Technical data

IP, IPX, and AppleTalk Dial-Up Environments 5-5
Configuring Point-to-Point Protocol (PPP) Access
Assigning IP Addresses to Dial-In Clients
This section describes the methods you can use to assign IP addresses to dial-in clients. The methods
are as follows:
• Method 1: Obtain Addresses from a Pool Configured in the Access Server
This is the simplest mechanism for assigning IP addresses to dial-in clients and is most useful
when there is only one access server providing access to the network. A set of IP addresses is
defined in a database that exists inside the access server. If there is more than one access server
providing access to the network, you should refer to method 2.
• Method 2: Obtain Addresses from a Pool Configured in a DHCP Server
This is the next most convenient method, and is most useful for a medium to large-size pool of
dial-in clients. A pool of IP addresses is defined inside of a centralized IP address server, called
a Dynamic Host Configuration Protocol (DHCP) server. This central database can serve
addresses to several different access servers at the same time. Although this method provides
long-term flexibility, it requires that you configure a third-party host (such as a UNIX computer)
as a DHCP server.
• Method 3: Assign Static IP Addresses to Each PC
This is the least efficient most time-consuming method of assigning IP addresses to clients. As
clients are added, removed, and moved in the network, IP addresses must be reassigned.
Method 1: Obtain Addresses from a Pool Configured in the Access Server
To configure the address pool locally on the access server, perform the following steps:
Step 1 Create a local IP address pooling mechanism in the access server:
2511(config)# ip address-pool local
Step 2 Assign a pool of specific IP addresses in a pool (addresses 172.16.80.0 through
172.16.80.16 in pool1):
2511(config)# ip local pool pool1 172.16.80.1 172.16.80.16
The address pool named pool1 is applied automatically to each asynchronous interface
configured for point-to-point access, so you do not have to apply it manually. If you need
to apply this pool manually to asynchronous interfaces, issue the peer default ip-address
pool pool1 interface configuration command.
For a comprehensive configuration example of PPP dial-in to an IP network, refer to the section
“Dial-In Configuration Examples” later in this chapter.
Method 2: Obtain Addresses from a Pool Configured in a DHCP Server
To configure the access server to obtain IP addresses from a DHCP server, perform the following
steps:
Step 1 Configure asynchronous interfaces on an access server to assign IP addresses to dial-in
clients from a DHCP server (in this example, a group async interface is configured):
2511(config)# interface group-async 1
2511(config-if)# peer default ip-address dhcp
Step 2 Configure the Cisco IOS software to query a DHCP server for IP addresses that can be
supplied to IP clients as they dial in:
2511(config)# ip address-pool dhcp-proxy-client