Archive for May 2011
Recently I tried updating the IOS of a Catalyst 2960 using it’s web interface (Why I don’t know), but like everything Cisco GUI related (SDM) I had trouble getting it to actually work. The page would just sit their and cycle. So I found myself unable to update the IOS using the GUI. So I extracted the files within the .tar file to flash, told to the switch to boot using the newer IOS then issued the reload command.
Start off by putting the .tar file on your tftp server like any normal IOS upgrade, the key difference here is you want to use the following command:
archive tar /xtract tftp://192.168.1.5/c2960-lanbasek9-tar.122-58.SE1.tar flash:
The variables here are the IP Address of the TFTP server and the IOS image file name.
Next you will see the switch extract the files within the .tar file
The last thing you can see is the .bin IOS file. Now I issue the boot system command:
boot system flash:/c2960-lanbasek9-mz.122-58.SE1/c2960-lanbasek9-mz.122-58.SE1.bin
Note: The contents on the .tar file are extracted into a folder
This tells the switch to boot this particular IOS file. Then after you issue the reload command and the switch boots up you will see the switch loads with the new IOS version.
Roaming is just another expectation from your end users. They expect to walk freely around the office to conference rooms or far off cubicles and have their laptop or handheld remain connected while downloading files or in the middle of a conversation. If the roaming process is not quick enough then you could see conversations and clients gets dropped forcing them reconnect to the WLAN, and I can guarantee you your end users will be calling.
Now, if you have done a proper site survey and have solid data to work off of, you can control the roaming behavior of your WLAN clients. The reason you need to know the details of your wireless environment is because you are going to set RSSI limits concerning when your clients should begin looking for a new AP to associate to and, how quickly they are roam between access points. Just keep in mind, making these settings will effect the entire WLAN not just individual sections.
I would also like to mention your clients should be CCXv4 or higher to take advantage of these features. To see if your clients are CCXv4 compliant go to Monitor -> Clients -> click on the client in question.
On your Cisco Wireless LAN Controller, you want to navigate to Wireless -> 802.11a/n or 802.11b/g/n (depending on which frequency you want to customize) -> Client Roaming.
The first thing you need to do when you want to customize these settings is change the mode to custom this will allow you to edit the default values for the rest of the parameters.
The next option is minimum rssi. If a clients RSSI value is below this threshold it will not associate/authenticate to the access point, instead it will continue to look for a better signal from different access points. Valid values for this field are -80 through -90. The understanding is that the signal strength/quality will be so low reliable communication will not be established.
Next we have a setting called hysteresis this value is in dB and states how much stronger the signal of another access point has to be before a client decides to roam to it. This is useful if you have multiple access points in close proximity of each other or clients are moving between the edge of coverage of different access point. The higher this value the closer a client needs to be to an access point for it to associate to the second access point. Valid ranges are from 2 through 4 dB.
Now we have the scan threshold this is another RSSI value range. When the wireless client’s RSSI drops below this threshold the client will begin actively scanning for another access point it can receive a stronger signal from. Valid values range between -70 through -77.
The last field on the page is the transition time this is the amount of a client is going to see a better signal from neighboring access, before it attempts to associate to the second access point. The client determines a better signal when its RSSI drops below the scan threshold and it sees a signal from a neighboring access point higher than the scan threshold.
So all these factors do work together and can be customized for your environment. Normal data traffic is more forgiving since it’s not as delay sensitive, but If you have voice on your WLAN you will want to fine tune these settings to avoid dropped calls.
The PPDIOO network life cycle is something covered in the CCDA Exam objectives, and it provides a foundation on how/when a network should be implemented/designed/upgraded, of course this is a “best practice” type of thing, and people do not have to adhere to this life cycle but after you go over it a few times you have to agree it does make sense.
Prepare – This first prepare phase is not very technical at all. In fact the primary purpose of this phase to justify the network upgrade. This phase will involve speaking with high level managers to figure out what business goals the company has and what products could be used to provide that functionality to the business.
Example: If the customer wanted to implement a WLAN you would want to ask various questions. How many users will use the WLAN, what kind of people will utilizing the WLAN (employees/guests), what kind of applications will run on the WLAN, required WLAN security (Do any compliances have to be taken into consideration SOX, HIPPA, etc), what kind of speeds will be required, and so forth. Then you would want to look for products that meet the customer’s requirements.
