Comtech EF Data CDM-IP 300L - Manual (Page 32)

CDM-IP 300L IP-Centric Satellite Modem Rev. 1
CD/CDMIP300L.IOM
4
All of the features that groom and optimize the satellite link in router mode are also
available in easyConnect
 mode.
easyConnect  Multicast Option – Multicast packets in easyConnect mode are
identified using multicast MAC address. These identified multicast packets are either
routed or dropped based on the easyConnect
 multicast option.
easyConnect  uses MAC (layer 2) 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 CDM-IP Ethernet interface in easyConnect  mode is configured to be in
promiscuous mode with a data rate of 10BaseT Half Duplex. The CDM-IP needs to
be in promiscuous mode in order to learn the attached networking devices.
Since easyConnect  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 CDM-IP learns which devices are attached to their local Ethernet interfaces,
the CDM-IP begins to filter packets which it has learned are locally attached to its
Ethernet interface.
The easyConnect  learning/forwarding algorithm is as follows:
If the packet is destined for the CDM-IP, process it locally.
If the packet is from the Ethernet interface, send it to the Satellite interface, unless
the destination layer 2 (MAC address) of the packets matches the source layer 2
address for a packet we have already seen, the destination MAC address of this
packet is on our local subnet; so why send it over the satellite interface. In this
case, the CDM-IP will drop the packet.
If the packet is from the satellite interface, send it out the Ethernet interface.
IMPORTANT
easyConnect  mode will automatically use Header Compression (even if Header
Compression option has not been purchased). Because of this, some of the initial
traffic sent between two devices will not be received over the satellite until a full
Header is transmitted. For example, the default Header Compression Refresh
Rate is 50 packets. If a ping is sent over the satellite it will time out until the full
Header packet is sent. The Header Compression Refresh Rate on the
Administration Menu can be reduced to minimize the amount of traffic lost when
traffic is first sent between two devices. Once communication between two
devices has been established, both CDM-IP modems will be able to receive all
traffic, unless one CDM-IP is power cycled or reset.