NAT and IPv4 Network Fundamentals

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Questions and Answers

What is the main reason why NAT is essential for the current Internet based on IPv4?

To address the issue of IPv4 address exhaustion

What is the purpose of NAT in a server farm?

To allow multiple servers to share the same IP address

What is the primary function of an edge router?

To configure the router next to the Internet

What is the main benefit of using NAT in a home network?

Multiple devices can share the same public IP address Signup and view all the answers

What is the consequence of IPv4 address exhaustion?

Limited availability of public IP addresses Signup and view all the answers

What is the primary advantage of NAT as IP masquerading?

Obscures an internal network's structure Signup and view all the answers

What happens when the destination IP:port matches the tcp NAT entry?

The router immediately converts the address and sends it to the appropriate local address. Signup and view all the answers

What is the purpose of port forwarding?

To redirect a service to an inside server. Signup and view all the answers

Which of the following services uses UDP port 53?

DNS Signup and view all the answers

What is the limitation of port forwarding?

Only 1 server can be configured for 1 port number. Signup and view all the answers

What is the purpose of the command 'ip nat inside source static udp 192.168.2.1 53 61.38.120.77 53'?

To configure port forwarding for DNS. Signup and view all the answers

What is the primary function of port forwarding?

To translate the destination IP address for packets traveling from the inside network to the outside network Signup and view all the answers

What is the maximum number of port numbers that can be redirected to a single private IP address using port forwarding?

1 Signup and view all the answers

What is the purpose of using a different external port number in the configuration 'R1(config)#ip nat inside source static tcp 192.168.2.2 80 200.1.1.2 2000'?

To add an extra private web server Signup and view all the answers

What is the term for the configuration where a private network goes through more than 1 stage of NAT (or PAT)?

Double NAT Signup and view all the answers

What is the IP address that the hosts of the outside network will use to access the HTTP, Telnet, and FTP services?

60.156.7.19 Signup and view all the answers

What is the term for the configuration 'R1(config)#ip nat inside source static tcp 192.168.2.1 80 200.1.1.2 80'?

Static NAT Signup and view all the answers

What is the purpose of PAT in a wireless router?

To share a single public IP among multiple devices in the network Signup and view all the answers

How does the world access a server in a private network?

By configuring port forwarding Signup and view all the answers

What is the format of static NAT mapping in port forwarding?

IP:port Signup and view all the answers

What happens to packets with a destination port 80 reaching the public IP in the example provided?

They are redirected to 192.168.1.11 Signup and view all the answers

What is the public IP address of the web server to the outside world?

11.11.100.123 Signup and view all the answers

What is the purpose of the 'ip nat inside source static' command?

To map a public IP and port to a private IP and port Signup and view all the answers

What is the reason for other subnets, except 192.168.1.0, to undergo PAT?

Security reason Signup and view all the answers

How does 172.16.5.0/24 access Server0?

By masquerading as 192.168.1.1 with PAT Signup and view all the answers

What is the purpose of the commands starting with 'ip nat inside source static'?

To allow access to private network servers from outside Signup and view all the answers

How does PC0 access all 4 private network servers via the public IP of 200.1.1.1?

Using PAT and double port forwarding Signup and view all the answers

What is the purpose of 'type rotary' in the NAT pool configuration?

To configure TCP load sharing Signup and view all the answers

How is the load of incoming requests handled in TCP load distribution?

In round robin fashion Signup and view all the answers

Study Notes

NAT (Network Address Translation)

One public IP can be used by thousands of private network computers
NAT obscures an internal network's structure and makes all network traffic appear to originate from a single IP address of a router

Why NAT is Important

IPv4 address exhaustion: NAT is crucial for IPv4 to function because there aren't enough IPv4 addresses to cater for every device
Many institutions have only 1 public IP to cater for thousands of PCs behind the edge router

Useful for server farms: multiple servers with similar functions can be represented by a single IP address
Handles the load of incoming requests by spreading the load among several mirrored servers

Port Forwarding

Also known as static NAT
Maps a public IP and port number to a private IP and port number
Allows external access to internal services behind a NAT router
Examples of services that use UDP port forwarding: DNS (port 53) and TFTP (port 69)

Configuring Port Forwarding

can be configured on a wireless router
Redirects incoming traffic to internal servers
Can map different local IPs and ports to a global IP and different ports

Double NAT/PAT

A private network can go through more than one stage of NAT (or PAT) and still function properly
Useful for security purposes
Example: Double NAT/PAT configuration with PAT entries

PAT (Port Address Translation)

Similar to NAT, but translates both IP addresses and port numbers
Automatically performed by some wireless routers for the user
Also known as IP masquerading

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