Chapter 6 LAN Setup
P-2812HNU-51c User’s Guide
146
Multicast
Traditionally, IP packets are transmitted in one of either two ways - Unicast (1
sender - 1 recipient) or Broadcast (1 sender - everybody on the network).
Multicast delivers IP 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 to
establish 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) but IGMP
version 1 is still in wide use. If you would like to read more detailed information
about interoperability between IGMP version 2 and version 1, please see sections
4 and 5 of RFC 2236. The class D IP address is used 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 multicast computers. The address
224.0.0.1 is used for query messages and is assigned to the permanent group of
all IP hosts (including gateways). All hosts must join the 224.0.0.1 group in order
to participate in IGMP. The address 224.0.0.2 is assigned to the multicast routers
group.
The P-2812HNU-51c supports both IGMP version 1 (IGMP-v1) and IGMP version
2 (IGMP-v2). At start up, the P-2812HNU-51c queries all directly connected
networks to gather group membership. After that, the P-2812HNU-51c
periodically updates this information. IP multicasting can be enabled/disabled on
the P-2812HNU-51c LAN and/or WAN interfaces in the web configurator (LAN;
WAN). Select None to disable IP multicasting on these interfaces.
IP Alias
IP alias allows you to partition a physical network into different logical networks
over the same Ethernet interface. The P-2812HNU-51c supports three logical LAN
interfaces via its single physical Ethernet interface with the P-2812HNU-51c itself
as the gateway for each LAN network.
When you use IP alias, you can also configure firewall rules to control access
between the LAN's logical networks (subnets).
Note: Make sure that the subnets of the logical networks do not overlap.
