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CRS-180 70/140 MHz IF 1:1 Redundancy Switch
Introduction
occurred at the same time (in fact, within a 0.5 second window), and infers that the fault is
external. Therefore, no unnecessary switchover is initiated.
1.2.1.1 1:1 IP Redundancy Data Switching – Functional Description
1.2.1.1.1 CDM-570 (with optional IP Module) Managed Switch or Router
Modes
•
Do not use the M&C Ethernet port (bottom RJ‐45 connector) when the optional
IP Module is installed.
•
All configuration changes can only be made to the Online Modem and will
require the User to
ensure the configuration change is also applied to the Backup Modem.
Managed Switch (Ethernet Bridge) Mode: For the CDM‐570 in Managed Switch Mode (also
known as "Ethernet Bridge Mode") the user MUST use an external Ethernet hub to insure that
traffic will continue after a switchover. If an Ethernet switch is used, there could be a several
minute outage while the Ethernet Switch "re‐learns" the correct output Ethernet port. Using a
"dumb" Ethernet hub allows LAN‐to‐WAN traffic to continue even after a switchover occurs
since both modems will be receiving the LAN traffic.
In Managed Switch Mode, both modems should be assigned a unique Management IP address
on the same subnet in order to share the parameter file.
Router Mode: For the CDM‐570 in Router Mode, the user should use an external Ethernet
switch. Router mode does not require a "dumb" hub as with Managed Switch Mode and, for
performance reasons, an Ethernet switch is highly recommended.
In Router Mode, both modems must be assigned a unique Management IP address on the same
subnet (172.18.10.21/24 and 172.18.10.22/24 as shown in Figure 1‐4 and Figure 1‐5). This is
used to share the param file. A Traffic IP address on the subnet must also be assigned
(172.18.10.20/24) in the Online modem.
Whichever modem is Online will assume the Traffic IP. When there is a switchover to the backup
modem, this modem will now assume the Traffic IP. As shown in Figure 1‐5, the backup modem
will also broadcast a "gratuitous ARP" that will tell all local devices to now associate a new MAC
address for the Traffic IP 172.18.10.20. Each device will update their ARP tables and traffic will
resume virtually instantaneously.
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Save Parameters to permanent storage
1–5
Revision 8
MN/CRS180.IOM
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