CCNP Week 1 – CEF, Windowing & IPv6 Migration

This is the first of many, many blog posts covering various topics I am studying for CCNP R&S. This week I am covering the Network Principles section from the ROUTE blueprint. These topics felt like a good way to get back into study mode. I had previously watched all of the ROUTE videos on CBTNuggets so I felt like diving into a book and getting into the ugly details was the way to go. I purchased “The Official Cert Guide CCNP Routing and Switching ROUTE 300-101” by Kevin Wallace off Amazon last week and got to it. Here are some talking points of the topics I’ve covered so far.

I was not familiar with Cisco Express Forwarding before this week. From my understanding CEF is a Layer 3 process which allows a Layer 3 switch or router to more efficiently (like wire speed) forward packets based on destination address prefix. The prefixes used to make forwarding decisions are stored in the forwarding information base (FIB) which is a mirror copy of the routing table! In addition to the FIB and routing table similarities, CEF also keeps an adjacency table. The adjacency table keeps track of nodes that are within a single Layer 2 hop. The setup of CEF is as easy as getting to global config mode to enable CEF, then adding a simple CEF configuration to an interface. Verification is as easy as issuing “show adjacency detail” command while in global config mode. I think I understand the concept of CEF, but I really don’t understand the use case yet. I don’t feel good about this topic at all. I’ll be spending some additional time in GNS3 to get a better grasp on the topic.

TCP Windowing is a topic that always catches my attention. It’s such a neat mechanism that always is forgotten until it’s broke. TCP is always labeled as the reliable protocol because of  its’ ability to sequence segments and request re-transmissions for the segments that were dropped or missed. To me, TCP is nearly as efficient as it is reliable. This is where windowing comes in. Windowing allows multiple TCP segments to be sent while only expecting a single ACK from the destination host. The number of segments sent from the source increases exponentially (1,2,4,8…..) until an ACK is not received back from the destination host. At this point I believe the number of segments sent will increment by 1 until the process fails again.  One area that did trip me up was understand how the sequence and acknowledgement numbers were generated for TCP headers. Essentially, the sequence number can be any number between 0 and 4,294,967,295 while the acknowledgement number is the sequence number + 1. This graphic from “The Official Cert Guide CCNP Routing and Switching” was a bit confusing because the ACK was the same number as the next TCP segment. In the end though, all the sequence numbers are essentially irrelevant.

IPv6 Migration is such a huge topic. It baffles me that it’s a subtopic of a subtopic in the CCNP ROUTE blueprint. Understanding the strategies of starting an IPv6 migration is the most important outcome from this section. Aside from the obvious guidelines, like making sure your network gear is IPv6 ready and checking to make sure your ISP supports IPv6 there are some interesting migrations strategies that can help cobble IPv4 and IPv6 together. The obvious choice when deploying IPv6 is to run IPv4 in parallel. This dual stack method will work well, but beware of any legacy clients or software that cannot do IPv6. This method allows a network engineer to slowly move from IPv4->Dual Stack->IPv6 once all legacy clients are out of the environment. It’s worth noting that IPv4 hosts cannot communicate with IPv6 hosts unless other migration strategies are used. These strategies include IPv6 NAT where we translate an IPv4 address to IPv6 address and 6to4 encapsulation where IPv6 packets are encapsulated in IPv4 packets. The book mentions two other strategies NPTv6 which is similar to NAT, but cannot do port translation aka overload. The other is IPv6-over-IPv4 tunnel which is similar to 6to4, but builds tunnel through the IPv4 portion of the network. Let’s argue about the differences another time.

I personally don’t see many Fortune 500 companies (outside of the large tech companies) moving to pure IPv6 anytime soon. It is certainly feasible for a company to provide access to the IPv6 Internet using one of the migration methods above, but there is little to be gained by deploying IPv6 internally. Eventually, when IPv6 does offer a better ROI it will be the legacy applications and devs that will hold progress back.

Here are some additional resources I found helpful.

CEF Overview

Understand CEF

Spanning Tree from PVST+ to Rapid-PVST Migration Configuration Example

See ya next week!!




My Path to CCNP R&S

Last weekend I graduated from The University of Toledo’s College of Engineering with Bachelor of Science in Information Technology. Undergrad work and being a Dad really limited the time I could spend becoming a better Network Engineer. Today, is the day that changes. Today, is the day that I start my journey towards CCNP R&S. Below is an overview of the time frame and the materials I’ll be using.


