LFCE Preparation Guide: Network Administration – Routing IP Traffic Statically and Dynamically

Introduction

This is another very robust, non-trivial competency listed for the LFCE examination.  I’m glad it’s included, actually, because networking is a very poorly-understood field among many IT professionals serving as system administrators or, worse, system engineers and beyond.  I have worked with numerous IT professionals who have virtually no knowledge of network infrastructure, routing, or any of the finer details of IPv4 or, much less, IPv6.  For this examination, I am presuming IPv4 to be the focus, though some IPv6 knowledge certainly wouldn’t hurt anyone (and you should really start building it now, ’cause it’s comin’!).

Knowing how to examine a system’s routing table and thoroughly test its networking capabilities often separates excellent system administrators from average ones, and it should be a defining quality of an engineer.  While operating in a simple networking infrastructure often affords too great an opportunity to ignore the skillset entirely, such ignorance becomes painfully clear when operating in a medium or large networking environment.  Knowing how to isolate networking issues as clearly as possible is essential to getting the right support involved when a problem afflicts one of your systems in a large environment.

So where to start?  Networking is a huge subject area and often full-time networking specialists are required to maintain and support medium and large infrastructures.  I began gaining knowledge of networking when I was quite young and I helped my parents to install and manage our first home network components.  I then worked in tier 1 through tier 3 capacity at a help desk whose services were very wide ranging and demanded basic networking analytic capabilities from its staff who operated in a reasonably easy-to-understand subsection of a very large academic networking environment.  I then solidified much of my current understanding over the years in large part by reviewing the CompTIA Network+ All-In-One Exam Guide before completing the MCITP: Enterprise Administrator on Windows Server 2008 materials in preparation for the corresponding MCITP certification.  I actually took an official Microsoft course for Configuring Active Directory (exam 70-640) and Configuring Networking Infrastructure (70-642) and I read the Microsoft Press book for Configuring Application Infrastructure (70-643) and the excellent Microsoft Press book for the Enterprise Administrator examination (70-647).  That learning path would, of course, take the reader quite outside the scope of the subject matter at hand, so I’d recommend the CCNA material I mention below as the way to go for someone in need of the fundamental knowledge of networking required to effectively utilize the tools available in the GNU/Linux environment.

One potentially interesting observation of this competency which I have to offer is this:  the conceptual knowledge required of candidates is far broader than the technical knowledge.  Using the ip utility to configure static routing table entries and routing policy rules is trivial, but understanding how to compose such entries requires broad understanding.  Similarly, the Quagga software is not overly complicated, but the knowledge necessary to properly implement its functionality is broad and deep.

So, my networking knowledge has been built over the past 7 years.  It’s a huge, intimidating field, but the best place to start is with the system you administer on your home network.  Check out its routing table and make sure you understand exactly how every packet gets to its final destination.  It isn’t too hard when you have a simple table with two routing entries (probably one for the default gateway and one for the local subnet) and it’s often the starting point from which you’ll begin an investigation of an unknown network.  From there, you can begin observing the impact of adding and removing routing table entries and policy rules and you can begin to investigate the various forms which such entries can take.

Static Routing

The easiest portion of this competency is without a doubt static routing.  Check out the manual page (section 8) for the ip command.  Though broader than this competency alone, my guess is that the successful candidate for the LFCE examination should be able to read and understand the entire thing.  It is a very useful study guide of sorts, as tools often are, for understanding the kinds of actions you may be interested in taking when it comes to routing.  Obviously, you might focus on the ip route and ip rule sections of the tool to understand the areas of particular relevance to the competency presently discussed.

At a minimum, you should understand the distinction between the routing tables and the routing policy database and how they interoperate.  You should be able to configure direct routes and gatewayed routes, and you should be able to quickly inspect and understand routing information on a system.

Dynamic Routing

This portion of the competency is much more difficult and requires specialized software with which most system administrators have probably never come into contact.  It appears that the TecMint guide recommends Quagga.  That seems a good choice to me, and it’s not overly burdensome to learn sufficiently to accomplish its most basic tasks.  I imagine a successful candidate should understand the distinction between interior gateway protocols and exterior gateway protocols, their purposes, and common usage.  Quagga supports the interior gateway protocols RIP (which is a distance-vector protocol), OSPF, and IS-IS (which are both link-state protocols).  It also supports the exterior gateway protocol BGP.  These are the most common routing protocols in use (in fact, BGP  is the only EGP in use today), so again, Quagga is a reasonably comprehensive choice.

