09-04-2012, 04:51 PM
INTRODUCTION TO ROUTERS
[attachment=19793]
ABSTRACT
A router is a computer networking device that forwards data packets toward their destinations through a process known as routing. Routing occurs at layer 3 of the OSI seven-layer model. Routing is most commonly associated with the Internet Protocol, although other less-popular routed protocols remain in use. In the original 1960s-era of routing, general-purpose computers served as routers. Although general-purpose computers can perform routing, modern high-speed routers are highly specialised computers, generally with extra hardware added to accelerate both common routing functions such as packet forwarding and specialised functions such as IPsec encryption .
Functionality
A router must be connected to at least two networks, or it will have nothing to route. A special variety of router is the one-armed router used to route packets in a virtual LAN environment. In the case of a one-armed router the multiple attachments to different networks are all over the same physical link. A router which connects end-users to the Internet is called Edge router; A router which serves to transmit data between other routers is called Core router. A router creates and/or maintains a table, called a "routing table" that stores the best routes to certain network destinations and the "routing metrics" associated with those routes. See the routing article for a more detailed discussion of how this works. In recent times many routing functions have been added to LAN switches, creating "Layer 2/3 Switches" which route traffic at near wire speed.
CPU
CPU performs functions just as it does in a normal PC. It executes commands given by the IOS using other hardware components. High-end routers may contain multiple processors or extra slots to add more CPUs later.
RAM
Random Access Memory; this component is dynamic. Meaning, its content changes constantly. The main role of the RAM is to: hold the ARP cache, Store routing tables, hold fast-switching cache, performs packet buffering, and hold queues. It also provides temporary memory for the configuration file of the router while the router is powered on.
NVRAM
Nonvolatile RAM is used to store the startup configuration files. This type of RAM does not lose its content when the router is restarted or powered off.
Flash
Flash memory is very important because it saves your configuration if you screw up the operating system configuration. It holds the Cisco IOS image file, as well as backups. This flash memory is classified as an EEPROM (Electronically Erasable Programmable Read Only Memory). The flash ROM is upgradeable in most Cisco routers.
ROM
The ROM performs the same operations as a BIOS. It holds information about the systems hardware components and runs POST when the router first starts up. This component can be upgraded by "unplugging" the chip and installing a new one. A ROM upgrade ensures newer versions of the IOS.
Router User Interface
A user interface is the system by which people (users) interact with a machine. The user interface includes hardware (physical) and software (logical) components. User interfaces exist for various system and provide a means of:
• Input, allowing the users to manipulate a system
• Output, allowing the system to indicate the effects of the users' manipulation
Cisco IOS software uses a Command Line Interface (CLI).The CLI environment is accessible
through a console session (No network configuration is required)
Dial-up connection
Telnet connection as a virtual terminal.
Establish a Console Session
• To establish a Hyper Terminal Session
– Connect the terminal with an RJ-45-to-RJ45 Rollover cable or
– RJ45-to-DB-9 or
– RJ45-to-DB-25 Adapter
Access control list (ACL)
An access control list (ACL), with respect to a computer file system, is a list of permissions attached to an object. An ACL specifies which users or system processes are granted access to objects, as well as what operations are allowed on given objects. Each entry in a typical ACL specifies a subject and an operation. For instance, if a file has an ACL that contains (Alice, delete), this would give Alice permission to delete the file.
[attachment=19793]
ABSTRACT
A router is a computer networking device that forwards data packets toward their destinations through a process known as routing. Routing occurs at layer 3 of the OSI seven-layer model. Routing is most commonly associated with the Internet Protocol, although other less-popular routed protocols remain in use. In the original 1960s-era of routing, general-purpose computers served as routers. Although general-purpose computers can perform routing, modern high-speed routers are highly specialised computers, generally with extra hardware added to accelerate both common routing functions such as packet forwarding and specialised functions such as IPsec encryption .
Functionality
A router must be connected to at least two networks, or it will have nothing to route. A special variety of router is the one-armed router used to route packets in a virtual LAN environment. In the case of a one-armed router the multiple attachments to different networks are all over the same physical link. A router which connects end-users to the Internet is called Edge router; A router which serves to transmit data between other routers is called Core router. A router creates and/or maintains a table, called a "routing table" that stores the best routes to certain network destinations and the "routing metrics" associated with those routes. See the routing article for a more detailed discussion of how this works. In recent times many routing functions have been added to LAN switches, creating "Layer 2/3 Switches" which route traffic at near wire speed.
CPU
CPU performs functions just as it does in a normal PC. It executes commands given by the IOS using other hardware components. High-end routers may contain multiple processors or extra slots to add more CPUs later.
RAM
Random Access Memory; this component is dynamic. Meaning, its content changes constantly. The main role of the RAM is to: hold the ARP cache, Store routing tables, hold fast-switching cache, performs packet buffering, and hold queues. It also provides temporary memory for the configuration file of the router while the router is powered on.
NVRAM
Nonvolatile RAM is used to store the startup configuration files. This type of RAM does not lose its content when the router is restarted or powered off.
Flash
Flash memory is very important because it saves your configuration if you screw up the operating system configuration. It holds the Cisco IOS image file, as well as backups. This flash memory is classified as an EEPROM (Electronically Erasable Programmable Read Only Memory). The flash ROM is upgradeable in most Cisco routers.
ROM
The ROM performs the same operations as a BIOS. It holds information about the systems hardware components and runs POST when the router first starts up. This component can be upgraded by "unplugging" the chip and installing a new one. A ROM upgrade ensures newer versions of the IOS.
Router User Interface
A user interface is the system by which people (users) interact with a machine. The user interface includes hardware (physical) and software (logical) components. User interfaces exist for various system and provide a means of:
• Input, allowing the users to manipulate a system
• Output, allowing the system to indicate the effects of the users' manipulation
Cisco IOS software uses a Command Line Interface (CLI).The CLI environment is accessible
through a console session (No network configuration is required)
Dial-up connection
Telnet connection as a virtual terminal.
Establish a Console Session
• To establish a Hyper Terminal Session
– Connect the terminal with an RJ-45-to-RJ45 Rollover cable or
– RJ45-to-DB-9 or
– RJ45-to-DB-25 Adapter
Access control list (ACL)
An access control list (ACL), with respect to a computer file system, is a list of permissions attached to an object. An ACL specifies which users or system processes are granted access to objects, as well as what operations are allowed on given objects. Each entry in a typical ACL specifies a subject and an operation. For instance, if a file has an ACL that contains (Alice, delete), this would give Alice permission to delete the file.