Archive for the ‘Network Design’ Category
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.
Often enough network engineers will be called upon to setup a network from the ground up. Whether it be a new branch office or a data center redesign it will be up to you to think up an efficient network design that can also be incorporated into the existing network seamlessly. Now depending on the size of the network that can be a daunting task, other times it could just be a simple ISR with an etherswitch module inside.
When you have to consider VLANs, Spanning-Tree, IP Addressing, Security, QoS, VoIP, Security, L3 redundancy, WAN connections, hardware models, software version, and the list goes on daunting at first yes? Cisco does have ample resources out there to aid you in your task of designing Cisco networks who would have thought?
One of the best resources I’ve found is the Cisco Design Zone this great website holds design details based on Technology, Industry, and architecture. While some of the guides can be quite large they go into very fine detail. The guides define advantages about using specific Cisco router or switch models along with sample configurations (best part in my opinion, seeing how it’s done) and some of the sample configurations have very convenient comments explaining the important points of the configurations. To sweeten the deal even more some of the guides show how the design correlates with Cisco’s SONA model which just adds volumes of worth while knowledge.
Addition resources can be found by looking at the Cisco design certification track the CCDA & CCDP programs have certification prep books from Cisco Press. They offer some great reference on best practice methodology concerning network design. The PPDIOO design model is also a good principle to abide by.
This PPDIOO design model is covered in great detail in the design track so if it’s something that interests you I would definitely pick up one of those books. (Just watch and make sure you get the book that correlates with the current exam version if you are planning to take the certification exam)
The last little piece I want to show is Cisco’s Campus Design model, it’s a nice extension of Cisco’s hierarchical model that’s shown in the CCNA track. (And once again, most if not all of the guides in the Design Zone will incorporate this model into the design)
You can still see the Core, Distribution, and Access layers but you can also see the addition of many other layers a WAN layer for branch office connectivity, Internet layer, E-Commerce layer concerning where the rest of the world interacts with your companies public facing services, along with a few others. It breaks down any complicated network into a structured module portioning out where each device belongs.
Now i’ve barely scratched the surface of Cisco’s network design concepts but if you want to see more definitely put the CDDA/CCDP books in your reading list, along with some guides from the Cisco Design Zone.