 224.0.0.0 to 239.255.255.255.The address 224.0.0.0 is not assigned to any group and is used by IP multicastcomputers. The address 224.0.0.1 is used for query messages and is assigned tothe permanent group of all IP hosts (including gateways). All hosts must join the224.0.0.1 group in order to participate in IGMP. The address 224.0.0.2 is assignedto the multicast routers group.The Business Secure Router supports both IGMP version 1 (IGMP-v1) andIGMP version 2 (IGMP-v2). At start up, the Business Secure Router queries alldirectly connected networks to gather group membership. After that, the BusinessSecure Router periodically updates this information. IP multicasting can beenabled or disabled on the Business Secure Router LAN, WAN or both interfacesin the WebGUI (LAN; WAN). Select None to disable IP multicasting on theseinterfaces.
