Comtech EF Data cdm-570a - CDM-570 A;570 AL-IP 1:1 IP Data Switching Functional Description

CDM-570A/570AL Satellite Modem with Optional Packet Processor
Revision 5
1:1 IP Redundancy N–6 MN-CDM570A
N.4 CDM-570A/570AL-IP 1:1 IP Data Switching Functional Description
When the CDM-570A/570AL-IP modem is using a serial data interface (for example, RS.422 or
V.35), the paired modems are connected to a CRS-180 (or CRS-170A) 1:1 Redundancy Switch
with an adapter Y-cable. When the CDM-570A/570AL-IP is using the optional Packet Processor
as the data interface, as shown in Figure N-2, you may use a standard Ethernet Layer 2 Switch
or Hub (it is recommended that you use a Layer 2 Switch).
Figure N-2. CDM-570A/570AL-IP 1:1 IP Redundancy Example
(Router Mode Shown, Modem ‘A’ Online)
For CDM-570A/570AL-IP IP 1:1 redundancy operation, both CDM-570A/570AL-IP s are assigned
a unique M&C IP address on the same subnet (in Figure N-2, 172,18.10.21/24 and
172.18.10.22/24). A Traffic IP address on the subnet is also assigned (172.18.10.20/24).
Whichever modem is online also assumes the Traffic IP.
When there is a switchover to the backup modem, this modem now assumes the Traffic IP. It also
broadcasts a “Gratuitous ARP” that tells all local devices to now associate a new MAC address
for the Traffic IP 172.18.10.20. Each device updates their ARP tables, traffic virtually resumes
instantaneously.