Tag Archives: SWITCH

Switch Vs Route

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I see a lot of people as Questions such as what is harder the Switch or the Route exam, Or Why is the Route coarse materials so much larger than the Switch, does this mean there is less to it? 642-902 ROUTE  642-813 SWITCH

So having now completed both foundation and cert guides here are my views.

First the two have very different goals that they are trying to teach, and approach things in the same way as you would likely see in the Real world.  

ROUTE

In the real world generally Routing protocols stand apart, while you may run EIGRP and OSPF with in he same organisation, most people will keep them separate and they will only interact at the borders. And there are only 3/4 major routing protocals that you woudl expect to see.

RIP,

OSPF,

EIGRP and

BGP.

While there are others these are the common ones that most people will using there jobs. So the ROUTE exam deals with these along with redistributing the routes between them.

This give the following Topics to study

EIGRP
OSPF
BRP
Redistribution and Patch control
IPv6

And each is covered in some detail.

SWITCH

On the other hand has many more topics, and in the case of switch’s many of these will be run on the same devices across the entire network, (eg. VLANS, Spanning Tree, ACL’s Switch Security) so the number of topics in the SWITCH exam is much higher. They are covered in less depth individual than the topics in ROUTE, however you are expected to understand how they all work together and how issues configuring one can cause issues in others.

A partial list of topics covered in switch are.

VLANS
Switch Operation (CAM TCAM and other switch tables)
CEF
VLANS
STP (all modes)
STP enhancements like BPDU guard and ULD detection.
Ether channels and port channels
Multilayer switches
High availabilities (redundet router and redundant supervisors)
IP telephony
Wireless
Securing switch devices
Port security
ACL’s
Vlan ACL’s
Private VLANS
QOS
and the list goes on….

So the question of what one is hard and what one is easy will very much depend on the person taking them, and the current experience they have. Many people do seem to find the Routing exam nicer and I think this is because you can take each topic seperatly and concentrate with out worrying about the rest. While I enjoyed Switch as it was lots of bite size chunks to get stuck in to.

People also ask what one to take first, honestly I don’t think knowing either one will help learning the other one, as long as you have  a decent understanding of networks. Personal I would first go for the one you have most experience with, and get it under your belt first.

The only one I would suggest leaving till last is the Trouble Shoot as this assumes you have knowlage of both Switch and Route.

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CCNP SWITCH EXAM

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Well I was going through emails a few weeks back and came across an email for cisco with an exam voucher for the switch exam. (from back last year when the exam crashed on me). Checking it out the date was 17th march!!! (today).

With new job and baby, i havent had much time to study, as the lack of posts should tell you. But rather than wast the voucher i booked the exam and dusted of the books. After 2 weeks of sporic studying i sat the exam.

I think i might of actuly punched the air when i saw i passed at the end!!! And actuly with a half decent score.

But even better I now feel like i have the bug again, work has taken me in a slightly different direction. Still network but managment and not quite as hands on. Time to change that I and get CCNP done and dusted.

Hope that will also mean more posts as well. 🙂

Take care all

DevilWAH

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Spanning Tree enhancements (Backbone Fast)

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Last time I look at the spanning tree enhancment I covered uplink fast, this is for detecting when a directly connected root port fails and switching over to a back up in the shortest time possible. But what happens if the link that fails is not directly connected. When a switch loses its link back to the root and needs to find an alternate path back. In the digram below switch B is blocking its port to Switch A to prevent loops.

The question is what happens if the link between Switch A and the Root fails? Well with out backbone fast the following sequince takes place.

When the link fails Switch A will no longer be receiving BPDU’s from the root, the direct link is down and the port on switch B is blocking so not forwarding BPDU’s.

Switch A will assume it is the new root and start to send BPDU’s towards Switch B declaring it is the root. However Switch B will see these are inferior BPDU’s to the on it has stored for the port connected to Switch A and ignore them.

This will continue to happen until the BPDU on the port times out, after which the port will go in to the listing and learning state before starting to forward. This is 20 seconds (max age timer) plus 2 x 15 seconds for the listing and learning stage. so a total of 50 seconds.

The idea behind Backbone fast is to cut this by 20 seconds by bypassing the max age timer. The idea is that if Switch B can confirm it still has a link back it’s current known root switch, then it can ignore the max age timer and start the listing and learning process on a port immidatly it receives a inferior BPDU.

Once backbone fast is enabled, when a switch receives a inferior BPDU on one of its ports, it will send a RLQ (root link query) packet out all it’s non designated ports including its root port (so all ports that lead back to the root). If it receives a RLQ response (these are sent from the bridge) then it knows it still has a link to root. It can then age out the port it is receiving the inferior BPDU’s on and start the listing learning stages. If it does not receive any responses then the switch has lost connectivity to the rest of the network and needs to start recomputing the whole STP.

Either way the max age time has been eliminated and 20 seconds have been shaved of the re convergence / fail over time.

Just like Uplink fast Backbone fast is configured on a switch level with the following command.

