Router physical characteristics
1.2.2 This page will help students identify the location of different components on a router.
It is not critical to know the location of the physical components inside the router to understand how to use the router. However in some situations, such as adding memory, it can be very helpful.
The exact components used and their location varies between router models. Figure identifies the internal components of a 2600 router.
Figure shows some of the external connectors on a 2600 router.
The next page will describe the external connections on a router.
Router external connections
1.2.3 This page will describe the three basic types of connections on a router, which are LAN interfaces, WAN interfaces, and management ports.
LAN interfaces allow routers to connect to the LAN media. This is usually some form of Ethernet. However, it could be some other LAN technology such as Token Ring or FDDI.
WANs provide connections through a service provider to a distant site or to the Internet. These may be serial connections or any number of other WAN interfaces. With some types of WAN interfaces, an external device such as a CSU is required to connect the router to the local connection of the service provider. With other types of WAN connections, the router may be directly connected to the service provider.
The function of management ports is different from the other connections. The LAN and WAN connections provide network connections through which packets are forwarded. The management port provides a text-based connection for the configuration and troubleshooting of the router. The common management interfaces are the console and auxiliary ports. These are EIA-232 asynchronous serial ports. They are connected to a communications port on a computer. The computer must run a terminal emulation program to provide a text-based session with the router. Through this session the network administrator can manage the device.
The next page will provide a detailed explanation of management ports.
Saturday, April 24, 2010
Routers / Introduction to WANs
Introduction to WANs
1.2.1 While the exact architecture of the router varies between router models, this page will introduce the major internal components. Figures and show the internal components of some of the Cisco router models. The common components are covered in the paragraphs below.
CPU – The Central Processing Unit (CPU) executes instructions in the operating system. Among these functions are system initialization, routing functions, and network interface control. The CPU is a microprocessor. Large routers may have multiple CPUs.
RAM – RAM is used for routing table information, fast switching caches, running configurations, and packet queues. In most routers the RAM provides run time space for executable Cisco IOS software and its subsystems. RAM is usually logically divided into main processor memory and shared input/output (I/O) memory. Shared I/O memory is shared among interfaces for temporary storage of packets. The contents of RAM are lost when power is removed. RAM is generally dynamic random-access memory (DRAM) and can be upgraded with the addition of dual in-line memory modules (DIMMs).
Flash – Flash memory is used for storage of a full Cisco IOS software image. The router normally acquires the default IOS from flash. These images can be upgraded by loading a new image into flash. The IOS may be in uncompressed or compressed form. In most routers an executable copy of the IOS is transferred to RAM during the boot process. In other routers the IOS may be run directly from flash. The flash single in-line memory modules (SIMMs) or PCMCIA cards can be added or replaced to upgrade the amount of flash.
NVRAM – NVRAM is used to store the startup configuration. In some devices, EEPROMs can be used to implement NVRAM. In other devices it is implemented in the same flash device from which the boot code is loaded. In either case these devices retain contents when power is removed.
Buses – Most routers contain a system bus and a CPU bus. The system bus is used to communicate between the CPU and the interfaces or expansion slots. This bus transfers the packets to and from the interfaces.
The CPU bus is used by the CPU for accessing components from router storage. This bus transfers instructions and data to or from specified memory addresses.
ROM – ROM is used to permanently store the startup diagnostic code, which is called the ROM monitor. The main tasks for ROM are hardware diagnostics during router bootup and loading the Cisco IOS software from flash to RAM. Some routers also have a scaled down version of the IOS that can be used as an alternative boot source. ROMs are not erasable. They can only be upgraded by replacing the ROM chips in the sockets.
Interfaces – The interfaces are the router connections to the outside. The three types of interfaces are LANs, WANs, and console or auxiliary (AUX). The LAN interfaces are usually one of several different varieties of Ethernet or Token Ring. These interfaces have controller chips that provide the logic for connecting the system to the media. The LAN interfaces may be a fixed configuration or modular.
The WAN interfaces include serial, ISDN, and integrated CSUs. As with LAN interfaces, WAN interfaces also have special controller chips for the interfaces. The WAN interfaces may be a fixed configuration or modular.
