Subnetting practice
Unlimited questions, each generated and checked in code: IPv4 network, broadcast and host ranges, VLSM, summary routes and IPv6. Type an answer, check it, and see the working.
Work it out by hand, then check.
The method in four lines
- Write the mask and find the interesting octet: the one that is not 255 or 0.
- The block size is 256 minus that octet’s mask value: /26 is 255.255.255.192, so blocks of 64.
- Count up in blocks to the one holding the address: that is the network; one less than the next block is the broadcast.
- Usable hosts are 2 to the power of the host bits, minus 2.
Then read the routers
Subnetting feeds routing-table, OSPF and ACL questions. The free show-command drill and the 15-question diagnostic put it to work.
Questions people ask
How much subnetting is on the CCNA exam?
Cisco's exam topics include configuring and verifying IPv4 addressing and subnetting (1.6) and IPv6 addressing and prefixes (1.8) under Network Fundamentals, which is 20% of the exam. Addressing also runs through routing, ACL and NAT questions.
What is the fastest way to subnet?
Find the interesting octet and its block size (256 minus the mask value in that octet), then count up in blocks to the one that holds the address. The block's first address is the network and its last is the broadcast.
How does VLSM work?
Sort the needs from largest to smallest, give each the smallest block that holds its hosts, and place each at the next free address that is a multiple of its block size.
Are the questions the same every time?
No. Each question is generated fresh, with its answer worked out in code, so you can practice as long as you like. Nothing is stored or sent.