Where does OSPF/EIGRP/ICMP Fit?

Hey guys,

Any thoughts on where in the OSI model EIGRP/OSPF fit?

Wikipedia places it at Layer 3. Other documents I have come across place it at L3 as well. The Cisco Press ROUTE FLG places them at the Transport Layer since they rely on IP. However, by that logic, shouldn't ICMP be considered Transport instead of Network?

RFC792 says:
ICMP, uses the basic support of IP as if it were a higher level protocol, however, ICMP is actually an integral part of IP, and must be implemented by every IP module.

Just curious on your thoughts.

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Comments

networker050184

There have been quite a few discussions on this if you search. In the end the OSI model is just that, a model. Not everything fits nice and neat in one layer or another.

Forsaken_GA

As it happens, we've already had this discussion!

http://www.techexams.net/forums/ccna-ccent/69539-rip-ospf-layer.html

martell1000

in the end everything is "layer 8" because we touch it use it configure it invent it ...

NetworkVeteran

The answer doesn't matter. The OSI model is a tool. Network engineers usually use it to understand and troubleshoot in a methodical fashion. Whether you call it tomaTO or toMAto, the work still gets done.

Consider--you have a problem pinging several remote IP addresses. It turns out traffic is not being routed across a backup link as expected due to an EIGRP misconfiguration. Gee, EIGRP is what you verify when you have network-layer issues! I'd add, more network engineers than not would consider this the right answer to the question, and in that role I'd usually pick this!

Consider--you've been hired to implement the EIGRP Reliable Transport Protocol for a new version of IOS. You might describe it as a way to provide TCP-like reliability. Gee, that'd make that part of EIGRP a transport-layer thingy.

Consider--BGP is a routing protocol that runs over TCP. You sometimes need to troubleshoot up the layers (link, ip, tcp) before identifying the BGP issue that's causing a loss of Internet connectivity at the layer-3/ip layer.

Now, if you tell me you're using EIGRP to try to cable two devices or correct a PPP authentication mismatch, you're just wrong!

Roguetadhg

I thought PPP's Chap was for Chapstick, a way to speed up the packets. PPP's Lubrication to make it work lie greased lightning?

up2thetime

Cool... thanks for the replies!

jibbajabba

NetworkVeteran wrote: »

The answer doesn't matter. The OSI model is a set of guidelines.

Fixed

Forsaken_GA

Parley?