ARP requests

yuriz43

Hello everyone,

I've been studying quite a bit for CCENT/CCNA, and I just tried the Boson practice exam. This brings me to some questions about ARP.

Are ARP requests purely layer 2 mechanisms?

I see a lot of information that refers to ARP requests as packets which is confusing because I know they aren't IP packets, and if anything they would be ARP protocol packets( Which is layer 3 right?)

How would you answer this on the test?

networker050184

ARP requests are Layer 2 broadcasts.

The word packet is used quite loosely so just because something says "packet" I wouldn't take it as a purely Layer 3 mechanism.

wat08

It's worth noting that ARP replies are unicast since the receiver will know both the source IP and MAC address.

dtlokee

You are correct in arp does not rely on IP as it's transport but ARP does operate at the Network Layer. ARP has an EtherType of 0x806 while IP has an EtherType of 0x800. This is used in a similar fashion as port numbers so the Data Link drivers know what Network Layer protocol to give the frame to.

yuriz43

Thanks...

So to put things in perspective:

ARP is a layer 3 protocol.

Ethernet is a layer 2 protocol.


Arp broadcasts/replies are encapsulated into Ethernet frames, such as the way IP packets are encapsulated into Ethernet frames...

tech-airman

yuriz43 wrote:

Hello everyone,

I've been studying quite a bit for CCENT/CCNA, and I just tried the Boson practice exam. This brings me to some questions about ARP.

Are ARP requests purely layer 2 mechanisms?

I see a lot of information that refers to ARP requests as packets which is confusing because I know they aren't IP packets, and if anything they would be ARP protocol packets( Which is layer 3 right?)

How would you answer this on the test?

yuriz43,

Check out the "Understanding Address Resolution Protocols and ICMP" episode of CCNA TV at the following link. In the middle column section titled "Understanding Address Resolution Protocols and ICMP" click the > _Watch Now_ link.

Source:

1. "Understanding Address Resolution Protocols and ICMP" episode of CCNA TV - https://cisco.hosted.jivesoftware.com/docs/DOC-1642

hectorjhrdz

...i didn't remember that ARP is a layer3 protocol............