50 Networking and Online Games: Understanding and Engineering
52 Networking and Online Games: Understanding and Engineering Multiplayer Internet Games R1 R2 R3 R4 R5 Forwarding plane Routing plane Figure 4.11 IP routing conceptually consists of separate forwarding and routing functions within each router terms of hops (the number of routers or links through which the packet passes) but may be defined using any metric desired by the network operator. The path with the lowest sum of metrics over the entire path is the shortest path. (for example, in Figure 4.7 the path through R1, R2 and R5 is the shortest path from 136.80.1.2 to 21.80.1.32 when measured by number of router hops.) Metrics may reflect physical characteristics such as available bandwidth (lower weighting typically given to links with more bandwidth), link delays (higher weighting typically given to links with higher delay) and link costs; or weights may simply represent the administrator s relative preference for traffic to be on a particular link. The results of a router s shortest-path calculations are stored as a set of forwarding rules in a forwarding table, sometimes also referred to as a Forwarding Information Base (FIB). Forwarding rules specify the appropriate next-hop destinations for packets matching various combinations of network/prefix pairs. To ensure that routers always utilise the most precisely specified path, they are required to implement a longest prefix match when forwarding packets. In essence, the forwarding table s entries must be searched for the entry with the longest prefix that matches a packet s destination. The entry thus discovered is the correct next hop. The routing protocol may also choose to use (or be required to account for) two extreme network/prefix pairs default routes and host routes. Default routes are represented by the network/prefix 0.0.0.0/0 a guaranteed match to any IP address. Because the prefix length is zero, this route is the last entry in a router s forwarding table. Default routes are the ultimate in aggregation if there is only one next-hop link out of the local network, a default route entry can point to that link (instead of having explicit forwarding rules for all the network/prefix pairs that can be reached in the world outside the local network). For example, in Figure 4.7 router R1 would have specific routes pointing into Network 1 for destinations under 128.80/16, and a default route entry pointing out toward the IP Backbone. Host routes are represented by the network/prefix w.x.y.z/32 a rule that only matches packets specifically destined for endpoint w.x.y.z. Host routes are discouraged because they are very difficult to aggregate and therefore can consume disproportionate amounts of memory resources in routers throughout the network. Each destination prefix (whether a network, subnet, or actual host) known to the local network s routing protocol is said to be the root of its own particular shortest-path tree.
Note: If you are looking for good and high quality web space to host and run your application check Lunarwebhost Mac Web Hosting services