Alloy programming for example network configuration

Question

Suppose there are 8 pcs and 1 switch, I want to divide three subnets.how to use alloy language program?Can you give an example?

Answer 1

Alloy is a modelling language used mainly to reason about designs. So Forget about "programming".

What you can do in Alloy is to define the general rules of how pc, switch and subnets relate to each other. You can then verify if those rules allow to divide those pc into three subnets, and if the division match your expecations. In the case it does not, congrats, you have found a "bug" in your specification, solving it will improve your understanding of the constraints inherent to the system you are currently modelling.

Answer 2

The following models a small network.

sig IP {}

some sig Subnet {
    range   : some IP
}

abstract sig Node {
    ips     : some IP
}

sig Router extends Node {
    subnets : IP -> lone Subnet
} {
    ips = subnets.Subnet
    all subnet : Subnet {
        lone subnets.subnet
        subnets.subnet in subnet.range
    }
}

sig PC extends Node {} {
    one ips
}


let routes = { disj s1, s2 : Subnet | some r : Router | s1+s2 in r.subnets[IP] }
let subnet[ip] = range.ip
let route[a,b] = subnet[a]->subnet[b] in ^ routes 

fact NoOverlappingRanges    { all ip : IP |  one range.ip }
fact DHCP           { all disj a, b : Node | no (a.ips & b.ips) }
fact Reachable          { all disj a, b : IP | route[a,b] }

run {
    # PC = 8
    # Subnet = 3
    # Router = 1
} for 12

If you run it:

┌───────────┬────────────┐
│this/Router│subnets     │
├───────────┼────┬───────┤
│Router⁰    │IP² │Subnet¹│
│           ├────┼───────┤
│           │IP³ │Subnet⁰│
│           ├────┼───────┤
│           │IP¹¹│Subnet²│
└───────────┴────┴───────┘

┌───────────┬─────┐
│this/Subnet│range│
├───────────┼─────┤
│Subnet⁰    │IP³  │
│           ├─────┤
│           │IP⁴  │
├───────────┼─────┤
│Subnet¹    │IP¹  │
│           ├─────┤
│           │IP²  │
│           ├─────┤
│           │IP⁵  │
│           ├─────┤
│           │IP⁶  │
│           ├─────┤
│           │IP⁷  │
│           ├─────┤
│           │IP⁸  │
│           ├─────┤
│           │IP⁹  │
│           ├─────┤
│           │IP¹⁰ │
├───────────┼─────┤
│Subnet²    │IP⁰  │
│           ├─────┤
│           │IP¹¹ │
└───────────┴─────┘

┌─────────┬────┐
│this/Node│ips │
├─────────┼────┤
│PC⁰      │IP¹⁰│
├─────────┼────┤
│PC¹      │IP⁹ │
├─────────┼────┤
│PC²      │IP⁸ │
├─────────┼────┤
│PC³      │IP⁷ │
├─────────┼────┤
│PC⁴      │IP⁶ │
├─────────┼────┤
│PC⁵      │IP⁵ │
├─────────┼────┤
│PC⁶      │IP⁴ │
├─────────┼────┤
│PC⁷      │IP¹ │
├─────────┼────┤
│Router⁰  │IP² │
│         ├────┤
│         │IP³ │
│         ├────┤
│         │IP¹¹│
└─────────┴────┘

You'd probably like to see what PCs are assigned to what subnet. Then go to the evaluator and type:

ips.~range

┌───────┬───────┐
│PC⁰    │Subnet¹│
├───────┼───────┤
│PC¹    │Subnet¹│
├───────┼───────┤
│PC²    │Subnet¹│
├───────┼───────┤
│PC³    │Subnet¹│
├───────┼───────┤
│PC⁴    │Subnet¹│
├───────┼───────┤
│PC⁵    │Subnet¹│
├───────┼───────┤
│PC⁶    │Subnet⁰│
├───────┼───────┤
│PC⁷    │Subnet¹│
├───────┼───────┤
│Router⁰│Subnet⁰│
│       ├───────┤
│       │Subnet¹│
│       ├───────┤
│       │Subnet²│
└───────┴───────┘

Disclaimer: This was quickly hacked together so there might be modeling errors.