IPv4 Routing

IPv4 Routing

1. Host Routing

   • Step 1. If the destination IP address is in the same IP subnet as I am, send the packet directly to that destination host.
   • Step 2. Otherwise, send the packet to my default gateway, also known as a default router.

2. Router Forwarding Logic

   • Step 1. Use the data link Frame Check Sequence (FCS) field to ensure that the frame had no errors; if errors occurred, discard the frame.
     • Step 2. Assuming that the frame was not discarded at Step 1, discard the old data link header and trailer, leaving the IP packet.
       • Step 3. Compare the IP packet’s destination IP address to the routing table, and find the route that best matches the destination address.
         • Step 4. Encapsulate the IP packet inside a new data link header and trailer, appropriate for the outgoing interface, and forward the frame.