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Migrate to a 40-Gbps Data Center…with Cisco QSFP BiDi Technology

June 10 2015 , Written by Cisco & Cisco Router, Network Switch Published on #Networking, #Cisco Modules & Cards

Cisco40G BiDi

Cisco40G BiDi

Cisco’s QSFP 40G BiDi (bidirectional) transceiver, allows zero-cost fiber migration by reusing the current 10-Gbit/sec cabling for 40-Gbit/sec device connectivity. With duplex LC ports, it enables 100 meters of 40G transmission over OM3, 125 meters over OM4 fiber, and 150 meters over certain “OM4+” fibers.

Migrate to a 40-Gbps Data Center with Cisco QSSFP BiDi Technology? Cisco makes the case for its transceiver technology, taking direct aim at “the need for a major upgrade of the cabling infrastructure” when transitioning from 10G to 40G, “which can be too expensive or disruptive to allow data centers to quickly adopt and migrate to the 40-Gbit/sec technology.”

“Existing short-reach transceivers for 40-Gbit/sec connectivity in a QSFP form factor … use independent transmitter and receiver sections, each with 4 parallel fiber strands. For a duplex 40-Gbit/sec connection, 8 fiber strands are required.

Both QSFP SR4 and QSFP CRS4 use MPO 12-fiber connectors. As a result, 4 fiber strands in each connection are wasted.

“With existing QSFP transceivers, each direct connection between two devices requires an MPO-to-MPO 12-fiber cable. In the case of structured cabling with patch panels and fiber trunks, a 40-Gbit/sec connection needs MPO-to-MPO fibers between devices and patch panels, and 4 duplex multimode fibers in the fiber trunk.

“In most of today’s data center networks, the aggregation fiber infrastructure is built for 10Gbit/sec connectivity that either supports direct connections between devices over LC-to-LC multimode fiber or uses LC-to-LC fibers to attach devices to patch panels and provides one duplex multimode fiber in the fiber trunk for each 10-Gbit/sec connection.

“40-Gbit/sec connectivity using traditional 40-Gbit/sec transceivers cannot reuse directly connecting LC-to-LC fibers. It also requires four to six times greater fiber density in the fiber trunks to meet the requirements of a 40-Gbit/sec connection. These characteristics make it expensive for customers to migrate from 10-Gbit/sec connectivity to 40-Gbit/sec connectivity in their existing data centers.

“The Cisco QSFP BiDi transceiver addresses the challenges of fiber infrastructure by providing the capability to transmit full-duplex 40 traffic over one duplex multimode fiber cable with LC connectors. In other words, the Cisco QSFP BiDi transceiver allows 40-Gbit/sec connectivity to reuse the existing directly connecting 10-Gbit/sec fibers and the existing fiber trunk without the need to add any fibers.”

The technical paper details two deployment scenarios/case studies to emphasize the savings accomplished by eliminating the parallel-optic cabling infrastructure. The first scenario is a 288x40G setup with unstructured cabling. The second is a 384x40G setup with structured cabling. In this second scenario, the paper explains, “Cisco QSFP BiDi technology allows the existing cabling system—including the patch cables, patch panels with MTP/MPO LC modules, and fiber trunks—to be repurposed for 40-Gbit/sec connectivity. In contrast, QSFP SR4 transceivers require new patch cables and patch panels because the connector types differ and the size of the fiber trunk needs to be quadrupled.”

From http://www.cablinginstall.com/articles/2014/03/cisco-qsfp-bidi.html

Migrate to a 40-Gbps Data Center with Cisco QSFP BiDi Technology” you can read the full paper report at


More benefits you can get from migrating to 40-Gbps Data Center with Cisco QSFP BiDi Technology


• Reuse existing 10GE fiber infrastructure for 40GE migration

• Lower CapEx and installation labor costs

• Minimal disruption to the data center during migration

• Four times the bandwidth over the same fiber plant

• Up to 70% savings over other current solutions

Cisco’s innovative 40-Gbps Quad Small Form-Factor Pluggable (QSFP) bidirectional (BiDi) transceiver is a pluggable optical transceiver with a duplex LC connector interface for short-reach data communication and interconnect applications. By using the existing 10 Gigabit Ethernet duplex MMF fiber infrastructure for 40 Gigabit Ethernet, the Cisco BiDi transceiver offers significant cost savings and simplifies data center upgrading.

The Cisco BiDi transceiver supports link lengths of 100m and 150m on laser-optimized OM3 and OM4 multimode fibers. It complies with the QSFP MSA specification, enabling customers to use it on all QSFP 40-Gbps platforms to achieve high-density 40 Gigabit Ethernet networks.

Use Your Existing 10 Gigabit Ethernet Fiber for 40 Gigabit Ethernet

Whether your cable plant is structured or unstructured, Cisco’s BiDi transceiver delivers significant savings and a smooth migration to 40 Gigabit Ethernet. The Cisco BiDi transceiver enables the use of an existing 10 Gigabit Ethernet fiber plant infrastructure for 40 Gigabit Ethernet, delivering four times the bandwidth over the same fiber plant and up to 70% savings over other current solutions.

For building out new data centers, deploying 40 Gigabit Ethernet for aggregation and core is no longer an option but a requirement to meet today’s data demands. Designing new cable plants using Cisco’s BiDi transceivers offers:

• 75% less fiber and MPO requirements

• Reduced cable sprawl and rack footprints

• Cost savings with the industry’s lowest-priced 40 Gigabit Ethernet transceiver

•Investment protection with future support for 100 Gbps over duplex fiber

Designing your new fiber cable plant with Cisco’s 40 Gigabit Ethernet BiDi transceiver allows you to reduce your fiber requirements and CapEx and OpEx while future proofing your data center for 100 Gigabit Ethernet.

Cisco’s QSFP 40 Gigabit Ethernet BiDi technology removes 40-Gbps cabling cost barriers for migration from 10-Gbps to 40-Gbps connectivity in data center networks. Cisco’s BiDi transceivers provide simpler and less expensive 40-Gbps connectivity compared to other 40-Gbps transceiver solutions. The Cisco QSFP BiDi transceiver allows organizations to migrate their existing 10-Gbps cabling infrastructure to 40 Gbps with little capital investment.


More Related: Move to 40G Today? Yes!

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40/100 Gigabit Ethernet for Virtualized Data Center and Campus Networks

January 22 2015 , Written by Cisco & Cisco Router, Network Switch Published on #Networking

It is difficult to achieve optimal performance of your data center and networks, especially in a virtualized environment. Fortunately, effective implementation of 40/100 Gigabit Ethernet (GbE) can help pave the way for a fully functional virtualized network. 

