Router Memory :
Similar yet different from a regular computer, the router has different kinds of memory ROM, Flash, NVRAM, and SDRAM which all have different functions:
- ROM – POST, Bootstrap, and ROMMON
- Flash – IOS
- NVRAM – Configuration File
- SDRAM – Running-Config, Routing Table, IOS (everything is loaded and executed from RAM)
The router is a computer but it does not have a traditional hard drive to store files and the operating system, this is accomplished in Flash memory and NVRAM memory.
Router Bootup Process:
- POST – ROM memory,
- Bootstrap – ROM memory,
- Load the IOS – the router has an ordered routine for loading the IOS
- Flash Memory – the IOS is typically loaded from Flash memory
- TFTP – if there is no IOS in Flash, the router will search for a network TFTP server,
- ROM – if there is no IOS found, the router defaults to a recovery IOS called Rommon,
- Load the Startup-Config – the router has an ordered routine for loading the startup-config file
- NVRAM memory – the startup-config file is typically loaded from NVRAM memory
- TFTP – if there is no config file in NVRAM, the router will search for a network TFTP server,
- Setup-Mode – if there is no configuration file found, the router defaults to setup-mode
The Router’s Purpose:
The router’s purpose or function is to find the best path (route) and switch out of the correct interface. The router will make the decision of the “best path” by first determining the destination network, and second by consulting its routing table.
Static Routing and Dynamic Routing:
Static routing is a good choice for networks that: never change, are small in size or have only one router, or have only one way out of the network.
Dynamic routing is a good choice if a network has multiple routers, is part of a larger network, or if the network changes frequently.
For example, in a situation where the network changes, with a dynamic routing protocol if a network goes down, the routers will inform each other automatically through the routing protocol, and the route will be removed from the routing table; with static routing, if a network goes down, an administrator will have to go in and remove the the static route manually.
Different types of interior gateway routing protocols: RIPv1, RIPv2, EIGRP, and OSPF.
IPX/SPX (Novell – no longer in use)
Apple Talk (Apple – no longer in use)
RIP v1 – interior gateway protocol, IETF – RFC1058, open standard
RIP v2 – interior gateway protocol, IETF, open standard
EIGRP – interior gateway protocol, Cisco proprietary
OSPF – interior gateway protocol, IETF, open standard
ISIS – interior gateway protocol
BGP – exterior gateway protocol
|Distance Vector||Link State|
|RIP v1||OSPF (VLSM/CIDR)|
|RIP v2 (VLSM/CIDR)||