Static Routes

Statics are build in the same way as defaults, in the sense that they have a destination a prefix and a next hop, the difference being that a static route informs the router about specif routes rather than an "any" route like a default does.

An example of the static would be:

Ip route 20.1.1.0 255.255.255.0 10.1.1.0

The first part of the route, the address "20.1.1.0" tells the device that this route specifies the destination of 20.1.1.0.

The second part tells the router which part of the destination address in the first part of the address it needs to look at, the "255.255.255.0" instructs the router to look at the first three octets in the destination address and ignore the 4th octet. We could have written the destination address as follows "20.1.1", but the command line will not allow us to do that.

The prefix tells the router which part of the destination address the router needs to look at.

Example 1: The following two statics are now in our example router:

1: Ip route 20.1.1.0 255.255.255.0 10.1.1.0

2: Ip route 20.1.0.0 255.255.0.0 10.5.5.0

Our router receives a packet with the destination address set to "20.1.1.23", the router will examine the routing table and choose between the two routes. The router will choose 1 since it is a closer match for the destination address in the packet header. The second one is less specific or "broader" matching "20.1.0.0 255.255.0.0" meaning "use this route if the packet wants to get to any destination starting with "20.1. anything. Anything" whereas the first route matches "20.1.1.anything" making this route more specific for routing the packet wanting to get to 20.1.1.23.

The very first choice that a router makes is longest match irrelevant of how the it was learnt.

Matching Routes

What would happen if the router has two matching routes:

1: Ip route 20.1.1.0 255.255.255.0 10.1.1.0

2: Ip route 20.1.1.0 255.255.255.0 10.5.5.0

The static routes above have the exact same destination addresses and the exact same prefix lengths, so which one will the router believe?. The router will in this case begin to share the traffic across both paths, if this is your desired result then you are done, what if it is not, how do we force the traffic to take one route over the other?. This is achieved by setting what is referred to as the "trust-ibilty" of the route. Every route that populates the routing table is assigned an "Administrative distance" between 0 and 255. The lower the value; the more desirable the route. All static routes have an Administrative distance of "1". This value can be changed.

Administrative distance is a local value on the router; a router never advertises this to any other router.

1: Ip route 20.1.1.0 255.255.255.0 10.1.1.0 1

2: Ip route 20.1.1.0 255.255.255.0 10.5.5.0 2

Even setting the Administrative Distance to 2 makes route two less desirable. The router now chooses to use route one to pass traffic to destination network "20.1.1.0"

Now we know that the router makes the following routing decisions in the following order

1. longest match irrelevant of how the route was learnt

2. Lowest Administrative distance



Article Source: http://EzineArticles.com/?expert=Joe_Spoto

Understanding routing processes

Routers route, that's what they do. A packet comes in and a packet goes out. What happens to the packet containing your data inside the router?, how does the router decide which output interface to transmit the packet out of?, what if the router has two routes to the same destination how does it deal with that decision making process?.

For a router to make a routing decision it needs to know how to get to the destination address which is described in the header of the IP Packet. Without this knowledge the router could ultimately drop the packet.

Our first job is to populate the routers routing table with relevant routes, we say relevant since routers will believe and trust any route placed into it's routing table and use it resulting in routing blackholes where traffic is lost in the network where the time to live in the packet headers expire and the traffic is then dropped.

Default Routes

There are various methods for populating the routing table, the most common of routes is called a "default route". A default route is written as follows (I am using Cisco command line)

Ip route 0.0.0.0 0.0.0.0 10.1.1.1

The route is simple to write and straight forward to understand. The first set of zeros after the "ip route" command which we will call the "destination" tells the router which destination this route represents. This route is effectively "matching" every single possible address that can be drawn up with the IPv4 address scheme.

The second row of four zeros which we will call the "prefix "shows the router which bits in the destination the router needs to look at.

Having any octet in the prefix set to all zeros (i.e 0 0 0 0 0 0 0 0 = 0) tells the router that it ought to ignore the corresponding octet in the destination. The order of the octets in the destination field correspond directly to the octets the second row.

The third address "10.1.1.1" is an example of what is referred to as a "next hop", (10.1.1.1 is an example address only for the purposes of this article only, your next hop will be different). The next hop address is the other side of the link on a point to point link or an interface in a multiaccess network like frame relay of Ethernet that can route the data.

