Packet flow of a Router

A router has ip address assigned to fa0/0 interface and ip address assigned to fa0/1 interface and a packet arrives at this router, so explain the packet flow process on how router will make the decision on where and how to forward this packet or how to discard this packet.

  1. Packet Arrival: The packet arrives at the router with a destination IP address.
  2. Destination IP Address Lookup:
  • The router checks the destination IP address of the packet.
  • It looks up the routing table to find the best matching route for the destination IP address.
  1. Longest Prefix Match (LPM):
  • The router uses the Longest Prefix Match algorithm to determine the most specific route entry that matches the destination IP address.
  1. Next-Hop Determination:
  • Once the best matching route is found, the router determines the next-hop IP address to which the packet should be forwarded.
  1. Outgoing Interface Selection:
  • Based on the next-hop IP address, the router determines the outgoing interface through which the packet should be forwarded.
  1. Packet Forwarding:
  • The router forwards the packet out of the determined interface towards the next-hop IP address.
  1. Destination Reached:
  • If the destination IP address is directly connected to one of the router’s interfaces, the packet is delivered directly to the destination host.

If there is no matching route in the routing table for the destination IP address, the router will drop the packet and may send an ICMP (Internet Control Message Protocol) message back to the source indicating that the destination is unreachable.