Ruediger Meier wrote:
At any given time, how many routing tables would you have in use?
I guess even you have more than one routing table in use. At least 4 ones: local/ipv4, local/ipv6, main/ipv6, main/ipv6.
What are you referring to be local and main? Routing is only used for destinations that are not on the local network. Therefore, there shouldn't ben any routing table entries for anything on the local network. The way this works is your computer compares the destination address with the subnet mask. If the destination is on the local subnet, the computer does an arp request (IPv4, IPv6 uses neighbour discovery and advertisements), to determine the MAC address of the destination and sends the packet to that MAC address. If the destination is not on the local netork, then the computer checks the routing tables to see if it's on a known network and uses the appropriate route. If it's not on a known network, then it uses the default route, so that the next router can try to forward it. If it also doesn't know, then it passes it along it's default route etc. This process ends when the packet reaches a router that knows how to get to the destination. Top level routers, that is those that tie the Internet together, do not have default routes, as they're supposed to know how to reach everywhere.