The console and AUX ports are serial ports that are used primarily for the initial configuration of a router. They are used for terminal sessions from the communication ports on the computer or through a modem.
Power Supply – The power supply provides the necessary power to operate the internal components. Larger routers may use multiple or modular power supplies. In some of the smaller routers the power supply may be external to the router.
The next page will describe the components of a Cisco 2600 router.
1.2.1 While the exact architecture of the router varies between router models, this page will introduce the major internal components. Figures and show the internal components of some of the Cisco router models. The common components are covered in the paragraphs below.
CPU – The Central Processing Unit (CPU) executes instructions in the operating system. Among these functions are system initialization, routing functions, and network interface control. The CPU is a microprocessor. Large routers may have multiple CPUs.
RAM – RAM is used for routing table information, fast switching caches, running configurations, and packet queues. In most routers the RAM provides run time space for executable Cisco IOS software and its subsystems. RAM is usually logically divided into main processor memory and shared input/output (I/O) memory. Shared I/O memory is shared among interfaces for temporary storage of packets. The contents of RAM are lost when power is removed. RAM is generally dynamic random-access memory (DRAM) and can be upgraded with the addition of dual in-line memory modules (DIMMs).
Flash – Flash memory is used for storage of a full Cisco IOS software image. The router normally acquires the default IOS from flash. These images can be upgraded by loading a new image into flash. The IOS may be in uncompressed or compressed form. In most routers an executable copy of the IOS is transferred to RAM during the boot process. In other routers the IOS may be run directly from flash. The flash single in-line memory modules (SIMMs) or PCMCIA cards can be added or replaced to upgrade the amount of flash.
NVRAM – NVRAM is used to store the startup configuration. In some devices, EEPROMs can be used to implement NVRAM. In other devices it is implemented in the same flash device from which the boot code is loaded. In either case these devices retain contents when power is removed.
Buses – Most routers contain a system bus and a CPU bus. The system bus is used to communicate between the CPU and the interfaces or expansion slots. This bus transfers the packets to and from the interfaces.
The CPU bus is used by the CPU for accessing components from router storage. This bus transfers instructions and data to or from specified memory addresses.
ROM – ROM is used to permanently store the startup diagnostic code, which is called the ROM monitor. The main tasks for ROM are hardware diagnostics during router bootup and loading the Cisco IOS software from flash to RAM. Some routers also have a scaled down version of the IOS that can be used as an alternative boot source. ROMs are not erasable. They can only be upgraded by replacing the ROM chips in the sockets.
Interfaces – The interfaces are the router connections to the outside. The three types of interfaces are LANs, WANs, and console or auxiliary (AUX). The LAN interfaces are usually one of several different varieties of Ethernet or Token Ring. These interfaces have controller chips that provide the logic for connecting the system to the media. The LAN interfaces may be a fixed configuration or modular.
The WAN interfaces include serial, ISDN, and integrated CSUs. As with LAN interfaces, WAN interfaces also have special controller chips for the interfaces. The WAN interfaces may be a fixed configuration or modular.
The console and AUX ports are serial ports that are used primarily for the initial configuration of a router. They are used for terminal sessions from the communication ports on the computer or through a modem.
Power Supply – The power supply provides the necessary power to operate the internal components. Larger routers may use multiple or modular power supplies. In some of the smaller routers the power supply may be external to the router.
The next page will describe the components of a Cisco 2600 router.
Academy approach to hands-on labs
Academy approach to hands-on labs
1.1.5 This page will help students understand how a lab is configured to simulate a WAN.
In the academy lab, all the networks will be connected with serial or Ethernet cables and the students can see and physically touch all the equipment. Unlike the academy lab setup, the serial cables in the real world are not connected back to back. In a real world situation, one router could be in New York, while another router could be in Sydney, Australia. An administrator located in Sydney would have to connect to the router in New York through the WAN cloud in order to troubleshoot the New York router.
In the academy lab, devices that make up the WAN cloud are simulated by the connection between the back-to-back DTE-DCE cables. The connection from one router interface s0/0 to another router interface s0/1 simulates the whole circuit cloud.
This page concludes the discussion about WANs. The next lesson will describe routers in greater detail.
