User's Guide

Chapter 10 WAN
EMG3435-Q20A User’s Guide
74
Multic a st
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.
Fig ure 53 Multicast Example
In the multicast example above, systems A and D comprise one multicast group. In multicasting, the
server only needs to send one data stream and this is delivered to systems A and D.
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. The EMG3435-Q20A supports both IGMP version 1
(IGMP- v1) and IGMP version 2 (IG MP- v2).
At start up, the EMG3435-Q20A queries all directly connected networks to gather group membership.
After that, the EMG3435-Q20A periodically updates this information. IP multicasting can be enabled/
disabled on the EMG3435-Q20A WAN interface in the Web Configurator (WAN). Select No ne to disable
IP multicasting on these interfaces.
Auto - IP C ha ng e
When the EMG3435-Q20A gets a WAN IP address or a DNS server IP address which is in the same subnet
as the LAN IP address 192.168.1.1, Auto-IP-Change allows the EMG3435-Q20A to change its LAN IP
address to 10.0.0.1 automatically. If the EMG3435-Q20A’s original LAN IP address is 10.0.0.1 and the WAN
IP address is in the same subnet, such as 10.0.0.3, the EMG3435-Q20A switches to use 192.168.1.1 as its
LAN IP address.
Fig ure 54 Auto-IP-Change Example
1 9 2 .1 6 8 .1 .1
1 9 2 .1 6 8 .1 .2 3
1 0 .0 .0 .1