Data Encapsulation

[Tech enthusiast1]

Greetings, I'm a bit confused regarding the encapsulation process of an ethernet 2 frame. It seems the destination IP address is obtained prior to data even reaching Layer 3 of the OSI model. Furthermore, in layer 4, to my understanding a virtual circuit is setup with the remote host for the exchange of data. How is the remote IP address obtained when the remote host contains a private IP address that is not routable threw the internet? Any kind soul out there that can help me understand this would be greatly appreciated. 

[M02@rt37]

Hello @Tech enthusiast1  

In the networking process, the encapsulation of an ethernet 2 frame occurs at Layer 2 of the OSI model, where the destination MAC address is determined for local network forwarding. However, the destination IP address is obtained at Layer 3, even before data reaches this layer, as IP addresses are crucial for routing. Devices determine the destination IP address using routing tables or ARP or hosts within the same network or consulting a gateway for hosts on different networks. As for Layer 4, virtual circuits for data exchange, such as those established by TCP or UDP, operate on top of the established IP connections.

Regarding private IP addresses that are not routable over the internet, NAT is used to translate private addresses to public ones at the edge of a private network, allowing communication over the internet. NAT ensures that packets are properly routed to the intended destination, even if it contains a private IP address.

[Joseph W. Doherty]

Possibly what you're overlooking is the over all process.

For example to access this site with a browser, we logically start with a host name of community.cisco.com but much happens before the HTTP session is established.  Suggest you review the overall process. Such review may help your understanding.