1.1.5 This page will help students understand how a lab is configured to simulate a WAN.
In the academy lab, all the networks will be connected with serial or Ethernet cables and the students can see and physically touch all the equipment. Unlike the academy lab setup, the serial cables in the real world are not connected back to back. In a real world situation, one router could be in New York, while another router could be in Sydney, Australia. An administrator located in Sydney would have to connect to the router in New York through the WAN cloud in order to troubleshoot the New York router.
In the academy lab, devices that make up the WAN cloud are simulated by the connection between the back-to-back DTE-DCE cables. The connection from one router interface s0/0 to another router interface s0/1 simulates the whole circuit cloud.
This page concludes the discussion about WANs. The next lesson will describe routers in greater detail.
Role of routers in a WAN
Role of routers in a WAN
1.1.4 This page will review WANs in relation to the OSI model and explain the functions of a router.
The standards and protocols or primary functions of a WAN operate at the physical layer and at the data link layer. This does not mean that the other five layers of the OSI model are not found in a WAN. It simply means that the standards and protocols that define a WAN connection are typically found at the physical and data link layers. In other words, the Layer 1 and Layer 2 WAN standards and protocols are different than the Layer 1 and Layer 2 LAN standards and protocols.
The WAN physical layer describes the interface between the data terminal equipment (DTE) and the data circuit-terminating equipment (DCE). Generally, the DCE is the service provider and the DTE is the attached device. In this model, the services offered to the DTE are made available through a modem or a CSU/DSU.
The main function of a router is to transmit data using Layer 3 addresses. This process is also called routing. Routing occurs at the network layer, which is Layer 3. If a WAN operates at Layers 1, 2, and 3, is a router a LAN device or a WAN device? The answer is both, as is so often the case in the field of networking. A router may be exclusively a LAN device, it may be exclusively a WAN device, or it may sit at the boundary between a LAN and a WAN and be a LAN and WAN device at the same time.
One of the roles of a router in a WAN is to route packets at Layer 3, but this is also a role of a router in a LAN. Therefore routing is not strictly a WAN role of a router. When a router uses the physical and data link layer standards and protocols that are associated with WANs, it is operating as a WAN device. Therefore, the main role of a router in a WAN is not to route. It is to provide connections between the various WAN physical and data-link standards. These standards and protocols that define and structure a WAN connection operate at Layers 1 and 2. For example, a router may have an ISDN interface that uses PPP encapsulation and a serial interface at the end of a T1 line that uses Frame Relay encapsulation. The router must be able to move a stream of bits from one type of service, such as ISDN, to another, such as a T1, and change the data link encapsulation from PPP to Frame Relay.
Many of the details of WAN Layer 1 and Layer 2 protocols will be covered later in the course, but some of the key WAN protocols and standards are listed here for reference.
Here is a list of WAN physical layer standards and protocols:
• EIA/TIA-232
• EIA/TIA-449
• V.24
• V.35
• X.21
• G.703
• EIA-530
• ISDN
• T1, T3, E1, and E3
• xDSL
• SONET (OC-3, OC-12, OC-48, OC-192)
Here is a list of WAN data link layer standards and protocols:
• High-level data link control (HDLC)
• Frame Relay
• Point-to-Point Protocol (PPP)
• Synchronous Data Link Control (SDLC)
• Serial Line Internet Protocol (SLIP)
• X.25
• ATM
• LAPB
• LAPD
• LAPF
The next page will describe how a WAN is simulated in a lab environment
1.1.4 This page will review WANs in relation to the OSI model and explain the functions of a router.
The standards and protocols or primary functions of a WAN operate at the physical layer and at the data link layer. This does not mean that the other five layers of the OSI model are not found in a WAN. It simply means that the standards and protocols that define a WAN connection are typically found at the physical and data link layers. In other words, the Layer 1 and Layer 2 WAN standards and protocols are different than the Layer 1 and Layer 2 LAN standards and protocols.
The WAN physical layer describes the interface between the data terminal equipment (DTE) and the data circuit-terminating equipment (DCE). Generally, the DCE is the service provider and the DTE is the attached device. In this model, the services offered to the DTE are made available through a modem or a CSU/DSU.
