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How many TCP/IP layers are involved when I am pinging my router and my PC?

My router : ping 192.168.1.1

My PC : ping 127.0.0.1

My PC : Ping 192.168.1.10

I need to know how the data is transferred in all the three cases through the layers.

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  • AFAIK Windows uses L4, too. Not pure L3 ICMP. – user2382 Aug 16 '13 at 13:45
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First of all, remember that TCP/IP has only 4 layers:

  • Application
  • Transport ( TCP/UDP )
  • Internet ( IP )
  • Link (Frame)

When you ping your PC from itself, doesn't matter if it is the "canonical" localhost or a user defined address, only the second of the four layers is involved since the network stack does not need to access any network to reach itself.

Contrary, when you send a echo request to another box ,the running OS first resolve the L2 mappings ( even dynamically or by configuration ) and then uses those information to build the packet and to send it to the destination box.

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To answer your first question, I would say ICMP run up on the third layer TCP/IP but don't use the fourth (TCP/UDP not involved) so I think it's correct to describe it as running on 3.5 Layer.

You can analyze yourself the data inside ICMP using a packet analyser (Wireshark recommended).

Here a picture to get a better idea. icmp_wireshark

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No matter what IP address is in question, ICMP packet will have the same format. ICMP is part of TCP/IP protocol suite which resides on layer 3. If you do a packet capture can easily see what type of information is sent. You can also see that ICMP is on top of IP so it is also said it is a on 3.5 layer. No matter what you ping (loopback or some distant address) packet must have all required layers (in this case from 1 through 3). The way the packet destined for loopback adapters is processed is another question but that does not affect the packet format or protocols/layers used.

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TCP/IP doesn't really map cleanly onto the OSI model (which was designed top-down by a committee). If you want the closest map onto the OSI layers, the answer is probably 3.5: ICMP (which is what ping uses) is implemented directly on top of IP packets and doesn't use a transport layer (OSI layer 4) like TCP or UDP.

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