Article Orange » Networking

Communication Between VLANs

anandsoft10 — Thu, 22 Jul 2010 22:27:57 +0000

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Virtual Trunking Protocol (VTP) is used for communication within VLANs. VLANs, short for Virtual LANs, are used in place for traditional LANs for ease of maintenance, and security. The article discusses different VTP protocols.

Body: Communicating within VLANs: There are different protocols available for communicating between VLANs. These encapsulation schemes are also known as VLAN trunking protocols. These protocols are based on Layer 2 of the OSI model.

These are:

Inter-Switch Link Protocol (ISL)
IEEE 802.10 Protocol
IEEE 802.1Q Protocol
ATM LANE Protocol

ATM LANE Fast Simple Server Replication Protocol (FSSRP)

Inter-Switch Link Protocol (ISL): The ISL protocol is used to interconnect two VLAN-capable Ethernet, Fast Ethernet, or Gigabit Ethernet devices. Here, VLAN information is tagged to the standard Ethernet frame. The packets on the ISL link contain a standard Ethernet, FDDI, or Token Ring frame and the VLAN information associated with that frame. ISL is a Cisco proprietary protocol.

IEEE 802.10 Protocol: This protocol provides connectivity between VLANs. The protocol incorporates authentication and encryption techniques to ensure data confidentiality and integrity. The protocol operates at layer 2 of OSI model, and hence ensures greater efficiency.

IEEE 802.1Q Protocol: This protocol is used to interconnect multiple switches and routers, and for defining VLAN topologies. IEEE 802.1Q is the industry standard for communicating within VLANs.

ATM LANE Emulation Protocol (LANE): Using LANE, you can benefit from the legacy LAN hardware. The LANE protocol operates over traditional LAN, emulating a broadcast environment like IEEE802.3. LANE makes. LANE allows standard LAN drivers like NDIS and ODI to be used. Applications can use normal LAN functions without the underlying complexities of the ATM implementation. Client work stations need LAN Emulation Client for running LANE protocol. The switches or routers also need to support appropriate LANE functionalities.

ATM LANE Fast Simple Server Replication Protocol (FSSRP): Cisco introduced the ATM LANE Fast Simple Server Replication Protocol (FSSRP). FSSRP provides better network redundancy. If a single LANE server is unavailable due to any technical reasons, the LANE client transparently switches over to the next LANE server and BUS.

Example:

Question:

Match the trunking protocols with respective media:

1. Inter Switch Link         A. FDDI
2. LANE                         B. Fast Ethernet
3. 802.10                         C. ATM

Choose the correct choice.

A. 1-> C, 2->B, 3->A

B. 1->B, 2->C, 3->A

C. 1->B, 2->A, 3->C

D. 1->A, 2->B, 3->C

Ans: B

Explanation: ISL, 802.1Q are the VLAN trunking protocols associated with Fast Ethernet. The VLAN trunking protocol defined by 802.10 is associated with FDDI. LANE (LAN Emulation) is associated with ATM.

Please visit CCNA Tutorials section for more information on VLANs, and VTP trunking.

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Internet Protocol (IP) Subnet masking

anandsoft10 — Mon, 12 Jul 2010 18:26:58 +0000

Subnetting an IP Network is done primarily for better utilization of available IP address space, and routing purpose. Other reasons include better organization, use of different physical media (such as Ethernet, WAN, etc.), and securing network resources.

A subnet mask enables you to identify the network and node parts of the address. The network bits are represented by the 1s in the mask, and the node bits are represented by the 0s. A logical AND operation between the IP address and the subnet mask provides the Network Address.

For example, consider the following IP address and the default Class C subnet mask

192.189.210.078 and subnet mask 255.255.255.0

We can get the network and host portions of the address by using AND operator on the binary equivalent of these addresses as below:

192.189.210.078: 1100 0000.1011 1101.1101 0010.0100 1110 Class C IP Address

255.255.255.000: 1111 1111.1111 1111.1111 1111.0000 0000 Default Class C subnet mask

Performing AND operation, we get:

192.189.210.0 1100 0000 1011 1101 1101 0010 0000 0000

As can be seen above, by using and AND operator, we can compute the network portion of an IP address. The network portion for the IP address given in the above example is 192.189.210.0, and the host portion of the IP address is 078.

