What would be the reason you would use the no ip subnet zero command?

Question

In networking and subnetting, why wouldn't you want to use the zero subnet? Is this a security reason, or another reason?

Answer 1

It's not entirely security based, using subnet zero for addressing can cause confusion because now you have a network and a subnet with indistinguishable addresses, and so the use of subnet zero was/is sometimes frowned upon.

Consider the IP address 172.16.1.10. The subnet address corresponding to this IP address is subnet 172.16.0.0 (subnet zero). This is confusingly identical to network address 172.16.0.0, which was subnetted in the first place, so whenever you perform subnetting, you get a network and a subnet (subnet zero) with indistinguishable addresses. This can be confusing.

Answer 2

Its security based. Subnet masks are used to separate computer networks. For instance, computers with a subnet mask of 255.255.0.0 and ips of 10.1.0.1 and 10.2.0.1 will not be able to communicate with each other without a router because of the subnet mask.

So a subnet mask of 0.0.0.0 would allow all computers to communicate without routers, which is a big security risk.