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Cisco CCNA, CCNP, CCENT Practice Questions: VLANs, IPv6

CCENT Certification:

Given the MAC address aa-bb-cc-11-22-33, identify the OUI.

Answer: The OUI is the first half of the MAC address, aa-bb-cc.

CCNA Certification:

Short answer: A frame is about to be transmitted over a trunk. What term describes the process of identifying the destination VLAN?

Answer: This is known as “tagging” the frame.

CCNP Certification / BSCI Exam:

Fill in the blank: An IPv6 address consists of ____________ bits.

Answer: 128 bits.

CCNP Certification / BCMSN Exam:

Approximately how long does it take a switch running RSTP to detect a down link?

A. 20 seconds (the MaxAge value).

B. 2 seconds (the Hello Time value).

C. 15 seconds (the Forward Delay value).

D. None of the above.

Answer: D. An RSTP port will detect a down link in about 6 seconds. When a RSTP port misses three BPDUs, the link is considered down. The RSTP Hello Time is 2 seconds.

CCNP Certification / ISCW Exam:

You’ve just created an IP inspection rule. How should it be applied?

A. Globally.

B. On a per-protocol basis.

C. On a per-interface basis.

D. On a per-access list basis.

Answer: C. IP inspection rules are applied on a per-interface basis.

CCNP Certification / ONT Exam:

Which of the following is NOT a service class found in the Customer Model service class?

A. best-effort

B. guaranteed

C. mission critical

D. scavenger

E. transpositional

F. collapsed core

G. scavenger

Answers: B, E, F. The service classes in the Customer Model are mission critical, best-effort, scavengerComputer Technology Articles, and transactional.

Home Network Data Storage

If you have two or more computers at home that are wired together to share resources, then you have a home computer network. Anyone who uses a computer, which encompasses almost everyone, should be aware of the need to back up important data. There are options available for network data storage that may not be available for the single computer. The first step in deciding how to conform your network data storage is to determine the type of backup you should use. Usually a backup is done by making a copy of all of the existing files, like a snapshot in time, and then adding backups of the changes as they occur. The other decision to make is the location of where to keep the backups.

Here, There and Everywhere

If you don’t store very much on your home computer network, you may be able to manage your home network data storage project on DVD’s. With a small amount of information needing backup, you might just use rewritable DVD’s and make a full copy of chosen files as needed. If there is one or more computers on your network that is primarily used for internet use, email, web surfing and games, then the need for data backup is limited. The benefit of this type of home network data storage is that you have control over whether or not to back up a file and you choose how often to do the backups. The downside that many people don’t update their backups often enough and frequently the discs become lost or damaged due to inadequate storage practices.

The next step up is to create a server to store backup files for all of the computers on the network. A server is simply a hard drive, and software is available for small home networks. There are also network-attached storage (NAS) devices which act as a dedicated backup server. The benefit here is that the software can be set to automatically perform backup procedures at regular intervals. The drawback is that the backups are in the same place as the computers, and may fall victim to whatever type of disaster makes it necessary to use the backups.

Finally, there are remote services that will automatically use the Internet for home network data storage. Once signed up, the user is charged according to the amount of storage is needed. The benefit is that data is stored remotely and the updates are automatic. Drawbacks are that large amounts of data can be costly and that it’s only as reliable as the company. The decision on the type of home network data storage to use is based on the needs and resources of the network users.

Proxy Servers Explained

On the web network, there are a lot of websites which offer features like file-sharing, instant messaging or leaving comments for the user’s profile. A lot of schools and universities have blocked such websites to be accessed from their locations to restrict people from logging in to these websites. But the use of proxy servers has a technological advance over these restrictions. The Proxy servers let you access websites from restricted locations and are a source to bypass secure sites from blocked locations, as they have the ability to bypass the network firewalls and filters. These proxy servers enable the users to surf the internet from blocked servers and are compatible to surf through sites which have audio and video streaming platforms like Youtube.

A proxy server is a computer program or application which processes a client request and forwards it to other servers. When you connect to a proxy server, and try to access some information available on another server, it forwards the request on your behalf and acts as the host server. In short, it becomes your face and represents you for access to the website or information. There are lots of types of proxy servers available based on your need, such as;

&bullWeb proxy
&bullCaching proxy server/ Http proxy
&bullAnonymous proxies
&bullIntercepting proxies
&bullHostile proxy servers
&bullReverse proxy servers
&bullForced proxy servers.

Usage of these proxy servers requires a simple process to be followed. You have to sign up to be able to use these proxies. Most of these proxy websites offer services without a cost. But, some of them may ask for a small fee to for the proxy services. After signup, the user can type the desired URL (for example: www.myspace.com) on the main page and all connections and traffic to and from the destination URL is redirected via the proxy, making it look as if the traffic is evolving from the main proxy , thus bypassing the domain based URL filtering blocking system. These proxies allow users to browse through the restricted websites and view profiles, post comments, blogs and surf the sites for music.

These proxies are reliable and secure. You have to agree to accept the strict set of terms and conditions like not to access websites that contain illegal content such as ware sites, use for spamming purposes, or distributing Spy ware or any other malicious script and you can surf the internet at school, universities, work and other places without any restriction, using the simple scripts which allow you to access the blocked websites.

