Discount Computers

CCNA and CCNP candidates are well-versed in Spanning-Tree
Protocol, and one of the great things about STP is that it works
well with little or no additional configuration. There is one
situation where STP works against us just a bit while it
prevents switching loops, and that is the situation where two
switches have multiple physical connections.

You would think that if you have two separate physical
connections between two switches, twice as much data could be
sent from one switch to the other than if there was only one
connection. STP doesn’t allow this by default, however in an
effort to prevent switching loops from forming, one of the paths
will be blocked.

SW1 and SW2 are connected via two separate physical connections,
on ports fast0/11 and fast 0/12. As we can see here on SW1, only
port 0/11 is actually forwarding traffic. STP has put the other
port into blocking mode (BLK).

SW1#show spanning vlan 10

(some output removed for clarity)

Interface Role Sts Cost Prio.Nbr Type

Fa0/11 Root FWD 19 128.11 P2p

Fa0/12 Altn BLK 19 128.12 P2p

While STP is helping us by preventing switching loops, STP is
also hurting us by preventing us from using a perfectly valid
path between SW1 and SW2. We could literally double the
bandwidth available between the two switches if we could use
that path that is currently being blocked.

The secret to using the currently blocked path is configuring an
Etherchannel. An Etherchannel is simply a logical bundling of 2
- 8 physical connections between two Cisco switches.

Configuring an Etherchannel is actually quite simple. Use the
command “channel-group 1 mode on” on every port you want to be
placed into the Etherchannel. Of course, this must be done on
both switches if you configure an Etherchannel on one switch and
don’t do so on the correct ports on the other switch, the line
protocol will go down and stay there.

The beauty of an Etherchannel is that STP sees the Etherchannel
as one connection. If any of the physical connections inside the
Etherchannel go down, STP does not see this, and STP will not
recalculate. While traffic flow between the two switches will
obviously be slowed, the delay in transmission caused by an STP
recalculation is avoided. An Etherchannel also allows us to use
multiple physical connections at one time.

Here’s how to put these ports into an Etherchannel:

SW1#conf t

Enter configuration commands, one per line. End with CNTL/Z.

SW1(config)#interface fast 0/11

SW1(config-if)#channel-group 1 mode on

Creating a port-channel interface Port-channel 1

SW1(config-if)#interface fast 0/12

SW1(config-if)#channel-group 1 mode on

SW2#conf t

Enter configuration commands, one per line. End with CNTL/Z.

SW2(config)#int fast 0/11

SW2(config-if)#channel-group 1 mode on

SW2(config-if)#int fast 0/12

SW2(config-if)#channel-group 1 mode on

The command “show interface trunk” and “show spanning-tree vlan
10″ will be used to verify the Etherchannel configuration.

SW2#show interface trunk (some output removed for clarity)

Port Mode Encapsulation Status Native vlan

Po1 desirable 802.1q trunking 1

SW2#show spanning vlan 10 (some output removed for clarity)

Interface Role Sts Cost Prio.Nbr Type

Po1 Desg FWD 12 128.65 P2p

Before configuring the Etherchannel, we saw individual ports
here. Now we see “Po1″, which stands for the interface
“port-channel1″. This is the logical interface created when an
Etherchannel is built. We are now using both physical paths
between the two switches at one time!

That’s one major benefit in action let’s see another.
Ordinarily, if the single open path between two trunking
switches goes down, there is a significant delay while another
valid path is opened – close to a minute in some situations. We
will now shut down port 0/11 on SW2 and see the effect on the
etherchannel.

SW2#conf t

Enter configuration commands, one per line. End with CNTL/Z.

SW2(config)#int fast 0/11

SW2(config-if)#shutdown

3w0d: %LINK-5-CHANGED: Interface FastEthernet0/11, changed state
to administratively down

SW2#show spanning vlan 10

VLAN0010

Spanning tree enabled protocol ieee

Interface Role Sts Cost Prio.Nbr Type

Po1 Desg FWD 19 128.65 P2p

SW2#show interface trunk

Port Mode Encapsulation Status Native vlan

Po1 desirable 802.1q trunking 1

The Etherchannel did not go down! STP sees the Etherchannel as a
single link therefore, as far as STP is concerned, nothing
happened.

