Intro to OSPFv2 – CCNA 200-301

TLDR, Summary of this lesson:

This solely focuses on OSPFv2, for IPv4. OSPFv3 will be touched on later. OSPF is the open shortest path first routing protocol, which uses the Link-State Routing Process. Has a shorter AD, Administrative Distance, than other routing protocols. The shortest path is determined based on Dijkstra’s Shortest Path First Algorithm. OSPF will send Hello packets to neighboring routers to begin adjacency and create an OSPF domain. Neighboring routers respond with their DBDs, Database description packets, which contain that routers link-state database. If more information is requested, a router will send an LSR, Link-state request. The receiving router will respond with an LSAck (Link-state acknowledgement) and reply with any LSUs (Link State updates). A router can also send an LSA (link-state advertisement), advertising it’s updates. OSPF will elect a DR, designated router, to act as its primary OSPF router in the domain. There is also a BDR, backup DR that is designated should the DR fail. These routers determine the shortest path for a packet to take based on AD.

Anything not touched on in detail here will be touched on in a later lesson.

WHAT IS OSPF?

OSPF means “Open Shortest Path First.” It’s a routing protocol that uses the Link State routing algorithm. This means that the routers in an OSPF network will communicate by sending Link-State messages. These Link-State messages are also called OSPF Packet Types. The OSPF packet types are as follows:

Hello – Establish and maintain adjacency (become an OSPF neighbor) with other OSPF routers

DBD – Database Description – Contains an abbreviated list of the sending router’s link-state database

LSR – Link-State Request – The receiving router will request more information about an entry in the DBD by sending LSRs

LSU – Link-State Update – This is in reply to an LSR and announces new information. These contain 11 types of LSAs (link-state advertisements) which, thankfully, we don’t need to know for the CCNA 200-301.

LSA – Link-State Advertisement – A router will advertise any updates to its routing table to all OSPF neighbors.

LSAck – Link-State Acknowledgement – After an LSU is received, the router will respond with an acknowledgement to confirm the receipt of the LSU.

LINK-STATE ROUTING PROCESS

Summary of how OSPF uses the Link-State Routing Process to maintain adjacency:

  1. Each router will learn its own links and its own connected networks. This is done by detecting the UP state, and the L3 address configured
  2. Each router is then responsible for establishing adjacency by exchanging Hello packets
  3. Each router builds an LSP (Link-State Packet) containing the state of each directly connected link. It records the Neighbor ID, link type, and bandwidth
  4. Routers flood the LSP to all neighbors, and each neighbor will store the LSP in a database. All the neighbors then flood the LSPs to their neighbors until all OSPF routers have received the LSPs. Each router stores these LSPs in the DBD.
  5. Each router uses the DBD to construct a map of the topology and determine the best path to each destination network based on the cost of the interfaces. All routers know the topology, but each router independently determines the shortest path to a specific destination.

DIJKSTRA’S SHORTEST PATH FIRST ALGORITHM

How does OSPF know the shortest path to take to route traffic? By default, each interface type has a ‘cost.’ The default cost of each interface is listed below:

10Gig/Gigabit/FastEthernet (100 mb/s or higher) – 1

Ethernet (10 Mb/s) – 10

E1 (2 Mb/s) – 48

T1 (1.544 Mb/s) – 64

There are costs for slower speeds, however, you won’t need to know them and it is unlikely you will encounter them. For determining the cost of a route, you would add the cost of the interfaces together. For instance, if RouterA is sending a packet to RouterC through RouterA’s f/a01 and RouterB’s g/i01 then the cost for the route would be 11, (1 + 10). Thankfully, any questions in the CCNA will provide you with the cost of the interfaces on a topology, and it will be up to you to determine the shortest path based on those costs.

You can also interfere with these elections by changing the default cost of an interface. You would do this to set a static route and make sure a router always sends traffic to a specific router through a specific route.

WHAT INTERFACE VALUES MUST BE MATCHING TO ESTABLISH ADJACENCY?

For two routers to establish and maintain adjacency and continue being neighbors, they must have certain matching values. Think of your neighbors, if you want to stay next to them, you have to have the same interest. So, what are those interests?

Hello Interval – By default, every 10 seconds the router will send a Hello to Multiaccess networks, and every 30 seconds to nonbroadcast multiaccess networks. Remember, Hello packets establish and maintain adjacency.

