Protocol numbers for TCP is 6 ;UDP-17 which are layer 4 protocols in OSI.

Protocol numbers for OSPF-89 but it is a layer 3 protocol in OSI .

Can anybody explain how they are in different layes when three of them are having protocol numbers?

(May be my interpretation of the literature is wrong)

Thanks & Regards

S.Swaminathan

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Thanks & Regards

S.Swaminathan

I think you may be getting confused.
Remember that all of those protocols move packets, what layer are packets layer 3, right.
So they are in themselves layer 3 protocols.
However how they communicate with eachother may involve another layer, in this case layer 4 for confirmation of packet delivery.
You just need a bit more reading, that's all

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Good Luck,

David

Do you mean the protocol field as specified here: http://tools.ietf.org/html/rfc791#page-14 ?
The simplest definition as to why OSPF is considered a layer 3 protocol and TCP / UDP are layer 4, well, I'll stand to be corrected but this is how I understand it.
Technologies operating in layer 4 provide transport services for other protocols higher up the stack; UDP carries data for RTP, TCP carries data for SMTP.
Technologies operating in layer 3 provide addressing services to get data from one network node to another; because OSPF also handles its transport of data by itself it doesn't need to reference higher-layer protocols.
The difference isn't clear-cut between layers, but I think what I've written above should give you a general picture.

Routing protocols are essentially Application Layer protocols, used by routers to exchange topology information.
Routers in turn use the topology information that they have gathered from other routers (by utilizing Routing protocols) to route Routed protocols.

OSPF does not use a TCP/IP transport protocol (UDP, TCP), but is encapsulated directly in IP datagrams with protocol number 89. OSPF could conceivably use TCP, but for reasons unbeknownst to me, OSPF's designers chose not to use TCP. Since most OSPF traffic is point-to-point over a direct link between two routers, a whole connection does not have to be established. Yet, TCP's reliable transfer feature is desirable, so OSPF doesn't use UDP or TCP.

I had similar questions when i first bumped into this. What i understood is that The OSI 7 layer concept is an aceademic and purely theoretical construct. It has never been implemented. Noone cares enough to implement it. The closer a structure came to the OSI 7-layer structure is the Internet Protocol Suite. (http://en.wikipedia.org/wiki/Internet_Protocol_Suite)
The IP Suite calls L2 = Link Layer, L3 = Internet Layer, L4 = Transport Layer, L5,6,7 = Application Layer.
Still, people in networking use the OSI layers to understand at what point in a network a service/protocol operates.
You should know what each layer in the OSI model refers to, but you will never see the OSI Layer be implemented somewhere.
btw, the Protocol field in the IP datagram defines the protocol used in the data portion of the IP datagram. The Internet Assigned Numbers Authority maintains a list of IP protocol numbers which was originally defined in RFC 790. There seems to be no limit as to what kind of data can be encapsulated. Some numbers:
1 - ICMP (the ping tool uses ICMP)
4 - IP in IP (encapsulation)
8 - EGP
9 - IGP
88 - EIGRP
89 - OSPF
All these protocols are not Transport (Layer 4) protocols. So there is no limit as to what layer the encapsulated protocol has to be.
Actually even Layer 2 protocols can be encapsulated in IP datagrams:
97 - Ethernet-within-IP Encapsulation (RFC 3378)

http://en.wikipedia.org/wiki/List_of_IP ... ol_numbers

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Rule #1 when troubleshooting: never give up

I understood from your reply with the wordings "the Protocol field in the IP datagram defines the protocol used in the data portion of the IP datagram" that what the protocol number means!

Thanks & Regards

S.Swaminathan

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Thanks & Regards

S.Swaminathan

The protocol field is what is read at the destination to determine what particular piece of software requires the packet.
So if the field was 88 it would be handed to the EIGRP software.

Please read what I said above.

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Good Luck,

David

If I am correctly understood now-----------------"You explained me with respect to layers from bottom to top in the receiving end or destination.

What I typed in my previous post is my perception with respect to layers from top to bottom at the source end

Please advise me if I am wrong!

thanks & regards

S.Swaminathan

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Thanks & Regards

S.Swaminathan

No it can't. Not as long as it uses a multicast destination address.

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blog.brokennetwork.ca

got it

@ Infinite

i was just thinking out loud, i guess a more correct sentence would be more like:
OSPF could conceivably use UDP, but for reasons unbeknownst to me, OSPF's designers chose not to use UDP.

_________________
Rule #1 when troubleshooting: never give up

If I'm not mistaken, John Moy discusses the reasons for keeping OSPF clean of upper-layer protocols in his book on the subject.
I'd quote the paragraph, but I don't have the book to hand.

Am I right in my perception? after few months I am asking this question

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Thanks & Regards

S.Swaminathan