User's Manual Part 1

66 APCD-LM043-8.0 (DRAFT C)
4: IP Network Planning
Note that with release V4.0 the CCU Ethernet port bridge table is limited to 256 entries. This
imposes a further limit to the size of the Ethernet broadcast domain in Switched Ethernet and
Through Only modes. A single CCU Ethernet port should see no more than 256 Ethernet
devices. To compute this, take the total number of Ethernet devices in the broadcast domain,
and subtract the number of Ethernet devices on the smallest radio network. For example, if
there are 3 CCUs with 40, 50 and 60 subscribers, each with an EUM, the total number of
Ethernet devices in the broadcast domain is at least 306 (150 EUMs, 150 Subscribers, 3
CCUs, 1 router, 1 switch). This configuration will work. Any CCU Ethernet port will only see the
MAC addresses for the EUMs and subscribers for the other CCUs plus devices directly on the
CCU Ethernet (e.g., 110 EUMs, 110 subscribers, and 5 other devices in the worst case, for the
first CCU). Any broadcast domain with no more than 250 Ethernet devices will also work. This
limitation will be removed for V4.1 and later releases.
For networks that are larger than 650 Ethernet devices, multiple Ethernet broadcast domains
should be used. Each broadcast domain will contain one or more IP subnets. Multiple Ethernet
broadcast domains can be realized by using multiple IP routers, IP routers with multiple ports,
or VLANs between a router and a multi-port Ethernet switch.
Using the CCUs in Routed mode is an example of the first method of dividing the broadcast
domain, using multiple routers, although the CCU as a router only supports one IP subnet over
the radio network.