Dead Interval – By default, the rate is 4x the Hello Interval. This is the amount of time that passes before a router determines that an adjacent neighbor has died, or is no longer available.

Network Type – Both routers must be on the same network with the same subnet mask, they must also both be set up for OSPF.

Area ID – The Area ID must match between both routers. This is not touched on in this lesson but will be detailed in the next lesson.

OSPF ELECTIONS

There are several issues inherent with OSPF working on multi-access networks :

The Creation of multiple adjacencies

Flooding of LSAs

So, how does OSPF combat this? The solution is by electing both a DR (direct router) and a BDR (backup direct router.) The direct router’s job is to update all other OSPF routers when a change occurs in the multiaccess network. The BDR monitors the DR to ensure that it is active, and will take over if the DR fails. All other routers in the OSPF network become DROTHERs, and the default operation is DROTHER 2-WAY.

As I said above, anything not touched in this basic overview will be discussed in a later section. I hope this helps and if you have any questions feel free to reach out. If you enjoy my guides and are currently studying for an IT certification, feel free to sign up for my newsletter to be notified when I post guides and general study and productivity tips.

Stay happy, healthy, and productive!

You’re Taking Notes Wrong

You’re Taking Notes Wrong

As a student of life and a student for life, taking notes is one of the most important skills you can cultivate and nurture and constantly improve. With that said, you’ve probably been taking notes wrong your entire life. Think of a time when you went back and revised or reviewed your notes before taking an exam or giving a presentation. Was it more of a cram session? Did you find yourself trying to memorize the notes you took as much as possible so you can word-vomit that information back out? It’s been shown that summarizing content with the book open next to you, or in a corporate environment, summarizing a speaker’s points while they’re speaking, isn’t the best method for retaining information. When it comes to learning new information, think of each subject as a roadmap for your brain. Initially, there’s no road to new information in your head, but as you continue to reinforce that information, a path begins to appear. So, if summarizing notes isn’t great for building a road, what is? Active recall. Well, active recall and spaced repetition to be exact.

Active Recall

To employ this successfully in your note-taking, I highly recommend you use the Cornell Note Taking System. I will include a template below (there is also a default Notion Template if you use Notion.) The Cornell Note Taking System allows you to ask yourself recall questions, then provide the answers in a separate “Notes” column. For example, I’m currently studying iOS development and learning Swift and SwiftUI programming languages. As I’m taking notes while going through practice problems and practice apps, it will look like this:

Embedding In Stacks

Recall Notes

What are the 3 most used stacks | VStack, HStack, ZStack

How are they oriented | Vertical, Horizontal, Depth-based

After I’ve finished writing my notes for that specific day’s subject and topics, there is a summary section on the bottom that I leave blank. I leave it blank, as this ties into the next section.

Spaced Repetition

A path is not built overnight, a road is not paved in a day. They take time and oft-repeated walks through the same area. The same applies to learning new information. The more often that information is recalled, the quicker your brain can link a path, and the easier it will be to recall that information when you need it. So, why space out the repetition then? Because of the “forgetting curve.” The forgetting curve is the time it takes after hearing new information to forget said information. We can bend that forgetting curve more in our favor by making sure we recall necessary information more often. In the template included for the Cornell Note Taking System, there is a “Summary” section on the bottom of each set of notes. The following day you take notes, review your Recall column, and answer those without looking at your notes section. If you can’t actively recall the information, then you can review your Notes section to reinforce the knowledge. Once you’ve finished going through your notes, summarize them in the “Summary” section. While this may seem repetitive, remember that you are actively trying to beat your own brain’s forgetting curve.

BONUS SECTION

I’m including this little bonus section for an extra tip and a thank you for sticking around. Another great way to retain information is to teach it. I use this when I post study guides for the CCNA 200-301 exam on this website. This will make you rethink your notes and thoughts on a subject and reframe them for someone who knows absolutely nothing about it. This will also force you to correct any information that you may not be comfortable with so you don’t provide other people with false or thinly detailed information. So remember! When you’re learning something new: recall, repeat, and teach!

I sincerely hope this helps and as always, best of luck with your learning. Stay healthy, positive, and productive!

