Cisco 1003 - 1003 Router Manual de usuario descargar pdf (Pagina 14)

11-14 Internetwork Design Guide

Dial-on-Demand Routing

The core router can assign IP addresses from a local pool maintained by the core router or from a

Terminal Access Controller Access Control System Plus (TACACS+) server or a Dynamic Host

Conﬁguration Protocol (DHCP) server, as shown in Figure 11-4.

Figure 11-4 IP Address Negotiation

Note The core router can be conﬁgured to assign addresses from more than one type of pool. For

example, the core router can be conﬁgured to obtain addresses from the local pool for certain dial-up

users and to obtain addresses from the TACACS+ server for other dial-up users.

IP address negotiation allows an organization to manage its address space centrally and to minimize

address utilization. With IP address negotiation, you need to provide only enough address space to

cope with worst case loading scenarios. Use of IP address negotiation also reduces conﬁguration text

in the core router. Because of the dynamic nature of IP address assignment, the core router no longer

needs to maintain a speciﬁc dialer map statement for each remote node. IP address negotiation

creates dynamic dialer maps for each individual connection and removes them at the end of the

session.

Note It is important to ensure that addresses are negotiated via PPP IPCP. Some client software

stacks support DHCP locally. If the remote node originates the DHCP request, the core router cannot

function as a DHCP proxy, so a return path will not be available through the core router.

Local Address Assignment

The core router can be conﬁgured to maintain several pools of IP addresses, with each pool holding

up to 255 addresses. Each pool has a free queue containing available addresses and a “used” queue

containing addresses that are currently in use. On receipt of the IPCP address negotiation request,

the core router retrieves an address from the free queue. The client can request the same address that

was used for the last connection. If this address is in the free queue, it is assigned. If the requested

address is in use, another address from the free queue is assigned.

PRI or BRI

interface

Core router

DHCP server

TACACS+ server

Local “pool” of

ISDN TA

LAN2LAN for ISDN card

addresses

S4441

ISDN

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Cisco 1003 - 1003 Router Manual de usuario Pagina 14