Computer Certification

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!

I was reading The Big Moo: Stop Trying To Be Perfect and Start Being Remarkable this morning
and I’d recommend a copy of this to anyone who wants to improve their career and their future. And that’s all of us
right?


There was one particular line that really stood out to me: Betting on change is always the safest bet available. That describes life perfectly
but it also describes a career in Information Technology perfectly as well. There is no field in the world that has the constant and never-ending changes that IT does. And every single one of us can look at this as a massive opportunity for personal and professional growth.


Is that how you’re looking at it? I remember when I passed my first certification exam
the Novell CAN
back in 1997. Man
I thought I knew it all then! But I quickly learned that you’ve got to keep learning in IT. I also learned that if you’re willing to put in the work and make the sacrifices
there’s no other field with the limitless potential for growth and excellence.


Like everyone else
my career has had its ups and downs
but I always kept learning and growing. Today
I’ve got my dream job
working with studI was reading The Big Moo: Stop Trying To Be Perfect and Start Being Remarkable this morning
and I’d recommend a copy of this to anyone who wants to improve their career and their future. And that’s all of us
right?


There was one particular line that really stood out to me: Betting on change is always the safest bet available. That describes life perfectly
but it also describes a career in Information Technology perfectly as well. There is no field in the world that has the constant and never-ending changes that IT does. And every single one of us can look at this as a massive opportunity for personal and professional growth.


Is that how you’re looking at it? I remember when I passed my first certification exam
the Novell CAN
back in 1997. Man
I thought I knew it all then! But I quickly learned that you’ve got to keep learning in IT. I also learned that if you’re willing to put in the work and make the sacrifices
there’s no other field with the limitless potential for growth and excellence.


Like everyone else
my career has had its ups and downs
but I always kept learning and growing. Today
I’ve got my dream job
working with students and customers just like you – to help you create your own future.


The next 18 months are filled with endless possibilities
particularly with the rapid growth of VoIP and Microsoft Vista on the horizon. There will be those who rationalize their inertia
saying “I’ll never have to support those
so I don’t need to learn them."


There will also be those who see VoIP and Vista as enormous opportunities to learn and advance in their careers and their lives. These people will get started today
learning the fundamentals of Cisco and advancing their networking knowledge in order to be ready for opportunities as they come along.


You can’t start studying and learning when the opportunity arrives – you’ve got to be ready when opportunity knocks. If you’ve been putting off studying for a Cisco or other computer certification – and I know the summer is a really good time for putting off studying – get back on track today.


Because you never know what opportunities are going to come along – but you do know that when they do
you’ve got to be ready to take advantage. After all
opportunity really does knock only once!
ents and customers just like you – to help you create your own future.


The next 18 months are filled with endless possibilities
particularly with the rapid growth of VoIP and Microsoft Vista on the horizon. There will be those who rationalize their inertia
saying “I’ll never have to support those
so I don’t need to learn them."


There will also be those who see VoIP and Vista as enormous opportunities to learn and advance in their careers and their lives. These people will get started today
learning the fundamentals of Cisco and advancing their networking knowledge in order to be ready for opportunities as they come along.


You can’t start studying and learning when the opportunity arrives – you’ve got to be ready when opportunity knocks. If you’ve been putting off studying for a Cisco or other computer certification – and I know the summer is a really good time for putting off studying – get back on track today.


Because you never know what opportunities are going to come along – but you do know that when they do
you’ve got to be ready to take advantage. After all
opportunity really does knock only once!

Planning for success on the CCNA
CCNP
and other Cisco exams is much like taking a trip in your car. You've got to plan ahead
accept the occasional detour
and just keep on going until you get there. But what do you do before you get started?

Create a road map - for success.

If you were driving from one side of the country to another
you certainly wouldn't just get in your car and start driving
would you? No. You would plan the trip out ahead of time. What would happen if you just got in the car and started driving in the hope that you would someday arrive at your final destination? You would never get there
and you'd spend a lot of time wandering aimlessly.

Don't spend your study time and slow your progress by studying for a Cisco exam without planning the trip. Schedule your study time as you would an appointment with a client
and keep that appointment. Make sure that your study time is quality study - turn your TV
iPod
and cell off. If you hit a bump in the road and don't get your certification the first time you take the exam
regroup and create another plan. Study until you get to the point that on exam day
you know that you are already a CCNA or CCNP and you’re just there at the testing center to make it official.

