Learn to compute IPv4 subnet masks by hand and verify results with simple Linux tools. 22.12.2025 | reading time: 2 min Draw the map before you deploy: subnet masks determine which part of an IP address identifies the network and which part identifies the host, and calculating them manually gives clarity when designing or troubleshooting Linux networks. Split a /24 into four /26 networks Start with the question and do the arithmetic: to split 192.168.10.0/24 into four equal subnets choose /26 because 32 minus 26 equals 6 host bits which gives block size 2^6 equals 64; the subnet mask is 255.255.255.192 so the networks are 192.168.10.0, 192.168.10.64, 192.168.10.128 and 192.168.10.192 with first usable addresses .1, .65, .129, .193 and broadcasts .63, .127, .191, .255; verify on a Linux box with a quick tool like this example: ```bash ipcalc 192.168.10.0/26 # output Address: 192.168.10.0 Netmask: 255.255.255.192 Network: 192.168.10.0 Broadcast: 192.168.10.63 Hosts/Net: 62 ``` What to calculate besides the mask Do not stop at dotted decimal: always compute the number of hosts per subnet, the wildcard mask, network increments and the usable host range; practice variable length subnet masking to pack different size subnets efficiently and perform route summarization to keep routing tables small. Quick Linux checks After doing the math, confirm results on the command line with `ip addr show` to see configured addresses and with utilities such as `ipcalc` or `sipcalc` to print networks and broadcasts; a short verification example for an interface might be: ```bash ip addr show eth0 # output 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 inet 192.168.10.130/26 brd 192.168.10.191 scope global eth0 ``` which shows the assigned prefix and the broadcast in one glance. Mastery and next steps Practice by sketching networks on paper, calculating masks mentally and then checking them on Linux until the steps become automatic; if this interests you, deepen your Linux networking knowledge and consider exam preparation for CompTIA Linux+ or LPIC-1 with intensive courses at bitsandbytes.academy to turn hands-on skill into certification. Join Bits & Bytes Academy First class LINUX exam preparation. network troubleshooting infrastructure
