My routers are connected each other through Hub with FastEthernet cables. When I looked into cdp packet captured by Ethereal software, I found CDP packet looks like this:
IEEE 802.3 Ethernet //layer2 Logical-Link Control //layer3 Cisco Discovery Protocol //layer4
Why CDP protocol is called as layer 2 ? Also if I get CDP packet over serial cable(PPP?), is CDP still layer 2 ? I think PPP protocol is layer 2.
I'm so confused. Help me out..
CDP is a layer 2 protocol ( data link layer).
"Logical Link Control layer
In the Open Systems Interconnection (OSI) model of communication, the Logical Link Control layer is one of two sublayers of the Data-Link layer and is concerned with managing traffic (flow and error control) over the physical medium."
further
CDP is a layer 2 discovery protocol allowing one to find out about the physical toplogy of a network.
It is not a data link protocol like HDLC or PPP for transporting higher layer protocols
Thanks for wonderful answer !!
Thanks for wonderful answer !!
"jh3ang" skrev i en meddelelse news: snipped-for-privacy@z34g2000cwc.googlegroups.com...
CDP is layer-2, and if you think closely, you will notice that CDP will run even though you do not have an IP address on a interface. Hence it can not be L3 or higher.
The fact that its layer-2 makes you able to verify connectivity, eventhough the upper protocol are not running, and hence it can be very usefull in throubleshhoting various problems.
HTH Martin Bilgrav
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