Cornell Note Taking Template (Courtesy of Notion):

Link to Template here as well, as I could not get it to copy and paste correctly onto the website:

https://www.notion.so/Cornell-Notes-System-dc73ad0caabf43949bf71325a879ef50

Divide your page into two columns.

The narrower left column is for recording keywords, questions, and recall prompts. The right column is for your actual notes taken during a lecture or class.

Recall Notes

KEYWORD | …

RELEVANT QUESTION | …

Create a summary section at the bottom.

When you review your notes, briefly summarize what you learned and what is important to retain from the full page of notes. This will help you internalize the information.

SUMMARY: Create a callout box like this one in Notion by typing /callout. It’s the perfect way to capture summaries that stand out.

Here’s your template!

Date: Oct 5, 2019

Topic:

Recall Notes

SUMMARY:

What I Learned From Doing Nothing

Self-Reflection

At the end of 2020, I found myself in a position of self-reflection. I had been made redundant from a job I held for most of my adult life and reevaluating whether it was a career I wanted to continue to hold. I decided to take some time off and do what I can to become a better version of myself. I do what every self-respecting 30 year old who’s been laid-off does… I started a blog. I started journaling (shameless self-promotion here: https://every-day-tech.com/2020/12/23/what-i-learned-from-talking-to-myself/), I write every day, and I started meditating. If 2020 me told 2019 me that I would start meditating, I probably would’ve known something life-changing was about to happen. I am not a “metaphysical” or “spiritual” person, yet here I was, in a guided meditation session being told to look into the darkness of my closed eyes and be aware of my own consciousness. But, while on paper it may not sound beneficial to a cold skeptic like myself, I can’t play down the benefits that only 2 weeks of daily meditation have provided.

I used Sam Harris’ “Waking Up” app for guided meditation. There are daily sessions ranging in length from 5 minutes (the shortest) to 13 minutes (so far the longest session.) It begins simply with the one thing that you can take with you throughout the day if it’s the only thing you take away from these; focus on your breath. Anytime you find your mind wandering and you’ve forgotten you’re even trying to meditate at all, come back to the breath. Focus on the tip of your nose when you breathe in, and again when you breathe out. I used to think the goal of meditation to sit still and stop thinking entirely. But it’s not. The goal is to allow those thoughts to come and go without impeding your focus. From there, we begin to focus on what happens when we notice and focus on those thoughts that draw our attention and focus away from where it should be. Turns out, when those intrusive thoughts are scrutinized in any way, they shy away. The first few days of meditation really point out just how messy our brains are. We spend so much time in a disorganized haze. Below are a few sections of the journal I kept, in which I would write down my thoughts immediately after finishing the session.

Day One:

12.10.20 – First day of meditation. It was short, only 5 minutes, focused mainly on breathing. I did repeat the ‘lesson’, as the app likes to call them. I did nearly fall asleep the second time, but it could’ve been because I was quite tired from being up at 5 a.m. that day. Overall, not bad for a first day.

12.11.20 – Day 2 of meditation. A 10-minute section this time. Focused mainly on breathing and noticing exactly when your thoughts would intrude upon your focus. Using the Waking Up app, Harris calls out the feeling exactly; that there are times my mind will wander and I’ll forget that I’m even trying to meditate in the first place. This happened at least twice. It’s nice coming out of the session though, it does help me feel less mentally cluttered. I’m looking forward to day 3.

Revelation

12.12.20 – Day 3 was a revelation. Harris introduces deliberately long pauses after his guidance. For instance, when asked to focus not solely on your breath and instead on the feeling of being seated and the feeling of the chair on the different parts of your body, there is what feels like a 10-minute pause. I noticed myself being able to catch where my thoughts were drifting and I was forgetting that I was meditating at all. I was able to catch those thoughts quicker and return to focusing on the meditation itself. I think I’m getting the hang of this. It could’ve also been helped by the fact that I replaced my cushion-less office chair with a padded one.

12.13.20 – I write these journals within 5 minutes of doing the meditation sessions, to make sure my thoughts on the matter are the clearest they can be. What this leaves out is what I do with those thoughts throughout the day after the day’s sessions. After yesterdays session, I found myself more able to draw my attention back to where I needed it to be simply by pausing the moment I notice myself wandering, and focusing on my breath. What I mean by that is, just focusing on what the sensation on the tip of my nostril is when I breathe in and exhale. Even for just a second, and I’m able to bring myself back to the moment. Today’s session added in environment sound: traffic, birds, animals, talking. Focusing on the sounds themselves and when they appear and leave, helps to realize that there isn’t really a distracting place to meditate. You can meditate on the sounds themselves and find enough peace and calm by simply experiencing those sounds. Sounds a bit too metaphysical for my liking, but we’ll see how it pans out as I work more after this session.