Network Time Synchronization & Accurate Time Server

Each PC has an integral real-time clock that maintains internal system time. PC clocks have low-cost crystal oscillators that are notoriously prone to drift. With time each computer in an organisation drifts at different rates. After a relatively short period of time, there can be large differences between the system times of each computer on the network. Unsynchronised computer time can lead to many problems.Computer TimeComputer system time is maintained by low-cost real-time clock and crystal oscillator components. Crystal oscillators are manufactured with relatively low tolerance; each one oscillates at a slightly different rate. Additionally, crystals change frequency slightly with temperature variance. This all has the effect that computers are notoriously poor at maintaining an accurate time. Each computers time in an organisation will drift at slightly different amounts unless they are synchronised in some way.

Network Synchronisation IssuesPoor network time synchronisation can cause a number of problems. In a transaction-processing environment, transactions generated from various PC’s may have an irregular time-stamp. Unsynchronised computers may be vulnerable to fraud, particularly in an environment where transaction time is an important issue. Additionally, problems can arise with shared network files, if computers with unsynchronised system times are using the same resource.

Network Time ServersNetwork time servers obtain accurate time from an external time reference and offer an accurate time resource to network time clients. Time servers utilise the Network Time Protocol (NTP), which is a UDP based protocol over TCP/IP. A number of external time references are available, such as GPS and regional radio frequency transmissions. The GPS (Global Positioning System) is a subscription free service that offers highly accurate time. GPS antennas require a good view of the sky in order to obtain timing information. Regional time and frequency transmissions include: MSF transmitted from Rugby (UK) with coverage of the British Isles and North-Western Europe; DCF-77 transmitted from Frankfurt (Germany) with coverage of much of Central Europe; WWVB transmitted from Colorado (US) with coverage of much of the US and Canada. Other regional radio time reference include: TDF (France); CHU (Canada); JJY (Japan) and HBG (Switzerland).

Internet Time ServersThere are many Internet based NTP time server resources available that can be utilised for network time synchronisation. However, utilising an Internet time server can have a number of issues. The time server is located outside of the firewall, so a port must be left open in order to access the time server. This obviously has security implications. Additionally, time server accuracy, reliability and provision of service may be problematic.

Local Dedicated Network Time ServerA local dedicated network time server overcomes many of the issues associated with Internet based references. A local time server is located inside the security firewall and so requires no external access, negating security issues. Additionally, a local time server will have improved accuracy due to consistent network paths between clients and server. Also there is no provision of service issues since the time server is owned by the organisation where it is installed.

SummaryNetwork time synchronisation is an important factor in modern computer network installations. Internet based network time servers may provide a solution to network synchronisation, but there are security issues that arise with there use. Local dedicated network time servers overcome the security and accuracy issues with internet based services by providing a secureFree Reprint Articles, accurate and reliable network time synchronisation solution.

What Is Structured Cabling For Computer LAN Networks?

Modern computer LAN (local area network) wiring has the concept of structured cabling.

With today’s high speed networks, people realize that the networking system must be broken up into shorter chunks that allow workstation wiring to be concentrated, with each cable length short enough to support the high data rate.

Based on aforementioned reasons, structured wiring standard has been developed to help define a computer wiring system that stays within the maximum wiring distance for various LAN topologies. For example, the horizontal cable wiring length is 100 meters for 100BaseT networks.

:: What do we do to observe the 100 meters wiring standard?

In order to achieve the wiring concentration standard, telecommunication rooms (wiring centers) are placed at planned locations in a building. These telecom rooms are then interconnected to provide the total network connectivity for the building.

This can be explained in a three stories building. At one same corner of each floor, a telecom rooms is constructed; these telecom rooms are then connected by backbone wiring (cables run vertically through the floors and link all telecom rooms together).

On each floor, a telecom room concentrates all workstation cables for that floor. Each workstation has a wall mounted jack. The network cable is terminated at that jack and runs directly to the telecom room. The cable may run in wire trays or conduit, or be draped over supports such as a drop ceiling. For larger floors, more than one telecom room may be needed.

:: Horizontal Cabling

The horizontal wires, which run from workstations on the same floor to the telecom room, are then terminated on punchdown termination, or directly onto a patch panel. The punchdown terminations or patch panels could be rack mounted (19″ or 23″ racks), cabinet mounted or wall mounted.

In the telecom room, network equipment such as a hub or switch is connected to each station cable, which electrically terminates the cable run. The hub or switch then passes the computer signal on to other work stations or servers, or even to other telecom rooms for ultimate connectivity with the entire network.

:: Vertical Cabling (Backbone Cabling)

Telecom rooms on each floor are then connected together by backbone cabling (also called vertical cabling for floor to floor connections). These backbone cablings typically are done from floor to floor to floor.

Usually telecom rooms should be located directly above one another in order to minimize the cable runs length, but this also varies from building to building.

With the emerge of Gigabit Ethernet and 10 Gigabit Ethernet, fiber optic cable is the most appropriate choice for backbone cabling since they provide much higher bandwidth than traditional Cat5, Cat6 or even Cat7 twisted pair copper cables. Another advantage of fiber is that fibers can run much longer distance than copper cable, which makes them especially attractive for backbone cabling.

:: The difference between backbone cabling and horizontal cabling

Since backbone cabling typically passes through from floor to floor, the cables used for backbone cabling have very different requirement than the horizontal cablings.

1. Fire ratings. Backbone cables must have standard imposed fire rating specifications. Typically this is OFNR (Optical Fiber Non-Conductive Riser) rated. If the backbone cable passes through plenum area (spaces in the building used for air return in air conditioning), the cable must be OFNP (Optical Fiber Non-conductive Plenum) rated.

2. Physical securing. Physical securing for vertical riser cables is also different than horizontal cables. So is the cable strength, since vertical riser cables need to have enough strength to support its own weight.