Switch Vs Route

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.  


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.





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

Redistribution and Patch control

And each is covered in some detail.


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.

Switch Operation (CAM TCAM and other switch tables)
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
Securing switch devices
Port security
Vlan ACL’s
Private VLANS
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.

Using Syslog while Studying in GNS3 (or indeed and cisco Lab)

I have been getting back in to my studying a lot lately and one thing I have found is the need to use a lot of debug commands so I can watch what is happening during things like routing updates and neighbour formation. One thing I do find though is that I am forever having to turn debug on and off, forgetting to do one or the other, and when it is on it clutters up the screen a breaks up the config I am entering making it difficult to read back.

Which got me thinking, I have used syslog servers a lot in the past, so why not send all the debugging out put to a syslog server and turn of logging to the console? This way I can have all the debugs in one place, and keep the console of the devices tidy so I can see what I am doing.

Now if you are doing this through GNS3 you will need a cloud connection so your PC can talk to your GNS3 network. If you are not sure how to do this there are lots of videos and walk though on the net, however the one below is one of the best I have found, very clear and complete.

How-To: Using the Cloud in GNS3 to Provide Internet Access from Matthew on Vimeo.

So once you have your cloud set up you then need to set up a simple GNS3 topology, Here I have set up 4 routers running OSPF connected through a switch as I am looking at the DR and BDR election process.

I have given R1 and R2 F0/1 address and, and the loopback adapter used by the cloud is Once the routers are booted and connected to the cloud, check they can ping the loop-back address (you may need to disable your fire wall on the loop-back connection.)

then of course you will need a SFTP server, in windows there are two good free choises, for a realy simple server that can run with out install try, http://tftpd32.jounin.net/tftpd32.html simple but does all you need, just make sure you disable dhcp and other none necessaries services in the settings. For a more complete tool try http://kiwisyslog.com/, they have a free syslog server offering that allows filtering and more.

In either case set it up and insure it is listing on the loopback interface, in the case of TFTP32d this is simple a case of choosing the interface from the drop down list.

Finale we need to change the logging setting of R1 and R2 to direct debugging message to the syslog server and not to the console. Remember debug messages are level 7 so we need to set console logging to level 6 or lower and trap logging to level 7. the following code will do just this from global config mode.

#logging console 6
#logging trap 7

So now we can enable the debugging and reset the neighbour relation ships to see what it looks like.

From the console

So not much there apart from we see the neighbours bounce as I clear the OSPF process.

So how about on the syslog server?? 

So here are all our debug messages, for us to scroll through and review at our leisure, If you have something like Kiwicat syslog server you could filer them in to views, based on device that sent it, or text with in message, ect.

You need to make sure of course that you either have the device connected directly to the syslog server network, or it has a route to get there. Directly connected is always best of course as you will insure that as long as that interface on the device is up you will catch all messages. On real hardware simply use a spare switch or create a separate VLAN and do exactly the same thing.

I have found for large labs this works great, indeed for testing setups for clients its great as well. once you have insured the correct debugging is enabled you can walk though test scripts and plans, safe in the knowledge that you have a full detailed log of every thing that has happened.

Simple to set up and hopefully some of you will find it useful.



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


Spanning Tree enhancements (Backbone Fast)

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.



In what I think will be the last post on EIGRP (I will save redistribution between routing protocols for another time), I want to look at what is needed to insure EIGRP runs smoothly over NBMA (non broadcast multi access) networks such as Frame Relay.

As I have covered before EIGRP relies on multicast hello messages to form its neighbour relationships, but NBMA network by default do not forward any broadcast or multicast traffic. So this is the first issue with getting it up and running.

To achieve this you have two choices. First you could if you wished manually set up the neighbours. Going under the EIGRP AS process you can issues the command

router#(config-router)#neighbor <IP ADDRESS>  <INT ID>

This need to be done on both ends of the link, and will change the interface from sending out multicast hello messages to directed broadcasts, so you need to enter addition neighbour statements for each neighbour you want to connect to.

For some NBMA networks (such as frame relay) CISCO has added in a command to allow the router to forward the broadcasts over the link. It does this by sending a copy of the multicast/broadcast packet to each neighbouring router. This is needed for multipoint networks

#router(config-inf)#frame-relay  map IP <neighbour IP>  <Local DLCI>  broadcast

Now rather than using the neighbour command the router will forward any EIGRP hello’s across the to any routers configured with the broadcast command in there mapping.

Either of these two methods will allow the formation across the NBMA.

