Avaya Configuring SNMP, BOOTP, DHCP, and RARP Services Manual de usuario descargar pdf (Pagina 55)

SNMP, BootP, BootP/DHCP Relay, DHCP Server, and RARP Concepts

117362-C Rev 00

2-25

Identifying DHCP Servers

Figure 2-9

shows the first stage of the process of acquiring a new IP address from

a DHCP server.

Figure 2-9. Identifying DHCP Servers

To identify DHCP servers, the DHCP client broadcasts a DHCPDISCOVER

packet on its local physical subnet. Table 2-4

describes the fields in the DHCP

packet. The packet release process uses these fields as follows:

A DHCP server receives the packet and finds an available IP address to assign

to the client.

The DHCP server sends an ICMP echo request to the prospective IP address

to determine whether the address is available. If the DHCP server receives a

response, the address is unavailable because it is being used by another host

on the network. The DHCP server selects another IP address to offer and

sends another ICMP echo request.

If there is no response to the ICMP echo request, the DHCP server sends a

DHCPOFFER packet that includes an available IP address to the target DHCP

client.

1. Client broadcasts

a DHCPDISCOVER

packet.

4. DHCP server

transmits

DHCPOFFER

packet to client.

2. DHCP server sends

ICMP echo request to

prospective IP address.

Router (DHCP server)

NetID

Server

Manager

DC0003A

The ICMP echo

request times out,

indicating that

request can be sent to client.

DHCP

client

DHCP

client

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