What is no IP subnet-zero?

The ip subnet-zero command provides the ability to configure and route to subnet-zero subnets. Subnetting with a subnet address of zero is discouraged because of the confusion inherent in having a network and a subnet with indistinguishable addresses.

What does 0 mean in a subnet?

The first subnet that we obtain from the subnetting process, that is 80.0.0.0, is called All-Zeros-Subnet or Subnet-Zero because in the IP address all the bits in the subnet field are set to ‘0’. If we convert from decimal to binary, we obtain the following: 80.0.0.0 = 01010000.

Why do we need IP subnetting?

One goal of a subnet is to split a large network into a grouping of smaller, interconnected networks to help minimize traffic. This way, traffic doesn’t have to flow through unnecessary routs, increasing network speeds. Subnetting, the segmentation of a network address space, improves address allocation efficiency.

What is IP classless command?

Description. This command enables routing based on “classless” addresses. With classless routing, packets can be routed if the router knows a route for a supernet of the addressee. Without classless addressing, the packet is discarded if it arrives at the router and there is no network route for its destination.

Is .255 a usable IP?

0 or . 255 are not usable… in most cases! The reason for this is because we tend to allocate full Class C type addresses to our networks, making it obviously very simple for us to administer. A standard Class C network consists of 256 addresses (0 to 255 inclusive), of which one is the network address (.

How do subnets work?

Subnetting works by applying the concept of extended network addresses to individual computer (and another network device) addresses. An extended network address includes both a network address and additional bits that represent the subnet number.

What is classless and Classful addressing?

Classful addressing is a technique of allocating IP addresses that divides them into five categories. Classless addressing is a technique of allocating IP addresses that is intended to replace classful addressing in order to reduce IP address depletion.

How do I use the subnet zero in Cisco IOS?

Even prior to Cisco IOS Software Release 12.0, subnet zero could be used by entering the ip subnet-zero global configuration command. On the issue of using subnet zero and the all-ones subnet, RFC 1878 states, “This practice (of excluding all-zeros and all-ones subnets) is obsolete.

Why is my IP address equal to the subnet zero address?

So IP address equal to address of (any) subnet is not useable and will be rejected by CLI. The subnet zero is first (thus name ‘zero’ as addresses are counted from zero) subnet of a natural/implicit network block of classfull addressing scheme.

What is the default subnet for a Cisco router?

As of Cisco IOS Software Release 12.0, Cisco routers now have ip subnet-zero enabled by default, but if the network engineer feels that it is unsafe to use subnet zero, the no ip subnet-zero command can be used to restrict the use of subnet zero addresses.

Is it possible to use subnet zero as a subnet?

It should be noted that even though it was discouraged, the entire address space including subnet zero and the all-ones subnet have always been usable. The use of the all-ones subnet was explicitly allowed and the use of subnet zero is explicitly allowed since Cisco IOS Software Release 12.0.