Loop Guard is one of the guarding protocols to prevent a network from getting switching loops.
Assume that port A from switch C receives BPDU's from port AA from switch B. Suddenly, a problem appears and makes switch B unable to send BPDU from switch C. This activates the MaxAge time counter on port A switch C and after the counter expires, port A on switch C will open its port from BLK to FWD mode and sends a BPDU to switch B. When loop guard is applied, this occurence will never happen because when the switch's port does not receive BPDU frames, it will put its port to a "loop inconsistent mode" (which is still in a BLK state). After port A switch C receives BPDU's again from switch B, the port returns back from loop inconsistent BLK to normal BLK mode.
The configuration command for loop guard is done in the switch's configuration mode which is "spanning-tree loopguard default".
Sunday, July 18, 2010
Thursday, July 15, 2010
Root Guard, BPDU Guard, BPDU Filtering
In this blog I will try to explain about Root Guard, BPDU Guard and BPDU filtering. All of these features to protect BPDU information from another switch.
Root guard can be applied on certain ports and protects downstream switches from becoming root switches. If a port on the switch is configured witch root guard, when it receives a superior BPDU, it will discard the BPDU and will put that port into "root-inconsistent" state and goes back normal when the port does not receive superior BPDU information.
The command for configuring root guard is on the interface configuration with the command "spanning-tree guard root".
There could be a possibility that one accidently applies portfast on a port and puts another switching device on the other side. This can lead to a switching loop and can be prevented by applying BDPU guard. When a BPDU comes into a port with BPDU guard applied to it, the port will be shut down and will show the "err-disabled" information.
The command for configuring BPDU guard is on the interface configuration with the command "spanning-tree bpduguard enable" or if you want to enable it on all ports you can do it on the switch configuration mode and enter the command "spanning-tree portfast bpduguard default".
The last one is BPDU filtering. This feature is used when we don't want the port to be disabled when it receives a BPDU. It can be configured globally and by interface but have different characteristics when applied:
1. If the BDPU filtering is applied globally, the portfast enabled port will stop running portfast when it receives a BPDU packet.
2. If the BDPU filtering is applied on an interface only, the incoming BPDU on the port with BPDU filtering will be dropped silently and no BPDU packets will be returned.
The command for configuring BPDU guard is on the interface configuration with the command "spanning-tree bpdufilter enable" or if you want to enable it on all ports you can do it on the switch configuration mode and enter the command "spanning-tree portfast bpdufilter default".
Hope this short explanation about Root Guard, BPDU Guard and BPDU Filtering can help you understand about these features and how and when to apply them.
Root guard can be applied on certain ports and protects downstream switches from becoming root switches. If a port on the switch is configured witch root guard, when it receives a superior BPDU, it will discard the BPDU and will put that port into "root-inconsistent" state and goes back normal when the port does not receive superior BPDU information.
The command for configuring root guard is on the interface configuration with the command "spanning-tree guard root".
There could be a possibility that one accidently applies portfast on a port and puts another switching device on the other side. This can lead to a switching loop and can be prevented by applying BDPU guard. When a BPDU comes into a port with BPDU guard applied to it, the port will be shut down and will show the "err-disabled" information.
The command for configuring BPDU guard is on the interface configuration with the command "spanning-tree bpduguard enable" or if you want to enable it on all ports you can do it on the switch configuration mode and enter the command "spanning-tree portfast bpduguard default".
The last one is BPDU filtering. This feature is used when we don't want the port to be disabled when it receives a BPDU. It can be configured globally and by interface but have different characteristics when applied:
1. If the BDPU filtering is applied globally, the portfast enabled port will stop running portfast when it receives a BPDU packet.
2. If the BDPU filtering is applied on an interface only, the incoming BPDU on the port with BPDU filtering will be dropped silently and no BPDU packets will be returned.
The command for configuring BPDU guard is on the interface configuration with the command "spanning-tree bpdufilter enable" or if you want to enable it on all ports you can do it on the switch configuration mode and enter the command "spanning-tree portfast bpdufilter default".
