I am familiar with the OSI model and all but there is something that's been on my mind: Do tools like nslookup and ping reside in the application layer only? They use supporting layers below but perhaps you just say it's in the application layer? Help me out here :)!
Tools such as
nslookup, etc. all work at application layer; but as you stated, the messages are sent up and down the protocol stack to work at all layers of the OSI model. Generally, you would say that this was an application layer command, but you are right in pointing out that the supporting layers are used.
Programs like Ping, Email etc on the application layer use transport layer protocols such as TCP and UDP.
These use network layer protocols such as IP, ICMP, ARP, RIP etc.
These use logical addresses which are associated with MAC addresses on the Data Link Layer.
The signals that makeup these packets are sent on the physical layer.
Its probably worth pointing out that Standards such as
nslookup are primarily based within the Session, Presentation and Application layers though.