ZyXEL Communications Prestige 650HW - Manual (Page 49)

Prestige 650HW ADSL Router User’s Guide
Internet Access 3-5
3.4 IP 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 is a third way to deliver IP packets to a group
of hosts on the network - not everybody.
IGMP (Internet Group Multicast Protocol) is a session-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 Prestige supports both IGMP version 1 (IGMP-v1) and version 2 (IGMP-v2). At start up, the Prestige
queries all directly connected networks to gather group membership. After that, the Prestige periodically
updates this information. IP Multicasting can be enabled/disabled on the Prestige LAN and/or WAN
interfaces using menus 3.2 (LAN) and 11.3 (WAN). Select None to disable IP Multicasting on these
interfaces.
3.5 IP Policies
Traditionally, routing is based on the destination address only and the router takes the shortest path to
forward a packet. IP Policy Routing (IPPR) provides a mechanism to override the default routing behavior
and alter the packet forwarding based on the policy defined by the network administrator. Policy-based
routing is applied to incoming packets on a per interface basis, prior to the normal routing. Create policies
using SMT menu 25 (see IP Policy Routing) and apply them on the Prestige LAN and/or WAN interfaces
using menus 3.2 (LAN) and 11.3 (WAN).
3.6 IP Alias
IP Alias allows you to partition a physical network into different logical networks over the same Ethernet
interface. The Prestige supports three logical LAN interfaces via its single physical Ethernet interface with
the Prestige itself as the gateway for each LAN network.