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Chapter 10 WAN
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.
Figure 39 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 NBG6816 supports both IGMP version 1
(IGMP-v1) and IGMP version 2 (IGMP-v2).
At start up, the NBG6816 queries all directly connected networks to gather group membership.
After that, the NBG6816 periodically updates this information. IP multicasting can be enabled/
disabled on the NBG6816 WAN interface in the Web Configurator (WAN). Select None to disable IP
multicasting on these interfaces.
Auto-IP Change
When the NBG6816 gets a WAN IP address which is in the same subnet as the LAN IP address
192.168.1.1, Auto-IP-Change allows the NBG6816 to change its LAN IP address to 10.0.0.1
automatically. If the NBG6816'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 NBG6816 switches to use 192.168.1.1 as its LAN IP
address.
Figure 40 Auto-IP-Change Example
192.168.1.23
192.168.1.1
10.0.0.1
NBG6816 User's Guide
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