There are primarily two types of subnets:

Classful subnet masking, and
Classless subnet masking.

What we discussed in the previous section is Classful subnet masking. A Subnetmask normally contains the host portion of the bits also. This is called Classless Inter Domain Routing (CIDR). This will enable more networks for a given class of network address. For example, allowing 3 host bits towards subnet portion in our previous IP address, will allow us to offer 2X2X2 or 8 additional subnetworks. Traditionally, all zeros, and all ones subnets are not used, and hence we are left with 6 subnets.

192.189.210.078: 1100 0000.1011 1101.1101 0010.0100 1110 Class C IP Address

255.255.255.224: 1111 1111.1111 1111.1111 1111.1110 0000 Class C subnet mask with 3 additional bits of host portion used for Subnetting.

Broadcast address: 1100 0000.1011 1101.1101 0010.0101 1111 :192.189.210.95

The above is the broadcast address for a given subnet (192.189.210.078). Under Classful routing, the broadcast address would have been 192.189.210.255.

Note that by using Subnetting, we are able to increase the number of networks available within a given IP address. On the other hand, we will be loosing the number of hosts available within a subnet to 24 or 16 hosts per subnet. Again, all zeros, and all ones host addresses are traditionally reserved for other purposes.

CIDR (Classless InterDomain Routing) notation: Subnet mask is also represented as below:

192.189.210.078/27, where 27 is the number of bits in the network portion of the IP address.

Why use CIDR?

Normally, ISPs allocate the IP addresses for individuals or Corporates. The reason being that it is almost impossible to allocate a classful IP address to every individual or a corporate. Using CIDR, the biggest ISPs are given large pool of IP address space. The ISP’s customers such as individual or Corporates are then allocated networks from the big ISP’s pool. This kind of arrangement will enable efficient management and utilization of the Internet.

Classful addresses can easily be written in CIDR notation

Class A = A.B.C.D/8, Class B = A.B.C.D/16, and Class C = A.B.C.D/24

Where A,B,C,D are dotted decimal octets.

More information on IP subnetworking is available at CCNA tutorial page of simulationexams.com

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Professional Website Design – Points to Consider

anandsoft10 — Mon, 12 Jul 2010 16:58:29 +0000

The article provides an itemized list of points to be considered while designing a professional website. It further discusses the recent trends and recommended practices.

1. Frames: Avoid frames. Though search engines have limited ability to crawl framesets, they have the following disadvantages:

1.1 Not all search engines have the ability to crawl and index pages using framesets.

1.2 Google discourages using frames, and as per Google frames tend to cause problems with search engines. If you use frames, use NOFRAMES tag to include no frames version of the content. Don’t just write “This page requires frames compatible browser, your browser does not support frames”.

1.3 Even when search engines crawl and index frames, it may so happen that a page appearing in search results may just be one frame of a frameset, and the visitor may be taken to a bare page without header and navigation buttons.

1.4 Conceptually, a html page consists of only one frame. When using multiple frames, it essentially mean using multiple html pages within one page. This is against the basic concept of a web page.

2. Graphics:

2.1 Avoid excessive graphics or graphic images that take long time to load.

2.2 Use a feature called anti-aliasing to smoothen the borders of any text or image that you develop.

2.3 Always use alternate text field when using a graphic. This will allow a description to be displayed on the browser screen even if the graphic display is turned off in the browser. Alternate text is also helpful for search engines in identifying the content.

3. Theme: Use a consistent theme for your web site. It includes layout, and design. As this is a very subjective matter, it differs from person to person. Try to use colors, fonts, styles that complement one another. From search engine point of view, avoid excessive formatting. It is not recommended to have HTML tags outweigh your actual content.

