1. CCNA 4 v3.1 Module 1 Scaling IP Addresses

2. Objectives

3. Private Addressing

4. NAT
A NAT-enabled device typically operates at the border of a stub network.

5. NAT Terms
Inside Local Addresses – An IP address assigned to a host inside a network. This address is likely to be a RFC 1918 private address.
Inside Global Address – A legitimate IP address assigned by the NIC or service provider that represents one or more inside local IP address to the outside world.
Outside Local Address - The IP address of an outside host as it known to the hosts in the inside network.
Outside Global Address - The IP address assigned to a host on the outside network. The owner of the host assigns this address.

6. NAT Features
Static NAT is designed to allow one-to-one mapping of local and global addresses.
Inside
Outside DA DA
Internet
Inside Global IP Address
Inside Local IP Address
NAT Table

7. NAT Features
Dynamic NAT is designed to map a private IP address to a public address.
Inside
Outside SA
Internet SA
Inside Global IP Address
Inside Local IP Address
NAT Table

8. PAT Features
PAT uses unique source port numbers on the inside global IP address to distinguish between translations.
Inside
Outside SA
:1345 SA
:2333
Internet SA
:2333
:2333
:2333
:1456
:1456
Inside Global IP Address
Inside Local IP Address
NAT Table
:80
:80
Outside Global IP Address
Outside Local IP Address SA
:1456

9. NAT Benefits
Eliminates re-assigning each host a new IP address when changing to a new ISP
Eliminates the need to re-address all hosts that require external access, saving time and money
Conserves addresses through application port-level multiplexing
Protects network security

10. Configuring Static NAT Translations
Static translation are entered directly into the configuration and are permanent in the translation table
Router(config)#ip nat inside source static

11. Inside/Outside interface
Inside Network
Outside Network
Inside Interface
Outside Interface
NAT
Inside Host
Outside Host
ip nat inside
ip nat outside
Router(config-if)#ip nat inside
An interface on the router can be defined as inside or outside
Translations occur only from inside to outside interfaces or vice versa—never between the same type of interface
What happens when a packet goes from an inside interface to an unmarked interface? No translation occurs. How about an unmarked interface to an outside interface? Again, no translation occurs. Translations only occur when going from an inside interface to an outside interface or vice versa.
I want to caution you about the significance of inside and outside. If you use this with inside local and outside local you will get confused. What you want to walk away with here is that a translation will only occur when going from inside to outside or vice versa. The only other place where inside and outside interface definitions are significant is which side can produce a new translation. For “ip nat inside source …” tells you that packets received on the inside interface can create new translation entry. DO NOT USE the inside and outside interfaces to explain Inside local and outside local!

12. Configuring Static NAT

13. Dynamic Translations
Dynamic translation specify the pool of global addresses that inside addresses can be translated into
Router(config)#ip nat pool nat-pool netmask
Dynamic translations use access lists to identify IP addresses that NAT should create translations for
Router(config)#ip nat inside source list 1 pool nat-pool
Router(config)#access-list 1 permit

14. Configuring Dynamic NAT

15. Configuring PAT
Establishes overload translation, specifying the IP address to be overloaded as that assigned to an outside interface
Router(config)#ip nat inside source list 1 interface serial0/0 overload
Establishes overload translation, specifying the IP address to be overloaded as that assigned to a pool name
Router(config)# ip nat pool nat-pool netmask
Router(config)#ip nat inside source list 1 pool nat-pool2 overload

16. Configuring PAT

17. Clearing the NAT Translation Table
Router#clear ip nat translation *
Clears all dynamic address translation entries

18. Verifying NAT and PAT Configuration

19. Troubleshooting NAT and PAT

20. Issues With NAT

21. DHCP
DHCP works by providing a process for a server to allocate the IP information to clients.

22. DHCP
Clients lease the information from the server for an administratively defined period.

23. BOOTP and DHCP Differences
DHCP defines mechanisms through which clients can be assigned an IP address for a finite lease period. This lease period allows for re-assignment of the IP address to another client later, or for the client to get another assignment, if the client moves to another subnet. Clients may also renew leases and keep the same IP address.
DHCP provides the mechanism for a client to gather other IP configuration parameters, such as WINS and domain name.

24. Major DHCP Features Automatic Allocation Manual Allocation
Dynamic Allocation

25. DHCP Operation

26. The Order of DHCP Messages Transmitting

27. Configuring DHCP

28. Configuring DHCP While Excluding IP

29. Verifying DHCP

30. Troubleshooting DHCP

31. DHCP Relay

32. Summary