IP Datagram Forwarding

Strategy:

• Every IP datagram contains destination’s address
• If directly connected to destination network, then forward to host
• If not directly connected to destination network, then forward to some router
• Forwarding table maps network number into next hop
• Each host has a default router
• Each router maintains a forwarding table

Example (router R2 wants to send a datagram):

R2’s forwarding table:

Algorithm:

• First find NetworkNum of destination
• If NetworkNum of destination equals NetworkNum of one of my interfaces, then deliver packet to destination over that interface
• Else, if NetworkNum of destination is in my forwarding table, then deliver packet to NextHop router
• Else deliver packet to default router