12.14.20 – Where yesterday and the day before were revelations, today felt more like a slide backward. Hard to focus on the meditation itself, my mind wandered constantly. But maybe that’s the point at this phase? Harris does specifically call out what you should do when you notice your mind wandering, and notice exactly what happens with those thoughts once you notice them. Here’s a secret, they go away. If you catch yourself lost in thought, focus on that last thought, and watch it fade away. Then take a deep breath, notice the breath, and begin again.

At this point, there is a break for twelve days where I let it get away from me. I still continued on, and will do so for the foreseeable future. But, looking back now, this might be a good point to decide if meditation is worth taking on. Is it worth all the hype? Did its absence mark a noticeable change in my day? Short answer, yes. Even a minute a day just focusing on your breath and drawing your attention to a single thing to notice just how scattered your brain really is, helps untangle that scattered mess. With 2021 well on its way, try adding a bit of meditation to your day. Even if you’re skeptical, as I was, it’s a small commitment with a huge payoff.

As always, I hope this is helpful to you. I hope you have a fantastic 2021 and stay healthy, productive, and positive.

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Top 5 Apps for 2021

Top 5 Apps for 2021

2020 was the year I learned how to break down my processes and reinvent them. I went on a deep-dive on how to be more productive and get the most out of my time. With that, came several apps that I added to my daily life to make everything work together. Below are my top 5 apps for 2021. These will be divided into two sections, 1. Productivity, and 2. Leisure.

Productivity

  1. Notion – I’ve been singing Notion’s praises all year. It’s a fantastic all in one app for writing, note-taking, day planning, and daily journaling. While I will be mentioning other apps that work in conjunction with Notion and provide more fleshed out versions of what Notion can do, you could take all of those away and just do it with Notion. I use it for the Cornell Note Taking template and as a daily journal. And best of all? It’s absolutely free. There are paid options but the average single user has no real reason to pay for the app unless you want to support the developers.
  2. Things 3 – A to-do list is a must to keep your day organized, and for me, to check things off to feel like I’ve actually made progress that day. Things 3 is a super-powered to-do list. You can set daily tasks, create new lists for tasks that you want to complete eventually. My own Things is comprised of a set of daily tasks, daily reminders for what I need to do that day that repeat on set increments (i.e. Every Monday at 10 a.m. it reminds me to plan the week’s content out.) In terms of productivity increase, it’s hard to beat what a well-structured task list, goals, and systems manager can do for you.
  3. Grammarly – Grammarly is an app that lets you either write in it, or paste your writings, and it points out your grammar mistakes, misspellings, active/passive voice usage, and tone and clarity. Don’t fall into thinking this is just a tool for writers. Having taught classes on how to properly compose a work email, I know for a fact that employers appreciate an employee who can clearly and succinctly write out a proper business email. This one is also completely free.

Leisure

  1. Waking Up – One thing I never thought I’d do in my life is meditate, but sure enough, 2020 was a strange year. I highly recommend combining this app with Notion and keeping a meditation journal. Author and Philosopher Sam Harris guides you through simple, 10-15 minute meditation sessions that help you focus on your breath, weed out distractions, and clear your mind. One of the biggest takeaways is the ability to focus on a single task, even with distractions around you. It teaches you to notice when your mind wanders, and when you’re lost in thought, and what to do with that. Another one that I can’t recommend enough, and is also free (for the first 5 days.)
  2. Kindle – I know, this one’s a bit of a cheat, everyone knows about Kindle. BUT, what you may not know is that Amazon has launched Kindle Unlimited. Kindle Unlimited gives you millions of bestselling books for only $10/month, with the first 3 months free. The Kindle app can also be added onto almost any device, and reading a book on your iPhone isn’t so bad. 2020 was a year of solitude and quarantine, and a lot of 2021 will be the same. Spend some of that time learning and reading.

I hope you can make use of these in the coming year and can keep to your resolutions. Here’s to a happier, more productive, and more positive 2021!

