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CCNA4_M1_Scaling_IP_Address

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					                                        CCNA – Semester4




                Module 1
           Scaling IP Address




Objectives




• Scaling networks with NAT and PAT
• Dynamic Host Configuration Protocol
            Scaling networks with
               NAT and PAT




Introducing NAT

• NAT is designed to conserve IP addresses and enable
  networks to use private IP addresses on internal
  networks.
• These private, internal addresses are translated to
  routable, public addresses.
NAT terms
•   Inside local address – The IP address assigned to a host on the inside network (not a
    legitimate IP address-RFC 1918 private address).
•   Inside global address – A legitimate IP address represents one or more inside local IP
    addresses to the outside world.
•   Outside local address – The IP address of an outside host as it is known to the hosts
    on 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.




Major NAT and PAT features

• NAT translations can be used for a variety of
  purposes and can be either dynamically or
  statically assigned.
• Dynamic NAT is designed to map a private IP
  address to a public address.
• Overloading, or Port Address Translation (PAT),
  maps multiple private IP addresses to a single
  public IP address.
• Realistically, the number of ports that can be
  assigned a single IP address is around 4000.
Major NAT and PAT features




NAT advantages

• Eliminates reassigning each host a new IP
  address when changing to a new ISP.
• Conserves addresses through application port-
  level multiplexing.
• Protects network security.
• Reduce address overlap occurrence.
NAT disadvantages

• Translation introduces switching path delays
  and processing overhead.
• Loss of IP end-to-end traceability.
• Certain application will not function with NAT
  enabled.




Cisco IOS NAT
Configure static NAT




Static translation
Configure dynamic NAT




Configure dynamic NAT
Configure dynamic NAT




Dynamic NAT example
Configure PAT




Clear NAT table
Show NAT translation




Troubleshooting NAT and PAT configuration

• Use the following steps to determine whether NAT is
  operating as expected:
   – Based on the configuration, clearly define what NAT is supposed to
     achieve.
   – Verify that correct translations exist in the translation table.
   – Verify the translation is occurring by using show and debug
     commands.
   – Review in detail what is happening to the packet and verify that
     routers have the correct routing information to move the packet along.
Debug IP NAT




     Dynamic Host Configuration
             Protocol
Introducing DHCP

• Dynamic Host Configuration Protocol (DHCP)
  works in a client/server mode.
• DHCP enables DHCP clients on an IP network to
  obtain their configurations from a DHCP server.
• Less work is involved in managing an IP
  network when DHCP is used.
• The DHCP protocol is described in RFC 2131.




Easy IP

• Cisco routers can use a Cisco IOS feature set,
  Easy IP, to offer an optional, full-featured DHCP
  server.
• Easy IP leases configurations for 24 hours by
  default.
• The DHCP service is enabled by default on
  versions of Cisco IOS that support it.
• To disable DHCP service, use the no service dhcp
  command.
BOOTP and DHCP

• Both protocols are client/server based and use UDP
  ports 67 and 68. Those ports are still known as BOOTP
  ports.
• The four basic IP parameters:
   –   IP address
   –   Gateway address
   –   Subnet mask
   –   DNS server address




DHCP Operation
DHCP Messages


 •   If the client detects that
     the address is already
     in use on the local
     segment it will send a
     DHCPDECLINE
     message and the
     process starts again.
 •   If the client received a DHCPNACK from the server after
     sending the DHCPREQUEST, then it will restart the process
     again.
 •   If the client no longer needs the IP address, the client sends a
     DHCPRELEASE message to the server.




CISCO IOS DHCP

• Cisco IOS DHCP server always checks to make
  sure that an address is not in use before the
  server offers it to a client.
• By default, router will issue 2 ICMP echo
  requests, or will ping, to a pool address before
  sending the DHCPOFFER to a client.
Configuring DHCP




Excluding IP
Key DHCP Server Commands




Verifying DHCP operation




    • To verify the operation of DHCP, the command show
      ip dhcp binding can be used.
    • To verify that messages are being received or sent
      by the router, use the command show ip dhcp server
      statistics.
Troubleshooting DHCP




Network services

• Remote clients will broadcast to locate servers
  while routers, by default, will not forward client
  broadcasts beyond their subnet.
IP helper-address
• Remote clients will broadcast to locate servers while
  routers, by default, will not forward client broadcasts
  beyond their subnet.
• When possible, administrators should use the ip helper-
  address command to relay broadcast requests for these
  key UDP services.
• By default, the ip helper-address command forwards the
  following eight UDP services:
   –   Time
   –   TACACS
   –   DNS
   –   BOOTP/DHCP Server
   –   BOOTP/DHCP Client
   –   TFTP
   –   NetBIOS Name Service
   –   NetBIOS datagram Service




DHCP Relay
Summary

    • NAT and PAT concepts and operation
    • NAT and PAT configuration and
      troubleshooting
    • Comparison between DHCP and BOOTP
    • Cisco Router DHCP configuration
    • DHCP relay with ip helper-address




Lab Topology
Lab Requirements

1. NAT/PAT
  •   Each Site use network address 10.x.0.0/16. Global
      address is 172.20.x.0/28. Network connecting to Center
      is 203.162.x.0/30.
  •   Configuring a static NAT mapping and dynamic NAT
2. DHCP
  •   Each Site use Router as a DHCP server to provide IP
      addresses to department network.




CCNA4 – Module1

				
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