The journey to success is not a straight line. When you look at a chart that shows a company's financial progress
the line never goes straight up. there are some ups and downs
but the overall result is success. The path to your eventual career and certification exam success may not be a direct one
but the important part is to get started - and to get any journey started
you've got to create a road map for a successful arrival at your destination.

Like TCP
BGP is connection-oriented. An underlying connection between two BGP speakers is established before any routing information is exchanged. This connection takes place on TCP port 179. As with EIGRP and OSPF
keepalive messages are sent out by the BGP speakers in order to keep this relationship alive.

Once the connection is established
the BGP speakers exchange routes and synchronize their tables. After this initial exchange
a BGP speaker will only send further updates upon a change in the network topology.

The IGP protocols that use Autonomous Systems
IGRP and EIGRP
require prospective neighbors to be in the same AS. This is not true with BGP. Routers can be in different Autonomous Systems and still exchange routes. The BGP neighbors do not have to be directly connected
and often are not
but do need to be able to reach the IP addresses they use in their neighbor statements.

A BGP peer that is in the same AS is referred to as an Internal BGP (iBGP) Peer
where a BGP peer in another AS is an External BGP (eBGP) Peer.

A sample iBGP configuration:

Router bgp 100

Neighbor 10.1.1.2 remote-as 100


A sample eBGP configuration:

Router bgp 100

Neighbor 10.1.1.2 remote-as 200

Cisco recommends that eBGP peers be directly connected
where iBGP peers generally will not be.

Before we get too much farther into BGP theory
let’s get a configuration started. You’ll use the router bgp command to configure a router as a BGP speaker. Right after that
the neighbor command will be used to identify this BGP speaker’s potential neighbors. (The terms "peer" and "neighbor" are interchangeable in BGP
but it's the neighbor statement that is used to statically define neighbors. BGP is not capable of discovering neighbors dynamically.)

R1(config-router)#neighbor 172.12.123.3 remote-as 200

While almost all of the neighbor options are just that -- optional -- you do have to specify the BGP AS of the remote router. BGP has no mechanism to dynamically discover neighbors. Remember
BGP speakers do not have to be in the same AS to become peers. To verify that the remote BGP speaker has become a peer
run show ip bgp neighbor.


R1#show ip bgp neighbor

BGP neighbor is 172.12.123.3
remote AS 200
external link

BGP version 4
remote router ID 0.0.0.0

BGP state = Active

Last read 00:01:39
hold time is 180
keepalive interval is 60 seconds

Received 0 messages
0
notifications
0
in queue

Sent 0 messages
0
notifications
0
in queue

Route refresh request: received 0
sent 0

Default minimum time between advertisement runs is 30 seconds

The output here can be a little misleading the first time you read it. The first highlighted line shows 172.12.123.3 is a BGP neighbor
is located in AS 200
and is an external link
indicating that the neighbor is in another AS entirely. The second highlighted line shows the BGP state as Active. This sounds great
but it actually means that a BGP peer connection does not yet exist with the prospective neighbor.

So even though the show ip bgp neighbor output indicated that this is an Active neighbor relationship
that’s not as good as it sounds. Of course
the reason the peer relationship hasn’t been established is that we haven’t configured R3 yet!


R3(config)#router bgp 200
R3(config-router)#neighbor 172.12.123.1 remote-as 100

Verify the peer establishment with show ip bgp neighbor:

R3#show ip bgp neighbor

BGP neighbor is 172.12.123.1
remote AS 100
external link

BGP version 4
remote router ID 172.12.123.1

BGP state = Established
up for 00:01:18

Last read 00:00:17
hold time is 180
keepalive interval is 60 seconds

Local host: 172.12.123.3
Local port: 179 (BGP uses TCP Port 179)

Foreign host: 172.12.123.1
Foreign port: 11007
The peer relationship between R1 and R3 has been established.

Now that you know how the neighbor relationship itself is built
you need to start learning the many options of the neighbor command. You’ll have to master these to become a CCNP and CCIE!

Passing the BSCI exam and earning your CCNP is all about knowing the details
and when it comes to EIGRP SIA routes
there are plenty of details to know. A quick check in a search engine for "troubleshoot SIA" will bring up quite a few matches. Troubleshooting SIA routes is very challengin in that there's no one reason they occur.

View the EIGRP topology table with the show ip eigrp topology command
and you'll see a code next to every successor and feasible successor. A popular misconception is that we want these routes to have an "A" next to them - so they're active. That's what we want
right? Active routes sound good
right?

