IP (Internet Protocol) Version 4 for CCNA R&S

Hello Rahul

You are correct that IP is a connectionless protocol. However the need to use TCP depends not on the connectionless nature of IP, but on the upper layer application being served. For web traffic, email or FTP for example, TCP (which creates sessions between hosts) must be used because the applications demand it.

Other applications do not require the connection-oriented nature of TCP such as Voice and Video, which use RTP, or DNS which uses UDP. These layer 4 protocols do not create sessions nor do they provide any reliability.

Some applications don’t even require a layer 4 structure at all. ICMP for example, which is what we use for ping does not have a layer 4 component. Routing protocols such as EIGRP, OSPF and RIP communicate and use only up to layer 3 encapsulation.

In the same way, traffic generators can generate traffic using only layer 3, as no session needs to be created.

Connection oriented protocols at layer 4 are used only if the upper layer applications it is supporting demand it.

I hope this has been helpful!

Laz

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