Hope this short explanation about Root Guard, BPDU Guard and BPDU Filtering can help you understand about these features and how and when to apply them.
Root Link Query
One of the spanning tree protocols which is Backbonefast uses Root Link Query
(RLQ) to detect link outage in the network. In this blog I will try to explain how RLQ works.
Basically RLQ is like a ping request. The RLQ request is sent from the outgoing port of the inferior switch to its root bridge asking for a response. The RLQ request contains information on what this swicth believes to be the root bridge. The RLQ response is then received from the same port and the switch inspects the response and compares whether the information of the root bridge in the RLQ response is the same as what the switch has requested.
There are several actions taken by the peering switch that receives the RLQ request which are:
1. It inspects itself and is indeed the root switch
2. The receiving switch is not the root switch, and based on the information this switch has, the switch information on the RLQ request is also NOT the root switch. It considers another switch to be the root switch.
3. The receiving switch is not the root switch but (after comparing to its table) agrees with information on the RLQ request on the root switch. In that case, the receiving switch will forward the RLQ request to its superior bridge again.
Hop my information is clear enough.
(RLQ) to detect link outage in the network. In this blog I will try to explain how RLQ works.
Basically RLQ is like a ping request. The RLQ request is sent from the outgoing port of the inferior switch to its root bridge asking for a response. The RLQ request contains information on what this swicth believes to be the root bridge. The RLQ response is then received from the same port and the switch inspects the response and compares whether the information of the root bridge in the RLQ response is the same as what the switch has requested.
There are several actions taken by the peering switch that receives the RLQ request which are:
1. It inspects itself and is indeed the root switch
2. The receiving switch is not the root switch, and based on the information this switch has, the switch information on the RLQ request is also NOT the root switch. It considers another switch to be the root switch.
3. The receiving switch is not the root switch but (after comparing to its table) agrees with information on the RLQ request on the root switch. In that case, the receiving switch will forward the RLQ request to its superior bridge again.
Hop my information is clear enough.
Portfast, Uplinkfast, Backbonefast
In switching there are some terms that we must know for advanced spanning tree protocol settings which are portfast, uplinkfast and backbonefast.
Portfast is one of the simplest implementation and is usually studied when you take your CCNA exam. Portfast is used when a switch port is directly connected to a single host (e.g. PC). This feature allows a port which runs STP to go from Blocking mode (BLK) to Forwarding mode (FWD). Remember not to use this feature on connecting hubs, switches etc since it can cause a switching loop. You can enable portfast on an interface with the "spanning-tree portfast" command or you can enable it globally on the config mode of the switch and enter the "spanning-tree portfast default" command.
Uplinkfast is used when a switch is connected to another bridging device such as to another switch. If the root bridge goes down, the port that goes to the alternate port goes from BLK mode to FWD mode in a few seconds. Remember that uplinkfast cannot be configured on a ROOT switch. Besides that, uplinkfast is enabled globally, so you cannot enable it on a port only. If the original root port goes up again, then the switch uses the formula : (2xFwdDelay + 5 seconds) before the original root port goes up again.
A non root switch cannot be a root switch in times when the root switch goes down because of 2 reasons which are:
1. The switch priority will be set to 49.152 (remember the default priority is 32768)
2. STP Port Costs to the particular switch will be increased by 3000
Backbonefast is used on the core switches because it can recover the switches from an indirect link failure. This means that if the switch detects a failure on a link that is NOT directly connected to the core switch, this feature goes on. Backbonefast applies when the core switch receives an inferior BPDU. An inferior BPDU is a BPDU that is received by the secondary root switch on a inferior switch telling that he is the actually root switch. (it can be known that the link between the route switch and the secondary root switch is broken).
One thing to remember is that Backbonefast skips the MaxAge stage, therefore the delay in this feature is cut off from 50 seconds to 30 seconds (if you use the default settings). Another thing to remember is that if we want to use the backbonefast feature, we must enable it on ALL the switches in the network since they need to detect all the RLQ (root link query) request.
So, I hope this blog can help you define and differentiate spanning-tree terms between portfast, uplinkfast and backbonefast.
