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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 45 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 NBG6815 supports both IGMP version 1
(IGMP-v1) and IGMP version 2 (IGMP-v2).
At start up, the NBG6815 queries all directly connected networks to gather group membership.
After that, the NBG6815 periodically updates this information. IP multicasting can be enabled/
disabled on the NBG6815 WAN interface in the Web Configurator (WAN). Select None to disable IP
multicasting on these interfaces.
Auto-IP Change
When the NBG6815 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 NBG6815 to change its LAN IP
address to 10.0.0.1 automatically. If the NBG6815'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 NBG6815 switches to use 192.168.1.1
as its LAN IP address.
Figure 46 Auto-IP-Change Example
192.168.1.23
192.168.1.1
10.0.0.1
NBG6815 User's Guide
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