The next hop does not have to be the address of the next hop, it can also be the local outbound interface.

All of our home broadband routers will have a default route helping the router to simply pass all traffic up to the ISP. Default routes are also known as "gateways of last resort"



Article Source: http://EzineArticles.com/?expert=Joe_Spoto

When it comes to retailing business as well as transportation, there have been many developments that have occurred over time. A large number of the operations have become quite automated and simplified for the benefit of consumers as well as the retail companies, which use such products. The main idea behind a barcode scanner is that it is held in the hand and is quite portable so that it does not have to be fixed at one place. This is why handheld barcode scanners are quite in vogue in this time and age. This is quite handy in keeping up with the times, where convenience as well as comfort is the most sought after in products and services around the globe.

A barcode reader or scanner is an electronic device which helps in OCR or optical character recognition. It consists of a light source as well as a lens and light sensor that can help in translating electrical impulses into electrical ones. This way, the matter which is located in the barcodes gets concerted into electronic form which it is then read by the handheld barcode scanners and the matter is decoded. This is quite a convenient feature as such scanners can be easily used at various places, in buses as well as retailing as well.

If you look at the retailing business, it has indeed been revolutionized by the use of handheld barcode scanners. In the good old days, when you went to some retail mart of a store, you would have to stand in line and have the store assistant calculate the expenses incurred manually using a calculator. Then the bill would be generated manually which would mean the spending of time. All of this can be easily avoided by using handheld barcode scanners. With these scanners one can scan the bar code on the product which is then fed into the machine directly and the price of the product is recorded after which it is fed out as a printed bill. All of this saves a lot of time and makes it possible to make the retail operations quite simple as well as streamlined.

The use of handheld barcode scanners in buses or other forms of public transport is also now well documented and wide spread. There are many bus companies that use these in order to read the pre-printed bus tickets that travelers use. This is very much convenient as this prevents the use of the manual tickets which was a cumbersome and time consuming process. This is why it always helps in using barcode scanners which are all so handy and convenient to use. There are many of these which can also be used at varying distances which make them so very simple as well as flexible in usage.



Article Source: http://EzineArticles.com/?expert=Gary_Hatcher

When the internet first came about the only way to access it was by using a computer to dial a connection to your internet provider using a modem and your telephone line. This was great when the internet first came about as webpages were very simple, businesses mainly used it for email and it wasn't used that much and not by many people. Once the internet started to grow, you were now able to access your business computer from home, watch videos online and access social networking sites, dial up started to become a thing of the past.

Dial up internet had a few drawbacks that would eventually find people dumping it for faster internet connections that wouldn't tie up your phone line, cost you a local call when you wanted to connect, would download webpages, emails etc a lot faster and would offer a lot more flexability when it came to networking and being able to travel and access the internet at the same time. The new types of connection were then referred to as Broadband as the connection was a faster (the bandwidth was larger) speed. Broadband is basically a marketing term and there are a few types of internet connections that fall into the "Marketing Term" Broadband.

ADSL - This type of internet connection uses an ADSL modem which connects to your phone line, downloads anywhere from 6 - 400 times faster than dial up but doesn't tie up your phone line meaning you make and receive calls while accessing the internet. There are many providers who offer ADSL and a few different speeds available. The two types of ADSL are ADSL 1 and ADSL 2+. Make sure to shop around if your looking into getting an ADSL or ADSL 2+ connection as different providers will offer different speeds at different prices which you will be amazed at how much it varies.

Cable Internet - This type of connection is only available in areas which have dedicated Cable Internet cabling installed. This type of connection uses a dedicated cable from the street, only provided by Telstra or Optus which doesn't need a phone line at all and downloads at speeds similar to those of ADSL.

Mobile Broadband or Wireless Mobile Broadband- This internet connection uses the mobile phone network and can be used anywhere you get mobile coverage or where your provider provides you coverage. There are a few providers you can choose from which offer different coverage areas as well as different prices, so once again shop around and ask about both coverage and price. This type of connection can be expensive and vary alot in speed, I would only recommend this as a second internet connection if you need the internet on the road or when cable or ADSL is not available.

There are other types of internet connections that are used but these are the most common types that are in use today in both Home and Businesses. When choosing a type of internet connection make sure to look at all your options and to find exactly what sort of speeds you will be getting, what sort of download limit and how much.



Article Source: http://EzineArticles.com/?expert=Maurice_Virduzzo