CCNA2 TEL III CHAPTER 8

CCNA2 TEL III CHAPTER 8

1. Introducing DHCPv4

   • DHCPv4 assigns IPv4 addresses and other network configuration information dynamically. Because desktop clients typically make up the bulk of network nodes, DHCPv4 is an extremely useful and timesaving tool for network administrators. A dedicated DHCPv4 server is scalable and relatively easy to manage. However, in a small branch or SOHO location, a Cisco router can be configured to provide DHCPv4 services without the need for a dedicated server. Cisco IOS software supports an optional, full-featured DHCPv4 server.

2. DHCPv4 Operation

3. DHCPv4 Message Format

   • The DHCPv4 message format is used for all DHCPv4 transactions. DHCPv4 messages are encapsulated within the UDP transport protocol. DHCPv4 messages sent from the client use UDP source port 68 and destination port 67. DHCPv4 messages sent from the server to the client use UDP source port 67 and destination port 68.

4. DHCPv4 Discover and Offer Messages

5. Configuring a Basic DHCPv4 Server

6. Verifying DHCPv4

7. DHCPv4 Relay

8. Configuring a Router as DHCPv4 Client

   • Sometimes, Cisco routers in small office/home office (SOHO) and branch sites have to be configured as DHCPv4 clients in a similar manner to client computers. The method used depends on the ISP. However, in its simplest configuration, the Ethernet interface is used to connect to a cable or DSL modem. To configure an Ethernet interface as a DHCP client, use the ip address dhcp interface configuration mode command. In Figure 1, assume that an ISP has been configured to provide select customers with IP addresses from the 209.165.201.0/27 network range. After the G0/1 interface is configured with the ip address dhcp command, the show ip interface g0/1 command confirms that the interface is up and that the address was allocated by a DHCPv4 server.

9. Configuring a Wireless Router as a DHCPv4 Client

10. Troubleshooting Tasks

11. Verify Router DHCPv4 Configuration

12. Debugging DHCPv4

13. Stateless Address Autoconfiguration (SLAAC)

14. SLAAC Operation

    • A router must have IPv6 routing enabled before it can send RA messages: Router(config)# ipv6 unicast-routing

15. SLAAC and DHCPv6

16. SLAAC Option

    • RA messages are configured on an individual interface of a router. To re-enable an interface for SLAAC that might have been set to another option, the M and O flags need to be reset to their initial values of 0. This is done using the following interface configuration mode commands: Router(config-if)# no ipv6 nd managed-config-flag Router(config-if)# no ipv6 nd other-config-flag

17. Stateless DHCPv6 Option

18. Stateful DHCPv6 Option

19. DHCPv6 Operations

20. Configuring a Router as a Stateless DHCPv6 Server

21. Configuring a Router as a Stateless DHCPv6 Client

22. Verifying Stateless DHCPv6

23. Configuring a Router as a Stateful DHCPv6 Server

    • Configuring a Router as a Stateful DHCPv6 Client
    • Verifying Stateful DHCPv6

24. Configuring a Router as a DHCPv6 Relay Agent

25. Verify Router DHCPv6 Configuration

26. Debugging DHCPv6

27. conclusion

    • All nodes on a network require a unique IP address to communicate with other devices. The static assignment of IP addressing information on a large network results in an administrative burden that can be eliminated by using DHCPv4 and DHCPv6 to dynamically assign IPv4 and IPv6 addressing information, respectively. DHCPv4 dynamically assigns, or leases, an IPv4 address from a pool of addresses for a limited period of time, as configured on the server, or until the client no longer needs the address. DHCPv4 involves the exchange of several different packets between the DHCPv4 server and the DHCPv4 client resulting in the lease of valid addressing information for a predefined period of time. Messages originating from the client (DHCPDISCOVER, DHCPREQUEST) are broadcast to allow all DHCPv4 servers on the network to hear the client request for, and receipt of, addressing information. Messages originating from the DHCPv4 server (DHCPOFFER, DHCPACK) are sent as unicasts directly to the clie

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