Basically, dynamic routing protocols exist to allow routing devices the ability to discover, choose, and implement routes to subnets.  With the complexity of modern internetworking, supporting routing infrastructure with dynamic routing protocols is practically necessary.  Without automated learning of this nature in routing devices, we’d need a whole lot of frustration-resistant network engineers.

I don’t know what the LFCE exam is going to expect of candidates in regard to configuring dynamic routing.  I continue to be surprised that it’s included, especially given the terse wording of the competency and the extreme breadth implied thereby.  I imagine this will be a big study topic requiring significant energy expenditure for most LFCE candidates.  It is my estimation that you’ll want to be sufficiently well prepared so that you don’t find yourself being asked to perform a task which you do not even understand (which would probably happen to most system administrators if they were asked to configure a routing device to use the Border Gateway Protocol to establish routes between autonomous systems).

Resources

  • Manual pages
    • ip(8)
  • Info pages
  • Recommended Textbooks (choose one and make sure you are comfortable with the information contained therein)

Techniques

  • Commands
    • ip
      • There are deprecated alternatives, such as the route command and ifconfig, but learn and use ip – it’s the far more powerful wave of the future.

Procedural Examples

  • Configure your machine to act as an OSPF neighbor to a connected routing device supporting OSPF.
  • Configure your machine to flood the network with OSPF routing information.
  • Configure your machine to act as a passive OSPF node on a particular interface.
  • Configure your machine to act as a routing device for a particular subnet, leveraging BGP to find external routes.

Tactical Exercises

The most powerful tool at your disposal regarding preparation for this competency is likely the ability to generate virtual networking environments using KVM.  Set up a virtual network, load up four small CentOS VMs (just a gig of RAM, or even less, will do), install Quagga on two of the systems and CentOS on two of the systems.  Make two distinct subnets, each containing a standard CentOS machine and a Quagga machine.  Make the two Quagga systems neighbors and use OSPF to communicate route information between them, allowing the two standard machines to communicate.  Change route information and see if the Quagga systems automatically detect and communicate the changes.

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4 Responses to LFCE Preparation Guide: Network Administration – Routing IP Traffic Statically and Dynamically

  1. Have you already take the Exam. I plan to sit the Exam in 2 Weeks and really surprised that they include dynamic routing. To be honest i never did this in the Past. What is the Weight for this Topic in the Scoring of this Exam?

    • I have not taken the exam, and I too plan to sit for it in about two weeks. I expressed my surprise at their inclusion of dynamic routing in my article, as well, and I recognize that it’s something which most system administrators are never going to have done (as I wrote). My guess is that the inclusion of dynamic routing configuration in the examination will be minimal, but it’s just a guess based on past experience with examinations that aren’t necessarily relevant to this one. Unfortunately, the information regarding the content of the LFCE examination is very rudimentary and data such as weights or intensity of focus for topics aren’t provided, as far as I know.

      The darkness shrouding this exam is the main reason I started this series! I’m all for rigorous examinations of great breadth and depth, but I do wish they’d clarify the scope of the exam by including information such as software packages whose mastery is expected and more detailed explanations of the breadth and depth of that mastery. As it is, I guess we’re just going to have to train as hard as we can and be ready for anything.

  2. I know you cant discuss the questions specifically but can you give an idea of the weighting of the Dynamic routing questions? I find a lot of the competencies in this exam are way outside anything I would ever expect to do and would usually use different methods to accomplish them (none of which are possible under a single terminal)

    • Well, I wish I could tell you more, but I have yet to take the exam myself (on account of various unexpected life obstacles). For what it’s worth, my guess is that dynamic routing in the way I’m describing it will be either completely absent from the exam or so obliquely referenced as to be not much of an issue. I really can’t imagine too many candidates for the LFCE examination have much experience at all with Quagga or other true dynamic routing solutions. It seems oddly out of scope to me.

      That said, I could be utterly wrong. Sorry I don’t have more concrete information here.

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