In the following guide it explores the benefits of 40/100 GbE implementation in a virtualized environment and how it can maximize existing infrastructure investments.

40/100GbE is rapidly gaining traction as a key foundation for building the next generation of virtualized data center and campus environments. The 40/100GbE-based architecture for virtualized data center and campus is illustrated in the paper. IT managers are increasingly aware of the benefits and advantages1 offered by 40/100GbE as well as its promise as an interconnect option among data centers and commercial buildings in the campus.

On the economic side, barriers to entry in the 40/100GbE space continue to fall. Capital investment in 10GbE networks today can be protected when upgrading to 40/100GbE networks in the future. The Ethernet switching and fiber cabling examples in this paper illustrate:

• 55 percent2 of on switching equipment can be protected

• 57 percent3 of investment on fiber cabling can be preserved

On the availability side, more vendors have supplied solutions for the 40/100GbE ecosystem, and a number of multi-vendor interoperability events on 40/100GbE technology have been hosted by the Ethernet Alliance? With both Cisco? and CommScope? Actively participating. So, early adoption anxieties over locked-in vendor relationships have evaporated. The greater availability from multiple vendors and declining deployment costs due to broader adoption in the marketplace make 40/100GbE infrastructure a sound and prudent investment, both for today and tomorrow.

The increased traction of 40/100GbE has led to its best practice status as the standard for the next generation of high-bandwidth virtualized applications. This adoption has been fueled by both its superior performance and economic benefits in virtualized environments.

40/100GbE based architecture for virtualized Data Center and campus


Virtualized Data Center

True data center virtualization is end-to-end virtualization, including server virtualization, storage virtualization, and network virtualization, and can result in many diverse benefits. Virtual machines and networks can be quickly and nimbly deployed. Their energy efficiency and capacity can dynamically scale to meet the demands of variable workloads without wasting resources. Disaster recovery is faster, and both initial and ongoing costs can be lower than those of traditional non-virtualized approaches.

In the journey to the virtualized data center and cloud, data center managers face a number of design and operational challenges. One of the most conspicuous challenges for network design is to provide enough bandwidth for the applications of today and the foreseeable future. With converged network technologies, 10GbE, which is becoming a de facto choice for server access networks, can be a good choice for a storage access network as well. Given 10GbE at the access layer, 40/100GbE is recommended for aggregation and core layers of networks in data centers, and this is where 40/100GbE removes the constraints that have previously prevented virtualized data centers from fulfilling their maximum potential.


Virtualized Campus

Video is a strongly growing application in campus networks. Video applications are more than just video conferencing or video streaming. Enterprise video applications include desktop high definition video, video phone, enterprise TV, IP video surveillance and other video generation and sharing. Bring your own device (BYOD) is another emerging trend in the campus network. Video, voice, data and BYOD put pressure on a campus’s distribution and core networks.

Compared to traditional layer 2 and 3 network design in the campus, the core and distribution networks can be virtualized by using Virtual Switching System (VSS) with Cisco Catalyst 6500 series switches. VSS is a network system virtualization technology that pools two or more Cisco Catalyst 6500 Series Switches into a virtual one. A VSS scales system bandwidth capacity with automatic load sharing. A VSS increases operational efficiency by simplifying the network and reducing switch management overhead by at least 50 percent. A VSS boosts nonstop communications with no disruption to applications. A VSS enhances existing multilayer switching architecture without fundamentally changing the architecture, resulting in ease of adoption and migration of the technology.



A list of examples of 40/100GbE Ethernet switching and cabling solutions from Cisco and CommScope.

40/100GbE ecosystem examples


The new Cisco Catalyst 6900 Series 4-Port 40GbE Fiber Module (WS-X6904-40G) for the Cisco Catalyst 6500 Series Switches was developed for deployment in the enterprise campus distribution layer and core layer, in traditional data centers with 10 Gigabit aggregation, and in metro-Ethernet-based data center interconnections, as well as in multipurpose service provider networks, which require high-performance data throughput coupled with security, manageability, virtualization, and quality of service.

The WS-X6904-40G module supports 10GbE and 40GbE interfaces. Figure 2 shows the 10GbE and 40GbE interfaces of Cisco Catalyst 6500 series switches. This new module is the only solution that supports both connections in a single format, for flexible migration. There are also many other new and exciting capabilities unique to the WS X6904-40G module, such as CTS (Cisco Trust Sec) for end-to-end role-based security deployment using SGT (Security Group Tagging) and SGACL (Security Group Access Control List) and link-by-link encryption based on IEEE 802.1AE MACsec (MAC based Security) standard, VNTag (Virtual Network Tag), and extensive quality of services features. The 40GbE Fiber Module is a perfect choice for forming a campus core network by interconnecting the physical switches of a VSS in core/distribution layer networks in the campus. It also can be utilized to connect access switches to a VSS at the distribution layer of the campus network. Users are deploying this module today and using it for four 10GbE links until they really need a true 40GbE channel.

Cisco Catalyst 10GbE and 40GbE Fiber Modules and optical transceivers


CommScope SYSTIMAX? InstaPATCH? 360 Pre-Terminated Fiber Solutions enable network operations in the data center at the current 10GbE speed of today, while provisioning for eventual upgrades to 40GbE and/or 100GbE. These solutions were tested, qualified and demonstrated in multi-vendor closed-door and open-to-public environments at both transceiver and system levels.4 Results repeatedly demonstrated that the performance of InstaPATCH 360 Pre-Terminated Fiber Solutions and LazrSPEED? Multimode fiber solutions far exceed the cable reach specified in IEEE Std. 802.3baTM-2010, “40 and 100 Gigabit Ethernet” standards.

SYSTIMAX InstaPATCH 360 Pre-Terminated Fiber Solutions utilize the standard Method B polarity scheme. Customers who have chosen the fiber solution have invested in high-performance and high-quality fiber solutions, but also have purchased peace of mind: their data center fiber cabling infrastructure is ready for 40/100GbE whenever and wherever they need it. The eventual upgrade can be a simple and painless process. Figure 3 shows samples of SYSTIMAX InstaPATCH 360 Pre-Terminated Fiber Solutions.

Samples of SYSTIMAX InstaPATCH 360 Pre-Terminated Fiber Solution



Solutions Designed to Maximize Return on Investment

The switching solutions from Cisco and cabling solutions from CommScope enable easy adoption of 10GbE today and seamless upgrades to 40/100GbE in the future.

