• First things first, what is a MAC address? A MAC address is a unique physical address assigned to a device that is 6 bytes in length. It is easily discernible by its hexadecimal format and an example of one is 2FF8.0A22.3B0E. As stated above, MAC addresses are completely unique and…

    First things first, what is a MAC address?

    A MAC address is a unique physical address assigned to a device that is 6 bytes in length. It is easily discernible by its hexadecimal format and an example of one is 2FF8.0A22.3B0E. As stated above, MAC addresses are completely unique and no two devices should have the same MAC, much like no two houses on the same street should have the same address, but a MAC can be spoofed or faked to impersonate a network device.

    If your curious to see your MAC address and your on a Windows machine, press the Windows Key + R, type CMD, and then type ipconfig /all and look for your physical address.

    What is the MAC Address Table?

    In every switch there is a piece of memory called the MAC address-table. This table is responsible for holding all of the known and active MAC addresses that the switch has learned. The switch then uses this information to efficiently switch packets from its source to its destination.

    Here is an example of what a MAC address-table looks like.

    Source: Cisco question regarding static MAC addresses on switch – Network Engineering Stack Exchange

    Using the show mac address-table (Cisco, Aruba devices) or show etherchannel-switching table (Juniper) command and moving across the headers left to right in the image above, we have,
    – The VLAN associated with that MAC,
    – The MAC Address itself,
    – The type, meaning if it was dynamically or statically learned which I will touch on.
    – The ports this MAC address is known on.

    These MACs are what the switch will use to determine where to send a packet.

    How does a switch learn about these MAC addresses?

    Let’s assume we have a switch established on the network and we connect a brand new PC to it. It’s evitable that the PC will send a packet out of its NIC towards the switch. Once the switch receives the packet it will look at the destination MAC address to see where it’s going and the source MAC address to see who and where it’s coming from.
    The switch will then compare the source MAC with it’s MAC address table to see if it knows about it, if it does it won’t take further action concerning the source MAC address, if it doesn’t it will add that MAC to the address table, along with the VLAN, how it was learned (dynamically or statically talked about later), and which interface it came out of.

    How long does a switch keep a MAC in the MAC address table?

    By default, switches (Cisco, Aruba, and Juniper to my knowledge) will keep a MAC for 300 seconds/five minutes. This of course can be changed, but it’s not recommended due to decreased network stability, compatibility issues with other network devices and protocols, and added difficulty in troubleshooting if something goes wrong.

    What are the differences between dynamic and static MAC addresses?

    Dynamic MAC Addresses

    A dynamic MAC address is simply one that is learned by the switch as part of the process mentioned above when a switch receives a source MAC address it doesn’t know. When you look at the show mac address-table command it will display Dynamic.

    Static MAC Addresses

    These are MAC addresses set by the administrator. Maybe they want a specific MAC address to stay in the switch instead of dropping off after 300 seconds.

    What happens if there are duplicate entries in the MAC address-table?

    Duplicate MAC addresses occur when a MAC is configured statically and a switch learns the same MAC dynamically.

    What happens? The static MAC address will be the chosen path on the switch! Almost any statically set configuration will near always be selected as the preferred option if there is a choice between that and a dynamically learned option. I say almost because, there has to be one catch out there I haven’t encountered yet 🙂

    And that’s a high level overview of MACs and the switches MAC address-table. Please ask any questions or if there is a discrepancy in what I’ve written let me know! I can learn and correct it.

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  • It’s crazy to think about but I’ve been out of the military for three years now. The climate has definitely changed since I EAS’d in 2019, and covid-19 didn’t help. The entire time I was getting my check out sheet signed off from my command I was freaking out, like…

    It’s crazy to think about but I’ve been out of the military for three years now. The climate has definitely changed since I EAS’d in 2019, and covid-19 didn’t help.
    The entire time I was getting my check out sheet signed off from my command I was freaking out, like I think most of us do, wondering if I had the skills to make it on the other side, but there were tons of programs and options that I was only made aware of toward the end of my enlistment that would’ve been beneficial to know about much, much sooner. These things are typically hidden away and only given to you when you take your transition assistance program, or you have a mentor, someone who’s been in your position, and wants you to succeed. That’s my goal today, to take a bit of the burden off your transition and help get you into the civilian side without much if any trouble!

    Microsoft Software & Systems Academy (MSSA)

    I was lucky to learn about this program a year before my EAS and was able to attend. The MSSA is and four and a half month program designed to get you spun up on the latest technologies and prepare you for life on the outside. There are three different tracks you can take depending on your interests, Server and Cloud Administration, Cloud application Development, Cybersecurity Operations.
    I beg you, don’t pick Cybersecurity Operations if you go the MSSA route. Cybersecurity is a huge field, no really, it’s massive, and I won’t tell you it’s impossible to land a job, but this is insane mode if you’re not coming into the class without having a background in information technology.
    This course will hook you up with a first round interview with Microsoft, a company whose specific purpose is to find you job opportunities, over 1k companies will receive you resume, and the course has an amazing track record of 95% of students graduating and over 99% employed or continuing their college education.
    Classes are split up into morning and afternoons. Mornings are strictly technically focused and the afternoons are professional development focused. If you’ve attended your separation class, it’s 4.5 months of that but with a ton more to learn. You’ll have an entire class to bounce your resume off of, get feedback, network, and grow together. If you get the chance, I highly recommend it.
    (Just not the cyber security one, don’t do that to yourself.)
    Microsoft Software & Systems Academy (MSSA) – Microsoft Military Affairs

    Certifications/COOL Program

    If you’re not coming from an IT job in your branch, this might be new territory for you. There are tons of certifications you can get that will help give you a good taste of a certain area of IT.
    If you’re new to IT and maybe aren’t very familiar with computers I recommend starting with CompTIA’s A+ certification, this is an entry level certification with a ton of knowledge that could help land you a help desk role. It’s a great place to learn the fundamentals of your own PC.
    After that CompTIA’s Network+, this will give you a high-level understanding of how computers talk to one another, but it won’t get into vendor specific configuration.
    And finally, CompTIA’s Security+, your introduction to security. This certification is required for any government IT work (at least everyone I’ve applied to) and will make you 8570 compliant, which I’ll talk about in more detail here.
    COOL Program
    A highly underutilized resource, the Credentialing Opportunities On-Line (COOL) program helps to get service members certifications for FREE depending on your military occupation. Each branch has it’s own COOL program for you to search for certs. Check it out here DOD COOL Portal – Homepage (osd.mil)

    College

    I don’t think I have to go into much detail here, but having a degree will definitely make you more valuable to potential employers as your transitioning and if you get a degree in a great IT program, maybe computer science? That will only excel you on the outside.
    At the very least take one class, just one a semester. I highly regret not doing just that.

    DIY

    home labs, this is the true battleground of someone trying to break into and continue to grow in tech. It seems daunting at first, but it doesn’t have to be complicated to start. Maybe poking around in your home router, googling how to best secure it and what all the options are for, sharing files between two computers on your home network, there are a few options you can play with until its time to upgrade, and when it is time to upgrade, eBay and craigslist will definitely be your friend when you’re trying to get better/more gear to play with.

    This is definitely a non-exhaustive list, and I will return as more resources are made and I find them, but these are just some of the ones I wished I would’ve jumped on sooner to help kick start my career.

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