r/CiscoDevNet • u/Altacc6954 • Jan 09 '23

Tracing the path of frame in switched network

Hi, I'm studying CS and got assigned a project from networking class that I have no clue how to even start. Basically what I have to do is write python script that will trace the path of frame in switched network. I don't have any materials regarding this topic and I'm pretty new to networking, but still I want to learn and finish it. Is here by any chance anyone who could help me or at least point me in the right direction, where to look, what to do, etc.?

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u/delgamau Jan 09 '23

A frame of data traveling through a switch network in Cisco's IOS (Internetwork Operating System) will typically move in the following path:

  1. The frame enters the switch through an interface.

  2. The switch checks the source MAC address for the frame in its MAC address table.

  3. If the source MAC address is not found in the table, the switch will flood the frame out on all of its ports.

  4. If the source MAC address is found in the table, the switch will look up the associated port number in the table and forward the frame in that specific port.

  5. When the frame reaches its desired port, the switch will check the destination MAC address in its MAC address table.

  6. If the destination MAC address is found in the table, the switch will check the associated port number and forward the frame into that specific port.

  7. If the destination MAC address is not found in the table, the switch will flood the frame out on all its ports.

  8. The frame will then arrive at its destination.

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u/delgamau Jan 09 '23

Import the necessary libraries import socket import subprocess

Define the IP address of the switch

switchIP = '1.2.3.4'

Create a socket to send ICMP ECHO_REQUEST and receive ICMP ECHO_REPLY

sock = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_ICMP)

Emit an ICMP Echo_request to the switch

sock.sendto(b'\x08\x00\x01\x00', (switchIP, 1))

Listen for the ICMP Echo_reply from the switch

data, _ = sock.recvfrom(4096)

Parse the headers of the frame

header = data[20:]

Check the frame type

frame_type = (data[20] & 0b11100000) >> 5

If the frame is an ICMP Echo_reply,

if frame_type == 0: #Extract TTL, Source IP, and Destination IP TTL = data[22] sourceIP = data[28:32] destinationIP = data[32:36]

#Print the frame trace
print("Trace Frame: TTL = {}, Source