Solved Network+ Objective 1.3 Lesson - Subnet Masks

---

Hello,

I was watching the video talking about private IPs, and I'm unclear why the subnet mask for class B private networks is 255.240.0.0. What's the 240 all about?

Thanks,

Andrew

@andrew-dorey said:

Hello,

I was watching the video talking about private IPs, and I'm unclear why the subnet mask for class B private networks is 255.240.0.0. What's the 240 all about?

Thanks,

Andrew

Ah the wonderful world of subnetting

Could you tell us which network+ video and time stamp you are referring too? I tried scrolling around to find exactly which video this refers to but it proved futile.

Class B addresses have a mask of /16 which is 255.255.0.0. so yes that 240 is peculiar, there has to be some context to that.

@andrew-dorey,

The way for to distinguish the Class B private IP address range.

The Class B range is from 172.16.0.0 - 172.31.255.255. The only way to limit the private IP addresses to that range was to give it a new default subnet mask of 255.240.0.0 ( or a /12).

It doesn't mean that you and I are limited to use only that but this is away for ISP to filter out this range from being allowed on the internet.

Cordially,
Ronnie Wong
Edutainer, ITProTV

Hello again,

Daniel, the video I was talking about is the Network+: IP Addressing video, from approx. 1:22:05 - 1:22:48.

Thanks for the explanation Ronnie

-Andrew