So I got a spanking big time from the INE ROUTE practice exam, which follows with video answers of both why the answer were either right or wrong, as well as highlighting where to look on the Topology to meet the criteria of the objective.
One thing that I picked up was a subnetting trick I maybe had long since forgotten, or never knew, I believe I always wrote out the binary math.
However when you are looking at “You need to create a subnetwork within the address space of 18.104.22.168 /24 while there is already x.x.x.x/27, x.x.x.x/28, x.x.x.x/28, …” etc. So you had to choose a mask to fit 5 hosts somewhere in this network that was already very covered already.
So there is a rule I don’t believe I ever used on test:
/32 = increments in 0
/31 = increments in 2’s
/30 = increments in 4’s
/29 = increments in 8’s
/28 = increments in 16’s
/27 = increments in 32’s
/26 = increments in 64’s
/25 = increments in 128’s
/24 = repeats into the lower octets
So you can use this not only to quickly identify okay I need a /29, but then you can immediately got to town finding the network ranges of the preconfigured networks, eliminating them rapidly rather than using binary math to find their network range (though it still is a valid way to do it).
You do also have to take into consideration the increments are minus 2 for a network and broadcast address. Otherwise you can use this to find the network range extremely faster than binary math!
I will add more tips as I find them to making it through this exam, back to explanations of the TONS of answers I got wrong, they have some monster Topology’s on their practice exams!
** BGP Redistributed routes are advertised with a default cost of 10**