The main function of a router is to transmit data using Layer 3 addresses. This process is also called routing. Routing occurs at the network layer, which is Layer 3. If a WAN operates at Layers 1, 2, and 3, is a router a LAN device or a WAN device? The answer is both, as is so often the case in the field of networking. A router may be exclusively a LAN device, it may be exclusively a WAN device, or it may sit at the boundary between a LAN and a WAN and be a LAN and WAN device at the same time.
One of the roles of a router in a WAN is to route packets at Layer 3, but this is also a role of a router in a LAN. Therefore routing is not strictly a WAN role of a router. When a router uses the physical and data link layer standards and protocols that are associated with WANs, it is operating as a WAN device. Therefore, the main role of a router in a WAN is not to route. It is to provide connections between the various WAN physical and data-link standards. These standards and protocols that define and structure a WAN connection operate at Layers 1 and 2. For example, a router may have an ISDN interface that uses PPP encapsulation and a serial interface at the end of a T1 line that uses Frame Relay encapsulation. The router must be able to move a stream of bits from one type of service, such as ISDN, to another, such as a T1, and change the data link encapsulation from PPP to Frame Relay.
Many of the details of WAN Layer 1 and Layer 2 protocols will be covered later in the course, but some of the key WAN protocols and standards are listed here for reference.
Here is a list of WAN physical layer standards and protocols:
• EIA/TIA-232
• EIA/TIA-449
• V.24
• V.35
• X.21
• G.703
• EIA-530
• ISDN
• T1, T3, E1, and E3
• xDSL
• SONET (OC-3, OC-12, OC-48, OC-192)
Here is a list of WAN data link layer standards and protocols:
• High-level data link control (HDLC)
• Frame Relay
• Point-to-Point Protocol (PPP)
• Synchronous Data Link Control (SDLC)
• Serial Line Internet Protocol (SLIP)
• X.25
• ATM
• LAPB
• LAPD
• LAPF
The next page will describe how a WAN is simulated in a lab environment
Router LANs and WANs
Router LANs and WANs
1.1.3 Routers can be used to segment LANs, but they are mainly used as WAN devices. This page will explain how routers are used in a network.
Routers have both LAN and WAN interfaces. WAN technologies are frequently used to connect routers. Routers use WAN connections to communicate with each other. Routers are the backbone devices of large intranets and of the Internet. They operate at Layer 3 of the OSI model, making decisions based on network addresses. The two main functions of a router are to select the best path for packets and to route packets to the proper interface. To accomplish this, routers build routing tables and exchange network information with other routers.
An administrator can configure static routes to maintain routing tables. However, most routing tables are maintained dynamically through the use of a routing protocol that exchanges network topology information with other routers.
For example, if Computer X needs to communicate with Computer Y and Computer Z in Figure , this requires a routing feature for information flow and redundant paths for reliability. Many network design decisions and technologies can be traced to this desire for Computers X, Y, and Z to communicate.
A correctly configured internetwork provides the following:
• Consistent end-to-end addressing
• Addresses that represent network topologies
• Best path selection
• Dynamic or static routing
• Switching
The next page will explain the function of routers in a WAN.
1.1.3 Routers can be used to segment LANs, but they are mainly used as WAN devices. This page will explain how routers are used in a network.
Routers have both LAN and WAN interfaces. WAN technologies are frequently used to connect routers. Routers use WAN connections to communicate with each other. Routers are the backbone devices of large intranets and of the Internet. They operate at Layer 3 of the OSI model, making decisions based on network addresses. The two main functions of a router are to select the best path for packets and to route packets to the proper interface. To accomplish this, routers build routing tables and exchange network information with other routers.
An administrator can configure static routes to maintain routing tables. However, most routing tables are maintained dynamically through the use of a routing protocol that exchanges network topology information with other routers.
For example, if Computer X needs to communicate with Computer Y and Computer Z in Figure , this requires a routing feature for information flow and redundant paths for reliability. Many network design decisions and technologies can be traced to this desire for Computers X, Y, and Z to communicate.
A correctly configured internetwork provides the following:
• Consistent end-to-end addressing
• Addresses that represent network topologies
• Best path selection
• Dynamic or static routing
• Switching
The next page will explain the function of routers in a WAN.
