Network routing protocols and algorithms

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.

7.6 Why are "all ones" and "all zeros" subnets not used?

All ones" and "all zeros" subnets are avoided because they can cause confusion on the network. All zeros create confusion between the network address and subnet addresses, whose prefixes are the same. A router would not be able to determine whether a packet was to be directed to the entire subnet or to a specific host on it. Similarly, all ones broadcast addresses can be confused with one another especially in directed and all-subnets directed broadcasting using class-based routing protocols.