Module 7

Module Overview

  • Module Title: DHCPv4

  • Course: Switching, Routing and Wireless Essentials v7.0 (SRWE)

Module Objectives

  • Implement DHCPv4 to operate across multiple LANs.

  • Topic Objectives:

    • Explain how DHCPv4 operates in a small- to medium-sized business network.

    • Configure a Cisco IOS DHCPv4 Server.

    • Configure a router as a DHCPv4 client.

DHCPv4 Concepts

Overview of DHCPv4

  • Dynamic Host Configuration Protocol v4 (DHCPv4): Assigns IPv4 addresses and other configuration information dynamically.

  • Useful for automatic management of IP addresses, particularly in networks with multiple desktop clients.

  • Can be managed through a dedicated server or less commonly, through a Cisco router in smaller locations.

DHCPv4 Server Operations

  • DHCPv4 server assigns or leases an IPv4 address from a pool for a limited time period.

    • Lease Duration: Can range from 24 hours to over a week.

    • Clients request a new address when their lease expires but often receive the same address if available.

DHCPv4 Communication

  • Client/Server Mode: Clients acquire IPv4 addresses and must periodically contact the DHCP server to extend their lease.

  • When a lease expires, the IP address is returned to the pool for reallocation.

Steps to Obtain a Lease

  • The client follows a four-step process:

    1. **DHCP Discover (DHCPDISCOVER)

    2. DHCP Offer (DHCPOFFER)

    3. DHCP Request (DHCPREQUEST)

    4. DHCP Acknowledgment (DHCPACK)**

Steps to Renew a Lease

  • A client begins a two-step process to renew:

    1. DHCP Request (DHCPREQUEST)

      • Sent to original DHCP server; if no DHCPACK is received, a broadcast is sent.

    2. DHCP Acknowledgment (DHCPACK)

      • Sent by the server in response to the DHCPREQUEST.

Configuring Cisco IOS DHCPv4 Server

Basic Configuration

  • A Cisco router can serve as a DHCPv4 server, managing IP address pools for clients.

  • Configuration Steps:

    1. Exclude IP Address Ranges:

      • Command: ip dhcp excluded-address low-address [high-address]

    2. Define a DHCP Pool:

      • Command: ip dhcp pool pool-name

    3. Configure the DHPC Pool:

      • Use commands to define the network pool, default router, and other optional settings.

Verification Commands

  • Use the following commands to verify DHCP server operation:

    • show running-config | section dhcp

    • show ip dhcp binding

    • show ip dhcp server statistics

Disabling the DHCPv4 Server

  • To disable DHCP service, use the command: no service dhcp. To enable again, use: service dhcp.

DHCPv4 Relay Concepts

Importance of DHCPv4 Relay

  • In networks where clients and DHCP servers are not on the same subnet, routers must be configured to relay DHCP requests.

Configuring DHCPv4 Relay

  • Use the command: ip helper-address address on the interface facing clients.

  • This command forwards various UDP services, including DHCP.

Configuring a DHCPv4 Client

Cisco Router as a DHCP Client

  • Configure a Cisco router as a DHCP client using the command: ip address dhcp on the Ethernet interface.

  • Home routers generally have DHCP clients enabled by default for automatic ISP assignments.

Practice and Quiz

In this Module Practice Packet Tracer, Objectives Includes:

  • Configure a router as a DHCP server.

  • Configure DHCP relay.

  • Configure a router as a DHCP client.

Key Terms and Commands

  • DHCP: Dynamic Host Configuration Protocol

  • Lease Process: DHCP Discover, DHCPOffer, DHCP Request, DHCP Acknowledgment

  • Commands include: ip dhcp excluded-address, ip dhcp pool, network, default-router, dns-server, lease, show ip dhcp, and ip helper-address.