User's Manual Part 1

70 APCD-LM043-8.0 (DRAFT C)
4: IP Network Planning
Through Only Mode
• For a PPPoE Network only, where all subscribers use a PPPoE server.
Routed Mode
• Networks with adequate public IP addresses for all Radio Network Devices
• Networks using private IP addresses for Radio Network Devices and NAT to map
subscribers to public IP addresses.
• Large networks where using added routers, multi-port routers or VLANs are not
options.
4.7.2 What are the DHCP considerations for the different protocol
modes?
DHCP
DHCP is a simple way to provision subscriber IP addresses and is highly recommended in all
modes. In general, it is a good idea to limit lease lengths in case it is necessary to change the
IP plan.
If DHCP Relay is enabled at a CCU, the CCU will intercept the DHCP request, which is in an
Ethernet broadcast packet and relays the request as a directed packet to the DHCP server.
The DHCP server can use the CCU IP address, which appears in the packet as the relay
agent to determine which pool to allocate from.
IP address assignment can be arbitrary, based on the subscriber’s Ethernet MAC address or
based on the subscriber’s computer’s hostname. The latter two approaches allow the WISP to
know which IP address is assigned to which subscriber, but require the hostname or Ethernet
MAC address to be known (or learned) by the DHCP server.
Routed mode
To use DHCP in Routed mode, the CCU must have DHCP relay enabled.
Use the CCU console command “arp map” to get a list of IP address-to-EUMID mappings.
Switched Ethernet Mode
If the DHCP server is in the Ethernet broadcast domain of the radio networks, it is to serve and
either a common pool of IP addresses must be used, or the Ethernet MAC or hostname must
be used to select a pool. DHCP relay is not required.
NOTE: Some DHCP servers do not support allocating addresses from an
IP subnet to which the relay agent does not belong.