It is a class B address (The first three numbers (octet) are between 128 and 191), meaning it has a subnet of 255.255.0.0, thus, 129.219 is the network portion, with 51.18 representing the host portion.
It represents the network portion
In an IP address, the network portion identifies the specific network to which a device belongs, while the host portion identifies the individual device within that network. This structure allows for efficient routing of data across the internet by segregating the address into parts that signify the network and the specific device. The division between the network and host portions is determined by the subnet mask, which specifies how many bits are allocated to each portion. For example, in the IP address 192.168.1.10 with a subnet mask of 255.255.255.0, "192.168.1" represents the network portion, and "10" represents the host portion.
Seeing as the IP address of 128.107.10.11 is a class B network, the host portion is 10.11
The host portion specifies the particular network interface's address. The network portion specifies the network address.
The last 3 octets represent the host portion in a class A address.
Network Portion Host Portion
When we express an IPv4 network address, we add a prefix length to the network address. The prefix length is the number of bits in the address that gives us the network portion. For example, in 172.16.4.0 /24, the /24 is the prefix length - it tells us that the first 24 bits are the network address. This leaves the remaining 8 bits, the last octet, as the host portion.
In the IP address 177.100.18.4, the network portion is determined by the subnet mask. Without knowing the subnet mask, it is impossible to accurately determine the network portion. The network portion is used to identify the specific network to which the IP address belongs, helping in routing and communication between devices.
To seprate an ip address from the network address we use subnet mask that can seprate the ip address from the network address
The host portion of an IP address of all zeros indicates that you are referring to 'this network'. For example, the address 145.5.0.0 means the network 145.5
When you set up a sub network you decide upon the subnet mask and this determines the network address (all zeros in the subnet portion of the address) and the broadcast address (all ones in the subnet portion of the address). When you assign the host addresses in your subnet, then you use the addresses between the network address and the broadcast address.
This is a class C address. The network portion is the first three octets, so it would be 209.240.80.0.