What layer of the TCP/IP would ARP and RARP belong to

ARP translates Layer 3 addresses to Layer 2 addresses, and knowing fully well that it is not an IP-only or Ethernet-only protocol. Can anyone help with this, it's getting a bit confusing.

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I have to disagree with the logic below. You are correct that using an IP address for management does not make a switch a layer 3 device. But if the switch uses IP to make forwarding decisions then it becomes a layer 3 device (IE the term ‘layer 3 switch’)

ARP does indeed use frames to forward the request but the response itself is actually an IP packet encapsulated in a frame (like everything else) so I have to agree with the original answer.

ARP IS layer 3.

If you need clarification please view RFC 826 at ietf.org


Switches are using IP addresses too (for management) but that doesn’t make them layer 3 devices.
I had similar question about ARP and found an answer. I ran packet analyzer while clearing my PC’s arp cache, then pinging remote host. ARP request is Ethernet broadcast – to address ff.ff.ff.ff.ff.ff. Which means ARP operates at layer 2.

Previous answer:
ARP/RARP would have to be at layer 3 since IP addresses are involved. This is where routing takes place. Bridging takes place at layer 2 or using MAC addresses. See this section of the TCP/IP guide for more information.

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  • BlankReg
    ARP is layer 3 - no doubt. It is an IP function, so is network layer. I would also like to make the point that ARP does not translate IP to MAC, it is the method that is used to get the MAC address for a particular IP address. Not a translation, just finding out where a particular IP address lives. Just like me asking you what your house number is, I still address the letter to you, but add the house address where you live.
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  • Routeranger
    It is a common misconception that has actually been promulgated by vendor exams that ARP operates at Layer 3 of the OSI model, however ARP was not written for the OSI model, it was written for the DOD IP Protocol Suite. It does not directly correlate to Layer 3 of the OSI model because Layer 3 or the "Network Layer" protocols would be routable at Layer 3. ARP is not routable at Layer 3, therefore it is inconsistent to assume it is a Layer 3 protocol. ARP actually functions at Layer 2 via Layer 2 broadcasts, however it is designed to assist layer 3 communications as it already has the layer 3 address and is simply mapping layer 3 addresses to a layer 2 MAC address. Thus if one is attempting to correctly classify ARP within the framework of the OSI model it would be most accurate to state ARP operates "BETWEEN" Layer 2 and Layer 3 of the OSI model. ARP is not passed at Layer 3. ARP is passed at Layer 2. But the information carried by ARP is a Layer 3 address. Thus it operates between Layer 2 and Layer 3 of the OSI model.
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