Which are functions of a router?

Which are functions of a router?

четверг, 25 июня 2009 г.

1.Describe the three layers of the hierarchical network model.
Access layer:
* Grants user access to network devices.
• In a network campus, the access layer generally incorporates switched LAM devices with
ports thai provide connectivity to workstations and servers.
* In the WAN environment, it may provide leleworkers or remote sites access to the corporate
network across WAN technology.
Distribution layer:
• Aggregates the wiring closets, using switches to segment workgroups and isolate network
problems in a campus environment.
* Similarly, the distribution layer aggregates WAN connections at the edge of the campus and
provides policy-based connectivity.
Core layer (also referred to as the backbone):
- A high-speed backbone thai is designed la switch packets as fast as possible,
• Because the core is critical for connectivity, it must provide a high level of availability and
adapt to changes very quickly. It also provides scalability and fast convergence.
Describe the five modules of the Cisco Enterprise Architecture.
Enterprise Campus Architecture:
• An enterprise campus network is a building or group of buildings connected into one
network that consists of many LANs.
• It is generally limited to a fixed geographic area, but it can span several neighboring
• The architecture is modular and scalable and can easily expand to include additional
buildings or floors as required.
Enterprise Branch Architecture:
• This module allows businesses to extend the applications and services found at the
enterprise campus to thousands of remote locations and users or lo a small group of
Enterprise Data Center Architecture:
• Data centers are responsible for managing and maintaining the many data systems that are
vital to modern business operations.
• This module centrally houses the data and resources to enable users to effectively create,
collaborate, and interact
Enterprise Tete worker Architecture:
• This module leverages the network resources of the enterprise from home using broadband
services such as cable modem or DSL to connect to the corporate network
• Typically implemented using remote access VPNs.
Enterprise Edge Architecture
• This module often functions as a liaison between the campus module and the other
modules in the Enterprise Architecture.

3. Compare and contrast the following WAN terms: CPE, CO, local loop, DCE, DTE, and demarcation paint.
Customer Premises Equipment (CPE):
• The devices and inside wiring located at the premises of the subscriber and connected with
a telecommunication channel of a carrier.
• The subscriber either owns the CPE or leases the CPE from the service provider.
Central Office (CO):
• A local service provider facility or building where local telephone cables link to long-haul, all-
digital, fiber-optic communications lines through a system of switches and other equipment.
Local Loop:
• Often referred to as the "last mile," it is the copper or fiber telephone cable that connects the
CPE at The subscriber site to the CO of The service provider.
Data Communications Equipment (DCE):
• Also called data circuit-terminating equipment, the DCE consists of devices that put data on the local loop.
• The DCE primarily provides an interface to connect subscribers to a communication link on the WAN cloud.
Data Terminal Equipment (DTE):
• The customer devices that pass the data from a customer network or host computer for
transmission over the WAN.
• The DTE connects to the local loop through the DCE,
Demarcation Point:
- Physically, the demarcation point is the cabling junction box, located on the customer
premises, that connects the CPE wiring to the local loop and officially separates the
customer equipment from service provider equipment.
- It is the place where the responsibility for the connection changes from the user to the
4. Compare and contrast the following WAN devices: modem, CSLJ/DSLJ, access server, WAN switch, and router.
• A voiceband modem converts and reconverts the digital signals produced by a computer
into voice frequencies that can be transmitted over the analog lines of the public telephone
• Faster modems, such as cable modems and DSL modems, transmit using higher
broadband frequencies
• Digital lines, such as T1 or T3 carrier lines, require a channel service unit (CSU) and a data
service unit (DSU).
• The two are often combined into a single piece of equipment, called the CSU/D3U.
• The CSU provides termination for the digital signal and ensures connection integrity through
error correction and line monitoring while the DSU converts the T-carrier line frames into
frames that the LAN can interpret.
Access server:
• Concentrates dial-in and dial-out user communications and may have a mixture of analog
and digital interfaces and support hundreds of simultaneous users.
WAN switch:
• A rnultiport internetworking device used in carrier networks to support Frame Relay, ATM,
or X.25.
• Provides internetworking and WAN access interface ports that are used to connect to the
service provider network.
• These interfaces may be serial connections or other WAN interfaces and may require an
external device such as, a DSU/CSU or modem (analog, cable, or DSL), to connect to the
service provider
5) Compare and contrast X.25, Frame Relay, and ATM.
• Older low-capacity WAN technology with a maximum speed of 48 kb/s, typically used in
dialup mode with point-of-sale card readers to validate transactions on a central computer.
• For these applications, the low bandwidth and high latency are not a concern, and the low
cost makes X.25 affordable.

• Frame Relay has replaced X.25 at many service provider locations.
Frame Relay:
• Layer 2 WAN protocol that typically offers data rates of 4 Mb/s or higher.

