PracNet Subnet Guide - VLSM

Practical Networking’s Subnetting Mastery playlist

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PracNet Subnetting - VLSM (Variable-Length Subnet Masks)

FLSM (Fixed-Length Subnet Masks)

• Up until now, we’ve been using FLSM (Fixed-Length Subnet Masks) to subnet our networks.
  • This means that all of the subnets use the same prefix length.
  • (ie. subnetting a class C network into 4 subnets using /26).

VLSM (Variable-Length Subnet Masks)

• VLSM (Variable-Length Subnet Masks) is where you make subnets of different (variable) sizes, in order to use your network addresses more efficiently.

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VLSM Steps (Through PracNet)

1. Determine required sub-network sizes.
2. Allocate IP blocks from largest to smallest (IP blocks is referring to the subnets that we’ve got).

PracNet’s Question and Answer

• PracNet solved R2’s subnet sizes inefficiently on purpose, in order to teach us how to use VLSM.
• R3’s subnet sizes were solved following steps 1 & 2.
• The point-to-point connection between R1-R2 & R1-R3 was solved using /31, as it allows for 2 addresses if we don’t allocate a Network Address and Broadcast Address, however, /30 would work as well. (According to Jeremy, it’s recommended to use /30 in the exam.)

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VLSM Steps (Through Jeremy’s IT Lab)

Despite the steps being a bit different, it’s still the same concept and VLSM is done the same way.

1. Assign the largest subnet at the start of the address space.
2. Assign the second-largest subnet after it.
3. Repeat the process until all subnets have been assigned.

Jeremy’s Question and Answer

My solution of the question in Inkodo:

• Additionally, I calculated the following variables in each subnet:
  1. Network Address
  2. Broadcast Address
  3. First Possible Address
  4. Last Possible Address
  5. Number of Usable Hosts

My solution