Comtech EF Data CDM-570A Installation And Operation Manual page 519

2. Do not enable IF Loopback (or link the TX to RX by a BNC cable or
satellite) on an IP modem operating in Managed Switch Mode when
connected to a LAN. In this configuration, Managed Switch Mode will
resend all Layer 2 broadcast packets and cause a "broadcast storm" on
the LAN. To perform a loop test to verify the modem or satellite link, do
one of the following:
a.
b.
Information about the function of Managed Switch Mode, as well as a detailed description for the
setup and configuration of a Managed Switch Mode pair, is as follows:
•
Because Managed Switch Mode is a "smart wire," the devices attached to it on either
side of the satellite should be on the same subnet and should not configure a next hop
address to be the CDM-570A/570AL-IP address (as should be done with router mode).
For purposes of configuration, Managed Switch Mode should be viewed to function in
much the same way as a bridge (however, without spanning tree protocol).
•
All of the features that groom and optimize the satellite link in router mode are also
available in Managed Switch Mode.
•
Managed Switch Mode Multicast Option – Multicast packets in Managed Switch Mode
are identified using multicast MAC address. These identified multicast packets are either
routed or dropped based on the Managed Switch Mode multicast option.
•
Managed Switch Mode uses Layer 2 (MAC) addresses to learn where to send packets.
In comparison, router mode uses the destination IP address in the packet in conjunction
with the route table to determine where to forward the packets.
•
The Packet Processor in Managed Switch Mode is configured to be in promiscuous mode
with a data rate of 10/100BaseT Half Duplex/Full Duplex. The Packet Processor needs to
be in promiscuous mode in order to learn the attached networking devices.
•
Since Managed Switch Mode does not use a routing table, the determination of where to
send a packet is made by a learning process. When the system is powered-up, all
packets from each subnet (local and remote) will be sent over the satellite interface.
However, as each Packet Processor learns which devices are attached to their local
Ethernet interfaces, the Packet Processor begins to filter packets which it has learned are
locally attached to its Ethernet interface.
•
The Managed Switch Mode learning/forwarding algorithm is as follows:
If the packet is destined for the Packet Processor, then process it locally.
o
If the packet is from the Packet Processor Interface, then send it to the Satellite
o
interface; OR if the destination Layer 2 (MAC) address of the packets matches the
source Layer 2 address for a packet we have already seen, then the destination MAC
address of this packet is on our local subnet; so why send it over the satellite
interface. In this case, the Packet Processor will drop the packet.
If the packet is from the satellite interface, then send it out the Ethernet interface.
o
Optional High Performance Packet Processor
CDM-570L/570AL Satellite Modem with Optional Packet Processor
Reconfigure the CDM-570A/570AL-IP interface selection: From the
front panel, select Config Intfc, and then select RS422, V.35, or
RS232.
- OR –
Set the Packet Processor to Router Mode.
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Revision 5
MN-CDM570A