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Happy New Year 2012

We would like to wish all our readers a very happy and prosperous new year.

 

The EIGRP (Enhanced Interior Gateway Routing Protocol) metric

EIGRP (Enhanced Interior Gateway Routing Protocol) is a network protocol that lets routers exchange information more efficiently than was the case with older routing protocols. EIGRP which is a proprietary protocol evolved from IGRP (Interior Gateway Routing Protocol) and routers using either EIGRP and IGRP can interoperate because the metric (criteria used for selecting a route) used with one protocol can be translated into the metrics of the other protocol. It is this metric which we will examine in more detail.

Using EIGRP, a router keeps a copy of its neighbour’s routing tables. If it can’t find a route to a destination in one of these tables, it queries its neighbours for a route and they in turn query their neighbours until a route is found. When a routing table entry changes in one of the routers, it notifies its neighbours of the change. To keep all routers aware of the state of neighbours, each router sends out a periodic “hello” packet. A router from which no “hello” packet has been received in a certain period of time is assumed to be inoperative.

EIGRP uses the Diffusing-Update Algorithm (DUAL) to determine the most efficient (least cost) route to a destination. A DUAL finite state machine contains decision information used by the algorithm to determine the least-cost route (which considers distance and whether a destination path is loop-free).

Figure 1

The Diffusing Update Algorithm (DUAL) is a modification of the way distance-vector routing typically works that allows the router to identify loop free failover paths.  This concept is easier to grasp if you imagine it geographically. Consider the map of the UK midlands shown in Figure1. The numbers show approximate travel distance, in miles. Imagine that you live in Glasgow. From Glasgow, you need to determine the best path to Hull. Imagine that each of Glasgow’s neighbours advertises a path to Hull. Each neighbour advertises its cost (travel distance) to get to Hull. The cost from the neighbour to the destination is called the advertised distance. The cost from Glasgow itself is called the feasible distance.
In this example, Newcastle reports that if Glasgow routed to Hull through Newcastle, the total cost (feasible distance) is 302 miles, and that the remaining cost once the traffic gets to Newcastle is only 141 miles. Table1 shows distances reported from Glasgow to Hull going through each of Glasgow’s neighbours.

Table 1

Glasgow will select the route with the lowest feasible distance which is the path through Newcastle.

If the Glasgow-Newcastle road were to be closed, Glasgow knows it may fail over to Carlisle without creating a loop. Notice that the distance from Carlisle to Hull (211 miles) is less than the distance from Glasgow to Hull (302 miles). Because Carlisle is closer to Hull, routing through Hull does not involve driving to Carlisle and then driving back to Glasgow (as it would for Ayr). Carlisle is a guaranteed loop free path.

The idea that a path through a neighbour is loop free if the neighbour is closer is called the feasibility requirement and can be restated as “using a path where the neighbour’s advertised distance is less than our feasible distance will not result in a loop.”

The neighbour with the best path is referred to as the successor. Neighbours that meet the feasibility requirement are called feasible successors. In emergencies, EIGRP understands that using feasible successors will not cause a routing loop and instantly switches to the backup paths.

Notice that Ayr is not a feasible successor. Ayr’s AD (337) is higher than Newcastle’s FD (302). For all we know, driving to Hull through Ayr involves driving from Glasgow to Ayr, then turning around and driving back to Glasgow before continuing on to Hull (in fact, it does). Ayr will still be queried if the best path is lost and no feasible successors are available because potentially there could be a path that way; however, paths that do not
meet the feasibility requirement will not be inserted into the routing table without careful consideration.

EIGRP uses a sophisticated metric that considers bandwidth, load, reliability and delay. That metric is:

256, *, left(K_1, *, bandwidth ,+, dfrac {K_2 ,*, bandwidth}{256 - load}, +, K_3 ,*, delayright), *,dfrac {K_5}{reliability ,+, K_4}

Although this equation looks intimidating, a little work will help you understand the maths and the impact the metric has on route selection.

You first need to understand that EIGRP selects path based on the fastest path. To do that it uses K-values to balance bandwidth and delay. The K-values are constants that are used to adjust the relative contribution of the various parameters to the total metric. In other words, if you wanted delay to be much more relatively important than bandwidth, you might set K3 to a much larger number.