Plan – In this phase, you would audit the existing network, now depending on the type of project would consider what you are going to look at. A few things you could look at in an audit is to inventory all affected networking devices checking on IOS versions, CPU/Memory utilization, look at the existing traffic via Netflow, link utilization, and so on making sure the network is in an already healthy state prior to making any changes and also to make sure the existing network can handle the additional project. Based on the results you will plan your implementation in this phase (who would have thought), step by step instructions including stop points to test the configuration and roll back plans in case things don’t go well. (Sure we hate to admit it but sometimes things happen out of our control)
Example: Your customer wants to implement an 802.11n WLAN, their are going to be a few things you want to verify (or plan for). Does the customer have 802.3at compliant switches to provide the required amount of power to operate 802.11n radios, does the customer have 1 GB switches to connect the AP’s to. It would also be wise to verify the network backbone will be able to handle the new traffic load. Also in this phase you will want to perform a site survey to locate sources of interference and existing WLANs.
Design – This is where some of the fun begins. Based on the business requirements (from the prepare phase) and the technical information (from the plan phase) you can begin designing the new network topology. The design you create in this phase will contain everything (IP Addressing, VLANs, Redundancy, Security, etc) you are going to need for the project and be referenced throughout the rest of the project.
Example: After performing the site survey, and inventorying the customer’s network you design a plan for customer to purchase multiple dual band 802.11n AP’s, the required amount of 802.3at compliant switches, dual WLC’s for redundancy, along with RADIUS software for security. You also provide and updated network diagram concerning how/where the new equipment will combine with their existing network.
Implement – As the title says, this is where the new equipment is configured and physically setup at the customer’s location. If you’ve spent a good amount of time in the plan phase, the implement phase is usually carried out word for word as described in the documentation. It is also best practice to test the design at certain points this way if you find that something does work it’s usually easier to troubleshoot before too many changes are in the equation. (I emphasized this point more then once for a reason.)
Example: The new switches, AP’s, RADUIS software have been purchased and have arrived at the customers site. You follow the implementation plan and begin the installation of the new switches, then setup the two WLCs, deploy the AP’s, verifying the AP’s power up and join the WLC as each of them are deployed, also testing WLAN client connectivity. You then proceed to setup the RADIUS server and configure the WLC & AP’s to authenticate through the RADIUS server, then verify client connectivity again.
Operate – The network has been deployed and is being utilized by the end users. Appropriate support personnel are also monitoring and maintaining the network. In this phase it is acceptable to perform software updates and monitor the overall health of the devices/links.
Example: The WLAN is fully configured and now end users and guests are able to bring in their laptops and PDA’s. They successfully associate/authenticate to the WLAN and access the company resources, all the while being mobile.
Optimize – In this phase the network is proactively monitored & changed to improve performance or resolve issues. These changes can be minor or major depending on the amount and type of issues that occur. If the changes are big enough this life cycle could begin again back at the prepare phase.
Example: WLAN users in a particular location are experience slow wireless performance and are disconnected from the WLAN multiple times throughout the day. Support personnel show up with a spectrum and protocol analyzer to investigate the issue, it appears a new cordless operating at 5 GHz has been placed in this area that was not previous there during the site survey. This leaves 2 options advise management to have the cordless phone removed, or move the users to another frequency that is uneffected by the phone.
Well, there is a quick and dirty look at the PPDIOO life cycle. More information can be found in Cisco’s design curriculum or Cisco Press’s network design publications. I would also like to add the examples I provided are merely that, simple examples real projects require much more documentation and detail.
Well, it appears after a few months of visiting CWNP’s website (Yes, even on the weekends) their daily questions have finally started to repeat themselves. I knew it would end eventually and considering the price (free) 3 months of questions is a pretty good deal.
I really recommend anyone who is studying for a CWNP exam (or anything wireless related) to head over to this page and take a shot at the daily question. Don’t let the fact that they are free put you off they are good quality questions, and every question has a detailed explanation so if you get the question wrong or don’t understand it at first the explanation will lead you in the right direction. These questions will also touch on many different topics within the world of wireless, I’ve seen stuff ranging from non-technical security questions to questions concerning the 802.11 frame so this is a quick and dirty way to see inside the CWNP Professional level tracks (CWSP, CWAP, CWDP) just no where near as in-depth.
You can find a link to the CWNP Question of the day right here, their is also a link my Blog Roll. I am going to leave the link in my Blog Roll for any new visitors to find, so it won’t be going anywhere anytime soon. Hopefully CWNP will update the question as time goes on so we will see.