Want to know how to be more productive this year?

VLAN and Trunking Concepts, Protocols, and Configuration

In This Lesson We Will:

  • Learn What VLANs are and why they are implemented
  • Learn about Trunking and why it is important
  • How configure VLANs and Trunking in your network

VLAN Definitions:

A VLAN is a Virtual LAN. This is a grouping of end devices within the same switch. A way to segment users by their department without using more hardware. In layman’s terms; You can put Accounting, Claims, and Security on one switch by subnetting their networks and placing them into separate VLANs. There are 4 types of VLAN that are focused on in the CCNA:

Default VLAN – This is VLAN1 on the switch that is already available upon startup. This is typically restricted to serve only L2 (data link layer) control traffic.

Data VLAN – Carries only user-generated traffic. This is used to keep voice and management traffic separate from data traffic.

Black Hole VLAN – The administrator would assign all unused ports on a switch to this VLAN. It acts as a dummy to prevent any unauthorized devices that may connect to unused ports from reaching the rest of the network.

Native VLAN– This is the common identifier on opposing ends of a trunk link.

VLAN Trunking:

Trunking – The process in which multiple VLANs are assigned on a single switch port between switches. Traffic is segmented on the line in a trunk. Below is an example of a trunk shown in a network topology:

A trunk will allow switches to switch and forward traffic from multiple VLANs with minimal ports. Think of how a tree “trunk” will distribute water to each branch and leaf individually; a switch will essentially stripe and distribute the specific VLANs traffic along its connection with the other switch so that only VLAN10 will get VLAN10 traffic from the other switch, and VLAN20 will only get VLAN20 traffic.

Configuring VLANs

You can create a VLAN in either global configuration (‘enable’ – ‘configure terminal’) or under a specific interface. Typically, you will create a VLAN in global config as this will allow you to create, name, and place the VLAN in fewer commands. Below is a screenshot of commands used to create, name, and assign VLANs in a Cisco Switch CLI:

Note – This will assume you have checked your available interfaces and know how to do so. I have touched on these in earlier lessons (linked here: )

How to implement trunking using DTP – Dynamic Trunking Protocol

DTP is Cisco’s proprietary protocol and it negotiates both the status of trunk ports and the trunk encapsulation of trunk ports. Below are descriptions of each trunking mode:

  1. Unconditional Trunking – Use CLI command “switchport mode trunk” This will send DTP messages to the remote port, advertising it is in an unconditional trunking state. Unconditional meaning it will always try to form a trunk.
  2. Dynamic Auto Trunking – Use the command “switchport mode trunk dynamic auto” This will advertise that it is ready to be trunked, but will not auto-negotiate a trunk. It will wait on the other end of the link to negotiate the trunk.
  3. Dynamic Desirable – Use the command “switchport mode dynamic desirable” This is a combination of the above two. If configured with this command, the switch will both advertise and request to negotiate a trunking state.
  4. No-Negotiate – Use the command “switchport nonegotiate” You would only this command when attempting to set up a trunk with a non-cisco switch. This operates as unconditional trunking.

Troubleshoot an active Trunk

Troubleshooting an active Trunk is relatively simple. Typically, if something is going to go wrong, it’s going to be one of four things. Below is a list of the most common issues and resolutions, in their respective orders in relation to troubleshooting trunking. All of these can be discerned by using the CLI command “show interface switchport” in global configuration mode:

  1. Identify all access interfaces and their VLANs. Reassign to correct VLANs as appropriate.
  2. Determine if the VLAN in fact exists and is active.
  3. Check allowed VLANs on both ends of the trunk.
  4. Make sure both switches are trunking.

Conclusion

This was a relatively simple breakdown of what a VLAN is, how they are implemented, and how to trunk them. I highly recommend you follow my lab to download packet tracer and play around with setting up your own VLANs and trunking them. I will post a specific lab on this topic at a later date as well.

As always, if you enjoy my content and labs, feel free to subscribe to my newsletter to be notified when I post new content.

Stay healthy, productive, and positive.