The Cisco Catalyst 6500 E-Series chassis, 6900 series 10GbE and 40GbE modules, and Supervisor T2 module provide the easy upgrades. End users’ investment protection can be achieved by redeploying the common components. The common switching components may include a Catalyst 6500 E-Series chassis, a supervisor module Sup2T, and two power supplies. As illustrated in the example in Figure 4, end users can save 55 percent1 of capital expense on the common components for 40GbE short reach (SR), or 47 percent1 of expenses for 40GbE long reach (LR) when upgrading from 10GbE.

40GbE deployment in campus


Similarly, CommScope SYSTIMAX InstaPATCH 360 Pre-Terminated Fiber Solutions offer seamless migration from 10GbE to 40/100GbE with investment preservation. A typical preterminated multimode fiber cabling channel is composed of components such as apparatus, patch cord, patch panel or shelf, and Multi-Fiber Push On (MPO) trunk cable. Figure 5 illustrates the fiber cabling channel for 10, 40 and 10 Gigabit Ethernet link, respectively. It’s noticeable that the common cabling component among the three channels in Figure 5 is the pre-terminated fiber trunk cable. Figure 5 also provides a cabling infrastructure migration path from 10GbE today to 40 or 100GbE in the future.

Fiber cabling migrations from 10GbE to 40/100GbE


Each physical Ethernet link has one cabling channel. The cabling cost of four 10GbE links (or channels), one 40GbE link, ten 10GbE links and one 100GbE. The cost is the result of adding the costs of all the cabling components and then dividing the sum by the number of Ethernet links (or cabling channels) for each corresponding speed.

The investment preservation example5 on pre-terminated fiber cabling


With the reuse of the common cabling components—which are the SYSTIMAX InstaPATCH 360 Trunk Cable and 360G2-1U Modular Shelf in this example—end users can save 57 percent2 of the capital expense on multimode fiber cabling when migrating from today’s 10GbE to either 40GbE or 100GbE in the future.

The costs for 4x10G and 10x10G fiber cabling are denoted in Figure 6 for a rough reference to their corresponding counterparts of 40 and 100GbE, respectively. The fiber cabling cost for 1x40G is close to the one for 4x10G, while the 1x100G cost is 19 percent less than the one for 10x10G’s cost, in this example.

You may be wondering why the cost of the MPO cable increases when migrating from 4x10G to 1x40G and from 10x10G to 1x100G. This is because, as there are unused fibers, only a fraction of the trunk cost is allocated to the 10GbE scenarios; but for the 40G and 100G scenarios, the total trunk cost is allocated. In other words, only four out of six possible fiber circuits are lit in the 4x10G case, so only 4/6ths of the cost is applied. Similarly, only 10 out of 12 possible fiber circuits are lit in the 10x10G case so only 10/12ths of the cost is applied. Notice that the 57 percent investment preservation on fiber is not the only saving for end users.

When the distribution and core layer networks migrate to 40/100GbE, the apparatus and cords can be reused in other parts of the networks: for example, the access layer network for 10GbE or even Fibre Channel SAN networks. By doing so, end users may preserve more of their investment.

The ongoing adoption of 40/100GbE is already redefining the IT landscape. It represents the first step toward the next generation of high-bandwidth connectivity demanded by virtualized data centers and campuses. As 40/100GbE continues to unlock the full performance and economic potential of virtualized environments and more campus deployments, it will undoubtedly solidify its position as the new standard for best practice, speed and reliability.

Because it affords instant benefits as well as a streamlined upgrade path, forward-looking IT managers would be well advised to include 40/100GbE as a key part of any upgrade or new deployment plans, particularly those that include a need for campus-wide interconnectivity between data centers, and inside data centers and office buildings. In particular, Cisco Catalyst 6500 series switches with their 40GbE fiber module and CommScope SYSTIMAX InstaPATCH 360 pre-terminated, LazrSPEED and TeraSPEED? fiber solutions deliver the performance and reliability that position today’ s investment for rich returns in the future.

References and Notes

1. G. Chanda from Cisco and Y. Yang from CommScope, “40 GbE: What, Why & Its Market Potential”, Ethernet Alliance white paper, November, 2010

2. The two percentages can vary based on a number of factors, such as hardware configurations, purchasing prices, etc. The new installation must be tested and meet the specifications issued by Cisco Systems.

3. The percentage can vary based on a number of factors, such as MPO trunk cable length, cabling channel configurations, purchasing prices, etc. The new installation must be tested and meet the specifications issued by CommScope SYSTIMAX.

4. D. Hall and Y. Yang from CommScope, “40/100 Gigabit Ethernet Eco-System is Alive and Well”, CommScope white paper, 2011

5. In the example of Figure 6, the MPO trunk cable length is 174 feet and the cord length is 10 feet. These lengths are determined based on Paul Kolesar’s contribution to IEEE 802.3 Next Gen 40G and 100G Optics Study Group in May 2012, “Cabling Cost-Centroid Lengths for Simplified Total Cost Comparisons”.

The multimode fiber cabling channel configuration for the example in Figure 6 is an interconnect configuration. In the 10GbE cabling channels, two fiber modules are connected back to back by MPO trunk cables, and LC jumpers are plugged in to connect the fiber modules at both ends. In the 40/100GbE cabling channels, two MPO adapter panels are connected back to back by an MPO trunk cable, and equipment cords are plugged into MPO adapter panels at both ends.

The following table lists the products used in the cost study for the investment preservation example5 on pre-terminated fiber cabling



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The Different Types of Ethernet Cables

December 31 2014 , Written by Cisco & Cisco Router, Network Switch Published on #Networking

As the standard cables that are commonly used to connect a modem to a router, and to connect a router to a computer’s network interface card (NIC), Ethernet cables have many different categories, such as Category 3, Category 5, Category 5e, Category 6, Category 6a, and Category 7. These types of Ethernet Cables have been developed, and each category has different specifications as far as shielding from electromagnetic interference, data transmission speed, and the possible bandwidth frequency range required to achieve that speed. It may be hard to decide which one you need while looking at all the available options for Ethernet cabling. Actually, the category of cable is usually clearly printed on the cable’s sheath, so there can be no doubt as to the type of cable being used. But do you know about the main differences between these categories of Ethernet cable? So in the following part we will tell about the main features of each type of Ethernet Cable.