You next need to understand the variables:

  • Bandwidth—Bandwidth is defined as (100 000 000 / slowest link in the path) kbps. Because routing protocols select the lowest metric, inverting the bandwidth (using it as the divisor) makes faster paths have lower costs.
  • Load and reliability—Load and reliability are 8-bit calculated values based on the performance of the link. Both are multiplied by a zero K-value, so neither is used.
  • Delay—Delay is a constant value on every interface type, and is stored in terms of microseconds. For example, serial links have a delay of 20,000 microseconds and Ethernet lines have a delay of 1000 microseconds. EIGRP uses the sum of all delays along the path, in tens of microseconds.

By default, K1=K3=1 and K2=K4=K5=0. Those who followed the maths will note that when K5=0 the metric is always zero. Because this is not useful, EIGRP simply ignores everything outside the parentheses. Therefore, given the default K-values the equation becomes:

256, *, left(1, *, bandwidth ,+, dfrac {0 ,*, bandwidth}{256 - load}, +, 1 ,*, delayright), *,dfrac {0}{reliability ,+, 0}

Substituting the earlier description of variables, the equation becomes 100,000,000 divided by the chokepoint bandwidth plus the sum of the delays:

256, *, left(dfrac {10^7}{min(bandwidth)}, +,sum,dfrac {delays}{10}right)

As a final note, it is important to remember that routers running EIGRP will not become neighbours unless they share K-values. That said however you really should not change the K-values from the default without a compelling reason.

Which website shopping cart?

We have recently undertaken a study to determine which of the many shopping cart systems we should use on a customers website. After a long process trawling through the myriad of options we finally reached a shortlist of 8 candidates.

These candidates were:

  • Avactis
  • CS Cart
  • Cube Cart
  • Magento
  • OS Commerce
  • Prestashop
  • Virtuemart
  • Zen Cart

Now, with that part done the hard work begins.

The fact of the matter is that all of the choices in the list above are great ones. Any of these shopping carts will, with the right implementation, produce an excellent level of functionality on any website. The trick is to understand your own requirements first and identify which of the options most closely fits your own requirements, not only today but also your anticipation of what they will be in 6 months, 1 year and possibly even more.

So lets look at the pros and cons of each.

You can find the comparison HERE.

 

Cisco Blog – Healthcare – BYOD! What do you bring to the party?

Historically Healthcare has the reputation of being behind the technology curve, however the next-generation worker is now driving the demand for the Bring Your Own Device business model.
“What? That’s crazy talk! How do I maintain a controlled secure environment?” Exclaims the IT Manager.

This new age of social intelligence and the evolution of social networks and mobility bring the expectation of free choice among the work force. Workers are putting the pressure on organizations for interoperability between the enterprise network and the devices of their choosing. Today the average person on the planet has 1.8 devices on today’s networks connecting over 13 billion devices in total. By the year 2015 that number is expected to rise to 25 billion equating to 3.47 devices per person.

Adoption and use of mobile devices by Doctors will continue to grow, according to a survey taken in May 2011 by QuantiaMD from 3,798 physician community members. We will continue to see more of what they refer to as “Super Mobile” Physicians who use Smartphones and tablets as mHealth platforms for patient care.

Mobile Health is a rapidly growing phenomenon. According to a recent article on biomedical-engineering-online.com titled How smartphones are changing the face of mobile and participatory healthcare, “Patients too are accessing health information, actively participating in their own care (participatory healthcare), and maintaining contact with their healthcare providers through Smartphones.” So what does this mean for the business hosting the party of devices?

IT managers have a whole new set of challenges in order to provide an open yet secure infrastructure which a traditional data center solution was not originally designed for. This deficiency in the market prompted Cisco to build theirs from the ground up reinventing Data Center with the demands of the Next Generation workflow in mind.

The BYOD model will inevitably demand new support and operational structuring requiring businesses to plan and budget accordingly. What’s clear is that the BYOD challenge is not going away.

According to Gartner the 2015 worker will be one of “Extreme Individualization”. Baby boomers will begin to retire as highly-interactive young adults enter the workforce. Gartner also reports in a maverick analysis that ”workers will spend more than 80 percent of their time working collaboratively, and not necessarily face-to-face”.

This wide utilization of innovative collaboration technologies for both personal and business use will only continue to put the pressure on businesses to enable the BYOD demand. Looking at the rate of adoption in the industry, Healthcare is no exception to the age of social intelligence.