SDL Episode28

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Secure Digital Life #28

Recorded August 15, 2017 at G-Unit Studios in Rhode Island!

Episode Audio

Coming Soon!


  • Doug White
    Cybersecurity professor, President of Secure Technology, and Security Weekly network host.
  • Russell Beauchemin
    Cybersecurity & Network Security Program Advisor and Director of Instructional Support & Learning Innovation at Roger Williams University.
  • Adventures in Subnetting

    Adventures in Subnetting, part Deux

    Some terms:

    Network Address -- The first address in a segment Broadcast Address -- the Last address in a segment CIDR == reference to /n where N is the number of bits in the network portion of the address viz. /24 for

    Example -- the network is and the broadcast is


    Remember, when bits in the Subnet Mask are ON, they assign that bit in the ip address to the network, when bits in the Subnet mask are off, they assign the corresponding bit in the ip address to the host.

    The Idea of VLS (variable length subnets)

    But, subnets don't have to be just /8 /16 and /24. They can really be any combination of bits on and off.

    VLS means you have a massive amount of flexibility about how your network is designed

    The danger of doing this, is complexity. A LOT of people don't understand this very well.

    Example /25 !! 1111 1111.1111 1111.1111 1111.1000 0000

    Basically if it's 0 - 127 it's one network 0, broadcast or 128-255 where the network is 128 and the broadcast is 255

    That's a legit mask but now to compute network and broadcast is a whole different thing.

    Do some examples on the tablet and show Russ' spreadsheet.

    Examples of Cisco CCNA problems

    You need to design a network which has 10 networks and 30 hosts per network maximize the number of hosts for

    Are and in the same network segment?

    Travis Nets

    //Thanks Travis Could you have a subnet mask like 1010 1010? Yep, but you better not.