Well
they sound good
but they're not. If a route shows as Active in the EIGRP topology table
that means that DUAL is currently calculating that route
and it's currently unusable. When a route is Passive ("P)
that means it's not being recalculated and it's a usable route.

Generally
a route shown as Active is going to be there for a very short period of time by the time you repeat the command
hopefully that Active route has gone Passive. Sometimes that doesn't happen
though
and the route becomes SIA - Stuck In Active.

A route becomes SIA when a query goes unanswered for so long that the neighbor relationship is reset. From experience
I can tell you that troubleshooting SIA routes is more of an art form than a science
but there are four main reasons a route becomes SIA:

The link is unidirectional
so the query can't possibly be answered.

The queried router's resources are unavailable
generally due to high CPU utilization.

The queried router's memory is corrupt or otherwise unable to allow the router to answer the query.

The link between the two routers is of low quality
allowing just enough packets through to keep the neighbor relationship intact
but not good enough to allow the replies through.

To sum it up
routes generally become SIA when a neighbor either doesn't answer a query
or either the query or reply took a wrong turn somewhere. I told you it wasn't the easiest thing to troubleshoot!

To pass the CCNP exams
you’ve got to master Quality of Service
and the first step in doing so is knowing the differences between the different QoS types.

Now this being Cisco
we can't just have one kind of QoS! We've got best-effort delivery
Integrated Services
and Differentiated Services. Let's take a quick look at all three.

Best-effort is just what it sounds like - routers and switches making their "best effort" to deliver data. This is considered QoS
but it's kind of a "default QoS". Best effort is strictly "first in
first out" (FIFO).

An entire path from Point A to Point B will be defined in advance when Integrated Services are in effect. Integrated Services is much like the High-Occupancy Vehicle lanes found in many larger cities. If your car has three or more people in it
you're considered a "priority vehicle" and you can drive in a special lane with much less congestion than regular lanes. Integrated Services will create this lane in advance for "priority traffic"
and when that traffic comes along
the path already exists. Integrated Services uses the Resource Reservation Protocol (RSVP) to create these paths. RSVP guarantees a quality rate of service
since this "priority path" is created in advance.

Integrated Services is defined in RFC 1613. Use your favorite search engine to locate a copy online and read more about this topic. It's a good idea to get into the habit of reading RFCs!

Of course
if you've got a lot of different dedicated paths being created that may or not be used very often
that's a lot of wasted bandwidth. That leads us to the third QoS model
the Differentiated Services model. Generally referred to as DiffServ
there are no advance path reservations and there's no RSVP. The QoS policies are written on the routers and switches
and they take action dynamically as needed. Since each router and switch can have a different QoS policy
DiffServ takes effect on a per-hop basis rather than the per-flow basis of Integrated Services. A packet can be considered "high priority" by one router and "normal priority" by the next.

Believe me
this is just the beginning when it comes to Quality of Service. It's a huge topic on your exams and in the real world's production networks
and as with all other Cisco topics
just master the fundamentals and build from there - and you're on your way to CCNP exam success!

Passing the BCMSN exam and getting one step closer to the CCNP certification means learning and noticing details that you were not presented with in your CCNA studies. (Yes
I know – you had more than enough details then
right?) One protocol you’ve got to learn more details about is VTP
which seemed simple enough in your CCNA studies! Part of learning the details is mastering the fundamentals
so in this tutorial we’ll review the basics of VTP.


In show vtp status readouts
the "VTP Operating Mode" is set to "Server" by default. The more familiar term for VTP Operating Mode is simply VTP Mode
and Server is the default. It's through the usage of VTP modes that we can place limits on which switches can delete and create VLANs.

In Server mode
a VTP switch can be used to create
modify
and delete VLANs. This means that a VTP deployment has to have at least one switch in Server mode
or VLAN creation will not be possible. Again
this is the default setting for Cisco switches.

Switches running in Client mode cannot be used to create
modify
or delete VLANs. Clients do listen for VTP advertisements and act accordingly when VTP advertisements notify the Client of VLAN changes.

VTP Transparent mode actually means that the switch isn't participating in the VTP domain as Servers and Clients do. (Bear with me here.) Transparent VTP switches don't synchronize their VTP databases with other VTP speakers. They don't even advertise their own VLAN information! Therefore
any VLANs created on a Transparent VTP switch will not be advertised to other VTP speakers in the domain
making them locally significant only. (I know you remember that phrase from your CCNA studies!)

