Unlike regular IP routes which are mainly concerned with next-hop information, subscriber-hosts are associated with an extensive set of parameters related to filtering, qos, stateful state (PPPoE/DHCP), antispoofing, and so on. Forwarding Database (FDB) is not suitable to maintain all this information. Instead, each subscriber host record is maintained in separate set of subscriber-host tables.
By pre-provisioning the IP prefix (IPv4 and IPv6) under the subscriber-interface and sub-if>ipv6 CLI hierarchy, only a single prefix aggregating the subscriber host entries is installed in the FDB. This FDB entry points to the corresponding subscriber-host tables that contain subscriber-host records.
When a IPv4/IPv6 prefix is not pre-provisioned, or the subscriber-hosts falls out of pre-provisioned prefix, each subscriber-host is installed in the FDB. The result of the subscriber-host FDB lookup points to the corresponding subscriber-host record in the subscriber-host table. This scenario is referred to as unnumbered subscriber-interfaces.
Unnumbered does not mean that the subscriber hosts do not have an IP address or prefix assigned. It only means that the IP address range out of which the address or prefix is assigned to the host does not have to be known in advance through configuration under the subscriber-interface or sub-if>ipv6 node.
An IPv6 example would be:
configure
router/service
subscriber-interface <name>
ipv6
[no] allow-unmatching-prefixes
delegated-prefix-length <bits>
subscriber-prefixes
This CLI indicates the following:
There is no need for any indication of anticipated IPv6 prefixes in CLI.
However, the delegated-prefix-length (DPL) command is required. The DPL (or the length of the prefix assigned to each Residential Gateway) must be known in advance. All Residential Gateways (or subscribers) under the same subscriber-interface share this pre-configured DPL.
The DPL range is 48 to 64.
If the prefix length in the received PD (through the DHCP server, RADIUS or LUDB) and the DPL do not match, the host creation fails.
If the assigned IP prefix/address (DHCP server, RADIUS, LUDB) for the host falls outside of the CLI defined prefixes and the allow-unmatching-prefixes command is configured, then the new address and prefix automatically installs in the FDB.