cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
359
Views
0
Helpful
2
Replies

Why there is not layer 3 ?

Heroz
Level 1
Level 1

In this network there are 4 laptops (picture 1).

Screenshot_2022-09-26-15-47-32-30_f9ee0578fe1cc94de7482bd41accb329.jpg

Mark's laptop pings to Lisa's laptop , I have one doubt ICMP ping request is a layered packet right ? So if it is packet in osi model should have layer3-1 right? But why in picture 2 there are only layer 1-2.

Screenshot_2022-09-26-15-47-43-79_f9ee0578fe1cc94de7482bd41accb329.jpg

Thank you.

2 Replies 2

Joseph W. Doherty
Hall of Fame
Hall of Fame

Your "picture 2" when expanded viewed, at least for me, is pretty much unreadable.

Assuming "picture 2" is showing some stats from a L2 switch, such a switch isn't involved if the L3 being used between your hosts.

I.e. between hosts on the same L2 domain, hosts can still do L3 through L7.  All the L2 switch does, is transmit the L2 frames, as created by the hosts, between them.

NetworkDave
Spotlight
Spotlight

Hello Heroz,

PDU information will only be shown if a layer is actively doing something. This also applies to inbound/outbound PDU's.
   Example 1: When a PC initiates a Ping (ICMP echo request) there is no inbound PDU information to display.
   Example 2: When a switch receives/forwards ICMP's (destination other than its own), only Layer 1&2 information is shown
                     (the switch is not actively doing anything with the inbound/outbound PDU's at layer 3).

In picture 2 the event list shows two events (ICMP PDU's).
   If you view first event, it will show outbound layer 2&3 information (Mark's PC is actively building the ICMP echo request PDU).
      No inbound information is shown for the same reason as example 1 above.
      No layer 1 information is shown because no PDU's are being sent yet.
      Unknown destination MAC address for Lisa's PC.
         Mark's PC at layer 2 initiates an ARP request and the ICMP echo request PDU is put in a buffer.
   The second event (viewed), shows that Layer 2 has completed ARP. ICMP echo request PDU is retrieved fron buffer and sent.
      No inbound information is shown for the same reason as example 1 above.
      No layer 3 information is shown because Layer 3 is not actively doing anything.

Let me know if this answers your question and clears up some of the confusion. 

 

Remember to mark helpful posts and mark correct answer as a solution, because that helps other users with similar questions.

Review Cisco Networking for a $25 gift card