Category 3

Category 3 Ethernet cable, also known as Cat 3 or station wire, is one of the oldest forms of Ethernet cable still in use today. It is an unshielded twisted pair (UTP) cable that is capable of carrying 10 megabits per second (Mbps) of data or voice transmissions. Its maximum possible bandwidth is 16 MHz. Cat 3 cable reached the peak of its popularity in the early 1990s, as it was then the industry standard for computer networks. With the debut of the faster Category 5 cable, however, Cat 3 fell out of favor. It still can be seen in use in two-line telephone systems and older 10BASE-T Ethernet installations.


Category 5

Category 5 (Cat 5) Ethernet cable is the successor to the earlier Category 3. Like Cat 3, it is a UTP cable, but it is able to carry data at a higher transfer rate. Cat 5 cables introduced the 10/100Mbps speed to the Ethernet, which means that the cables can support either 10 Mbps or 100 Mbps speeds. A 100 Mbps speed is also known as Fast Ethernet, and Cat 5 cables were the first Fast Ethernet-capable cables to be introduced. They also can be used for telephone signals and video, in addition to Ethernet data. This category has been superseded by the newer Category 5e cables.


Category 5e

The Category 5e standard is an enhanced version of Cat 5 cable, which is optimized to reduce crosstalk, or the unwanted transmission of signals between data channels. This category works for 10/100 Mbps and 1000 Mbps (Gigabit) Ethernet, and it has become the most widely used category of Ethernet cable available on the market. While Cat 5 is common in existing installations, Cat 5e has completely replaced it in new installations. While both Cat 5 and Cat 5e cables contain four twisted pairs of wires, Cat 5 only utilizes two of these pairs for Fast Ethernet, while Cat 5e uses all four, enabling Gigabit Ethernet speeds. Bandwidth is also increased with Cat 5e cables, which can support a maximum bandwidth of 100 MHz. Cat 5e cables are backward compatible with Cat 5 cables, and can be used in any modern network installation.


Category 6

One of the major differences between Category 5e and the newer Category 6 is in transmission performance. While Cat 5e cables can handle Gigabit Ethernet speeds, Cat 6 cables are certified to handle Gigabit Ethernet with a bandwidth of up to 250 MHz. Cat 6 cables have several improvements, including better insulation and thinner wires, that provide a higher signal-to-noise ratio, and are better suited for environments in which there may be higher electromagnetic interference. Some Cat 6 cables are available in shielded twisted pair (STP) forms or UTP forms. However, for most applications, Cat 5e cable is adequate for gigabit Ethernet, and it is much less expensive than Cat 6 cable. Cat 6 cable is also backwards compatible with Cat 5 and 5e cables.


Category 6a

Category 6a cable, or augmented Category 6 cable, improves upon the basic Cat 6 cable by allowing 10,000 Mbps data transmission rates and effectively doubling the maximum bandwidth to 500 MHz. Category 6a cables are usually available in STP form, and, as a result, must have specialized connectors that ground the cable.


Category 7

Category 7 cable, also known as Class F, is a fully shielded cable that supports speeds of up to 10 Gbps (10,000 Mbps) and bandwidths of up to 600 Mhz. Cat 7 cables consist of a screened, shielded twisted pair (SSTP) of wires, and the layers of insulation and shielding contained within them are even more extensive than that of Cat 6 cables. Because of this shielding, they are thicker, more bulky, and more difficult to bend. Additionally, each of the shielding layers must be grounded, or else performance may be reduced to the point that there will be no improvement over Cat 6, and performance may be worse than Cat 5. For this reason, it’s very important to understand the type of connectors at the ends of a Cat 7 cable.

 The following table summarizes the most common types of Ethernet cables, including their maximum data transmission speeds and maximum bandwidths. 


Cable Type

Maximum Data Transmission Speed

Maximum Bandwidth

Category 3


10 Mbps

16 MHz

Category 5


10/100 Mbps

100 MHz

Category 5 e


1000 Mbps

100 MHz

Category 6


1000 Mbps

250 MHz

Category 6 a


10,000 Mbps

500 MHz

Category 7


10,000 Mbps

600 MHz

With each successive category, there has been an increase in data transmission speed and bandwidth. To fully future-proof a network installation, the highest categories are recommended, but only if all of the other equipment on the network is capable of similar speeds. Otherwise, expensive cables will be only as fast as the slowest piece of hardware on the network.


Ethernet Cable Connectors

The ends of Ethernet cables that connect into a NIC, router, or other network device are known by several names. Modular connector, jack, or plug are the most commonly used terms. Shorter lengths of Ethernet cable are usually sold with the connectors already installed, but for custom installations requiring longer lengths, cable is often sold in bulk quantities, and connectors must be installed on the ends.

The most common type of connector for Ethernet installations is referred to as an "RJ-45" connector. It is officially known as an 8P8C connector, but this term is rarely used in the field, and the term "RJ-45" which was the telephone industry’s term for this connector’s wiring pattern, has become the customary colloquial name for the connector itself. Categories 3 through 6 all use the RJ-45 connector, but Cat 7 utilizes a specialized version of the RJ-45 called the GigaGate45 (GG45), which grounds the cable and allows for higher data transmission rates. There are two standard pin assignment configurations for RJ-45 connectors: T568A and T568B. The T568A standard is typically used in home applications, while T568B is used in business applications.

In every case, the specifications of the cable, such as its category, whether or not it is shielded, and whether or not it needs to be grounded, must match the specifications of the connector. For those who are confused or uncertain about crimping and installing connectors to cables manually, it is best to buy cables that already have connectors professionally installed.


Other Qualities of Ethernet Cables to Consider

There are a few important considerations that apply to all Ethernet cables. Data transmission rate and bandwidth both decrease with the increase of cable length, so the shorter the length, the better. For 10/100/1000BASE-T networks (those that have maximum speeds of 10, 100, or 1000 Mbps, including all the aforementioned cable types except for Categories 6a and 7), 100 meters is the maximum allowable cable length before the signal will degrade. For category 6a cables running at 10 Gbps speeds, 55 meters is the maximum allowable length, and even this length is only allowed in very good alien crosstalk conditions, or areas of low interference, such as when the cable is located far away from other cables that could cause interference.

There are some other terms regarding cable terminations that can complicate the shopping experience. Some cables are referred to as patch cables, while others are called crossover cables. Even though crossover and patch cables may look the same, they function differently. A patch cable is one that terminates with the same type of connector standard at both ends. The connectors terminating a patch cable can use the T568A or T568B standards, but both ends must be the same. A crossover cable, on the other hand, has one end that terminates in a T568A connector and another that terminates in a T568B connector. Patch cables are used to connect devices that are different from one another, such as a switch and a computer. Crossover cables are used to connect similar devices, as when a switch is connected to another switch, for example.