What I Learned From Talking to Myself

It’s no secret that I’m a fan of Notion for basically everything: Note-taking, video scripting, blog writing, and journaling. For the past 30 days, since I’ve been made redundant from my job, I took it upon myself to embark on a journey of self-improvement. Part of that journey involved introspection. Something I’d shied away from, similarly to meditation, which I’ve now taken up as well and will be writing on soon enough. But, just in the way meditation helped with clearing my thoughts, journaling my thoughts at the end of the day helped keep both my positive and self-defeating emotions in check. Or at least out in the open where I could confront them. Of course, with all new things, it didn’t come immediately. It is possible to be shy even when you’re talking to yourself. But after a few days, I noticed my journals getting longer, and I found it easier to compile my thoughts into something that made sense. It was easier to look back at my day and reflect on what I thought went well, what needed improvement, and what should be avoided.

As I said, it didn’t come easy the first few days. My journals were short and I wasn’t sure what to write, or if what I wrote made sense. Which is dumb if you think it through. I’m only talking to myself after all. Below is a screenshot of my first journal when I started this on 11.20.20:

It’s small. I was self-conscious about journaling even though I’m really the one who’s going to see them. Eventually, though, I got better at sharing my thoughts with myself:

I use Notions daily journal template which asks that I detail my intentions for the day, what happened that day, the things I’m grateful for (I choose to write down 3 every day,) and my task list for the day which I combine with Notions built-in task list. I touch the journal twice a day. Once in the morning to gather my thoughts and goals and tasks for the day, and at the end of the day to reflect and gauge if I met the goals and intentions I set for myself. Below is a screenshot of my intentions from 11.22.20:

Would I recommend journaling for everyone? Absolutely. Does it need to be every day? Probably not. Especially if you’re like me and stuck in the house on quarantine:

For me, it was hard to keep track of a digital journal and remember to write in it every day. While I wouldn’t recommend going out and buying a moleskin journal, if you intend on taking up the habit of talking to yourself, remember to do it more often than not. I found myself forgetting for several days at a time that I was journaling. Once I got back into it though, I did remember the benefits.

What are the benefits? Well, self-reflection is a great tool that can be carried with you every day. If you get better at recognizing when you are being self-destructive or recognizing what you are grateful for every day, you can take that with you and it does genuinely make your days easier. Additionally, writing every day and making yourself a better writer who can organize your thoughts more clearly will pay off in dividends in your professional life. Even if you don’t intend on being a writer. Someone who can organize themselves and their thoughts will thrive.

So remember, talk to yourself. Become friends with yourself. Keep yourself accountable. You will one day thank your past self for starting that journey of introspection and for keeping you healthy, motivated, and productive.

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https://www.youtube.com/channel/UCXTzK5VorZZ565fEWuD02bQ

Thank you!

IPv4 Addressing

In This Lesson We Will:

  • Dissect the IPv4 Header
  • Learn the IPv4 classes
  • Learn the purpose of the subnet mask
  • Review IPv4 Subnetting and VLSM

Introduction:

While IPv6 is quickly gaining popularity in networks, most networks still work with private, classful IPv4 addresses. In fact, if you open up your command prompt or terminal on your computer and type ‘ipconfig’ you’ll see your network is implementing a private IPv4 address. Additionally, the CCNA will require that you know how to subnet an IPv4 address quickly, so I’ll recap what I believe is the quickest method of IPv4 subnetting. I won’t touch on the binary just yet, because trust me when I say, it’s dry and boring. But you will need to know it. I will dedicate a section on its own to the binary behind subnetting in the next lesson.

IPv4 Header Dissected:

All IPv4 addresses have this header. It’s worth knowing what the header contains, however, the CCNA does not require that you know all aspects of the IPv4 header. Additionally, IPv4 addresses consist of “Network bits” and “Host bits” and contain both the source address and the destination IPv4 address.

Classful IPv4 Addresses:

There are five classes of IPv4 addresses. The class of the address determines the subnet mask:

Class A – First Octet range of 1-127 – 8 Network Bits – 24 Host Bits- Subnet mask 255.0.0.0

Class B – First Octet range of 128-191 – 16 Network Bits – 16 Host Bits – Subnet mask 255.255.0.0

Class C – First Octet range of 192-223 – 24 Network Bits – 8 Host Bits – Subnet mask 255.255.255.0

Class D – First Octet range of 224-239 – These are not used for addressing. Class D networks are used for Multicast addresses

Class E – First Octet range of 240-255 – These are not sued for addressing. Class E networks are reserved for Research

Subnet Mask:

The subnet mask is the network bits of the classful address in binary bits. So, for a class A address of 10.0.0.0, the default subnet mask is 255.0.0.0, because there are 8 total host bits. 8 binary bits = 255. An L3 device will use the subnet mask to determine the network address for a packet by finding the bit boundary where the series of binary 1s ends and the binary 0s begin. This bit boundary for default masks is always on the octet boundary.

