Question

Select the correct statement about TTL (Time to Live) field in IP:

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I.  TTL value can never be increased while the packet is going from source machine to destination machine.

II. Whenever TTL value is decreased at each intermediate node, its value is alwyas decrmeented by 1 , not more than that.

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a. I only

b. II only

c. Both I and II

d. Neither I nor II

Comments

IS RECEIVER ALSO CONSUME ONE TTL VALUE???

Answer 1

I.  TTL value can never be increased while the packet is going from source machine to destination machine. False since TTL value set by source = 1 ans send in network to found route . max limit also known so loop not formed.

II. Whenever TTL value is decreased at each intermediate node, its value is always decrmented by 1 , not more than that. True. 

TTL Value is equal to number of hops since when we go from 1 hop we decrease 1 only .

http://www.cisco.com/c/en/us/support/docs/ip/ip-routed-protocols/22826-traceroute.html

Comments

TRACEROUTE https://en.wikipedia.org/wiki/Traceroute

I think in trace route also we cannot increment TTL value of a single packet.
Trace route works in this manner.

Send a packet with TTL =1

Send next packet with TTL =2

Send next  packet with TTL =3 and so on..

Here for a single packey while travelling from source to destination TTL is not increasing

COrrect me if I am wrong

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http://www.cisco.com/c/en/us/support/docs/ip/ip-routed-protocols/22826-traceroute.html

check here.

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i think we are SETTING the value of ttl as 1,2,3,..... at the source .we are not incrementing the ttl field while it is in transit.so ttl can never be incresed. there is a lot of difference between setting and incrementing ttl

Answer 2

Statement1: TRUE bcoz TTL will never be incremented. it will either decrease or remain same when it pass through a node
statement2:TRUE  bcoz when TTL is decremented it gets decremented by only 1 not more than that.
so i think it is option C

Comments

yes... word used here is "source"..means u r sending packet from here only..its like ur airport..if it would have been after takeoff like on links,intermediate nods or routers or anything then yes we cant increase TTL there

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which you set at the source is initial value of the TTL. you cant say its it getting increased at the source, that itself is the initial value of TTL. when i day TTL is getting increased at this point, current TTL shud be > previous TTL
at source what is the previous TTL?

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sry i didnt get u.....i meant that u can set TTL at source only and it will nt be changed via transmission....and we can increase it also like for finding trace route we use increasing TTL value each time....but that is done when icmp packets are returned by each successive router back to the source....

Answer 3

Amswer is C (Both statements are true)

You can verify this with your home router also.

setup:

Take n routers and connect them Lan.

Now ping one router from another router(in between say there is n-2 routers) , you will get TTl as XYX , and now move closer and now ping from another router(in between n-3 routers) , you will find the TTL is decresed by 1 , i.e (XYZ-1)

You can ping router by attaching to laptop and in command prompt type Ping followed by Ip address.