Introduction to routers in a WAN
Introduction to routers in a WAN
1.1.2 This page will provide a brief review of routers.
A router is a special type of computer. It has the same basic components as a standard desktop PC. It has a CPU, memory, a system bus, and various input/output interfaces. However, routers are designed to perform some very specific functions that are not typically performed by desktop computers. For example, routers connect and allow communication between two networks and determine the best path for data to travel through the connected networks.
Just as computers need operating systems to run software applications, routers need the Internetwork Operating System (IOS) software to run configuration files. These configuration files contain the instructions and parameters that control the flow of traffic in and out of the routers. Routers use routing protocols to determine the best path for packets. The configuration file specifies all the information for the correct setup and use of the selected, or enabled, routing and routed protocols on a router.
This course will demonstrate how to build configuration files from the IOS commands in order to get the router to perform many essential network functions. The router configuration file may seem complex at first, but it will be easier to understand by the end of the course.
The main internal components of the router are random-access memory (RAM), nonvolatile random-access memory (NVRAM), flash memory, read-only memory (ROM), and interfaces.
RAM has the following characteristics and functions:
• Stores routing tables
• Holds ARP cache
• Holds fast-switching cache
• Performs packet buffering as shared RAM
• Maintains packet-hold queues
• Provides temporary memory for the configuration file of a router while the router is powered on
• Loses content when a router is powered down or restarted
NVRAM has the following characteristics and functions:
• Provides storage for the startup configuration file
• Retains content when a router is powered down or restarted
Flash memory has the following characteristics and functions:
• Holds the IOS image
• Allows software to be updated without removing and replacing chips on the processor
• Retains content when a router is powered down or restarted
• Can store multiple versions of IOS software
• Is a type of electrically erasable programmable read-only memory (EEPROM)
ROM has the following characteristics and functions:
• Maintains instructions for power-on self test (POST) diagnostics
• Stores bootstrap program and basic operating system software
• Requires replacing pluggable chips on the motherboard for software upgrades
Interfaces have the following characteristics and functions:
• Connect routers to a network for packet entry and exit
• Can be on the motherboard or on a separate module
The next page will describe the role of routers in WANs and LANs.
1.1.2 This page will provide a brief review of routers.
A router is a special type of computer. It has the same basic components as a standard desktop PC. It has a CPU, memory, a system bus, and various input/output interfaces. However, routers are designed to perform some very specific functions that are not typically performed by desktop computers. For example, routers connect and allow communication between two networks and determine the best path for data to travel through the connected networks.
Just as computers need operating systems to run software applications, routers need the Internetwork Operating System (IOS) software to run configuration files. These configuration files contain the instructions and parameters that control the flow of traffic in and out of the routers. Routers use routing protocols to determine the best path for packets. The configuration file specifies all the information for the correct setup and use of the selected, or enabled, routing and routed protocols on a router.
This course will demonstrate how to build configuration files from the IOS commands in order to get the router to perform many essential network functions. The router configuration file may seem complex at first, but it will be easier to understand by the end of the course.
The main internal components of the router are random-access memory (RAM), nonvolatile random-access memory (NVRAM), flash memory, read-only memory (ROM), and interfaces.
RAM has the following characteristics and functions:
• Stores routing tables
• Holds ARP cache
• Holds fast-switching cache
• Performs packet buffering as shared RAM
• Maintains packet-hold queues
• Provides temporary memory for the configuration file of a router while the router is powered on
• Loses content when a router is powered down or restarted
NVRAM has the following characteristics and functions:
• Provides storage for the startup configuration file
• Retains content when a router is powered down or restarted
Flash memory has the following characteristics and functions:
• Holds the IOS image
• Allows software to be updated without removing and replacing chips on the processor
• Retains content when a router is powered down or restarted
• Can store multiple versions of IOS software
• Is a type of electrically erasable programmable read-only memory (EEPROM)
ROM has the following characteristics and functions:
• Maintains instructions for power-on self test (POST) diagnostics
• Stores bootstrap program and basic operating system software
• Requires replacing pluggable chips on the motherboard for software upgrades
Interfaces have the following characteristics and functions:
• Connect routers to a network for packet entry and exit
• Can be on the motherboard or on a separate module
The next page will describe the role of routers in WANs and LANs.
