self doubt

Question

If packet with TTL value = 0 received at destination, then destination discard that packet or accept that packet.

Comments

at destination firstly TTL will be decremeted...now even if TTL becomes zero and if its at correct destination ..it will be accepted..else rejected...

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no, if TTL becomes 0 after it is decremented by destination, then this packet should be rejected.

for example, a packet should not got out side the local network, so we keep TTL=1, if packet reaches the first router by mistake, then at router TTL decrements and it becomes 0 so router discards this packet.

hence, Destination should reject in this case if ttl is 0 after decrement.

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can you provide any resource??

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@shubham Sending you from my own notes, which i copied from some standard book(forozuan or Kurose or tanenbaum):

 

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just tell me this ...

when TTL=0..at destination(means destination has decremented it from 1 to 0 )this clearly indicate that we have correctly predicated the hops ..then why should i discard the packet ??..

what i know is its accepted..

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TTL is always double of the number of hops on the way.

if packet reached Destination on TTL=0 thwn where was it roaming for half of the time. there is nothing about prediction.

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@manu sir,

Every source is going to set its TTL value (for eg:4), it means source is saying this my packet will not take more than 4 hops, I mean there are 3 routers are in the middle and initially at the source TTL value was 4 and then At router 1 value will decrement to 3 and at router 2 value will be decremented to 2 and router 1  value will be decremented to 1 and at destination value will be decremented to 0 but at this point Destination must take this packet , it will not discard it because packet take only 4 hops.

And the question is if at destination TTL -0, it means the just previous router before this node destination node already packet has been discarded, it means there is no meaning of discarding at this final destination...

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@akash this is what we are assuming that it should be this way.

but if the TTL is 0 packet has to be discarded. anyway 0 is not a valid TTL value.

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If already TTL 0 is arrived at destination then it would be discarded at destination. Because destination can’t further decrement it and can’t accept it

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@Manu Thakur, u r right, i also studied this from forouzan book, it should be discarded. I marked this option and got it wrong in the madeeasy test series.

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@  Manu Thakur sir plz check this and suggest what is correct..????

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@  Bikram sir could you plz answer this basic doubt.....???

Answer 1

https://networkengineering.stackexchange.com/questions/10929/when-is-an-ipv4-ttl-decremented-and-what-is-the-drop-condition

check this, so now according to this if the router is the destination, packet with TTL will not be discarded.