IPv4 Subnetting:

I’ve touched on IPv4 subnetting previously, I will link to that post here as it explains how to subnet and find the wildcard mask within seconds:

IPv4 Subnetting By Hand – Every Day Tech – CCNA 200-301 (every-day-tech.com)

How To Configure Your Switch

In This Lesson We Will:

  • Learn How To Connect Devices
  • How to configure your Cisco Switch
  • Learn Various CLI commands

Configuring Your Switch

Once you’ve unboxed your switch, it’s basically ready to go and forward traffic immediately after connecting it to your network. Switches are handy that way, they’re plug-n-play. However, they do require some configuration if you wish to connect remotely using SSH or Telnet, configure VLANs, etc. We’ll touch on that today. However, because the set up is so similar to setting up a router, I recommend you read this lesson alongside the Router Configuration lesson (Setting Up Your Cisco Router – Every Day Tech CCNA 200-301 – (every-day-tech.com))

Once you’ve connected your switch, there are two modes, much like in your router, that you’ll have access to configure through, and you must connect physically to the switch as Telnet or SSH won’t be set up:

Standard/User EXEC Mode – This is the mode the user is placed when immediately upon opening the CLI for the switch. Very limited monitoring and troubleshooting commands, ‘show’ and ‘ping’

Privileged EXEC Mode – This provides full access to the device commands, including configuration and management. This is your “enable” mode.

Helpful Tips

If you’re ever not sure which command to use or how to complete the command, you can simply start typing the command, and press ‘?’, and the CLI will give you the option for outputs:

The IOS is also set up to notify you whenever a command is input incorrectly and will display an error message.

Switch History and Examination Commands

Switches also keep a history buffer of the last 10 commands that were input. To see the history buffer, use ‘show history’ to display the commands currently stored in the buffer, and ‘terminal history’ to enable a longer terminal history length. Terminal History can store up to 256 command lines.

Below is a list of ‘show’ commands, and what they verify when you are troubleshooting your switch:

Show – Output

  • interface – shows the available interfaces on the switch
  • flash – shows the operating systems
  • startup-config – shows the NVRAM, backup configuration
  • memory – shows configured memory
  • stacks – shows configured stacks
  • buffers – shows configured buffers
  • running-config – shows the active configuration file

Common Switch Configuration Commands

Below is a table of most, if not all of the configuration CLI commands you would use to set up your switch for the first time. These aren’t in order of use:

Configure VLAN1:

Configure and interface to a new VLAN:

Duplexing and Port Speeds

There are three things to keep in mind when setting up ports on a switch. It’s worth noting though, for the most part, the switch will auto-config these settings for optimal performance. There are times though when an administrator would need to manually configure the duplex and speed of ports and interfaces.

Half-Duplex – Unidirectional data flow. A device can only send or receive on an ethernet LAN, one at a time.

Full-Duplex – Bidirectional data flow. A device can both send and receive on an ethernet LAN simultaneously. This means that a full-duplex port can take the bandwidth of both the device and its own port, and effectively double it. Two 100mpbs interfaces can transmit and receive at 100mbps, providing 200mbps of bandwidth.

Port Speed – This simply the bandwidth the port is running at. The most common speeds are 100mbps, 1Gbps, and 10Gbps.

Line, Protocol, and Interface Status

The CLI command ‘show interfaces’ will give you vital information about the performance of all interfaces on the switch. Interfaces on a switch are typically either ‘up’ or ‘down’, with some variation between the two depending upon how the interface has been set up. Below is a list of interface codes, and what they mean:

Line Status – Protocol Status – Interface Status – What It Means

Administratively Down – Down – disabled – ‘shutdown’ cmd configured

Down – Down – notconnect – Typically a cabling issue

Up – Down – notconnect – A L2 problem on L3 switches

Down – Down (err-disabled) – err-disabled – Port security disabled interface

Up – up – connect – Interface working as expected

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