Network Address Translation (NAT) Interview Questions & Answers

Q :- What is NAT?
Ans :- Network Address Translation (NAT) is intended for informatics address conservation. It allows personal informatics networks that use unregistered informatics addresses to attach to the net. NAT operates on a router, sometimes connecting 2 networks along, and interprets the personal (not globally unique) addresses within the internal network into legal addresses, before packets square measure forwarded to a different network.

As a part of this capability, NAT are often designed to advertise just one address for the complete network to the surface world. This provides further security by effectively concealment the complete internal network behind that address. NAT offers the twin functions of security and address conservation and is usually enforced in remote-access environments.

Q :- However will NAT work?
Ans :- Basically, NAT permits one device, like a router, to act as AN agent between the net (or public network) and an area network (or personal network), which suggests that solely one distinctive informatics address is needed to represent a whole cluster of computers to something outside their network. confer with however NAT Works for a lot of data.

Q :- However do I piece NAT?
Ans :- So as to piece ancient NAT, you would like to create a minimum of one interface on a router (NAT outside) and another interface on the router (NAT inside) and a group of rules for translating the informatics addresses within the packet headers (and payloads if desired) ought to be designed. so as to piece Nat Virtual Interface (NVI), you would like a minimum of one interface designed with NAT modify at the side of constant set of rules as mentioned higher than.

Q :- What square measure dynamic NAT translations?
Ans :- In dynamic NAT translations, the users will establish dynamic mapping between native and international addresses. Dynamic mapping is accomplished by process the native addresses to be translated and therefore the pool of addresses or interface informatics address from that to assign international addresses and associating the 2.

Q :- What is ALG?
Ans :- ALG is AN Application Layer entree (ALG). NAT performs translation service on any Transmission management Protocol/User Datagram Protocol (TCP/UDP) traffic that doesn’t carry supply and/or destination informatics addresses within the application information stream.

These protocols embrace FTP, HTTP, SKINNY, H232, DNS, RAS, SIP ,TFTP, telnet, archie, finger, NTP, NFS, rlogin, rsh, rcp. Specific protocols that imbed informatics address data among the payload need support of AN Application Level entree (ALG).

Q :- What is transmission control protocol timeout, and the way will it relate to the NAT transmission control protocol timer?
Ans :- If the three-party acknowledgement isn’t completed and NAT sees a transmission control protocol packet, then NAT can begin a 60-second timer. once the three-party acknowledgement is completed, NAT uses a 24-hour timer for a NAT entry by default.
If AN finish host sends a RESET, NAT changes the default timer from twenty four hours to sixty seconds. within the case of FIN, NAT changes the default timer from twenty four hours to sixty seconds once it receives FIN and FIN-ACK.

Q :- What is Service supplier PAT Port Allocation improvement for RTP and RTCP?
Ans :- The Service supplier PAT Port Allocation improvement for RTP and RTCP feature ensures that for SIP, H.323, and thin voice calls. The port numbers used for RTP streams square measure even port numbers, and therefore the RTCP streams square measure consecutive ulterior odd port range.
The port range is translated to variety among the vary such that orthodox to RFC-1889. A decision with a port range among the vary can end in a PAT translation to a different port range among this vary. Likewise, a PAT translation for a port range outside this vary won’t end in a translation to variety among the given vary.

Q :- What is Session Initiation Protocol (SIP) and may SIP packets be NATted?
Ans :- Session Initiation Protocol (SIP) is AN ASCII-based, application-layer management protocol that may be wont to establish, maintain, and terminate calls between 2 or a lot of endpoints. SIP is an alternate protocol developed by the net Engineering Task Force (IETF) for transmission conferencing over informatics. The Cisco SIP implementation allows supported Cisco platforms to signal the setup of voice and transmission calls over informatics networks. confer with summary of SIP for a lot of data.

Q :- Does NAT support voice co-located solution?
Ans :- No. The co-located answer is presently not supported. the subsequent readying with NAT (on constant box) is taken into account a co-located solution: CME/DSP-Farm/SCCP/H323.

Q :- What’s NAT NVI?
Ans :- NVI stands for NAT Virtual Interface. It permits NAT to translate between 2 completely different VRFs. This answer ought to be utilized in part of Network Address Translation on a Stick. confer with NAT Virtual Interface for a lot of data.

Q :- Name one instance where static NAT is used in a real world deployment
Ans :- It is used for mapping a public IP address for a Server with a private IP address.

Q :- Why does Active FTP not work with NAT in an Internet environment.
Ans :- In Active FTP, the data connection is established to a port on the FTP client by the FTP server. The port number along with the IP address to which the server needs to initiate the connection is provided by the FTP client after the control connection is succesfull. When the client is behind the NAT router, the FTP server cannot initiate the connection to the provided IP address , as typically it would be a private IP address not routable on the internet.

Q :- How does NAT work in situations where transport layer protocols are not used. For ex: Ping
Ans :- Ping does not use transport layer protocols. It uses ICMP at the network layer. NAT uses the sequence number field in the ICMP header to identify packets on which NAT is applied.

Q :- How many times can NAT be applied on a packet before it reaches the destination
Ans :- Any number of times.

Q :- Two computers are behind a NAT router. The computers use the routers public IP address for sharing internet connection.If a user on the internet pings the public IP address of the router, which device would respond
Ans :- The router would respond as it is configured for the public ip address.

Q :- Give a good reason as to why a NAT router is preferred over a Proxy for sharing internet connection
Ans :- NAT works at the network layer. This means that irrespective of the application, all packets can be sent out on the internet. Proxy is application specific. So if a HTTP proxy is deployed, it can send out only HTTP based traffic on to the internet.Other traffic like ping, FTP etc would be blocked.

Q :- Does TCP checksum change after NAT is applied
Ans :- TCP checksums are calculated based on a pseudo header which also includes source IP address of the IP header. Since, the source IP header address is modified when NAT is applied, the checksum would be affected.

Q :- What is difference between Static NAT, Dynamic NAT and Overloading NAT?
Ans :- There are three Types of NAT in the Network—
Static NAT – In Static NAT Only One Computer IS Connected To Internet. For That We Define The Mapping Of That Particular Computer in The Network.

Dynamic NAT – In Dynamic NAT We Define the Pool. In This NAT Only Some Computer Is Connected To Internet At A Same Time.
Overloading NAT (PAT) – Overloading NAT Is Also Called PAT (port Address Translation). With The Help of PAT All of the Internal User Are connected to internet through Single Public IP Address In the network. In this NAT All User Query Are Differentiate Through port Basis in the network, that’s why it is Called PAT.

Q :- What is PAT {Port Address Translation}?
Ans :- Overloading NAT Is Also Known As PAT. PAT stands For Port Address Translation. With The Help of PAT All of the Internal User are connected to internet through single Public IP Address. In PAT all Of the Users Query are Differentiated Through port Basis, that’s why it is Called PAT.

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Wednesday, October 16, 2019

Network Address Translation (NAT) Interview Questions & Answers

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