Routing: Split Horizon

Split horizon

Split horizon is a technique used by routing protocols to help prevent routing loops. The split-horizon rule states that an interface will not send routing information out an interface from which the routing information was originally received. Split horizon can cause problems in some topologies, such as hub-and-spoke Frame Relay configurations.

Routing: Route Summarization

Route - Summarization

Summarization is the process in which the administrator collapses many routes with a long mask to form another route with a shorter mask. Route summarization reduces the size of routing tables and makes routing function more efficiently. Route summarization also helps make networks more stable by reducing the number of updates that are sent when subnets change state. Route summarization makes classless inter-domain routing (CIDR) possible. Variable-length subnet masking (VLSM) promotes the use of route summarization. Some dynamic routing protocols engage in route summarization automatically for changes in a major classful network, whereas others do not.

MEMORY ELEMENTS OF ROUTER

RAM(random access memory) Used to hold packet buffers, ARP cache, routing 

tables, and also the software and data structures that allow the router to

function.Running--config is stored in RAM, and most routers expand the IOS

from flash into RAM upon boot.

Flash Memory Stores the IOS by default. Flash memory is not erased when the

router is reloaded. It is EEPROM(electronically erasable programmable read-only

memory) made by intel.

NVRAM(non-volatile RAM) Used to hold the router and switch configuration.

NVRAM is not erased when the router or switch is reloaded. Does not store an

IOS.

ROM(read-only memory) Used to start maintain the router. Holds the POST and mini IOS.