This page will provide a brief review of routers.
A router is a special type of computer. It has the same basic components as a standard desktop PC. It has a CPU, memory, a system bus, and various input/output interfaces. However, routers are designed to perform some very specific functions that are not typically performed by desktop computers. For example, routers connect and allow communication between two networks and determine the best path for data to travel through the connected networks.
Just as computers need operating systems to run software applications, routers need the Internetwork Operating System (IOS) software to run configuration files. These configuration files contain the instructions and parameters that control the flow of traffic in and out of the routers. Routers use routing protocols to determine the best path for packets. The configuration file specifies all the information for the correct setup and use of the selected, or enabled, routing and routed protocols on a router.
This course will demonstrate how to build configuration files from the IOS commands in order to get the router to perform many essential network functions. The router configuration file may seem complex at first, but it will be easier to understand by the end of the course.
The main internal components of the router are random-access memory (RAM), nonvolatile random-access memory (NVRAM), flash memory, read-only memory (ROM), and interfaces.
RAM has the following characteristics and functions:
Stores routing tables
Holds ARP cache
Holds fast-switching cache
Performs packet buffering as shared RAM
Maintains packet-hold queues
Provides temporary memory for the configuration file of a router while the router is powered on
Loses content when a router is powered down or restarted
NVRAM has the following characteristics and functions:
Provides storage for the startup configuration file
Retains content when a router is powered down or restarted
Flash memory has the following characteristics and functions:
Holds the IOS image
Allows software to be updated without removing and replacing chips on the processor
Retains content when a router is powered down or restarted
Can store multiple versions of IOS software
Is a type of electrically erasable programmable read-only memory (EEPROM)
ROM has the following characteristics and functions:
Maintains instructions for power-on self test (POST) diagnostics
Stores bootstrap program and basic operating system software
Requires replacing pluggable chips on the motherboard for software upgrades
Interfaces have the following characteristics and functions:
Connect routers to a network for packet entry and exit
Can be on the motherboard or on a separate module
The next page will describe the role of routers in WANs and LANs.
A router is a special type of computer. It has the same basic components as a standard desktop PC. It has a CPU, memory, a system bus, and various input/output interfaces. However, routers are designed to perform some very specific functions that are not typically performed by desktop computers. For example, routers connect and allow communication between two networks and determine the best path for data to travel through the connected networks.
Just as computers need operating systems to run software applications, routers need the Internetwork Operating System (IOS) software to run configuration files. These configuration files contain the instructions and parameters that control the flow of traffic in and out of the routers. Routers use routing protocols to determine the best path for packets. The configuration file specifies all the information for the correct setup and use of the selected, or enabled, routing and routed protocols on a router.
This course will demonstrate how to build configuration files from the IOS commands in order to get the router to perform many essential network functions. The router configuration file may seem complex at first, but it will be easier to understand by the end of the course.
The main internal components of the router are random-access memory (RAM), nonvolatile random-access memory (NVRAM), flash memory, read-only memory (ROM), and interfaces.
RAM has the following characteristics and functions:
Stores routing tables
Holds ARP cache
Holds fast-switching cache
Performs packet buffering as shared RAM
Maintains packet-hold queues
Provides temporary memory for the configuration file of a router while the router is powered on
Loses content when a router is powered down or restarted
NVRAM has the following characteristics and functions:
Provides storage for the startup configuration file
Retains content when a router is powered down or restarted
Flash memory has the following characteristics and functions:
Holds the IOS image
Allows software to be updated without removing and replacing chips on the processor
Retains content when a router is powered down or restarted
Can store multiple versions of IOS software
Is a type of electrically erasable programmable read-only memory (EEPROM)
ROM has the following characteristics and functions:
Maintains instructions for power-on self test (POST) diagnostics
Stores bootstrap program and basic operating system software
Requires replacing pluggable chips on the motherboard for software upgrades
Interfaces have the following characteristics and functions:
Connect routers to a network for packet entry and exit
Can be on the motherboard or on a separate module
The next page will describe the role of routers in WANs and LANs.
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