• It provides permanent, shared, medium-band width connectivity using virtual circuits capable
of carrying both voice and data traffic.
• VCs are uniquely identified by a DLCI, which ensures bidirectional communication from one
DTE device to another.

пятница, 27 марта 2009 г.

Which are functions of a router?

Which are functions of a router?
**packet switching
extension of network segments
**segmentation of broadcast domains
**selection of best path based on logical addressing
selection of best path based on physical addressing

Describe the internal and external router hardware components and the purpose of each.

Central Processing Unit (CPU)Executes operating system instructions, such as system

initialization, routing functions, and network interface control.

Random-Access Memory (RAW)Stores the routing table and other data structures that the router

needs when forwarding packets.

Read-Only Memory (ROM) Holds basic diagnostic software used when the router is powered on.

Non-Volalile RAM (NVRAM)Stores the startup configuration, including IP addresses, routing

protocol and other related information NVRAM is a portion of the Boot ROM chip

Flash memory Stores the operating system (Cisco IDS) and other files.

LAN interfaces such as Ethernet and FastEthernet are used for connecting to different LANs

WAN interlaces are used for connecting to a variety of serial links including T1. DSL and ISDN.

Describe the router bootup process from power on to final configuration.

Test router hardware:

1. Perform POST.

2. Execute Bootstrap Loader.

Locale and load the Cisco IDS software:

3. Locate the IOS.

4. Load the [OS.

Locate and load the startup configuration file or enter Setup mode:

5. Locate the Configuration File.

6. Execute the Configuration File.

7. Enter Setup Mode.

Note: If a full IOS image can not be located, a scaled-down version of the IOS is copied from ROM into RAM. This version of IOS is used to help diagnose any problems and can be used to load a complete version of the IOS into RAM. If the startup configuration file does not exist in NVRAM, the router may search for a TFTP server. If the router detects that it has an active link to another configured router it sends a broadcast searching for a configuration file across the active link

What important features does a router add to the network?

Determining the best path to send packets

Forwarding packets toward their destination

Describe the steps necessary to apply a basic configuration to a router.

Name the router

Set passwords

Configure interfaces

Configure a banner

Save changes on a router

Verify basic configuration and router operations

Describe the importance of the routing table. What purposes does it serve?

A routing table provides the router with the necessary information to carry out its primary functionforwarding packets toward the destination network.

What are the three basic ways a router learns about networks?

Connected Routes

Static Routes

Dynamic Routes

For your current studies what are the most important fields in the IP header and why are they important?

Versionversion of IP currently used is IPv4

Time to Live (TTL)number of routers a packet can traverse before being dropped

Source IP address32-bt source IP address

Destination IP address32-bit destination IP address

Describe the encapsulation/decapsulation process as a packet travels from source to destination

The source encapsulates data in a packet with soure and destination IP addresses. It then encapsulates the packet into a frame with source and destination MAC addresses and sends the frame out as bits on the wire The frame is received by the source's gatewaya routera is decapsulated. If the destination MAC address is the router then the router will search the routing table for an outgoing interface to the destination, encapsulate the packet in the appropriate frame format for the outgoing interface with new source and destination layer 2 addresses and forward the frame out the interface. This process is repeated at each router along the path until the packet reaches the destination From source to destination the layer 2 addresses change at each hop. However, the source and destination addresses do not change.

When you think about the difference between the hardware and software of a PC and a router, what do you see as the strengths and weaknesses of each device? Which device do you think is the more powerful and why?

Your answer should revolve around the understanding that a router is a single-purpose device and a computer is a multi-purpose device

As you study, learn, and use the command line interface on a Cisco router, do you see a time when you may not need to use the CLI to configure routers and switches? What does your vision of network configuration tasks look like without the CLI?

Answers will vary. However. CLI is still the dominate way to complete configuration tasks. Like DOS commands. CLI commands will most likely continue to be favored among network administrators as the primary way to complete many configuration or verification tasks even when a more intuitive and easier to use GUI becomes available.

If you could design your own routing protocol algorithm to route packets, what would its mam features be? How would your protocol decide on the best route? Remember, a computer is going to implement your idea: therefore, be specific

Answers will vary Your description should include a step-by-step process. To see pseudocode for current routing algorithms, seach the web for Bellman-Ford and Dykstra algorithms.

Although the Internet Protocol is now consider the only protocol to use for Layer 3 addressing, this was not always the case. Investigate and report on some other Layer 3 protocols that serve the same purpose. What features do they share in common with IP7 How are they different?

A hierachical structure is common to all layer 3 addressing protocols. Each one identifies a network portion and a host portion. How each does this is different. For example Novell's Internet Packet Exchange uses an 30-bit address. The first 32 bits are designated network bits and are determined by the administrator. The remaining 48 bits are the same as the MAC address of the host.