Based on DHCP and L2 NAT configuration on the ISA, the configured IP address (l2-aware-ip-address configured under vlan-tag-ranges range start vlan-id end vlan-id or vlan-tag-ranges range default) is assigned to the user via DHCP. A different DHCP lease-time can be configured for an un-authenticated and an authenticated user for which an ESM or DSM host has been created. DHCP return options, for example, DNS and NBNS server addresses can be configured. This configuration can be per soft-wlan-gw group interface (by explicitly configuring it under vlan-tag-ranges range default), or per VLAN range (where a VLAN tag corresponds to an SSID). By default, for open SSIDs, DHCP DORA is completed, and authentication request is sent to AAA server only on reception of the first Layer 3 packet. However, with a authenticate-on-dhcp command configured under vlan-tag-ranges range default (default or specific range), authentication can be triggered on received DHCP DISCOVER or REQUEST when no UE state is present. If UE anchoring on GGSN/PGW is required, then authenticate-on-dhcp must be enabled, because the decision to setup GTP tunnel (in which case the IP@ for the UE comes from the GGSN/PGW) is based on RADIUS response.
To support unique inside IP addresses, the ISA Pool Manager can be used. Pools are allocated to each ISA in large blocks, requiring an IPv4 subnet with prefix-length 16. From this prefix, the subnet address (x.x.0.0), broadcast address (x.x.255.255), and gateway address (x.x.0.1) are reserved and not allocated to UEs, reducing the total number of available addresses by three. NAT pools are only available in non-retailer subscriber interfaces. Any retail service ID derived from configuration or AAA is only used for IPv6 pool selection and is ignored for IPv4 NAT pools. Forwarding in a different VRF can be achieved by selecting a different NAT policy and outside VRF.