4. Flash: This has been discussed in another page. Check out Flash advantages and disadvantages.

5. Meta tags: Always use Title, Description, and Keywords meta tags. Use other meta tags as per the requirement. From Google search engine point of view, Title and Description meta tags are very important.

6. Avoid redirects. Search engines may interpret redirect as spam. The reason being, that a redirected page is seen by the search engine but not by an individual browsing the site. If at all you need to redirect a page, use permanently 301 redirect. A less preferred option is to use a script with at least 6 seconds of delay in forwarding the visitor to the new destination.

7. Keep the web page within 50-80 KB, so the there won’t be noticeable delay in loading of the web page. If the page has content that takes more time, consider splitting the page into two or more pages. This preferred from search engines point of view as well. If the content is too long, it is likely that some portion of the page is not indexed by search engines.

8. Use of scripts: Use scripts only if necessary. It is recommended not to load a web page with too much of script, as this is likely to confuse the search engines. Client side scripting relieves the server from script processing, and loads the page faster.

9. Use H1, H2 tags to identify your content headlines.

10. Use CSS: Extensively use Cascading Style Sheets for formatting your website content.

11. Validate your web pages after composing. You can use W3c validator for this purpose.

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Computer Communication Connections (e.g. Bluetooth, infrared, cellular WAN, WiFi)

anandsoft10 — Mon, 12 Jul 2010 16:55:59 +0000

With the recent advent of wireless communications, several wireless technologies have come to the fore. Notable among these are Blue tooth, Infrared, Wimax, and WiFi. Each of these communications methods is discussed in the article.

Bluetooth:

Bluetooth bandwidth is up to 2.1Mbps for version 2.0, and its range is only 10 meters (30 feet). Devices with a Bluetooth radio and an antenna can speak to each other with little or no preparation. For example, conference attendees can readily transfer files across a table using their Bluetooth-enabled notebooks. You can also send a file to a Bluetooth-enabled printer without downloading drivers. Bluetooth may soon be a standard interface on many cell phones, handheld computers, and even home appliances. Bluetooth operates at 2.4GHz.

Infrared:

Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of microwave radiation. It is a line of sight communication, and any obstruction to line of sight is going to disrupt communication. One every day use of IR communication is your television remote. Most tv remotes use IR communication, and requires line of sight.

Wimax:

WiMAX (short for Worldwide Interoperability for Microwave Accessis), a wireless digital communications system, also known as IEEE 802.16, that is intended for wireless “metropolitan area networks”. WiMAX can provide broadband wireless access (BWA) up to 30 miles (50 km) for fixed stations, and 3 – 10 miles (5 – 15 km) for mobile stations. In contrast, the WiFi/802.11 wireless local area network standard is limited in most cases to only 100 – 300 feet (30 – 100m).

WiFi:

Wi-Fi (short for “wireless fidelity”) is used for wireless local area networks (WLAN) and fully described in the 802.11 family of specifications. The term Wi-Fi was created by an organization called the Wi-Fi Alliance, which oversees tests that certify product interoperability. A product that passes the alliance tests is given the label “Wi-Fi certified” (a registered trademark). Wi-Fi network can be susceptible to access by unauthorized users if not protected adequately. The activity of locating and exploiting security-exposed wireless LANs is called war driving. Homes or Organizations that use a wireless LAN should secure the WLAN by using Wired Equivalent Privacy (WEP) encryption standard, or Wi-Fi Protected Access (WPA) or MAC address filtering.

Read more about wireless communications at A+ Tutorial

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The OSI Model – An Introduction

anandsoft10 — Mon, 12 Jul 2010 16:55:22 +0000

Open Systems Interconnection (OSI) model is a reference model developed by ISO (International Organization for Standardization), as a conceptual framework of standards for communication in a network across different applications by different vendors. It has become the primary architectural model for inter-computing and internetworking communications. Most of the network communication protocols used today have a structure based on the OSI model. The OSI model defines the communications process into 7 layers, which divides the tasks involved with moving information between networked computers into seven smaller, more manageable task groups.

