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what i know is that tcp has its error control mechanism so it  does not depends on icmp but udp does not have any error control mechanism so it depends on icmp hence option option A is correct ……..

is it correct?

asked in Computer Networks by Loyal (7.1k points) | 70 views

according to me option A is correct . read the comment of Rakesh K in the link i've attached. the image he has attached is from Kurose and Ross, and the question too is from that book only.


 thank u so much 

but in book Forouzan ,it is clearly mention that both will generate ,because in data of icmp message ,8 byte provide information about port no.(which can be of UDP or TCP) and sequence no.if icmp is not generated for tcp then what is use of 8 byte info.(sequence no. which is not used by UDP)

Yes I agree with @Prateek Raghuvanshi

If the n/w layer is using I/P protocol then ICMP will be generated irrespective of what protocol its Transport layer is using.

But then why this conflict of concept in Kurose :/


 i dont read this topic from book but in coaching it was taught  to us that  tcp has its error control mechanism so it  does not depends on icmp but udp does not have any error control mechanism so it depends on icmp

I'm trying to provide a reference from a real life example.maybe this could be wrong... But anyways.

Suppose there are two person who are told to deliver a packet to a destination. One is responsible, other is not.

Both went to a house to deliver a packet.

The irresponsible person just put the packet on the doorstep and ran away.

  The responsible person stood there till the receiver of the packet verifies that whether the packet he has got is actually for him or not.

After verification, the receiver found  out that it's not for him.

Now, since the irresponsible person ran away, the receiver of the packet has to find out one of his assistant to go to the sender of the packet and tell him that it's wrongly delivered to his doorstep.

But since responsible person was standing there for verification, if the packet comes out to be wrongly delivered, he himself will go to the sender and tell him that something goes wrong. Here no need to bother the assistant.

Just substitute irresponsible person by UDP, responsible person by TCP, wrong house to UNREACHABLE PORT, assistant to ICMP.

I don't know whether it's correct or not, but I guess I should be happening there.


Nicely described :) But since this is totally theoretical and all we know is from the books only, there's hardly any space to apply real life logic in such cases and be ascertain of it. You might be right but since I read from Forouzan, this is what I knew.


as i know TCP uses RST for  DESTINATION UNREACHABLE information.. it doesnt mean Destination Unreachable ICMP not genrated. TCP not going to use it but it is generated at network layer.

This is what Digvijay commented below the selected answer.


@MiNiPanda Thats what I am trying to say. In case of TCP, the error won't reach to IP. TCP itself can solve the solve. And I don't think 2 error messages for the same situation will be generated. And TCP is at there when the error generated, so it only will report the error message... Not ICMP. 

@Prateek Raghuvanshi @MiNiPanda What your are talking about forouzan is in wrong context. In forouzan, it's written that error messages will be generated for both TCP and UDP( which is true, because error can be at routers too, and in that case it will be for TCP also, as routers don't have transport layer, so TCP itself can't report error, so ICMP comes to rescue at that time), but it has never been written that port unreachable message will be generated for TCP, because it's not, as port unreachable message generated at the destination, and destination has transport layer, hence TCP can itself generate error message.

and yes destination unreachable message can be generated for both TCP as well as UDP as because it can be generated at router as well as host.

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