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Equal-Access Mode Overview
In equal-access mode, the router enables
access to non-PPP users. Non-PPP equal access requires the use of
the router’s DHCP local server and SRC software, which communicates
with a RADIUS server.
The DHCP local server performs the following functions
in equal-access mode:
- Communicates with SRC software.
- Assigns an IP address that enables the subscriber to access
services.
Local Pool Selection and Address Allocation
The DHCP local server selects a DHCP pool from
which to allocate an address using the framed IP address or pool name
parameters. The router compares the parameters with the local DHCP
pools in the order presented in Table 95. When
the router finds a match, it selects a pool based on the match and
does not examine other parameters.
Table 95: Local Pool
Selection in Equal-Access Mode
|
Field
|
How the DHCP Local Server Uses the Field
|
|
Framed IP address
|
The
client’s RADIUS entry can be configured with a framed IP address,
which the DHCP local server can get from the SRC software.
If the router selects a pool using a framed IP address, the
DHCP local server attempts to allocate the framed IP address from
the pool. If the framed IP address is not available, then the server
allocates the next available address in the pool to the client.
|
|
Pool name
|
Each DHCP
local pool has a pool name. The client’s RADIUS entry can also
be configured with a pool name, which the DHCP local server can get
from the SRC software. The SRC software must be configured to send
RADIUS attributes to DHCP.
|
|
Domain name
|
You can
use a domain name as the name of a DHCP local pool. If the client
logs onto the SRC software and RADIUS authenticates the client using
a domain name, the DHCP local server receives the domain name from
the SRC software.
If the client’s domain name does not match the name of
the DHCP local pool, the router attempts to match the client’s
domain name to the domain name field within the pool.
|
|
Giaddr
|
A DHCP local pool is
configured with a network address. A gateway IP address (giaddr),
which indicates a client’s subnetwork, can be presented to the
DHCP local server in the client’s DHCP request message. The
giaddr field in the DHCP request message usually contains the IP address
of a DHCP relay server. The router attempts to match the giaddr address
in the DHCP request message with the network address of a DHCP local
pool.
|
The Connection Process
The following sequence describes how the subscriber
connects to the network for the first time using equal-access mode. Figure 11 illustrates the process.
- The subscriber’s computer boots and issues a DHCP
request.
- The DHCP local server uses the SRC client to issue a COPS
request to retrieve address pool information.
- After standard DHCP negotiations, the DHCP local server
supplies an IP address to the subscriber’s computer from a local
address pool, as described in the previous section.
The router maintains a host route that maps the
IP address to the router’s interface associated with the subscriber’s
computer.
- The subscriber’s computer retains the IP address
until the subscriber turns off the computer.
 |
Note:
If a DHCP client attempts to renew its address and the DHCP
server receives the request on a different interface than the interface
that the client originally used, the DHCP server sends a NAK message
to the client, forcing the client to begin the DHCP connection process
again.
|
Figure 11: Non-PPP Equal Access via the Router
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