How It Works - Cisco ASR 5000 series Product Overview

ASN Gateway Overview

How it Works

The DHCP proxy server and the IP pool hosted locally on the ASN Gateway provide the primary IP address from a
primary IP pool to the WiMAX customer premise equipment (CPE). The CPE is identified by its WiMAX R6 MSID (6-
byte MAC address).
Important:
Once a primary IP address is assigned dynamically to the WiMAX CPE, additional IP addresses are assigned
dynamically to other IP hosts. Each of the IP hosts is identified by its unique 6-byte MAC address. The DHCP proxy on
the ASN Gateway manages the IP addresses by mapping them to the unique MAC addresses supplied by the client in
the chaddr option field in DHCP DISCOVER or REQUEST messages.
The primary IP address is assigned to the CPE first via DHCP. It is followed by requests for additional IP addresses by
individual IP hosts behind the CPE. The ASN Gateway allocates secondary hosts on-demand, up to the configured limit
of 4.
Primary IP addresses assigned to WiMAX CPE and secondary IP addresses assigned to the IP hosts, are configured in
separate IP pools or the same IP pool. Accounting is based on the primary IP address assigned to CPE and UDR
accounting is enabled only for the primary session (flow/session based). No accounting is performed for secondary sub-
sessions.
Using the device credentials of the WiMAX CPE, authentication is performed with the EAP-TLS method. There is no
authentication for each assigned IP address, and no validation of MAC addresses contained in DHCP requests, except to
make sure that they are unique across all subscribers connected to the DHCP proxy server.
IP Address Allocation through DHCP
The dynamic IP address allocation procedure for primary node and secondary hosts is described below:
After the initial network entry for WiMAX CPE is completed, the WiMAX CPE acts as a primary node and
starts the DHCP process with the WiMAX ASN Gateway.
The DHCP proxy server hosted on the ASN Gateway allocates the Primary IP address to the WiMAX CPE as a
primary node from the configured primary IP Pool.
The primary IP address is the first IP address assigned to the WiMAX CPE. The DHCP DISCOVER and
REQUEST messages for this must contain the WiMAX R6 MSID as the chaddr field. After this IP address is
assigned, the session goes into Connected state and is ready to accept DHCP requests for additional IP
addresses for other IP hosts.
Once the primary IP address is assigned to the primary node (WiMAX CPE), hosts behind the CPE start the
DHCP process with the WiMAX ASN Gateway for each host mapping to its 6-byte MAC address.
The DHCP proxy server hosted in the ASN Gateway allocates the secondary IP addresses to the hosts behind the
CPE as an auxiliary node from the configured secondary IP Pool.
When session termination is requested, the primary IP address is the last IP address to be released by the clients
and ASN Gateway. This means the primary IP address must be in use and in lease for the session to continue in
Connected state. When the Primary IP address is released, the ASN Gateway session is terminated and all IP
addresses are freed.
OL-22938-02
Multiple IP hosts feature is not supported for Proxy-MIP session.
Supported Features ▀
Cisco ASR 5000 Series Product Overview ▄