10.0.0.0/24: Range, Gateway 10.0.0.1 and Overlap Risks

What 10.0.0.0/24 is

It is a private /24 with 254 usable addresses. The gateway is conventionally 10.0.0.1.

Because it sits at the very start of 10.0.0.0/16, it is also the first subnet of almost every VPC created with default settings.

Home gateways

Comcast Xfinity gateways default to 10.0.0.1 with a 10.0.0.0/24 LAN, and other ISP devices do the same.
Cloud examples and labs

Terraform examples, CloudFormation templates and training labs very often use 10.0.0.0/24 as "subnet 1" inside 10.0.0.0/16.

Remote workers on Xfinity. If your VPC or office uses 10.0.0.0/24, users at home on an Xfinity gateway can't reach it over the VPN. Their laptop routes 10.0.0.x to the local LAN.
Copy-pasted infrastructure. Two VPCs built from the same tutorial both have 10.0.0.0/24 subnets. Check before peering with the overlap checker.

Going from /24 to /25 borrows 25 − 24 = 1 bit from the host part.
Each borrowed bit doubles the number of subnets: 2¹ = 2 subnets.
Each /25 keeps 32 − 25 = 7 host bits: 2⁷ = 128 addresses, so 126 usable after removing network and broadcast.
The new mask is 255.255.255.128, so subnets step by 128 in the fourth octet: 10.0.0.0/25, 10.0.0.128/25 up to 10.0.0.128/25.

Ways to split 10.0.0.0/24
Split into	Subnets	Usable each	First blocks	Good for
/25	2	126	10.0.0.0/25, 10.0.0.128/25	Two halves, e.g. app and database tiers.
/26	4	62	10.0.0.0/26, 10.0.0.64/26, …	Four subnets — one per AZ plus a spare.
/28	16	14	10.0.0.0/28, 10.0.0.16/28, …	Sixteen /28s, the smallest AWS subnet size (11 usable each).

What is the gateway for 10.0.0.0/24?

Usually 10.0.0.1. On AWS the VPC router always uses the network address plus one, which is 10.0.0.1 for this subnet.

How many hosts are in 10.0.0.0/24?

254 on a normal network. In an AWS subnet, 251 because AWS reserves 5 addresses.

Is 10.0.0.0/24 the same as 10.0.0.0/8?

No. 10.0.0.0/24 is 256 addresses; 10.0.0.0/8 is 16.7 million. Mixing them up in a firewall rule is a common and serious mistake.