1. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE I Chapter 6 1 Implementing IP Addressing Services Accessing the WAN – Chapter 7

2. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 2 Objectives  Configure DHCP in an enterprise branch network  Configure NAT on a Cisco router  Configure new generation RIP (RIPng) to use IPv6

3. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 3 DHCP  What is DHCP?  Every device that connects to a network needs an IP address.It can be static or dynamic.  Administrators enter static IP addresses manually when they configure devices to join the network.  However, computers in an organization often change locations, physically and logically. Administrators are unable to keep up with having to assign new IP addresses every time an employee moves to a different office or cubicle. So the solution to this is DHCP.  Administrators typically prefer a network server to offer DHCP services, because these solutions are scalable and relatively easy to manage.  However, in a small branch or SOHO location, a Cisco router can be configured to provide DHCP services without the need for an expensive dedicated server.

4. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 4 DHCP Operation  DHCP includes three different address allocation mechanisms to provide flexibility when assigning IP addresses:  Manual Allocation: The administrator assigns a pre-allocated IP address to the client and DHCP only communicates the IP address to the device.  Automatic Allocation: DHCP automatically assigns a static IP address permanently to a device, selecting it from a pool of available addresses. There is no lease and the address is permanently assigned to a device.  Dynamic Allocation: DHCP automatically dynamically assigns, or leases, an IP address from a pool of addresses for a limited period of time chosen by the server, or until the client tells the DHCP server that it no longer needs the address.

5. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 5 Conti…  Step 1: DHCPDISCOVER  Step 2: DHCPOFFER  Step 3: DHCPREQUEST  Step 4: DHCPACK

6. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 6 BOOTP and DHCP  BOOTP is predecessor of DHCP. BOOTP is a way to download address and boot configurations for diskless workstations.  Use ports 67 and 68

7. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 7 DHCP Message Format  Operation Code (OP) - Specifies the general type of message. A value of 1 indicates a request message; a value of 2 is a reply message.  Hardware Type - Identifies the type of hardware used in the network. For example, 1 is Ethernet, 15 is Frame Relay, and 20 is a serial line.  Hops –  Transaction Identifier - 32-bit identification generated by the client to allow it to match up the request with replies received from DHCP servers.  Seconds - Number of seconds elapsed since a client began attempting to acquire or renew a lease  Flags - A client that does not know its IP address when it sends a request, sets the flag to 1. This value tells the DHCP server or relay agent receiving the request that it should send the reply back as a broadcast.  Client IP Address - The client puts its own IP address in this field if and only if it has a valid IP address while in the bound state; otherwise, it sets the field to 0.

8. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 8 Conti…  Your IP Address - IP address that the server assigns to the client.  Gateway IP Address –  Client Hardware Address –  Server Name –  Boot Filename - Optionally used by a client to request a particular type of boot file in a DHCPDISCOVER message.  Options - Holds DHCP options, including several parameters required for basic DHCP operation. This field is variable in length. Both client and server may use this field.

9. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 9 Configuring a DHCP Server  The steps to configure a router as a DHCP server are as follows:  Step 1. Define a range of addresses that DHCP is not to allocate.  Step 2. Create the DHCP pool using the ip dhcp pool command.  Step 3. Configure the specifics of the pool. E.g  ip dhcp excluded-address 192.168.10.1 192.168.10.9  ip dhcp excluded-address 192.168.10.254  ip dhcp pool LAN-POOL-1  network 192.168.10.0 255.255.255.0  default-router 192.168.10.1  domain-name span.com  Disabling DHCP  To disable the service, use the no service dhcp command.

10. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 10 Conti…  Verifying DHCP configuration  show ip dhcp pool, show ip dhcp server statistics, show ip dhcp server statistics  Configuring DHCP Client  To configure an Ethernet interface as a DHCP client, the ip address dhcp command must be configured.

11. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 11 DHCP Relay  In a complex hierarchical network, enterprise servers are usually contained in a server farm. These servers may provide DHCP, DNS, TFTP, and FTP services for the clients.  The problem is that the network clients typically are not on the same subnet as those servers. Therefore, the clients must locate the servers to receive services and often these services are located using broadcast messages.  To configure router R1 as a DHCP relay agent, you need to configure the nearest interface to the client with the ip helper-address interface configuration command.

12. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 12 Conti… . By default, the ip helper-address command forwards the following eight UDP services:  Port 37: Time  Port 49: TACACS  Port 53: DNS  Port 67: DHCP/BOOTP server  Port 68: DHCP/BOOTP client  Port 69: TFTP  Port 137: NetBIOS name service  Port 138: NetBIOS datagram service  To specify additional ports, use the ip forward-protocol command to specify exactly which types of broadcast packets to forward.

13. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 13 Trouble shooting  R2# show ip dhcp conflict

14. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 14 Verify Router DHCP/BOOTP Relay Configuration  Step 1. Verify that the ip helper-address command is configured on the correct interface.  It must be present on the inbound interface of the LAN containing the DHCP client workstations and must be directed to the correct DHCP server.  Step 2. Verify that the global configuration command no service dhcp has not been configured. This command disables all DHCP server and relay functionality on the router.  The command service dhcp does not appear in the configuration, because it is the default configuration  Verify that the Router Is Receiving DHCP Requests Using debug Commands..  debug ip dhcp server events | packets

15. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 15 Public and Private IP Address  Without a translation system, private hosts behind a router in the network of one organization cannot connect with private hosts behind a router in other organizations over the Internet.  Network Address Translation (NAT) provides this mechanism. Before NAT, a host with a private address could not access the Internet.  Using NAT, individual companies can address some or all of their hosts with private addresses and use NAT to provide access to the Internet.

16. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 16 What is NAT?  NAT has many uses, but its key use is to save IP addresses by allowing networks to use private IP addresses.  NAT translates private, internal addresses into public, external addresses.  NAT has an added benefit of adding a degree of privacy and security to a network because it hides internal IP addresses from outside networks.  A NAT  This section uses the following terms when discussing NAT: - enabled device typically operates at the border of a stub network.  Inside local address –  Inside global address –  Outside global address –  Outside local address -

17. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 17 How Does NAT Work?  Dynamic Mapping and Static Mapping  Dynamic NAT uses a pool of public addresses and assigns them on a first-come, first-served basis.  Static NAT uses a one-to-one mapping of local and global addresses, and these mappings remain constant. Static NAT is particularly useful for web servers or hosts that must have a consistent address that is accessible from the Internet.  NAT Overload  NAT overloading (sometimes called Port Address Translation or PAT) maps multiple private IP addresses to a single public IP address or a few addresses.  With NAT overloading, multiple addresses can be mapped to one or to a few addresses because each private address is also tracked by a port number.

18. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 18 Benefits and Drawbacks of Using NAT  Benefits and Drawbacks

19. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 19 Configuring Static NAT

20. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 20 Dynamic NAT

21. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 21 NAT Overload

22. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 22 Conti…

23. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 23 Port Forwarding  Port forwarding (sometimes referred to as tunneling) is the act of forwarding a network port from one network node to another.  This technique can allow an external user to reach a port on a private IP address (inside a LAN) from the outside through a NAT-enabled router.  Typically, peer-to-peer file-sharing programs and key operations, such as web serving and outgoing FTP, require that router ports be forwarded or opened to allow these applications to work.

24. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 24 Verifying NAT and NAT Overload  show ip nat translations  show ip nat statistics  By default, translation entries time out after 24 hours, unless the timers have been reconfigured with the ip nat translation timeouttimeout_ seconds command in global configuration mode.  clear ip nat translation *  debug ip nat  debug ip nat detailed

25. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 25 Summary  Dynamic Host Control Protocol (DHCP) This is a means of assigning IP address and other configuration information automatically.  DHCP operation –3 different allocation methods Manual Automatic Dynamic –Steps to configure DHCP Define range of addresses Create DHCP pool Configure DHCP pool specifics

26. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 26 Summary  DHCP Relay Concept of using a router configured to listen for DHCP messages from DHCP clients and then forwards those messages to servers on different subnets  Troubleshooting DHCP –Most problems arise due to configuration errors –Commands to aid troubleshooting Show ip dhcp Show run debug

27. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 27 Summary  Private IP addresses –Class A = 10.x.x.x –Class B = 172.16.x.x – 172.31.x.x –Class C = 192.168.x.x  Network Address Translation (NAT) –A means of translating private IP addresses to public IP addresses –Type s of NAT Static Dynamic –Some commands used for troubleshooting Show ip nat translations Show ip nat statistics Debug ip nat

28. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 28 Summary  IPv6 –A 128 bit address that uses colons to separate entries –Normally written as 8 groups of 4 hexadecimal digits  Cisco IOS Dual Stack –A way of permitting a node to have connectivity to an IPv4 & IP v6 network simultaneously  IPv6 Tunneling –An IPV6 packet is encapsulated within another protocol

29. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 29 Summary  Configuring RIPng with IPv6 1 st globally enable IPv6 2 nd enable IPv6 on interfaces on which IPv6 is to be enabled 3 rd enable RIPng using either ipv6 rotuer rip name ipv6 router name enable

30. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 30