Switch(config)#spanning-tree backbonefast

and it needs to be configured on all switches on the network.

CISCO’s document HERE explains it in much more details and more examples.

DevilWAH

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Spanning Tree enhancements (Uplink fast)

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In my last job, I jumped straight in to configuring Rapid spanning Tree, I mean what is the point of running Standard STP with its 50second fail over times, when you can enable Rapid-STP and gain sub second fail over??

Well if you want to pass your CCNP SWITCH you need to know it, and you need to know how to configure the enhancements. Actually having read through them and labed them up. They do help in understanding how STP works and how the original protocol was improved in a number of way, before CISCO took all the enhancements and came up with Rapid-STP.

Over the next few post I will be covering all of the basic enhancements, including uplinkfast, backbone fast, portfast, loopguard etc..

Uplinkfast.

This is normaly configured on access switchs that have two links back to the root, in these cases after the initial STP algrothem has run, one of the ports (lowest priority back to the root bridge) will be designated as the root port, while the other will be blocked. See digram below.

Now with standard STP, if the active link fails, the switch sees the root port link has fail and as it is receiving root BPDU’s on the backup blocked port it starts to bring this up. However with out uplink fast enabled this requires the port to go through the listening and learning stages. By default this is 30 seconds of outage, and even with best STP tuning it still results in a 14 second outage.

However with uplink fast configured the switch keeps track of the blocked ports that point back to bridge and forms them in to an “uplink group”. Now if the primary link goes down the switch can pick the next best root port and immediately places it in the forwarding mode as this will not be creating a loop. This creates an almost instant fail over of the primary link. However switch CAM tables will now be out of sync, which could result in frames being sent down the wrong links. To sort this out, the switch creates dummy frames with source address from its CAM table, and destination of multicast address. this updates the other switches on the network.

Now when the link comes back up, the switch waits twice the forward delay + 5 seconds before it switches back over. This allows the core switch at the other end of the link to have time to run through STP and start forwarding on the port.

And that’s Uplink fast. Providing a method to allow instant fail over of directly redundant links towards the root.

Configuration is very simple and is carried out in global config mode.

Switch(config)Spanning-tree uplinkfast

DevilWAH

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CCNP SWITCH (retake)

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Well one more update. I have just checked my email and it seems that CISCO have responded to my comments about the SWITCH exam, and provided me with a re-sit voucher!

I think this says something about the quality of this exam as this is the second voucher I have received. The first was after the exam crashed on me. So hats of to CISCO for that. But this time no excuses, I still don’t think the course material if fit for its purpose, and does not really prepare you for the exam. But having sat it twice, I can’t claim I don’t know the focus, or where my weaknesses lay.

So my intention is to start my new job, get hold of some lab equipment and do some hard studying on the topics I need to. Then I think I should be able to pass this no problem. I did notice the First chapter of the ROUTE foundation seems to cover some of the planning topics nicely so I might flick through it a little more to see if there are any other relevant bits.

DevilWAH

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CCNP SWITCH update

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Well no luck I’m afraid 🙁

I agree with many of the other complaints about this exam, there seems to be a large number of questions that are not covered in the course material. I say that having read the foundation guide, cert guide, flash cards, and quick reference sheets.

CISCO have now made a statement that due to the high levels of complaints they will be reviewing the exam. So rather than wast time trying to pass it again. I will carry on my studies with the ROUTE course, which has had much better reviews, and come back to the SWITCH. Hopfuly by then CISCO will have sorted out the issues.

DevilWAH

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CCNP EXAM

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Well you might notice I am not updating and working on this blog much this week. Main reason is I have my CCNP SWITCH Exam coming up in a few days and hard at work revising!

I think I have it sorted just as long as no silly planning questions catch me out. It seems as though Cisco want you to “forget” things you know, and only come to the exam with the exact information in the book. It doesn’t matter if something is actual correct.. If its not in the book then you are not expected to know it.

config wise and technology I think I am fine though. I have been working on LAYER 2 for 5 years now so apart from a few small bits running through the book has been confirming lots of what I have learnt on the job over that time.

Still had time to play with the links in the blog and add a few more quotes.

And later I have a part 2 for trouble shooting with ACCL’s to write up, and a nice layer 3 NAT scenario to lab up soon to show a use for the “NAT enable” and virtual NAT interfaces. Hopefully get one of them at least sorted out this week, but if not I will do it after my celebrations (I’m thinking positive here) at passing.

DEVILWAH

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CCNP SWITCH CERT Updates

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Those of you doing you switch exam my be interested to read these. Some updates to the CCNP SWITCH cert guide have been released. It looks like they cover some the the Planning topics, and also in there is some SVI stuff.

There has been a lot of discussion over CISCO’s handling of the planing part of this exam, so hopefully this extra material will help clear it up. Having glanced though it I remain to be convinced, but I will reserve full judgement till later.

Enjoy the read and will be back later with a new CCNP topic to review.

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