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VLSM and CIDR |
| Variable Length Subnet Masking (VLSM, RFC 1009) and Classless Inter Domain Routing (CIDR, RFCs 1517-1520) are technologies that simplify the task of assigning subnets to ports and SUs in a routed system configuration. The IP Routing protocol implementation in the Aperto BSU supports both VLSM and CIDR. When the BSU is configured in the Router mode, then these technologies enable the operator to take a single Class C IP Address Space, and divide up the addresses among the four wireless ports as well as to the routed SUs, in a flexible manner. |
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| The following example illustrates a practical deployment that takes advantage of VLSM features. A BSU is expected to serve up to 256 SUs, therefore the 11.1.1.0/24 subnet has been allocated by the operator. The 11.1.1.0/24 subnet is configured with a /26 extended-network-prefix to allow for 4 sub-subnets (one per Wireless port). With this configuration each wireless sector can serve up to 63 SUs. Note also that in sector 2 (WSS-2) of the BSU, an SU has been configured as a router with a /29 extended-network-prefix so that it can serve up to 6 hosts behind it (two addresses are reserved for the Wireless and LAN interfaces of the SU). |
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