Devices running VTP Transparent mode do have a little something to do with the other switches in the VTP domain
though. When a switch running in Transparent mode receives a VTP advertisement
that switch will forward that advertisement to other switches in that VTP domain.

Configuring switches as VTP Clients is a great way to “tie down” VLAN creation capabilities to switches that are under your physical control. However
this occasionally leads to a situation where only the VTP clients will have ports that belong to a given VLAN
but the VLAN still has to be created on the VTP server. (VLANs can be created and deleted in transparent mode
but those changes aren't advertised to other switches in the VTP domain.)


In the next BCMSN tutorial
we’ll take a look at the details of VTP.

To pass the CCNA exam and earn this important certification
you’ve got to know switching inside and out. While you’re learning all the basic switching theory
make sure to spend some time with the one of three switching modes Cisco routers can use.

Store-and-Forward is exactly what it sounds like. The entire frame will be stored before it is forwarded. This mode allows for the greatest amount of error checking
since a CRC (Cyclical Redundancy Check) is run against the frame before it is forwarded. If the frame contains an error
it is discarded. If there’s no problem with the frame
the frame is then forwarded to its proper destination.


While store-and-forward does perform error checking
the delay in processing the frame while this error check is run results in higher latency than the other modes you’re about to read about. The latency time can also vary
since not all frames are the same size.

Cut-through switching copies only the destination MAC address into its memory before beginning to forward the frame. Since the frame is being forwarded as soon as the destination MAC is read
there is less latency than store-and-forward. The drawback is that there is no error checking.

There is a middle ground
fragment-free switching. Only part of the frame is copied to memory before it is forwarded
but it’s the first 64 bytes of the frame
not just the destination MAC. (Why? Because if there is a problem with the frame
it’s most likely in the first 64 bytes.) There is a little more error checking than cut-through
but not as much latency as with store-and-forward.

Note that the latency of both cut-through and fragment-free is fixed; these modes always look at the first six or 64 bytes
respectively. Store-and-forward's latency depends on the size of the frame.
Learning the similarities and differences between these modes is an often-overlooked part of CCNA studies. Spend some time studying this important CCNA topic – you’ll be glad you did!

CCNA and CCNP candidates who have their own Cisco home labs often email me about an odd situation that occurs when they erase a switch's configuration. Their startup configuration is gone
as they expect
but the VLAN and VTP information is still there!

Sounds strange
doesn't it? Let's look at an example. On SW1
we run show vlan brief and see in this abbreviated output that there are three additional vlans in use:

SW1#show vlan br


10 VLAN0010 active

20 VLAN0020 active

30 VLAN0030 active

We want to totally erase the router's startup configuration
so we use the write erase command
confirm it
and reload without saving the running config:

SW1#write erase

Erasing the nvram filesystem will remove all configuration files! Continue?

[confirm]

[OK]

Erase of nvram: complete


00:06:00: %SYS-7-NV_BLOCK_INIT: Initalized the geometry of nvram

SW1#reload

System configuration has been modified. Save? [yes/no]: n

Proceed with reload? [confirm]

The router reloads
and after exiting setup mode
we run show vlan brief again. And even though the startup configuration was erased
the vlans are still there!

Switch#show vlan br


10 VLAN0010 active

20 VLAN0020 active

30 VLAN0030 active

The reason is that this vlan and VTP information is actually kept in the VLAN.DAT file in Flash memory
and the contents of Flash are kept on a reload. The file has to be deleted manually.

There's a little trick to deleting this file. The switch will prompt you twice to ask if you really want to get rid of this file. Don't type "y" or "yes"; just accept the defaults by hitting the return key. If you type "y"
the router attempts to delete a file named "y"
as shown here:

Switch#delete vlan.dat

Delete filename [vlan.dat]? y

Delete flash:y? [confirm]

%Error deleting flash:y (No such file or directory)



Switch#delete vlan.dat

Delete filename [vlan.dat]?

Delete flash:vlan.dat? [confirm]


Switch#

The best way to prepare for CCNA and CCNP exam success is by working on real Cisco equipment
and by performing lab tasks over and over. Repetition is the mother of skill
and by truly erasing your VLAN and VTP information by deleting the vlan.dat file from Flash
you'll be building your Cisco skills to the point where your CCNA and CCNP exam success is a certainty.