Comtech EF Data CRS-300 - Manual (Page 233)

A–1
Appendix A. ETHERNET
NETWORK CONFIGURATIONS
A.1 Overview
For operations requiring Ethernet-based terrestrial data handling, it is important to emphasize
the need for you to avoid Ethernet looping connection problems – with or without use of the
CRS-300 1:10 Redundancy Switch.
The intent of this appendix is to outline the differing methods for Ethernet-based data handling
with the various modems featured throughout this manual. Additionally, this appendix outlines
use of the CDM-700 Satellite Modem in redundancy. The CDM-700 provides the added
functionality of multiple data type handling simultaneously with Ethernet; i.e., Ethernet & HSSI,
Ethernet & G.703, etc.
A.2 Ethernet Routers vs. Switches
Routers and switches allow connection of one or more computers or networked devices to
other computers or network devices. Each has two or more connectors, called ports, in which
cables connect to other network devices.
An Ethernet router determines where to forward IP traffic based upon the destination IP address
and the Route table entries in the router. An Ethernet router can be programmed to understand
and route the data it is directed to handle; for example, broadband routers include the ability to
"hide" computers behind a type of firewall, which involves slightly modifying the packets of
network traffic as they traverse the device. All routers include some kind of user interface for
configuring how the router will treat traffic: larger routers include the equivalent of a full-blown
programming language to describe how they should operate, as well as the ability to communicate
with other routers to describe or determine the best way to direct network traffic from ‘Point A’ to
‘Point B’.
An Ethernet switch examines the traffic that comes across it, and learns where particular MAC
addresses are. An Ethernet switch maintains what is known as a CAM (Content Addressable
Memory) table, listing the MAC addresses for each switch port. The Ethernet switch uses the CAM
table to determine where to forward Ethernet frames. By default, Ethernet switches will update
the CAM table automatically; for example, if an Ethernet switch sees traffic from ‘Machine A’