INTERVIEW QUESTIONS NETWORKING NETWORKS SECURITY DETAILS

Question: How does traceroute work? Now how does traceroute make sure that the packet follows the same path that a previous (with ttl - 1) probe packet went in?

Answer: See traceroute works using ICMP packets. First source sends an ICMP packet with Time to Live (TTL) field as 1 to the destination address. Now intermediate router receives the packet and sees that TTL field has expired, so it sends a ICMP TTL expired reply. Now the source machine again sends the ICMP packet with TTL field as 2. This time second intermediate router replies. This process is repeated till destination is reached. That way the source can get the entire route upto destination.

See traceroute works using ICMP packets. First source sends an ICMP packet with Time to Live (TTL) field as 1 to the destination address. Now intermediate router receives the packet and sees that TTL field has expired, so it sends a ICMP TTL expired reply. Now the source machine again sends the ICMP packet with TTL field as 2. This time second intermediate router replies. This process is repeated till destination is reached. That way the source can get the entire route upto destination. Source: CoolInterview.com

Answers:

ARP(ADDRESS RESOLUTION PROTOCOL) is a network layer protocol which associates the physical hardware address of a network node(commonly known as a MAC ADDRESS) to its ip address. now an ARP creates a table known as ARP CACHE/TABLE that maps ip addresses to the hardware addressess of nodes on the local network.

if based on the ip address it sees that it has the node's mac address in its ARP TABLE then transmitting to that ip address is done quicker because the destination is known and voila network traffic is reduced.


Source: CoolInterview.com

We can use traceroute to determine the route taken by packets across an IP network.

It is important to make a difference between Windows and Unix implementations of traceroute.

The Windows version using ICMP on the contrary in Unix traceroute using UDP.

In windows the command is
"tracert" while in Unix the equivalent of that is "traceroute".

By following the source and the destination one can observe the actual path between them.

For security reasons some router can block the ICMP protocol therefore the given value so called,"hop count" might be incorrect.

In these scenarios one can use a different protocol to find out the actual route.This technique is beyond the scope of the sufficient answer for the above question, therefore I leave it unexplained.

The new IPv6 variant traceroute6 is also available. Source: CoolInterview.com

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