PPP for IPv4
On IPv4 networks, PPP negotiates the IP address and DNS server address during IPCP negotiation.
IP address negotiation
IP address negotiation enables one end to assign an IP address to the other.
An interface can act as a client or a server during IP address negotiation:
Client—Obtains an IP address from the server. Use the client mode when the device accesses the Internet through an ISP.
Server—Assigns an IP address to the client. Before you configure the IP address of the server, you must perform one of the following tasks:
Configure a local address pool and associate the pool with the ISP domain.
Specify an IP address or an address pool for the client on the interface.
When IP address negotiation is enabled on a client, the server selects an IP address for the client in the following sequence:
If the AAA server configures an IP address or address pool for the client, the server selects that IP address or an IP address from the pool. The IP address or address pool is configured on the AAA server instead of the PPP server. For information about AAA, see Security Configuration Guide.
If an address pool is associated with the ISP domain used during client authentication, the server selects an IP address from the pool.
If an IP address or address pool is specified for the client on the interface of the server, the server selects that IP address or an IP address from that pool.
DNS server address negotiation
IPCP negotiation can determine the DNS server IP address.
When the device is connected to a host, configure the device as the server to assign the DNS server IP address to the host.
When the device is connected to an ISP access server, configure the device as the client. Then, the device can obtain the DNS server IP address from the ISP access server.