Default subnet mask

Ran into an interesting set of mixups.

Watching testout video series, the instructor says the default subnet mask is always 255.255.0.0 but on the chapter tests the default sub net is 255.255.255.0

So which is the "default" sub net mask?

I am guessing it is 255.255.255.0 but just wanted to make sure.

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Comments

sprkymrk

Default subnet mask for what? Class A, B, or C network?
Class A = 255.0.0.0
Class B = 255.255.0.0
Class C = 255.255.255.0

bcairns

sprkymrk wrote:

Default subnet mask for what? Class A, B, or C network?
Class A = 255.0.0.0
Class B = 255.255.0.0
Class C = 255.255.255.0

Hmmm yes I know the classes, the instructor just said the "default" subnet and the test questions said "default".

Most off the shelf stuff tends to gravitate tward class c - so I was guessing C is the default

darkuser

default = classful ???

Slowhand

There is no one single default subnet mask, but there is a set of defaults, one corresponding to each class, in this context. If you're using the CBT Nuggets, you should be able to find a good explanation about fifteen minutes into the nugget called "IP Addressing" on how it breaks down. In the video, I believe he uses a 172.16.x.x address, which would be a class B address, so it uses the default subnet mask of 255.255.0.0. If your book was using a class C address, (the private range being 192.168.x.x) then it would be a subnet mask of 255.255.255.0. Understanding IP addressing and subnetting is a key topic on this exam, you'll need to understand these kinds of basics in order to really grasp things like DHCP and custom subnetting.

bcairns

Slowhand wrote:

There is no one single default subnet mask, but there is a set of defaults, one corresponding to each class, in this context. If you're using the CBT Nuggets, you should be able to find a good explanation about fifteen minutes into the nugget called "IP Addressing" on how it breaks down. In the video, I believe he uses a 172.16.x.x address, which would be a class B address, so it uses the default subnet mask of 255.255.0.0. If your book was using a class C address, (the private range being 192.168.x.x) then it would be a subnet mask of 255.255.255.0. Understanding IP addressing and subnetting is a key topic on this exam, you'll need to understand these kinds of basics in order to really grasp things like DHCP and custom subnetting.

Thanks !!