Portfast is one of the simplest implementation and is usually studied when you take your CCNA exam. Portfast is used when a switch port is directly connected to a single host (e.g. PC). This feature allows a port which runs STP to go from Blocking mode (BLK) to Forwarding mode (FWD). Remember not to use this feature on connecting hubs, switches etc since it can cause a switching loop. You can enable portfast on an interface with the "spanning-tree portfast" command or you can enable it globally on the config mode of the switch and enter the "spanning-tree portfast default" command.
Uplinkfast is used when a switch is connected to another bridging device such as to another switch. If the root bridge goes down, the port that goes to the alternate port goes from BLK mode to FWD mode in a few seconds. Remember that uplinkfast cannot be configured on a ROOT switch. Besides that, uplinkfast is enabled globally, so you cannot enable it on a port only. If the original root port goes up again, then the switch uses the formula : (2xFwdDelay + 5 seconds) before the original root port goes up again.
A non root switch cannot be a root switch in times when the root switch goes down because of 2 reasons which are:
1. The switch priority will be set to 49.152 (remember the default priority is 32768)
2. STP Port Costs to the particular switch will be increased by 3000
Backbonefast is used on the core switches because it can recover the switches from an indirect link failure. This means that if the switch detects a failure on a link that is NOT directly connected to the core switch, this feature goes on. Backbonefast applies when the core switch receives an inferior BPDU. An inferior BPDU is a BPDU that is received by the secondary root switch on a inferior switch telling that he is the actually root switch. (it can be known that the link between the route switch and the secondary root switch is broken).
One thing to remember is that Backbonefast skips the MaxAge stage, therefore the delay in this feature is cut off from 50 seconds to 30 seconds (if you use the default settings). Another thing to remember is that if we want to use the backbonefast feature, we must enable it on ALL the switches in the network since they need to detect all the RLQ (root link query) request.
So, I hope this blog can help you define and differentiate spanning-tree terms between portfast, uplinkfast and backbonefast.
Thursday, July 1, 2010
The 1-4-5 chord progression
Playing music can sometimes be difficult. There are hundreds of different chords to play and lots of patterns to remember. This can create a headache for beginners who wants to play music. However, playing music has not to be as difficult as it looks. A basic technique for playing chords is the 1-4-5 chord progression.
The 1-4-5 chord progression - also known as the Nashville Notation Sytem or the Figured Bass - is a basic pattern to remember when playing instrumental tools that relies on chords such as guitar and piano. You can play almost all songs with the 1-4-5 chord progression (although it sometimes sounds bored).
The pattern is to play chords with the 1st note chord, 4th note chord and the 5th note chord. So, if you play a song in C then the chords that you need to play is the 1st note (C), 4th note (F) and the 5th note (G).
Another example: If you play a song in G, then the chords that you should play varies between the G chord, C chord and D chord.
Now a song example. Everybody knows the kids song "Twinkle Twinkle Little Star". You can play this easily in the A chord:
A___________D__A
Twinkle, twinkle little star.
D____A____E______A
How I wonder what you are.
A__D______A_____E
Up above the world so high,
A____D_____A___E
Like a diamond in the sky.
A___________D__A
Twinkle, twinkle little star.
D____A____E______A
How I wonder what you are.
Try it by yourself the song above and try to implement this technique to other songs.
The 1-4-5 chord progression - also known as the Nashville Notation Sytem or the Figured Bass - is a basic pattern to remember when playing instrumental tools that relies on chords such as guitar and piano. You can play almost all songs with the 1-4-5 chord progression (although it sometimes sounds bored).
The pattern is to play chords with the 1st note chord, 4th note chord and the 5th note chord. So, if you play a song in C then the chords that you need to play is the 1st note (C), 4th note (F) and the 5th note (G).
Another example: If you play a song in G, then the chords that you should play varies between the G chord, C chord and D chord.
Now a song example. Everybody knows the kids song "Twinkle Twinkle Little Star". You can play this easily in the A chord:
A___________D__A
Twinkle, twinkle little star.
D____A____E______A
How I wonder what you are.
