Routing tables, split horizon, and subnet addressing in network routing

Networking/Routing

Why do hosts have routing tables even if they only have one interface?

Hosts such as individual servers or PCs use routing table to optimize the way they handle and direct packet data. Without the routing table, a host would not be able to specify the default gateway on a subnet with multiple gateway points. The routing table allows multiple subnets and local nets, alerting hosts about the default gateways and network addresses. Even when using only one interface, the host still needs to specify destination gateways and routing tables. Routing tables also allow for default routing.

How does split horizon work?

Split horizon works with distance vector protocols like routing information protocol (RIP). Using the split horizon command, the network avoids creating packet loops, which can create inefficient data streams. Instead of sending packets back along the same route, the split horizon forces packets through and prevents packets from being sent back along the same interface. Essentially, split horizon works by preventing a router from advertising itself on the same network. Split horizon may also work through "poisoning" the packet to prevent re-transmission.

7.7 How does direct broadcast work using Figure 7-18 as an example?

The directed broadcast specifies all network hosts, allowing packets to be broadcast from the source to the entire network. When the source computer broadcasts information, it will received by Router B. With direct broadcast enabled, router B. will forward to Router a. A will then forward to 10.2.0.0 and 10.1.0.0 and any other hosts on that network. Without direct broadcast, Router B. would not redirect the packet, or Router a would rest at forwarding it to 10.1.0.0