The last subnet in a subnetted network is typically reserved for broadcast addresses, which are used to send data to all devices on that subnet. This means that the broadcast address cannot be assigned to any individual device. As a result, the last subnet is effectively unusable for host assignments, limiting the number of available subnets for actual device connections.
It depends on whether you are using a default subnet mask or you are subnetting the class B network. A default subnet mask would be 255.255.0.0, but if you are subnetting the last 2 octets in the subnet mask could be anything (up to 255 per octet).
The first and last IP address on each network. e.g. In a classful class C network, the IP addresses x.x.x.0 and x.x.x.255 are invalid and cannot be assigned to a network interface card. x.x.x.0 is the network address for the subnet. x.x.x.255 is the network broadcast address for the subnet.
Assuming a default subnet mask of 255.255.255.0 for the IP address 192.168.10.51, the Network ID is 192.168.10.0. The first three octets (192.168.10) represent the network portion, while the last octet (51) identifies the specific host within that network. Thus, the Network ID indicates the entire subnet where the host resides.
In a subnet mask, the last octet value of 252 corresponds to the binary representation of 11111100. This means that the first six bits are used for the network part, while the last two bits are for the host part. Therefore, a subnet mask of 255.255.255.252 allows for only two usable IP addresses within that subnet.
For a start, two computers on the same network should have the same subnet mask. If two computers that are indeed on the same network have different subnet masks, there is a design problem. Now, even if you look only at the last subnet mask - the least restrictive one - the computers are NOT on the same subnet mask. The subnet mask 255.255.0.0 indicates that the first two bytes (or the first 16 bits) of an IP address have to match, to be considered part of the same network. If you look at the IP addresses, this is not the case.
Since a subnet mask is used to separate the network id from the host id, any 1 bits indicate the network portion and the 0 bits indicate host portion. As an example, in the subnet mask: 255.255.0.0 This indicates the first two octets are used for the network, and the last two octets (ipV4) are used for host portion of an address.
A class A network has more IP addresses - you can connect more hosts on it.A class C network has 256 IP addresses (of which you can use 254), a class B network about 65,000, a class A network about 17 million.More specifically, a Class A network can have 16,777,214 usable host addresses per network whereas a Class B network can have 65,6534 usable host addresses per network.Another advantage is the ridiculous amounts of subnetting you can do. For example, in a Class C network, you can't borrow the same number of bits as you can with a Class A because you only have the last octet to work with for the host portion. With a Class A network, the last three octets are the entire host portion, so you have 24 bits to work with for subnetting (technically 23 since you can't subnet down through all available bits and have no bits left for hosts =p). Due to the amount of subnets you can have and the 16+ million hosts you can potentially have on the same network, Class A networks are reserved for super big applications (ISPs and gigantic companies).
It must be an IP address in the same subnet. Other than that, the network designer has the flexibility to assign any IP address in the same subnet. Quite often, the first or last IP addresses in a subnet are used, so if a certain interface on this router has IP address 10.0.5.1, and the network mask is 255.255.255.0, I would strongly suspect that the other router has IP address 10.0.5.2 (10.0.5.0 can't be used for this subnet).For serial (point-to-point) connections, to save address space, quite often a subnet /30 is used (that is, a subnet mask of 255.255.255.252), in which case the other router has the only other usable IP address in the subnet. For example, if this router has IP address 10.0.8.26 and a subnet mask 255.255.255.252, the subnet has addresses in the range 10.0.8.24 - 10.0.8.27, but since the first and last addresses can't be used, the only option for a router or other machine on the other end is 10.0.8.25.It must be an IP address in the same subnet. Other than that, the network designer has the flexibility to assign any IP address in the same subnet. Quite often, the first or last IP addresses in a subnet are used, so if a certain interface on this router has IP address 10.0.5.1, and the network mask is 255.255.255.0, I would strongly suspect that the other router has IP address 10.0.5.2 (10.0.5.0 can't be used for this subnet).For serial (point-to-point) connections, to save address space, quite often a subnet /30 is used (that is, a subnet mask of 255.255.255.252), in which case the other router has the only other usable IP address in the subnet. For example, if this router has IP address 10.0.8.26 and a subnet mask 255.255.255.252, the subnet has addresses in the range 10.0.8.24 - 10.0.8.27, but since the first and last addresses can't be used, the only option for a router or other machine on the other end is 10.0.8.25.It must be an IP address in the same subnet. Other than that, the network designer has the flexibility to assign any IP address in the same subnet. Quite often, the first or last IP addresses in a subnet are used, so if a certain interface on this router has IP address 10.0.5.1, and the network mask is 255.255.255.0, I would strongly suspect that the other router has IP address 10.0.5.2 (10.0.5.0 can't be used for this subnet).For serial (point-to-point) connections, to save address space, quite often a subnet /30 is used (that is, a subnet mask of 255.255.255.252), in which case the other router has the only other usable IP address in the subnet. For example, if this router has IP address 10.0.8.26 and a subnet mask 255.255.255.252, the subnet has addresses in the range 10.0.8.24 - 10.0.8.27, but since the first and last addresses can't be used, the only option for a router or other machine on the other end is 10.0.8.25.It must be an IP address in the same subnet. Other than that, the network designer has the flexibility to assign any IP address in the same subnet. Quite often, the first or last IP addresses in a subnet are used, so if a certain interface on this router has IP address 10.0.5.1, and the network mask is 255.255.255.0, I would strongly suspect that the other router has IP address 10.0.5.2 (10.0.5.0 can't be used for this subnet).For serial (point-to-point) connections, to save address space, quite often a subnet /30 is used (that is, a subnet mask of 255.255.255.252), in which case the other router has the only other usable IP address in the subnet. For example, if this router has IP address 10.0.8.26 and a subnet mask 255.255.255.252, the subnet has addresses in the range 10.0.8.24 - 10.0.8.27, but since the first and last addresses can't be used, the only option for a router or other machine on the other end is 10.0.8.25.
A class C network has a subnet mask of 255.255.255.0 and can have 254 IP addresses, for example from 192.168.0.1-192.168.0.255 A class B network has a subnet mask of 255.255.0.0 and can have 255 X 254 IP addresses, for example from 192.168.0.1 - 192.168.255.255
A subnet mask typically appears in the same format as an IP address, consisting of four octets separated by periods (e.g., 255.255.255.0). It identifies the network and host portions of an IP address, with the network part represented by consecutive ones (1s) in binary and the host part by zeros (0s). For example, in the subnet mask 255.255.255.0, the first three octets (255) indicate the network portion, while the last octet (0) indicates the host portion. Subnet masks can also be represented in CIDR notation, such as /24, which signifies that the first 24 bits are used for the network.
because these two subnet are reserve
In the IP address 121.234.52.65, the host portion depends on the subnet mask used. If we assume a common subnet mask of 255.255.255.0 (or /24), the host portion would be the last octet, which is 65. This means that the network portion is 121.234.52, while 65 identifies the specific device within that network.