Apps Trader Logo

IP Prefix Sizes

Version 1.0

Content Rating 4+

User Rating 1 / 5

Votes 1

IP Prefix Sizes

Anders Pedersen

Education

IOS
GBP 0.00


Download IP Prefix Sizes on the Appstore





* About this app *
This app is created to be used for practicing IP addressing, prefix lengths and routing entries. There are four quiz modes:
- Prefix Length: an IP address and a network prefix is given (e.g. 192.168.1.30 and 192.168.1.24) and the correct prefix length should be selected
- Subnet mask: an IP address and a network prefix is given (e.g. 192.168.1.30 and 192.168.1.24) and the correct subnet mask should be selected
- Network ID: an IP address and a prefix length is given (e.g. 192.168.1.1/24) and the correct network prefix should be selected
- Route Entry: an IP address is given (e.g. 192.168.1.30) and the correct route entry should be selected


* Subnetting and prefix sizes *
The prefix size can both be written as a number (e.g. /24) or as a subnet mask (e.g. 255.255.255.0). Both numbers express the same thing. Namely how many bits of a given 32-bit IPv4 address is assigned as network prefix.

A subnet mask is a bitmask and you can get the network prefix by applying it with a bitwise AND operation to an IP address. A subnet mask can be translated to a prefix size by counting the number of bits that are set (i.e. equals 1).
Example: the subnet mask 255.0.0.0 have 8 bits out of 32 bits set and hence correspond to the prefix size /8.

The remaining the bits of the IP address are assigned as host field. The larger the host field the more host can be assigned within the IP routing prefix.


* Longest match shortest path *
When a router forward an IP packet it needs to find a route entry in its routing table to find the next hop information.
The default criteria for the best route is simple:
- The route entry need to match the destination IP address of the packet
- Of all matching route entries the longest match is preferred (longest prefix length)
- Of all longest matches the shortest path is preferred (smallest metric)

* Calculator *
A calculator which converts between prefix lenght and subnet mask is included. Move the slider to adjust the value.





IP Prefix Sizes screenshot oneIP Prefix Sizes screenshot twoIP Prefix Sizes screenshot threeIP Prefix Sizes screenshot four