Basic Networking question regarding ping

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Feb 12th, 2010
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hi guys,

it's a basic question but i am stuck with it

we know that osi model consists of 7 layers

when we ping from one system to another, will the process starts from layer 7 [application layer]or does the process start from layer3 [network layer]

am thinking that it starts from layer 3,

but as ping is an application which we use to start ping process and as we are interacting with it is in layer7[application layer], so does pinging between two systems start from layer 7 or layer 3

thanks in advance

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Jon Marshall Fri, 02/12/2010 - 10:33
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jhones999 wrote:


hi guys,


we know that osi model consists of 7 layers

when we ping from one system to another, will the process starts from layer 7 [application layer]or does the process start from layer3 [network layer]

am thinking that it starts from layer 3,

but as ping is an application which we use to start ping process and as we are interacting with it is in layer7[application layer], so does pinging between two systems start from layer 7 or layer 3

thanks in advance


Couple of things here.


Firstly the TCP/IP model doesn't really map to the OSI 7 layer model. It can vary but a common approach is to say that TCP/IP has 4 layers -


application

transport

network

L2/physical


ICMP is part of the TCP/IP protocol suite so it's best to talk about it in reference to the TCP/IP model and not the OSI model.


Still the question remains. ICMP works at the network layer but you don't have direct access to the network layer. When you ping something you are indeed starting from the application layer and remember if you ping a hostname rather than an IP then before any ICMP is involved the hostname must be resolved to an IP address.


So the actual ICMP packets go between 2 systems and go from the network layer down through the L2/physical and up the L2/physical and network layer on the other system. They start at the network layer and finish at the network. But your application then interprets and presents the results to you. It is the app that instructs your system to form an ICMP packet and send it to the other system.


Jon

Ganesh Hariharan Fri, 02/12/2010 - 23:33
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hi guys,


it's a basic question but i am stuck with it



we know that osi model consists of 7 layers




when we ping from one system to another, will the process starts from
layer 7 [application layer]or does the process start from layer3
[network layer]



am thinking that it starts from layer 3,




but as ping is an application which we use to start ping process and as
we are interacting with it is in layer7[application layer], so does
pinging between two systems start from layer 7 or layer 3



thanks in advance


Hi,


ICMP work with internet protocol (ip) at layer 3 of osi model and inernet layer of tcp model.This layer, also known as the Network layer, accepts and delivers packets for the network. It includes the powerful Internet protocol (IP), the ARP protocol, and the ICMP protocol.


ICMP packets are genrated by nic to specific destination address if you see header of ICMP packets ethernet header-ip hearder-icmp header-data-ethernet crc.so icmp is genrated at layer 3 with ip address mentioned of the destionation end.


Hope to help


Ganesh.H

jhones999 Sun, 02/14/2010 - 07:02
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thanks for your replies jon.marshall and ganeshh.iyer


what i don't understand is when ping process starts from ping executable which runs at application layer why do we consider pinging process as layer 3 process



how can ping start with out getting request from application layer






please correct me if i am wrong



thanks in advance

Ganesh Hariharan Sun, 02/14/2010 - 07:32
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thanks for your replies jon.marshall and ganeshh.iyer


what i don't understand is when ping process starts from ping executable which runs at application layer why do we consider pinging process as layer 3 process



how can ping start with out getting request from application layer






please correct me if i am wrong



thanks in advance

Hi Jhones,


Ping is an application which tests to see if a particular computer is available online. An ICMP echo request/reply is used ,whenever you sniff icmp packet in your network you will only see  that the IP datagram within this packet has protocol number 01, which is the protocol number for ICMP. This means that the payload of the IP datagram is an ICMP packet.


Hope to help !!


Ganesh.H

VishnuAsok1 Tue, 08/10/2010 - 23:25
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I guess John is trying to understand if ping works on layer 3 or layer7.


PING works on layer 7 of the OSI. However PING uses ICMP which is a layer 3 to test the availability of the remote system.

The Host will send a echo request(ICMP type 8) and the remote system echoes with ICMP type 0 if its on network and allowed to respond back.

In many sites I see them mentioning Ping works on L3, which I understand is incorrect(Confusing between PING and ICMP) and should be on L7.


Correct me if I am wrong.

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