A while ago one of my students in the US – let’s call him Jason – asked me about the Nokia NRS1 study materials. he worked for an ISP and had already passed his CCNA, but his employer was asking that he passed the NRS1 in the next 3 months – now for those of you that don’t know the NRS1 stands for Nokia Certified Network Routing Specialist 1 and it is Nokia’s equivalent of the CCNA. There is an official study guide available, but it appears that blogs and videos are a bit thin on the ground. Now I did do a NRS2 video series on youtube a few years ago – 2016 to be exact, but it still seems that 7 years later there still aren’t that many study materials around – also what devices do you use and how to practice them?
So I suggested that if they decided to go the self-study route they should find and use the official Nokia study guide which is the called “Alcatel-Lucent Scalable IP Networks”, then find an image of the Nokia 7750 and install it on VMWare workstation, GNS3 or my preferred choice which is EVE-ng. This is because theory is great but to really solidify the theory you need to be able to lab and put those thoughts into practice, then after all this go and attempt the 40 or so Nokia NRS1 practice questions – you can find the link here:
The other option is to jump on a routercoach bootcamp which will provide rack rentals via my lab setup, I’ve got videos explaining important concepts and we do live training. Anyway, enough of the salesy pitch – let’s get back to the point of this blogpost.
After a short while – I would say a couple of weeks – Jason said that it was taking too much time as he had already spent 2 weeks and was stuck on question 4 of the practice test. Now, he saw the answer in the answer key but didn’t know why. He also said that if I could explain this one to him he would join the bootcamp! That was an opportunity that I couldn’t pass up so this blogpost is detailing both the question and answer to this query.
Question 4 goes like this:
Module 2: Introduction to the 7750 Service Router
4. Which of the following shows a typical data packet flow when egressing a Nokia 7750 SR?
a. SF/CPM -> MDA -> IOM -> SFP
b. SF/CPM -> SFP -> IOM -> MDA
c. SF/CPM -> IOM -> MDA -> SFP
d. MDA -> IOM -> SF/CPM -> SFP
The SF/CPM stands for the switching Fabric Control Processing Module where the switching fabric is a combination of hardware and software that controls traffic to and from a device using multiple Control Processing Modules.
The IOM is a hot-swappable linecard that has the a CPU responsible for managing the forwarding hardware.
The MDAs plug into the IOM and provide the physical interfaces – like Ethernet.
The SFPs plug into MDAs and enable the device to connect to fibre and Ethernet cables of different types and speeds.
We need to pay attention to the wording – the question is asking about “packet flow when egressing a Nokia 7750,” which means how data leaves the devices. Now, I know that the last touchpoint – the last piece of equipment in the router that the data passes through is the SFP – SFP stands for “small form-factor pluggable” and is a physical device that most often fibre cables connect into and can both transmit and receive data. From this short explanation we can rule out answer b because SFP has to be at the end – but that still leaves us 3 potential answers a,c & d.
OK, so now we need to look at the architecture of the device and the linecards to get a better understanding. This is probably best seen through a set of diagrams which are displayed on pages 75 & 76 of the study guide. I’ve redrawn them here for better effect:
So we can see from this diagram that the data packet originates from the SF/CPM Module then passes to the linecard which is the IOM. The MDA is connected into the IOM and the SFPs are plugged into the MDA. So the egress flow is:
SF/CPM -> IOM -> MDA -> SFP
That means the answer is c.