ccna4 m1 scaling ip address
TRANSCRIPT
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CCNA – Semester4
Module 1Scaling IP Address
Objectives
• Scaling networks with NAT and PAT
• Dynamic Host Configuration Protocol
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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.
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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.
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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.
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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
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Configure static NAT
Static translation
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Configure dynamic NAT
Configure dynamic NAT
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Configure dynamic NAT
Dynamic NAT example
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Configure PAT
Clear NAT table
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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 debugcommands.
– Review in detail what is happening to the packet and verify thatrouters have the correct routing information to move the packet along.
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Debug IP NAT
Dynamic Host Configuration Protocol
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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 dhcpcommand.
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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
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DHCP Messages
• If the client detects thatthe address is already in use on the local segment it will send a DHCPDECLINEmessage 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 aDHCPRELEASE 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.
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Configuring DHCP
Excluding IP
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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.
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Troubleshooting DHCP
Network services
• Remote clients will broadcast to locate servers while routers, by default, will not forward client broadcasts beyond their subnet.
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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
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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
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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