A__D______A_____E
Up above the world so high,
A____D_____A___E
Like a diamond in the sky.
A___________D__A
Twinkle, twinkle little star.
D____A____E______A
How I wonder what you are.
Try it by yourself the song above and try to implement this technique to other songs.
Minor Scale
I have written before about the major scale. Another basic theory that you must know is the counterpart of the major scale which is the minor scale.
The minor scale is another one of the diatonic scales (a scale with 7 intervals on an octave) which has the following pattern based on the range of the interval:
The minor scale is another one of the diatonic scales (a scale with 7 intervals on an octave) which has the following pattern based on the range of the interval:
whole:half:whole:whole:half:whole:whole
Check on my previous post on whole and half intervals.
Now the example:
If you play on a C scale, then the notes on a minor scale are C-D-Eb-F-G-Ab-B-C. On a piano, these notes would be all “white” notes except 2 notes which is the 3rd and the 6th note. These notes are "black" notes. If you play it on a D scale, then lower the 3rd and 6th note by half compared to the major scale note. So, if the major scale notes on D are D-E-F#-G-A-B-C#-D , then for the minor notes you have D-E-F-G-A-Bb-C#-D.
On a guitar the same counting method as the major scale except a different pattern of course. For a whole interval you should skip one fret and for a half interval you should play on the adjecent fret of the current note.
Hope this blog can explain and helps you a little but about the minor scale.
If you play on a C scale, then the notes on a minor scale are C-D-Eb-F-G-Ab-B-C. On a piano, these notes would be all “white” notes except 2 notes which is the 3rd and the 6th note. These notes are "black" notes. If you play it on a D scale, then lower the 3rd and 6th note by half compared to the major scale note. So, if the major scale notes on D are D-E-F#-G-A-B-C#-D , then for the minor notes you have D-E-F-G-A-Bb-C#-D.
On a guitar the same counting method as the major scale except a different pattern of course. For a whole interval you should skip one fret and for a half interval you should play on the adjecent fret of the current note.
Hope this blog can explain and helps you a little but about the minor scale.
The Advantage of Solar Energy over other Renewable Energy
There are several renewable energy sources such as Solar, Wind, Hydro, Biomass etc. All of the technologies has its own strength and weaknesses. In this blog, I want to explain about the advantages of Solar Energy.
Solar Energy has a main advantage over other technologies which is durable. It can be placed just outside your house and stand up to 30-40 years producing electricity for your needs which is longer than any other technology. Imagine yourself installing an array of PV cells at your rooftop. Just a one time installment and you have energy for 40 upcoming years of your life.
This technology can be durable because PV cells do not have any moving parts in it. This is really a striking point over any other techonology. In PV cells nothing moves or generates friction between parts such as in hydro or wind energy which uses generators and magnets to create electricity. The only thing that moves are the electrons generated by a wave of photons. This also means less costs and time for maintenance or breakdowns.
Another advantage of solar energy is that it does not produce any pollution to the nature. Wind energy could have the potential to create sound pollution because of the swinging blades. Hydro energy could have the potential to harm the nature or surrounding environment in the water. Solar energy does not have a negative effect to the nature.
These are the main advantages of solar energy over other renewable technologies. However, it doesn't mean that this technology is the perfect technology. There are several still some main disadvantages of solar energy which I will cover in my next blog.
This technology can be durable because PV cells do not have any moving parts in it. This is really a striking point over any other techonology. In PV cells nothing moves or generates friction between parts such as in hydro or wind energy which uses generators and magnets to create electricity. The only thing that moves are the electrons generated by a wave of photons. This also means less costs and time for maintenance or breakdowns.
Another advantage of solar energy is that it does not produce any pollution to the nature. Wind energy could have the potential to create sound pollution because of the swinging blades. Hydro energy could have the potential to harm the nature or surrounding environment in the water. Solar energy does not have a negative effect to the nature.
These are the main advantages of solar energy over other renewable technologies. However, it doesn't mean that this technology is the perfect technology. There are several still some main disadvantages of solar energy which I will cover in my next blog.
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