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Chapter 7 WAN
EMG1302-R10A User’s Guide
55
WAN MAC Address
The MAC address screen allows users to configure the WAN port's MAC address by either using the
factory default or cloning the MAC address from a computer on your LAN. Choose Factory Default
to select the factory assigned default MAC Address.
Otherwise, click Clone the computer's MAC address and enter the IP address of the computer on
the LAN whose MAC you are cloning. Once it is successfully configured, the address will be copied to
configuration file. It is recommended that you clone the MAC address prior to hooking up the WAN
Port.
Maximum Transmission Unit
A maximum transmission unit (MTU) is the largest size packet or frame, specified in octets (eight-
bit bytes) that can be sent in a packet- or frame-based network. The Transmission Control Protocol
(TCP) uses the MTU to determine the maximum size of each packet in any transmission. Too large
an MTU size may mean retransmissions if the packet encounters a router that can't handle that
large a packet. Too small an MTU size means relatively more header overhead and more
acknowledgements that have to be sent and handled.
7.3.2 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 25 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 EMG1302-R10A supports both IGMP
version 1 (IGMP-v1) and IGMP version 2 (IGMP-v2).
At start up, the EMG1302-R10A queries all directly connected networks to gather group
membership. After that, the EMG1302-R10A periodically updates this information. IP multicasting
can be enabled/disabled on the EMG1302-R10A LAN and/or WAN interfaces in the Web Configurator
(LAN; WAN). Select None to disable IP multicasting on these interfaces.
A
B
C
D
Server