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OSPF , RIP , IGRP, IS-IS and IP packet

Posted on 2006-06-22
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http://highered.mcgraw-hill.com/sites/0072515848/student_view0/chapter20/powerpoint_slides.html
"There are five network layer protocols: ARP, RARP, IP, ICMP, and IGMP".


The author says that : ARP,RARP,ICMP,IGMP they will be encapsulated within an ip packet, "Local Area Network" Book by  author Forouzan chapter 18 Page 389, under topic NETWORK LAYER, he says:

"At the network layer (or, more accurately , the internetwork layer), TCP/IP supports the internetwork protocol (IP). IP, in turn, contains four supporting protocols: ARP,RARP, ICMP,and IGMP. Each of these protocols is described later in this chapter".

If you look to the slide below , you can see that the fours protocol (ARP, RARP, ICMP, IGMP) within ip packet
http://img154.imageshack.us/img154/3216/withinippacket9zy.jpg

And he says about ICMP:
"ICMP itself is a network layer protocol. However, its messages are not passed directly to the data link layer as would be expected. Instead, the messages are first encapsulated inside ip datagrams before going to the lower layer".


The author said that there are five protocols reside within network layer and encapsulated within ip packet , what about the other like RIP, OSPF, IS-IS, IGRP, EIGRP ,,,,etc ??
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Question by:zillah
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by:Don Johnston
ID: 16958838
If you're looking for consistancy in how different people see the OSI model and where the protocols fit... good luck! :-)

While some of the protocols are strictly defined, others are somewhat vague as to where they reside in the OSI model.

One of the worst interpetations I've seen in the protocols/OSI model is the Cisco Intro courseware. They show RIP as being a layer 4 protocol!
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by:harbor235
ID: 16959028
He is speaking in generalities to introduce the material to you, there are plenty more protocols. What is your specific question ?

harbor235 ;}
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by:zillah
ID: 16959041
((What is your specific question ?))
This is my question
((The author said that there are five protocols reside within network layer and encapsulated within ip packet , what about the other like RIP, OSPF, IS-IS, IGRP, EIGRP ,,,,etc ??))
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by:Don Johnston
ID: 16959142
Those protocols are not layer 3 protocols. They are carried by IP.

RIP, for example as an application that is transported by UDP which in turn is carried by IP.
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by:zillah
ID: 16959183
((Those protocols are not layer 3 protocols.))
That is fine.

What about all the other routing protocols (OSPF, IS-IS, IGRP, EIGRP ,,,,etc ) Are they carried by ip packet as well or they have thier own packets which are different from ip packet (layer 3 packet) ?
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by:rsivanandan
ID: 16960031
Zillah,

  You have the answer in your question itself. Basically if you look at it broadsense, there are 2 types of protocols that fit OSI layer.

1. Routed protocols : These are the ones which actually gets routed, example would all you mentioned (tcp,udp etc).

2. Routing protocols : This is kind of an application which basically works using the underlying routed protocols. So for example RIP can be considered to be an application which does a specific thing for 'Layer 3'. But RIP by itself is not a protocol (routed). It will be running based off a 'routed protocol' which is UDP.

Same applies for all. Hope this gives some explanation.

Cheers,
Rajesh
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by:Don Johnston
ID: 16961646
>What about all the other routing protocols (OSPF, IS-IS, IGRP, EIGRP ,,,,etc )

They are all carried in IP packets. Some routing protocols have their own protocol numbers (EIGRP = 88), some are carried by TCP (BGP = 179)  and some are carried by UDP (RIP = 520).
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by:zillah
ID: 16961786
((They are all carried in IP packets)).
Ok.


((Some routing protocols have their own protocol numbers (EIGRP = 88), some are carried by TCP (BGP = 179)  and some are carried by UDP (RIP = 520).))
As you know that TCP, UDP are transport layer,,,,Am I right ?
Shouldn't they (TCP,UDP) be encapsulated into layer 3 packet for trasmission ?
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Don Johnston earned 250 total points
ID: 16964781
> Shouldn't they (TCP,UDP) be encapsulated into layer 3 packet for trasmission ?

Yes. TCP and UDP are ALWAYS carried in an IP packet.

What I was trying to say was that ALL of these protocols (RIP, IGRP, EIGRP, OSPF, BGP) are carried in an IP packet. Either directly (EIGRP, for example), or inside another protocol that is carried in an IP packet.
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by:zillah
ID: 16968685
((Yes. TCP and UDP are ALWAYS carried in an IP packet.))
Thanks for that.

Since we have got more than one transport protocols (TCP, UDP, GRE, ,,,,, etc)
http://www.networksorcery.com/enp/topic/ipsuite.htm#Transport%20layer%20protocols

and Since some routing protocols rely on other than TCP and UDP protocols, like EIGRP rely on "Reliable Transport Protocol" (RTP) which is also a trasnport protocol (layer 4),,,that means all these layer 4 protocols (TCP,UDP, RTP,,etc), will be encapsulated within ip packet .
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by:zillah
ID: 16977463
((Yes. TCP and UDP are ALWAYS carried in an IP packet.))
((They are all carried in IP packets))

As proof to what you have mentioned the author says in his book "Data Communications and Networking", 3Ed, page 521:

"An IP datagram can encasulate data from several higher-level protocols such as TCP,UDP,ICMP, and IGMP".


((They are all carried in IP packets. Some routing protocols have their own protocol numbers (EIGRP = 88), some are carried by TCP (BGP = 179)  and some are carried by UDP (RIP = 520).)).
Adding to what you have mentioned cisco says "Advanced Routing Book, Chapter 8 page 342":

"While OSPF does not use a Layer 4 protocol".
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by:Don Johnston
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This is all correct.

Does this answer your question?
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