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Posts Tagged ‘ccnp’

BGP is one of the most complex topics you’ll study when pursuing your CCNP, if not the most complex. I know from personal experience that when I was earning my CCNP, BGP is the topic that gave me the most trouble at first. One thing I keep reminding today’s CCNP candidates about, though, is that no Cisco technology is impossible to understand if you just break it down and understand the basics before you start trying to understand the more complex configurations.

BGP attributes are one such topic. You’ve got well-known mandatory, well-known discretionary, transitive, and non-transitive. Then you’ve got each individual BGP attribute to remember, and the order in which BGP considers attributes, and what attributes even are… and a lot more! As with any other Cisco topic, we have to walk before we can run. Let’s take a look at what attributes are and what they do in BGP.

BGP attributes are much like what metrics are to OSPF, RIP, IGRP, and EIGRP. You won’t see them listed in a routing table, but attributes are what BGP considers when choosing the best path to a destination when multiple valid (loop-free) paths exist.

When BGP has to decide between such paths, there is an order in which BGP considers the path attributes. For success on the CCNP exams, you need to know this order. BGP looks at path attributes in this order:

Highest weight (Cisco-proprietary BGP value)
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To earn your CCNA or CCNP certification, you’ve got to understand the basics of trunking. This isn’t just a CCNA topic – you must have an advanced understanding of trunking and etherchannels to pass the BCMSN exam and earn your CCNP as well. Before we address those advanced topics, though, you need to master the fundamentals!

A trunk allows inter-VLAN traffic to flow between directly connected switches. By default, a trunk port is a member of all VLANs, so traffic for any and all VLANs can travel across this trunk. That includes broadcast traffic!

The default mode of a switch port does differ between models, so always check your documentation. On Cisco 2950 switches, every single port is in dynamic desirable mode by default, meaning that every port is actively attempting to trunk. On these switches, the only action needed from us is to physically connect them with a crossover cable. In just a few seconds, the port light turns green and the trunk is up and running. The command show interface trunk will verify trunking.

How does the receiving switch know what VLAN the frame belongs to? The frames are tagged by the transmitting switch with a VLAN ID, reflecting the number of the VLAN whose member ports should receive this frame. When the frame arrives at the remote switch, that switch will examine this ID and then forward the frame appropriately.

There are two major trunking protocols you must understand and compare successfully, those being ISL and IEEE 802.1Q. Let’s take a look at the details of ISL first.

ISL is a Cisco-proprietary trunking protocol, making it unsuitable for a multivendor environment. That’s one drawback, but there are others. ISL will place both a header and trailer onto the frame, encapsulating it. This increases the overhead on the trunk line.

You know that the default VLAN is also known as the “native VLAN”, and another drawback to ISL is that ISL does not use the concept of the native VLAN. This means that every single frame transmitted across the trunk will be encapsulated. Read the rest of this entry »

To pass the Cisco CCNA and CCNP certification exams, as well as becoming a world-class networker, you’ve got to know how and when to use floating static routes. And if you’re wondering what makes them “float” — read on!

In this example, R1 and R2 are running OSPF over a Frame Relay network, 172.12.123.0 /24. They’re also connected by a BRI ISDN link, 172.12.12.0 /24. R1 is advertising a loopback network, 1.1.1.1 /32, via OSPF. We want R2 to have a route to that loopback even if the frame goes down – and here, we’ll use a floating static route to make that happen.

R2 sees the route to the loopback interface via OSPF, and can ping that interface successfully.

R2#show ip route ospf

1.0.0.0/32 is subnetted, 1 subnets

O 1.1.1.1 [110/65] via 172.12.123.1, 00:00:02, Serial0

R2#ping 1.1.1.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 68/68/68 ms

This is when it’s important to know your administrative distances…. or at least know where to look to see them! The AD of OSPF is 110, which means we can configure a static route to 1.1.1.1 /32, and as long as the AD of the static route is higher than 110, it won’t be used unless the OSPF route leaves the routing table. That’s why this kind of route is called a “floating” static route – the route “floats” in the routing table and isn’t seen unless the primary route leaves the table.

You learned how to write a static route in your CCNA studies, but you also remember that the default AD of a static route is either 1 or 0… and both of those values are less than 110! To change the AD of a static route, configure the desired distance at the end of the ip route command.

R2(config)#ip route 1.1.1.1 255.255.255.255 bri0 ?

Distance metric for this route

A.B.C.D Forwarding router’s address

name Specify name of the next hop

permanent permanent route

tag Set tag for this route

R2(config)#ip route 1.1.1.1 255.255.255.255 bri0 111

The static route has an AD that’s only one higher than that of the OSPF route, but that’s enough to make the route “float” and not yet be seen in the routing table.

R2#show ip route

1.0.0.0/32 is subnetted, 1 subnets

O 1.1.1.1 [110/65] via 172.12.123.1, 00:06:44, Serial0

172.12.0.0/24 is subnetted, 2 subnets

C 172.12.12.0 is directly connected, BRI0

C 172.12.123.0 is directly connected, Serial0

Let’s see the effect on the routing table when the Serial0 interface is closed.

R2(config)#int s0

R2(config-if)#shutdown

12:04:53: %OSPF-5-ADJCHG: Process 1, Nbr 172.12.123.1 on Serial0 from FULL to DOWN, Neighbor Down: Interface down or detached

12:04:55: %SYS-5-CONFIG_I: Configured from console by console

12:04:55: %LINK-5-CHANGED: Interface Serial0, changed state to administratively down
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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.”

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