Building an Etherchannel and knowing how it can benefit your
network is an essential skill for CCNA and CCNP success, and it
comes in very handy on the job as well. Make sure you are
comfortable with building one before taking Cisco’s exams!

About the author:
Chris Bryant, CCIE #12933, owns The Bryant Advantage
(http://www.thebryantadvantage.com), home of free CCNA and CCNP
tutorials, Pass the CCNA exam with Chris Bryant!

A digital camera battery is probably the most important digital
camera accessory. Some digital cameras can consume power at an
alarming rate, providing no more than a few hours of continuous
shooting time before the battery is drained. Other cameras are
renowned for the long life of their digital camera battery which
allows users to snap away with barely a thought to power
consumption. It is important to know how you intend to use your
camera and what type of battery it needs.

There are two types of digital camera battery. The most widely
available digital camera battery is a standard AA-size battery.
The other type of digital camera battery is a rechargeable
battery that is made by the manufacturer, otherwise known as a
proprietary battery.

A proprietary digital camera battery offers the advantage of
being lighter and more compact, but they are substantially more
expensive, making the prospect of buying one or two backup sets
much less appealing.

The alkaline AA-size digital camera battery usually has a very
short life – less than an hour in extreme cases – when used in a
digital camera. This type of battery makes an acceptable
emergency backup, especially if you are travelling with your
camera. However, the Nickel Metal Hydride (NiMH) digital camera
battery can be used instead of the alkaline ones with a charger
and this rechargeable NiMH digital camera battery has a
substantially longer life at an affordable price.

Another type of AA-size battery is the non-rechargeable Lithium
batteries and rechargeable Nickel Cadmium (NiCD) batteries. The
lithium digital camera battery has a superior life to alkaline
AA’s and offers good cold-weather performance but their price
and non-rechargeable nature make them less useful than
rechargeable NiMH batteries. It is also important to ensure that
your camera can take a lithium digital camera battery. On the
other hand the NiCD digital camera battery offers the advantage
of retaining their charge while unused, unlike NiMH cells, but
have shorter lives and need to be discharged completely before
recharging which can be extremely inconvenient.

The LCD screen of a digital camera is responsible for consuming
the most power from a digital camera battery so it is worth only
using the LCD when necessary to help conserve the battery life.
Always try to carry at least one backup set of batteries,
especially if you plan on being away from power outlets for an
extended period of time. The universally-available alkaline
AA-size battery can make a convenient emergency backup if your
regular digital camera battery fails.

About the author:
Steve Gargin is the administrator of
http://digital-camera-reviews.helper-guru.com/dsc717/index.html
which is a great website dedicated to giving free advice on
Digital Cameras.

Question : Every time when I sign in to MSN messenger I get this
message:

“Internet Explorer Script Error. An error has occured in the
script on this page.

Line: 455 Char: 3 Error: object doesn’t support this property or
method Code: 0 URL: http//t.msn.com/en-my/default.aspx? Do you
want to continue script on this page? Yes/No” How do I fix it?

Answer : This either means that there’s a bug in the script on
that page, or the software being used is out of date. To attempt
to solve it, download and install the latest version of Internet
Explorer (IE). The latest version of IE can be found at
windowsupdate.microsoft.com or at
http://www.microsoft.com/windows/ie/default.mspx — just point
to “downloads” and select the latest version of IE from there.

All too often, when people update the operating system, they
forget to update the browser. This will break compatibility with
a lot of pages and applications which attempt to use functions
that are only available in the latest versions. Because of this,
the browser should be updated when the operating system is
updated.

If the error still occurs after the browser is updated, then
it’s a good bet that there’s a bug in the script on that page.

About the author:
No technical
problems