Another important distinction in Ethernet cables is whether they contain solid or stranded conductors.


Solid conductor cables have one solid wire per conductor, while stranded conductor cables have several strands of wire (typically seven) wrapped around each other to form a single conductor. Each type has its own advantages and disadvantages. Solid conductor cables are best for fixed wires within the walls or structure of a building. The single conductors are sturdy enough to be punched down into wall jacks and patch panels, but not as easy to install into a typical RJ-45 connector. Stranded conductors, on the other hand, can fray when punched down into wall jacks, so they are better suited to be crimped into an RJ-45 connector. They are also more flexible and forgiving when bent at sharp angles, so they are better suited for patch cables and applications where the cable may be rolled up or otherwise moved around.

So when you’re setting up an Internet connection in your home or office, you’ll need to obtain the proper Ethernet cable to attach your computer to the modem. While connecting the cable is typically a simple task, finding the right one may be a bit more complex. While Ethernet cables may all look similar to one another, their specifications vary widely. It’s important to research what type of cable will work with your equipment, and you’ll also want to consider things like the price and quality of the cable, as well as the types and number of devices you’ll be connecting to your network. You could go for a cheap, industry standard solution such as Cat 5e cable or future-proof your network by opting for a Cat 7 cable. If you’re looking to connect one switch to another or bypass a router, maybe crossover cables are the solution, or maybe you need a lot of patch cables to connect more devices to your network. In any case, you’ll also want to ensure you’re purchasing the right length of Ethernet cable, and properly addressing any interference concerns. No matter what your networking needs are, eBay is sure to have the category, length, and condition of Ethernet cable to get you connected.


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CAT5 vs. CAT5e vs. CAT6

December 3 2014 , Written by Cisco & Cisco Router, Network Switch Published on #Networking

What is the difference between CAT5, CAT5E and CAT6 cable? Most people may be familiar with them. Because they are often used in computer networks, and also can be used to move data in home theatre applications. Category 5 (CAT5), Category 5E (CAT5E) and Category 6 (CAT6) cables are all twisted pair cables, available in solid and stranded varieties. What are their own features? In the following part, we will talk about the main difference between CAT5, CAT5e and CAT6.



CAT5 cable is the most common, and comes in two types—Unshielded Twisted Pair, known as UTP, and Screened Twisted Pair, called SCTP. The SCTP cable has an extra shield to limit outside interference, and is generally only used in Europe. UTP cables are used all over the states and come either solid or stranded. Solid CAT5 cables are stiff and the best choice for long distance transmissions. Stranded CAT5 is bendier and is often used as patch cable. The standard amount a CAT5 cable can handle is 100MHz, with the option for 10 or 100 Mbps Ethernet. A CAT5 cable can also carry more than one signal—such as two phone lines and a single 100BASE-T channel in one cable.


CAT5e is very similar to CAT5,the ‘e’ standing for enhanced. This cable has more ability for data transmission, with the option to transfer data at 1000 Mbps. Cat5e can also be used with Gigabit Ethernet and generally has less near-end crosstalk, or NEXT than standard CAT5 cables. When installing a new system, CAT5e cables are almost always used over CAT5, though most existing installations are still CAT5.

The most sophisticated of the three cables is CAT6. Although it is also comprised of four pieces of twisted pair copper wire, it has a longitudinal separator. This allows the cables to be separated from each other and, in turn, allows not only for an increased data transfer speed, but less crosstalk and double the bandwidth. CAT6 cabling is a good choice for most new systems, especially those that are evolving and might need more options in the future. CAT6 is perfect for 10 Gigabit Ethernet and can work at up to 250 MHz. The really intelligent aspect of CAT6 is that it is compatible with already installed CAT5 and CAT5e cabling.

With the ever-changing landscape of technology, when you are installing a new system, the best choice for an easily adaptable future is CAT6. However, CAT6 is more expensive, and often some companies just don’t need anything quite that sophisticated. If you are just wanting to expand your network a bit, CAT5e is a more cost-effective and the simpler choice. CAT5, though perfectly adequate for many existing systems, will just not be able to keep up with the speed and performance needs of tomorrow.

Category 5 Network Cable

Bandwidth up to 100MHz

Supports 10/100 Ethernet (Ethernet and Fast Ethernet)

Category 5E Network Cable

Bandwidth up to 350MHz

Supports 10/100/1000 Ethernet (Ethernet, Fast Ethernet, and Gigabit Ethernet)

Backwards compatible with CAT5 cable

Reduced crosstalk compared to CAT5

Category 6 Network Cable

Bandwidth up to 550MHz

Supports 10/100/1000 Ethernet (Ethernet, Fast Ethernet, and Gigabit Ethernet)

Backwards compatible with CAT5/CAT5E cable

Reduced crosstalk compared to CAT5/CAT5E

CAT5E supports Gigabit networking, but CAT6 is certified for Gigabit networking and will perform better over longer distances. Keep in mind that your network is only as fast as your slowest component, so unless every piece of your network (routers, cables, etc.) supports Gigabit Ethernet, you will not be able to reach those speeds.


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How to Connect 2 Routers and 3 Switches Correctly?

July 2 2014 , Written by Cisco & Cisco Router, Network Switch Published on #Networking

How to connect 2 routers and 3 switches correctly? It’s a common question for users to set or reset their network. What’s your experience and suggestions about this? One of Cisco champions called Hamza shared his problem of connecting 2 routers and 3 switches. And more Cisco champions discussed it together. Let’s check it. Any idea? Welcome…

The problem is: “I know how to connect a router with two switches and they're able to do successful communication. But If I extend the scenario to two routers and three switches, they don't communicate…

Consider the scenario details in the image


The thing is router 1 is unable to communicate with the third network. Similarly third network is unable to communicate with the first one.”

Adam Loveless: My guess would be that you need to configure some routing. Please either post up your sanitized configs or the Packer Tracer file.

Kev Santillan: Hello, you need some form of routing. A router will make its decision based on the information that it has in its own routing table. If Router 1 or Router 0 does not have a route to each remote network, then you will not be able to establish communication. Either use static routes or a routing protocol.

I also noticed that you have the same address ( for both routers. Is this just a typo?

…Hamza uploaded the pkt file



Kev Santillan (again): The reason why the routes are not learned by each node is because you have assigned a duplicate address ( to the interfaces that are in the same segment. Change the address of one of the routers to any other address within the /24 subnet and things will work as expected.

Hamza: So basically they should be of the same class in order to work but not the same id i.e the gateway?

