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Posts Tagged ‘CCNA’

More CCNA and CCNP candidates than ever before are putting together their own home labs, and there’s no better way to learn about Cisco technologies than working with the real thing. Getting the routers and switches is just part of putting together a great CCNA / CCNP home lab, though. You’ve got to get the right cables to connect the devices, and this is an important part of your education as well. After all, without the right cables, client networks are going to have a hard time working!

For your Cisco home lab, one important cable is the DTE/DCE cable. These cables have two major uses in a home lab. To practice directly connecting Cisco routers via Serial interfaces (an important CCNA skill), you’ll need to connect them with a DTE/DCE cable. Second, if you plan on having a Cisco router act as a frame relay switch in your lab, you’ll need multiple DTE/DCE cables to do so. (Visit my website’s Home Lab Help section for a sample Frame Relay switch configuration.) Read the rest of this entry »

When you’re studying for the CCNA and CCNP exams, you’ve got a lot of different choices when it comes to training. One popular choice is choosing one of the many “boot camps” and five-day in-person courses that are out there. I’ve taught quite a few of these, and while many of them are good, they do have drawbacks.

Of course, one is cost. Many employers are putting the brakes on paying for CCNA and CCNP boot camps, and most candidates can’t afford to pay thousands of dollars for such a class. Then you’ve got travel costs, meals, and having to possibly burn your own vacation time to take the class. Add in time away from your family and boot camps become impractical for many CCNA / CCNP candidates.

Another issue is fatigue. I enjoy teaching week-long classes, but let’s face facts – whether you’re training for the CCNA or CCNP exams, you’re going to get a lot of information thrown at you in just a few days. You’re going to be mentally and physically exhausted at the end of the week, and that’s when some boot camps actually have you take the exam! You’ve got to be refreshed and rested when you take the exam to have your best chance of success.
Read the rest of this entry »

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

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OSPF is a major topic on both the CCNA and CCNP exams, and it’s also the topic that requires the most attention to detail. Where dynamic routing protocols such as RIP and IGRP have only one router type, a look at a Cisco routing table shows several different OSPF route types.
R1#show ip route
Codes: C – connected, S – static, I – IGRP, R – RIP, M – mobile, B – BGP
D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2
E1 – OSPF external type 1, E2 – OSPF external type 2, E – EGP
In this tutorial, we’ll take a look at the difference between two of these route types, E1 and E2.
Route redistribution is the process of taking routes learned via one routing protocol and injecting those routes into another routing domain. (Static and connected routes can also be redistributed.) When a router running OSPF takes routes learned by another routing protocol and makes them available to the other OSPF-enabled routers it’s communicating with, that router becomes an Autonomous System Border Router (ASBR).
Let’s work with an example where R1 is running both OSPF and RIP. R4 is in the same OSPF domain as R1, and we want R4 to learn the routes that R1 is learning via RIP. This means we have to perform route redistribution on the ASBR. The routes that are being redistributed from RIP into OSPF will appear as E2 routes on R4:
R4#show ip route ospf
Read the rest of this entry »