Week 1 (Dec 22nd – Jan 2) – ROUTE – 1.0 Network Principals

Week 2 (Jan 3rd – Jan 9th) – ROUTE – 2.0 Layer 2 Technologies

Week 3 (Jan 10th – Jan 16th) – ROUTE – 3.0 Layer 3 Technologies 3.1 – 3.10

Week 4 (Jan 17th – Jan 23rd) – ROUTE – 3.0 Layer 3 Technologies 3.11 – 3.23

Week 5 (Jan 24th – Jan 30th) – ROUTE – 3.0 Layer 3 Technologies 3.24 – 3.32

Week 6 (Jan 31st – Feb 6th ) – ROUTE – 3.0 Layer 3 Technologies Lab

Week 7 (Feb 7th – Feb 13th) – ROUTE – 4.0 VPN Technologies

Week 8 (Feb 14th – Feb 20th) – ROUTE – 5.0 Infrastructure Security

Week 9 (Feb 21st – Feb 27th) – ROUTE – 6.0 Infrastructure Services

Week 10 (Feb 28th – Mar 5th) – ROUTE – Review and Lab of 1.0 & 2.0

Week 11 (Mar 6th – Mar 12th) – ROUTE – Review and Lab of 3.0

Week 12 (Mar 13th – Mar 19th) – ROUTE – Review and Lab of 4.0

Week 13 (Mar 20th – Mar 26th) – ROUTE – Review and Lab of 5.0 & 6.0

Week 14 (March 28th) – ROUTE – Exam Date March 28th, 2016 – ***Paid and Scheduled

SWITCH – Exam Date June 6th, 2016

TSHOOT – EXAM Date June 27th, 2016

Training Aids:

Let me start out by saying that my learning style is to watch, dive in, break stuff, watch more stuff, fix stuff. The material I’m using is pretty common knowledge for those in the networking industry, but I thought it was worth mentioning.

CBTNuggets – If I could recommend a single source to get you started, it would be @CioaraJeremy and @KeithBarkerCCIE over at CBTNuggets. Their content is up to date with the new exams and you won’t fall asleep listening to them. I queue up videos on my commute into work and absorb as much knowledge as I can. CBTNuggets is subscription based, so thanks to my very generous employer for picking that cost up.

GNS3 – Excellent “free” simulation software for ROUTE. One thing to note is that you need to posses actual Cisco IOS images for this to work. There is more to GNS3 than I care to cover and in all honesty there could be a cert track for GNS 3. These links should help you get started for Windows and Mac

Books – I use books to dive deeper into topics. Jeremy and Keith from CBTNuggets are very good at covering the basics and giving you enough information to get started. Getting to the details is best done through a study guide. I’ve not done much research on study guides. I would seem to default to whatever book CiscoPress has out, but if you have a suggestion leave a comment or tweet me.

Home Network – My home setup is close to a legit CCNP lab. I have a 1921 router, a 48 port 2960 switch (non-POE) and a 24 port 2960 switch (POE) that I keep unplugged because the bearings in the fan are going bad. This equipment is in production and my wife requires change control be completed 24 hours before any outage.

This Blog – When I was studying for CCNA I could judge how well I knew a topic by how well I could explain it. I’m hoping to use this blog as a dumping ground for exactly that. If I’m wrong I’m sure someone on the Internet will correct me.



3.2 Identify IPv6 addressing and subnetting – I’m interested in IPv6, but my lack of experience makes going beyond that basics a topic I’ll have to hit hard.

3.8 Configure and Verify VRF lite – Completely unfamiliar with this topic.

3.30 Describe, configure, and verify BGP peer relationships and authentication – Most of my real life experience with BGP has come though templated Router configs.

3.31 Configure and verify eBGP (IPv4 and IPv6 address families) – Same as above.

3.32 Explain BGP attributes and best-path selection – Same as above.

4.2 Describe DMVPN (single hub) – Understand the concepts of DMVPN, very little real life experience.


1.6 Configure and verify spanning tree – Not so much a weakness, but I don’t deal with Spanning Tree on a day to day basis. The skills I learned in CCNA really aren’t necessary for the networks I work on.

3.1 Configure and verify first-hop redundancy protocols – Again, I don’t see much of this on a day to day basis.


All of the above.


That’s the plan. I’ve paid for and scheduled the first exam. I think the dates might be a bit aggressive, but the people I’ve talked to say it’s certainly achievable. If you want to follow me on Twitter I am @Eric_Stover and I’ll be posting all my updates there. Next week’s topic is going to be the first section of the ROUTE topics “Network Principles”. See you then.