Chandan Singh Takuli: Router conencts 2 different networks of any class or classless. If you know a & i know a too why would i ask you. same happens in routers too.

Every router must have all of its interface in different networks and every port must have a unique ip in a single topology or network. so that it can be identified accurately and reached.

Gateway is just like a door of a room. a single network/subnet is like a room. So when you wanna go to another network or room, you need to go through gateway or door in the room. 

Gateway ip must be a part/ip of the source network/subnet.


More than this problem

Rick raised his question: to Kev and Chandan: I tried that out-change one of the router interfaces from to But ping from far left hosts still can't reach far right hosts.  And for the two hosts in the middle, what default gateway can they use?

Kev Santillan: Hi Rick, ‘I tried that out-change one of the router interfaces from to  But ping from far left hosts still can't reach far right hosts.’ I believe modifying either of the addresses in Hamza's file should make things work immediately. Note that he is using /16 for the 172.16.X.X network. Check the mask that you have specified. Otherwise, please share the PT file.

‘And for the two hosts in the middle, what default gateway can they use?’ They can use either of the routers' addresses. If the "middle LAN" uses Router 2's address as the DG and tries to reach non-local networks, it will always pass through Router 2 first before being routed elsewhere. You can also use HSRP to have one dedicated gateway address but the logic will be the same. The active router will be the one to route traffic accordingly.

What’s your idea? Share here…

Discussion from https://learningnetwork.cisco.com/thread/72202?tstart=0


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Network Types: LAN, WAN, PAN and MAN

May 12 2014 , Written by Cisco & Cisco Router, Network Switch Published on #Networking

Learning the networking technology can help you understand the internet better. This is the media of connecting one or more persons with each other. By using internet, we can share our stories, knowledge, opinions and experiences with other people. We also can discuss interesting and hot topics with new friends by internet. Through internet you also can broaden our minds. Well, wow, wow, we know that internet is a network of networks. The main network types: LAN, WAN, PAN, and MAN. Are you confused with these network types? What do they all mean? In this article we will discuss and talk about what the exact LAN, WAN, PAN, and MAN network types are. The key difference is the geographical areas they serve.



LAN (Local Area Network) stands for local area network. It covers, as the name suggests, a local area. This usually includes a local office and they're also pretty common in homes now, thanks to the spread of Wi-Fi.

Whether wired or wireless, nearly all modern LANs are based on Ethernet. That wasn't the case in the 80s and 90s, where a number of standards, including NetBEUI, IPX and token ring and AppleTalk. Thanks in large part to its open technology, Ethernet rules supreme. It's been around since the early 70s and isn't going away anytime soon.

There are two ways to implement Ethernet: twisted-pair cables or wireless. Twisted pair cables plug into switches using RJ-45 connectors, similar to phone jacks. (Remember those?). Cables plug into switches, which can be connected to other networks. A connection to another network is a gateway that goes to another LAN or the Internet.

The other popular Ethernet access method is over Wi-Fi under the IEEE 802.11 standard. Almost all new routers can use the b/g/n standards. IEEE 802.11b and g operate in the 2.4 Ghz spectrum, while n operates in 2.4 and 5 Ghz, allowing for less interference and, thus, better performance. The downsides to wireless are the potential for interference and potential eavesdropping.


WAN (Wide Area Network), in contrast to a LAN, refers to a wide area network. The name is exactly what it sounds like: a network that covers an area wider than a LAN. Beyond that, the definition is less clear. Distances can range from a network connecting multiple buildings on a corporate or college campus to satellite links connecting offices in different countries. The most popular WAN is the one you're using to read this article: the Internet. It's actually a collection of other networks, including other LANs and WANs - hence, the name.

WANs can be wired, using fiber-optic cable, for example, or wireless. A wireless WAN might use microwave or infrared (IR) transmission technology, or even satellite. Laying fiber may make sense when connecting a campus but becomes more expensive when connecting greater distances. To save money, an organization may opt for wireless technology or lease lines from a third party.

Virtual Private Network (VPN)

Another method that has become popular in recent years is the use of a virtual private network, or VPN. It uses the Internet to allow people to log into a network remotely and access its resources, but encrypts the connection to thwart eavesdroppers. If your company sets you up with a VPN, you can access your corporate intranet, file servers or email from home or a coffee shop - just as if you were using it in your office. This makes VPN a popular way to support remote workers, especially in fields where privacy is paramount, such as healthcare. Windows, Mac OS X and many Linux distributions can act as VPN clients’ right out of the box.

Remote desktop virtualization takes this process even further. The entire desktop and applications run on a remote server, and are accessed from a client, which can run on a conventional laptop or even on mobile devices such as tablets or smartphones. This makes virtual desktops great for supporting BYOD (bring your own device) schemes. If a device is lost or stolen, the data is safe because it lives on a central server. Citrix and VMware are the biggest known vendors of virtual desktops.

Personal Area Network (PAN)

PAN stands for personal area network, and again, it's exactly what it sounds like: a network covering a very small area, usually a small room. The best known wireless PAN network technology is Bluetooth, and the most popular wired PAN is USB. You might not think of your wireless headset, your printer or your smartphones as components in a network, but they are definitely talking with each other. Many peripheral devices are actually computers in their own right. Wi-Fi also serves as a PAN technology, since Wi-Fi is also used over a small area.


A MAN (Metropolitan Area Network) (not to be confused with "man pages" in the UNIX and Linux world) connects nodes located in the same metro area. For example, a company located in the San Francisco Bay Area might have its buildings in San Francisco, Oakland and San Jose linked together via a network.

One of the most common ways for organizations to build this kind of network is to use microwave transmission technology. You might have seen a microwave antenna on a TV news van, extended high in the air, beaming video and sound back to the main TV studio. It's also possible to wire buildings together using fiber-optic cable, but as with WANs, most organizations that use wires will lease them from another carrier. Laying cable themselves is quite expensive.

In the past, organizations that had a MAN used asynchronous transfer mode (ATM), FDDI or SMDS networks.

After we have got the main information of these main network types, we find that the concepts are really self-explanatory. We hope these tips and information useful for you to understand the essential internet in our life.

Rs from http://www.techopedia.com/2/29090/networks/lanwanman-an-overview-of-network-types

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Cisco Network Design Model Overview

April 28 2014 , Written by Cisco & Cisco Router, Network Switch Published on #Networking

This article focuses on another important network model, the Cisco hierarchical network design model. Very different that the OSI model, this model is used as the basis for designing Cisco networks for security and performance. The article provides an overview of the roles and responsibilities of each of the model’s 3 layers.

