cs601
CS610-Computer Networks
Lecture No.38
Lecture Handout
Computer Networks
Lecture No. 38
VARIANTS OF NAT:
There are also some variants of NAT due to some of its drawbacks.
The basic NAT simply changes IP addresses. But Network Address and Port
Translation (NAPT) (which is another modified form of NAT) changes IP addresses and protocol port numbers too. It is the most popular form of NAT.
Twice NAT is another variant of NAT. it is used with site that runs server. In this process NAT box is connected to Domain Name.
NETWORK ADDRESS AND PORT TRANSLATION (NAPT):
It is by far the most popular form of NAT that can change TCP or DP protocol port numbers as well as IP addresses.
It allows multiple computers at site to communicate with single destination as well as multiple users on given computer to communicate with same destination.
EXAMPLE NAPT TRANSLATION TABLE:
An example NAPT translation table is shown in the figure below. We can see that not only the private addresses but also the port numbers are translated too.
Figure 38.1
Each entry in the table records protocol port numbers as well as IP address. The port numbers are reassigned to avoid conflicts.
129
© Copyright Virtual University of Pakistan
CS610-Computer Networks
Lecture No.38
TCP SPLICING:
A popular use of NAPT is TCP Splicing. It interconnects two independent TCP connections and performs segment rewriting. It is extremely efficient and avoids overhead of extracting data from one connection and sending to the other. It uses extended translation table.
TWICE NAT:
Basic NAT does not work well for communication initiated from the Internet.
Twice NAT allows a site to run servers. It requires the DNS to interact with the NAT device. Twice NAT fails if an application uses the IP addresses instead of Domain Name.
CAT:
Cable TV providers offering Internet services through Cable Modems propose it.
It includes NAPT plus additional functionality. The
Lecture No.38
Lecture Handout
Computer Networks
Lecture No. 38
VARIANTS OF NAT:
There are also some variants of NAT due to some of its drawbacks.
The basic NAT simply changes IP addresses. But Network Address and Port
Translation (NAPT) (which is another modified form of NAT) changes IP addresses and protocol port numbers too. It is the most popular form of NAT.
Twice NAT is another variant of NAT. it is used with site that runs server. In this process NAT box is connected to Domain Name.
NETWORK ADDRESS AND PORT TRANSLATION (NAPT):
It is by far the most popular form of NAT that can change TCP or DP protocol port numbers as well as IP addresses.
It allows multiple computers at site to communicate with single destination as well as multiple users on given computer to communicate with same destination.
EXAMPLE NAPT TRANSLATION TABLE:
An example NAPT translation table is shown in the figure below. We can see that not only the private addresses but also the port numbers are translated too.
Figure 38.1
Each entry in the table records protocol port numbers as well as IP address. The port numbers are reassigned to avoid conflicts.
129
© Copyright Virtual University of Pakistan
CS610-Computer Networks
Lecture No.38
TCP SPLICING:
A popular use of NAPT is TCP Splicing. It interconnects two independent TCP connections and performs segment rewriting. It is extremely efficient and avoids overhead of extracting data from one connection and sending to the other. It uses extended translation table.
TWICE NAT:
Basic NAT does not work well for communication initiated from the Internet.
Twice NAT allows a site to run servers. It requires the DNS to interact with the NAT device. Twice NAT fails if an application uses the IP addresses instead of Domain Name.
CAT:
Cable TV providers offering Internet services through Cable Modems propose it.
It includes NAPT plus additional functionality. The