Route Lookup Process

When a router receives a packet on an interface, the router examines the header of the packet and identifies the destination IPv4 address, and proceeds through the router lookup process.

Step-1

  1. The router examines level 1 route, as well as network routes and supernet routes; for the best match with the destination address of the IP packet.
  2. If the best match is a level 1 route, ultimate route, or supernet route then the packet is forward to the destination using the best match route.
  3. If the best match is a level 1 parent route, continue to the next step.

Step-2

  1. The router examines level 2 child routes of the level 1 parent route for the best match.
  2. If there match with a level 2 child routes found, the router forwards the packet to the destination using this route.
  3. If no match is found with any of the level 2 child routes, continue to the next step.

Step-3

  1. the router starts lookup best match in level 1 supernet routes in the routing table, including the default route.
  2. If there is now a smaller match with a level 1 supernet or default routes; the router uses that route to forward the packet.
  3. If a match to the destination not found with any route in the routing table, the router drops the packet.
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