While the OSI model is concerned with how different systems communicate over networks, the Cisco hierarchical model is a blueprint of types that defines how networks should be designed in layers. Each layer is meant to have its own roles and responsibilities, but the goal is to create a network that delivers high performance, is manageable, and keeps required roles in their place. While this model was designed by Cisco, its use can by all means be adapted to account for the switching and routing equipment of any vendor.

The model is made up of three layers, including Core, Distribution, and Access. The diagram below shows each of these layers relative to one another.



The Core layer of the network would be considered along the same lines as the backbone – high speed and redundant. The Distribution layer would contain intermediate switches and routers, such as those used to route between subnets or VLANs. The Access layer is literally where user’s PCs plug into their local switch, somewhere like an area wiring closet. While this is a simplified view of the network, it provides a general high-level overview.

Getting a little deeper into things, each layer of the model is actually home to multiple roles and responsibilities. Remember that this is a model, and as such not all networks will necessarily look like this – many, especially smaller ones, may not even be close. Instead, think of this model as one that outlines best practices to ensure that the network is reliable, scalable, and meets performance requirements. 

The Layers 
Each layer in the model has a general level of responsibility, in terms of what capabilities should be implemented there, and with a particular emphasis on how that layer should perform. Each of the layers is outlined in more detail below. 

Core Layer 
The responsibility of the core layer is to act as a high-speed switched backbone. Notice that the backbone is expected to switch traffic, and not route it. Routing can severely impact performance, mainly because each frame needs to be recreated as it passes through each router, as we’ll look at a little later in the series. Switching provides much higher performance, mainly because a frame can travel across the backbone without needing to be recreated at each switch. That’s not to say that the frame isn’t inspected at every switch (it will be to varying degrees), but everything stays at OSI layers 1 and 2 instead of having to be considered at Layer 3. The Core layer is usually comprised of a relatively small number of high-end switches. Growth should not add devices, but rather replace devices with higher-speed equipment as necessary. 

The Core Layer is also responsible for providing a degree of redundancy by providing multiple paths. That is, you want to be sure that even if a backbone link goes down, another path exists over which frames can travel. We’ll consider this in a diagram shortly. 

In general, you want to be sure that the only traffic that moves across the backbone is that which is moving between different Distribution-layer devices. A design that moves traffic over the Core layer when it isn’t necessary will not provide the best performance. To that end, the core should also never be used to implement traffic filters such as access lists – these should be implement at other layers instead. 

To summarize, the Core Layer should:

  • Be used to provide high-speed switching.
  • Provide reliability and fault tolerance.
  • Grow by using faster, and not more, equipment.
  • Never implement performance-decreasing elements such as access lists.

Distribution Layer 
The distribution layer acts as an intermediary between the Core and Access layers, and is usually where the routing functions (and more) on a well-designed network are found. An example of the type of interconnection here includes those between different types of media such as Ethernet and Token Ring. The distribution layer is also where policies are usually implemented using Access Lists. 

To get a feel for the function of the distribution layer, remember that a great deal of routing will usually happen on a network. Clients on one subnet may need to talk to servers on another. In some cases this traffic is localized, such as with departmental file or database servers. However, there are often servers that need to be accessed by many subnets even within a given location, such as mail servers. The distribution layer would be responsible for this routing function. In all, this layer serves a number of purposes including the implementation of

  • Security, in the form of Access Lists and filtering.
  • A boundary for route aggregation and summarization (for example, many subnets can be hidden behind a single routing table entry, making these entries smaller, and routing more efficient).
  • Broadcast domains. A broadcast domain is a layer 2 concept that defines how far a broadcast will travel on a given network. By default, routers usually do not pass broadcasts, acting as the demarcation point between broadcast domains.
  • Routing. Almost all routing is done at this layer, which keeps it away from the backbone. This also acts as the intermediate point between where static and dynamic routing are used on the network.

Access Layer 
The Access Layer acts as the point as which end stations connect to the network, usually by plugging into Layer 2 switches or hubs. As such, this layer is usually used to define network collision domains. The Access layer is also sometimes used to define additional network security policies and filtering if necessary. 

How it fits together 
The diagram below shows how a typical network might be configured to account for the Cisco hierarchical network design model. Remember that the Core layer switches might be geographically dispersed, and that the distribution layer routers might be connected to the core via a WAN link of similar.


Rs from http://archive.networknewz.com/2004/0206.html

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Top 10 Things You Should Know about VLANs and Subnets

March 31 2014 , Written by Cisco & Cisco Router, Network Switch Published on #Networking

Subnets and VLANs are two concepts that go hand-in-hand.


Best networking practice is a one-to-one relationship between VLANs and subnets. 

Here are the top 10 things you should know about these critical components of Converged Plantwide Ethernet (CPwE) Design and Implementation:

  1. A Layer-2 network also refers to a subnet, broadcast domain and a virtual LAN (VLAN). Best practice is a 1:1:1 relationship between subnets, broadcast domains and VLANs. The Layer-2 network infrastructure devices in the Cell/Area zone are predominantly access switches. 
  2. Layer-3 switches or routers are used in manufacturing environments. Layer-3 switches or routers forward information between different VLANs or subnets. They use information in the IP header (Layer 3) to do so. Regardless of the specific layer being connected, switches provide Industrial Automation Control System (IACS) networks with many of the safeguards realized by the natural separation inherent in existing IACS-optimized networks. Some switches promoted as Layer 2 switches also support limited routing capabilities, like static routing. 
  3. Devices and controllers configured for multicast delivery need to be located within the same Cell/Area IACS network because these packets cannot be routed, meaning that any router will drop the packet before forwarding it outside the subnet/VLAN. Devices and controllers configured for unicast delivery, Implicit I/O or explicit messaging do not need to be within the same Cell/Area zone because that communication is routable. 
  4. Logical segmentation is the process of outlining which endpoints need to be in the same LAN. Segmentation is a key consideration for a Cell/Area IACS network. Segmentation is important to help manage the real-time communication properties of the network while supporting the requirements defined by the network traffic flows. Security is also an important consideration in making segmentation decisions. A security policy may call for limiting access of plant floor personnel (such as a vendor or contractor) to certain areas of the plant floor (such as a functional area). Segmenting these areas into distinct subnets and VLANs greatly assists in the application of these types of security considerations. 
  5. Network developers should strive to design smaller LANs or VLANs, while recognizing that the traffic patterns of an IACS may make this difficult if routing is required. 
  6. Use VLANs in addition to any physical segmentation, and connect all Cell/Area LANs to Layer-3 distribution switches to maintain connectivity. 
  7. Trunks are also an important concept when deploying VLANs. The inter-switch connections in a Layer-2 network deploying VLANs are referred to and configured as trunks because they carry traffic for multiple VLANs. The relevant standard is IEEE 802.1Q, which specifies VLAN tagging to carry multiple VLANs on Ethernet links between switches. IEEE 802.1Q is the prevalent and most often used standard. 
  8. Management VLANs are also an important consideration when establishing a VLAN concept. In the IT and enterprise network, management VLANs are commonly used to access the network and IT infrastructure, separate from the data VLANs. If IT is involved in managing the IACS network, they may want to establish management VLANs on which only the network infrastructure has IP addresses. 
  9. Two important considerations in designing a VLAN network are the use of VLAN 1 and the native VLAN. The native VLAN is the VLAN to which a port returns when it is not trunking. VLAN 1 is the default native VLAN on trunk ports on Cisco-based switches and therefore may use by a number of network infrastructure protocols. 
  10. Define IACS devices to use a specific VLAN other than the native VLAN and VLAN 1; do not use VLAN 1 for any purpose. Some security threats assume that VLAN 1 is the default VLAN for data and/or management traffic and may target VLAN 1 in their attacks.

