Card 10/ 10
Recap: IP Addresses and Subnets
A prefix splits an address in two, a count follows from the host bits, and ranges must never overlap.
IP addresses let a packet cross networks, and the prefix is the key to every question about them.
- The network layer gives each machine an address that means something across networks. IP does its best and promises nothing more.
- An IPv4 address is 32 bits, split by the prefix into a network part and a host part. The all-zeros and all-ones host values are reserved.
- Reading a block: 32 minus the prefix gives the host bits, 2 to that power gives the addresses, and subtracting two gives the hosts.
- Same network or not depends on the prefix: compare the network parts.
- Private ranges are 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. NAT rewrites the source address and port on the way out.
- IPv6 has 128-bit addresses, /64 subnets and no shortage, so it rarely needs NAT.
- Ranges must not overlap if two networks will ever be joined. Plan them before the first one is built.
| Question | Method |
|---|---|
| How many addresses in this block? | 2 to the power of (32 minus the prefix); subtract 2 for usable hosts, and more on a cloud platform |
| Are these two addresses on the same network? | Set the host bits of each to zero under the shared prefix, and compare |
| Do these two ranges overlap? | Write each as first to last address; they overlap if either range contains the other's first address |
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