The ISO OSI model is explained below. The seven layers of the OSI model are:

Application
Presentation
Session
Transport
Network
Data Link
Physical

1 Application layer:
This layer provides a means for the user to access information on the network through an application. Many user applications that need to communicate over the network interact with the Application layer protocol directly. The user applications are not part of OSI Application layer; use the networking services offered by the networking protocol suite. Application layer functions typically include identifying communication partners, and determining availability of required resources. Some examples of application layer implementations include Telnet, File Transfer Protocol (FTP), and Simple Mail Transfer Protocol (SMTP).

2 Presentation layer:
Presentation layer converts local host computer data representations into a standard network format for transmission on the network. On the receiving side, it changes the network format into the appropriate host computer’s format so that data can be utilized independent of the host computer. ASCII and EBCDIC conversions, cryptography, and the like are handled here.
Examples of Presentation layer coding and conversion schemes include common data representation formats, conversion of character representation formats, common data compression schemes, and common data encryption schemes.

Presentation layer implementations are not typically associated with a particular protocol stack. Some well-known standards for video include QuickTime and Motion Picture Experts Group (MPEG). QuickTime is an Apple Computer specification for video and audio, and MPEG is a standard for video compression and coding.

3. Session layer:
The session layer establishes, manages, and terminates communication sessions. Communication sessions consist of service requests and service responses that occur between applications located in different network devices. These requests and responses are coordinated by protocols implemented at the session layer. Some examples of session-layer implementations include AppleTalk’s Zone Information Protocol (ZIP), and Decent Phase Session Control Protocol (SCP).

4.Transport layer:
Transport layer is responsible for providing reliable service between the hosts. Upper layer datagrams are broken down into manageable datagrams and then appropriate header information (such as sequence number, port number, etc.) is added to the datagram before passing it on to the Network layer. Two frequently used transport protocols are the TCP (Transmission Control Protocol) and the UDP (User Datagram Protocol).

Important features of Transport layer:

Transport layer ensures reliable service.
Breaks the message (from sessions layer) into smaller datagrams, and appends appropriate unit header information.
Responsible for communicating with the Session layer

Important features of TCP/UDP:

TCP/IP widely used protocol for Transport/Network layers
TCP: (Transport Control Protocol) TCP ensures that a packet has reached its intended destination by using an acknowledgement. If not, it retransmits the lost messages. Hence, TCP is called a connection oriented protocol.
UDP (Universal Data gram Protocol): UDP simply transmits packets over the internet. It does not wait for an acknowledgement. It is the responsibility of upper layer protocols to ensure that the information had reached the intended partner(s). Hence, UDP is often called connectionless protocol.
Application programs that do not need connection-oriented protocol generally use UDP.

5. Network layer:
Network layer is responsible for the routing of packets through the entire network. The layer uses logical addressing for this purpose. Note that the physical address (like MAC address) keeps changing from hop to hop when a packet travels from source to destination. As a result, an address that doesn’t change is required to ensure continuity between hops. This is nothing but logical address. For IP networks, IP address is the logical address; and for Novell network, IPX address is the logical address, and so on. This layer also provides for congestion control, and accounting information for the network. IP (Internet Protocol) is an example of a network layer protocol.

6. Data link layer:
Data link layer provides delivery of information frames between communicating partners. This layer is responsible for flow regulation, error detection and correction, and framing of bits for transmission. The network data frame is made up of checksum, source address, destination address, and the data itself. The largest frame size that can be sent is known as the maximum transmission Unit (MTU).

Important features of Data link layer:

Assembles bits into frames, making them ready for transmission over the network.
Provides error detection, and correction to transmitted frames. If the checksum is not correct, it asks for retransmission. (Send a control message).
Consists of two sub layers:
- Logical Link Control (LLC): Defines how data is transferred over the cable and provides data link service to the higher layers.
- Medium Access Control (MAC): Controls media access by regulating the communicating nodes using pre-defined set of rules. (i.e. Token passing, Ethernet [CSMA/CD] all have MAC sub-layer protocol).

