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

5 pts.
Tags:
Arp
RARP
TCP/IP
TCP/IP layers
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.
ASKED: January 19, 2009  4:22 PM
UPDATED: April 2, 2014  10:16 PM

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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

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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.

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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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