However there’s is now the issue of split horizon. Imagen you have a central router connected to two remote routers, each with there own routing tables. Split horizon says that a route update received on an interface will not be sent back out that same interface.  This means that if one of the remote routers sends an update to the central router, it will not then be relayed over to the second remote router.. To allow this to happen you must manually disable split horizon (it is disabled by default on a physical interface but enabled on sub interfaces). The command is as follows

router(config-inf)#no ip split-horizon eigrp <AS>

So recapping there is two parts to this, first allowing the hello messages across the NBMA, and then insuring the updates get copied to all routers.

These problems mainly occur when using the multipoint method, using point to point (although requiring more IP addresses and subnetting) avoids both the split horizon issue and the non broadcast issues, and is generally the recommended option.


Simulating PC’s in GNS3

One of my main issues with GNS3 for studying that there are no end devices (PC’s) by default. Ok you can set up loopback interfaces, or add in an extra router and just configure one interface with an IP to act an an end device. But loopbacks don’t really show well when looking at the topology on screen, and adding a whole router (or creating a Qemu host) seems to be a bit much when all you need is a device that can reply to and send pings and/or run trace routes.

However the other day I came across VPCS! There is actuly a down load for this at the bottom of the GNS3 site (here), and it is so simple and easy to get up and running that I suggest any one who uses GNS3 has a look.

Simple unpack the zip file to a folder and then run the VPCS.exe file. this will by default create 3 PC’s with various IP addresses. However it is simple to configure it to create up to 9 separate simulated PC’s with either static or DHCP assigned addresses. These can then be easily added to GNS3 topologies by adding a cloud (see later in the post for how to make them look pretty), and configuring a NIO_UDP port. Really it takes all of 10 seconds to get it up and running. Then you have a simple CLI interface to the “virtual PC’s” where you can run Pings and Traceroutes.

There is only one thing to be careful of. You may find the cygwin1.dll file is a different version in GNS3 as to the version that comes with VPCS and this can casue issues. I find the simple way around this is to delete the cygwin1.dll file from the VPCS folder, and then copy the one form the GNS3 program folder in. (even better copy it to a system path such as c:\window\system32, and then delete it from both folders, and just keep a single copy they both can use).

The following is a link to a blog post on www.firstdigest.com with a video tutorial of how to set it up. (GNS3 and VPCS Video)

Now your GNS3 topology’s can actuly look and run like proper topologies and with our the overheads of emulating entire routers of operating systems. OK if you really need more complex hosts then there are other ways to do that, but for simple end devices that can ping and be pinged it is GREAT!!


Spanning Tree enhancements (Uplink fast)

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..


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


CCNP ROUTE (Part 9 EIGRP Authentication)

Seeing as we just finished up a simple EIGRP lab, it seems a good opportunity to add one more simple thing in to the mix.

At the moment any one could in theory add a router in to the network, sniff for packets to determined the AS number we are running EIGRP on, and start advertising routes and forming neighbours. This is not something we want to happen, even if not a malicious attack a rogue router sending EIGRP hellos and updates could cause havoc with a network.

So like all good network administrators it is important to secure EIGRP against such happenings. This is achieved in EIGRP by means of md5 authentication and key-chains.

The theory works some thing like this. All routers must be in time with each other, if possible a time protocol such as NTP should be used, but you could also set the clocks manually (just remember to redo this after a reboot as the router will lose its time). One they are in sync we can set up the key-chains. Each key chain has a number, time frame in which it will be sent and a time frame in which it will be accepted, along with the actual key value its self.

For a key to be accepted as valid by a router, when it receives it, the key-chain number and the key value must match on both devices, and it must be revived with in the accepted time frame. Below is a generic template for setting up a key-chain.

Router(config)#key chain

The idea is that you may use one key each month for example, with the accept and send time of the next key in the chain over lapping with the last slightly (if you have NTP the over lap can be a matter of seconds due to the increased sync of the routers clocks), to insure the neighbours do not get dropped during the change over of keys.

Once the keys have been set up you apply them to the interface which is sending out EIGRP updates as below.

interface FastEthernet0/0
 ip authentication mode eigrp <AS> md5
 ip authentication key-chain eigrp <AS> <keychain name>

I have set this up in the GNS3 lab here.. to get it working you will need to set the time on router 1 to 00:00:00 24th october 2010 (#clock set 00:00:00 24 october 2010), and then on router 2 remove and re-add the NTP server. This will sync up the clocks to the correct time for the configured key chains. You should then see the neighbours come up. Running a #Debug eigrp packets, and you will see the hellos and updated getting sent with the md5 authentication.


CCNP SWITCH (retake)

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.