Packet Processing Interface to Interface, Part 3: Determine Destination

• The packet is for this router if

• • Destination matches any of the routers’ IP addresses
  • Broadcast
  • If multicast, check further
  • Any of these cases except possibly multicast, packet is not forwarded

• Otherwise, do route lookup

• • Simplest lookup is based on destination IP
  • • Longest prefix-match algorithm (several variations, some complex)
  • May also include source IP, TOS, source port, destination port, protocol, other fields
  • If more than one route, choose one with best metric
  • • Lowest load, least number of hops, etc
    • All metrics the same? Do something intelligent!