Different Data link layer protocols define different network and protocol characteristics, including physical addressing, network topology, error notification, sequencing of frames, and flow control. Physical addressing (as opposed to logical addressing) defines how devices are addressed at the data link layer. The protocols used in Data link layer are SLIP, PPP, and CSLP.

7. Physical layer:
This is the bottom-most layer of the OSI model. The Physical layer handles the bit-level communications across the physical medium. The physical medium could be made up of wired electrical signals, or light, or radio (wireless) signals. Physical layer specifications define characteristics such as media, data rates, maximum transmission distances, and physical connectors.

Some of the important standards that deal with physical layer specifications are:

RS-232(for serial communication lines), X.21, EIA 232, and G730.

Physical layer and Data link layer implementations can be categorized as either LAN or WAN specifications.

link: http://www.tutorialsweb.com/networking/computer-networking.htm

keywork: Computer Networking

URL: http://www.tutorialsweb.com/networking/computer-networking.htm

key word: 7 Layers of OSI Model

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Fault Tolerance in Computer Networks

anandsoft10 — Tue, 06 Jul 2010 21:34:05 +0000

Summary: Security of information is important when the information is stored or transferred over the public Internet. To address the security concerns of Internet users, several algorithms are being used depending on the type of security and level of protection required. The article discusses about these algorithms, and the levels of protection available in each of these standards.

Body:

There are three types of cryptographic algorithms that are commonly used. They are:

I. Hashing algorithms

II. Symmetric key-based algorithms

III. Asymmetric key-based algorithms

Hashing algorithms: Hashing is not an encryption scheme, but ensures that the transmitted data is not tampered with. Common hash algorithms include the following:

1. Secure Hash Algorithm (SHA, SHA-1): Developed by NSA, SHA-1 can generate a 160-bit hash from any variable-length string of data.

2. MD4, MD5: MD series of encryption algorithms generate a hash of up to 128-bit strength out of any length of data.

II. Symmetric algorithms: As the name suggests, symmetric key algorithms use the same key to encrypt as well as decrypt message. Some of the commonly used symmetric key algorithms are:

DES (Data Encryption Standard): DES uses a 56-bit key on each 64-bit chunk of data. It is limited in used due to its short key length.

3DES (Triple DES): 3DES greatly improves the security by providing three distinct keys. The total bit strength is 168 bits.

AES (Advanced Encryption Standard): AES is successor to DES, and can create keys from 128-bit to 256-bit length.

Blowfish Encryption Algorithm: It is another flexible, and secure symmetric encryption algorithm. It can perform encryption with encryption key length up to 448 bits. It can encrypt any length of data chunk.

IDEA (International Data Encryption Algorithm): It can encrypt 64-bit blocks of data and uses a 128-bit strength encryption key.

RC5, RC6 (Rivest Cipher): These are the most commonly used encryption security ciphers.

III. Assymetric algorithms: Also known as public key algorithms, these algorithms use asymmetric keys for encoding and decoding a message. Given below are some of the popular asymmetric algorithms:

* RSA algorithm: Widely used for encryption and digital signatures. Uses public key and private key for encryption and decryption.

* Deffie-hellman Key Exchange: This is one of the early key exchange algorithm.

* Elliptic Curve Cryptography (ECC): This is another form of asymmetric key algorithm. One advantage of ECC algorithm is that they are very compact, and more efficient compared to RSA.

Not all algorithms are suited for any given situation. Depending on the type of security required, and the level of protection, one needs to select suitable algorithm.

Please see Security+ questions for some frequently asked questions on Security+ certification.

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Cryptography – Information Security on the Internet

anandsoft10 — Tue, 06 Jul 2010 00:01:30 +0000