IP Packet Doubt

[saishreevj]

Why payload is there in IP packet as well which we have already in ethernet frame? It should have IP header only right? When we are sending a packet from one server to another in a same segment. 

[Giuseppe Larosa]

Hello @saishreevj ,

the term payload indicates the data portion of the packet/frame,  in the case of IP packets the payload usually contain an upper layer protocol like TCP or UDP or ICMP or GRE just to mention the most common. After the L4 protocol identifier if any, there is the L4 payload

At OSI layer 4 the payload of a L4 segment is in the case of TCP an ordered sequence of bytes that are meaningful at application layer.

This is what is called the layered approach that is described in the OSI model. TCP/IP differs from 7 layers OSI.

Ethernet header ||  IP heade || Protoco type || L4 payload                ||   L2 FCS

so the IP packet is the payload of the ethernet frame and a TCP segment L4 PDU is the payload of an IP packet.

Hope to help

Giuseppe

[saishreevj]

@Giuseppe Larosa so ethernet frame, payload contains L3 information such as icmp?                                                                                                        I'm a beginner, trying to understand and prepare for ccna exam. 

[Giuseppe Larosa · Accepted solution]

Hello @saishreevj ,

the ethernet frame payload is an IP packet with IP protocol type = ICMP and then there is the ICMP header and data.

ICMP is over IP and IP is over Ethernet

L4                L3                       L2

I hope this is more clear for you. You can find a lot of packet captures examples

see

https://wiki.wireshark.org/SampleCaptures

If  you have a chance you can download wireshark for free and then  install it on your computer and you can make captures by yourself !

You will need wireshark to open the sample captures.

Hope to help

Giuseppe