I am confused when many books including the CISCO press books are not clear about these.Some portions says that it is present in the application layers while the same book elsewhere says its in the Transport/Network layer!!
i find it all confusing..
but the best thing to do is understand that in reality we are working with TCP/IP and not OSI
so some things dont quite fit correctly into the model
take ARP and RARP
the truth of the matter is
these protocols send out IP addresses in order to get back MAC addresses.
so i would say that in all honesty if you were to map them to the OSI model.
then they would be in both IP layer 3.....and MAC layer 2 .....protocols.
but i think you can take it that in general ARP and RARP are classed as layer 3 by most ...but that is not entirely correct as you can see....layer 3 because the whole process begins with an ip address for which the device requires a mac address.
and as for DNS ...that is apparently meant to be on the application layer 7.
maybe its because the user keys in a name ...and then the name is sent out to a dns server.as a udp packet in a datalink frame.
but then the dns server returns an ip address...
but it all begins at the application layer....so i think thats why they call it layer 7
as per mine, DNS, ARP and RARP works at layer 3.
what do you understanding by working of protocols ta layers? it means which top layer data (pdu) they are involved or need to access info. as DNS, ARP and RARP all are ip dependent protocol so simply they will work on layer 3 protocol. when we say layer 3 it means layer 2 and layer one also included becasue every layer is dependent of its below layer
Here is the correct answer to your query,
1. DNS works at Application Layer.
2. ARP works at Network Layer.
3. RARP works at Network Layer.
I hope this answers your query.
Hi to All,
As per my humble knowledge, i totally agree with the above three answer
OSI model define these protcols as,
Apllication Layer: DNS
Network Layer : ARP and RARP
TCP/IP or Internet model layered these protocol as,
Application Layer: DNS
Link Layer: ARP and RARP or InARP
To learn more about these proctols you can check the follwing IETF RFC's (Request For Comment)
ARP :RFC 826,
RARP: RFC 903,
DNS: RFC 882 and 883.
The Malang Palsapi
ARP and other ARP flavors liek Inverse ARP is Layer Two Protocol but sometimes we call it Layer 2 & 1/2 protcol
since it commuincate with Layer three to resolve Ip address to mac address
DNS is Layer 7 protocol like tens of protocols :
yep i digged out and found dns is a lyer 7 protocol.
RARP is layer 2 i guess
Reverse Address Resolution Protocol (RARP) is a network protocol used to resolve a data link layer address to the corresponding network layer address. For example, RARP is used to resolve a Ethernet MAC address to an IP address. RARP belongs to the OSI data link layer (layer 2).
You can check more about RARP at the following link:
I hope this information is useful for you.
Have a great weekend and enjoy your Cisco study time.
ARP and RARP belong to both net and datalink layer. Basically its the mapping that is happening between L2 and L3 in ARP whereas the there is mapping occuring between L3 and L2 in RARP. All the information is stored in TCAM table which is infact having L2 and L3 details. So its both L2 and L3
Hello all, I was searching this topic to find out why ARP does not operate at layer 3 because in Cisco 2 routing fundamentals the course states that this is the case. While explaining about ACL's in ipv6 and nd-na and nd-ns it say's, "ND messages are encapsulated in IPv6 packets and require the services of the IPv6 network layer while ARP for IPv4 does not use layer 3."
That's why I got turned around about it. I wondered what ARP is doing to get the IP addresses if not from the network?
With all due respect to Cisco, sometimes their study materials have typos, quite a lot actually, so I'm not sure if this is a case of one of those.
"... while ARP for IPv4 does not use layer 3."
What that is telling you is ARP is not routable, which is a distinction from how ND works in IPv6.
OK, thanks for this one. Now I am going to have to go back into the books and find out why DNS is a layer 7 and not a lower layer. Maybe 5?
DNS is layer 7 because DNS is an application. Processing occurs in the daemon (or executable if you're on Windows) that is over and above the network protocol.