Article Source from http://www.industrial-ip.org/en/industrial-ip/convergence/vlans-and-subnets-10-things-you-need-to-know

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To Make Your Network Device Smarter

January 3 2014 , Written by Cisco & Cisco Router, Network Switch Published on #Networking

Cisco is always focusing on making network devices smarter and providing more intelligent and safer networking solutions for customers.

One of typical examples is Cisco Adaptive Security Appliance (ASA).  When it encounters a critical unrecoverable error condition, it reloads itself and then automatically sends in the error report.  This report is analyzed by Cisco and compared against all known issues.  If Cisco has seen this issue before, we will:

  • Alert the customer via e-mail that their device encountered a problem
  • Include the bug ID and Headline of the problem the device experienced
  • Indicate what versions contain a fix to this issue


This provides you with everything you need to know about the problem.


How is that for Smart? 
The Cisco ASA also detects other error conditions, these (i.e.: fan failures, interface failures, other environmental alerts, etc…) and securely reports those back to Cisco. For critical events, it will automatically open a TAC case and start working on the problem. That may be initiating an RMA and shipping the part on-site, or it could be that a TAC engineer will call you to alert you to the problem and what the next steps are. For non-critical events, you will receive an e-mail to alert you to the problem and include guidance on the next steps.

In addition to this, we are investing in big data initiatives to mine the data being sent in and obtain insights on how we can better improve our software quality, or to quickly be alerted to any critical issue affecting multiple customers-all in an automated fashion.

Note: Find out how to enable SCH on the ASA here. You can also check out the Smart Call Home Support Forums Community, and see Cisco's full list of Smart enabled devices.

Reference From: https://supportforums.cisco.com/docs/DOC-35118

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Logging Options in the Cisco IOS

December 16 2013 , Written by Cisco & Cisco Router, Network Switch Published on #Networking

For any network administrator, it is a necessary to know how to properly use logging. The Cisco IOS offers a great many options for logging. To help you know them well, we will discuss how to configure logging, how to view the log and its status, and list three common errors when it comes to logging.

The logging command in Global Configuration Mode and the show logging command in Privileged Mode are two simple but powerful tools to configure and show all Cisco IOS logging options. Let's take a closer look.

Configure logging in the Cisco IOS

When configuring logging, the most important command to know is the logging command, used when in Global Configuration Mode. Here's an example of this command and its options.


In order to help you know these options in a good way, let’s look at the most common ones.

You can configure the router to send buffered logging of its events to the memory. (Rebooting the router will lose all events stored in the buffered log.) Here's an example:

Router(config)# logging buffered 16384

You can also send the router's events to a syslog server. This is an external server running on your network. Most likely, the syslog server is running on a Linux or Windows server. Because it's external to the router, there's an added benefit: It preserves events even if the router loses power. A syslog server also provides for centralized logging for all network devices.

To configure syslog logging, all you need to do is use the logging command and the hostname or IP address of the syslog server. So, to configure your Cisco device to use a syslog server, use the following command:

Router(config)# logging

The Cisco IOS enables logging to the console, monitor, and syslog by default. But there's a catch: There's no syslog host configured, so that output goes nowhere.

There are eight different logging levels.









The default level for console, monitor, and syslog is debugging. The logging on command is the default. To disable all logging, use the no logging on command.

By default, the router logs anything at the level of debugging and greater. That means that logging occurs from level 7 (debugging) up to level 0 (emergencies). If you want to par down what the system logs, use something like the logging console notifications command.

In addition, the router doesn't enable logging to the system buffer by default. That's why you must use the logging buffered command to enable it.

View the status of logging and the logging itself

To view the status of your logging as well as the local buffered log, use the show loggingcommand. Here's an example:


Note that this router has enabled syslog logging and is sending it to host In addition, console logging is at the debugging level, and the setting for local buffered logging is 10,000,000 bytes.

Three common logging errors

Logging can be frustrating at times. To help prevent some of that frustration, let's look at three common errors.

Not setting the terminal to monitor logging

If you Telnet into a router and can't see some of the logging you're expecting, check to see if you've set your terminal to monitor the logging. You can enable this with the terminal monitor command. To disable it, use the terminal no monitor command.

To determine whether you've enabled monitoring, use the show terminal command, and look for the following:

Capabilities: Receives Logging Output

If you see this, you're monitoring logging output. If it returns none for capabilities, then the monitoring is off.

Using the incorrect logging level

If you can't see logging output, you should also check whether you've set the level correctly. For example, if you've set the console logging to emergencies but you're running debugging, you won't see any debugging output on the console.

To determine the set level, use the show logging command. Keep in mind that you need to set the level to a higher number to see all levels below it. For example, setting logging at debugging shows you every other level.

In addition, make sure you match the type of logging that you want to see with the level you're configuring. If you configure monitor logging to debug but you're on the console and you've set it to informational, you won't see the debug output on the console.

Displaying the incorrect time and date in logs

You may see log messages that don't exhibit the correct date and time. There are a variety of options to control the date and time that appear on logging output (either to the screen or to the buffer). To control this, use the following command:

Router(config)# service timestamps debug ?

  datetime      Timestamp with date and time

  uptime        Timestamp with system uptime

More Notes: Remember that many problems require some kind of historical log to help find a solution. That's why it's important to make sure you've properly configured logging so you can use your logs to see the past.

Reference from http://www.techrepublic.com/

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