1. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 1 Version 4.0 Implementing IP Addressing Services Accessing the WAN – Chapter 7

2. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 2 Objectives  Configure DHCP in an enterprise branch network  Configure NAT on a Cisco router

3. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 3 Function of DHCP  To allocate IP addresses, mask, gateway to devices that are not always on, or that move

4. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 4 Configure DHCP in an Enterprise Branch Network  DHCP provides a device with several important pieces of information The device's IP address The netmask for the network The IP address of the default gateway The IP addresses of the local DNS servers The domain name and port for the local web proxy server  Some of these things are optional  In fact, DHCP can provide a lot of optional networking information to clients as they are booting

5. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 5 Process to Obtain DHCP Information  Four-step process (DORA)

6. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 6 Configure DHCP in an Enterprise Branch Network  We can configure a router to act as a DHCP server  It needs to know: what addresses are in the pool of available addresses, what addresses are excluded, and what other optional information to advertise  Setting up the excluded addresses

7. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 7 Configure DHCP in an Enterprise Branch Network  Setting up the pool of available IP addresses

8. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 8 Configure DHCP in an Enterprise Branch Network  The rest of the configuration

9. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 9 Verifying DHCP Operation

10. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 10 Troubleshooting DHCP Operation

11. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 11 Private IP Addresses  Not routed across the Internet

12. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 12 NAT: Network Address Translation  NAT allows a network using private IP addresses to be hidden behind a device with one or more public IP addresses  The device modifies the addresses in each packet so that the private addresses are not seen on the Internet

13. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 13 Advantages and Disadvantages of NAT

14. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 14 Three Types of NAT  Static NAT: one private IP tied to one public IP  Dynamic IP: pool of public IPs. As a private IP device needs to communicate on the Internet, a mapping is made to one of the public IPs in the pool  NAT Overload (or Port Address Translation) Only one or a few public IPs, but many private IPs We rewrite source port numbers as well as private IP addresses, so that the intenal devices can share the public IP addresses

15. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 15 Configuring Static NAT  This also allows connections from the Internet into the private device

16. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 16 Configuring Dynamic NAT  Public IPs are not shared between devices  Connections cannot come in from the Internet

17. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 17 Configuring NAT Overload  Ports are used to share the one (few) IP addresses

18. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 18 Verifying NAT

19. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 19 Verifying NAT

20. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 20