# Basic examples to get started with NeST

This directory contains the following examples to get started with `NeST`,
and we recommend that the beginners walk through these examples in the same
order as they are presented:

## 1. point-to-point-1.py
This program emulates a point to point network between two hosts `h1` and
`h2`. Five ping packets are sent from `h1` to `h2`, and the success/failure
of these packets is reported. The main aim of this example is to demonstrate
the usage of basic APIs of NeST to create a network topology, configure link
attributes, assign IPv4 addresses and test the connectivity between two hosts.

<!-- The below snippet will render example code in docs website -->
{download}`Source code <point-to-point-1.py>`
```{literalinclude} point-to-point-1.py
---
language: python
linenos:
---
```


## 2. point-to-point-2.py
This program emulates point to point networks that connect two hosts `h1`
and `h2` via a router `r1`. Five ping packets are sent from `h1` to `h2`, and
the success/failure of these packets is reported. This example extends the
`point-to-point-1.py` example. The main aim of this example is to demonstrate
how two networks can be interconnected by using a router. The steps to enable
IPv4 forwarding in the router and setting default routes in the hosts are
covered in this program. We manually set the routes because we are not using
dynamic routing protocols like RIP, OSPF and others.

<!-- The below snippet will render example code in docs website -->
{download}`Source code <point-to-point-2.py>`
```{literalinclude} point-to-point-2.py
---
language: python
linenos:
---
```


## 3. point-to-point-3.py
This program emulates point to point networks that connect two hosts `h1`
and `h2` via two routers `r1` and `r2`. Five ping packets are sent from `h1`
to `h2`, and the success/failure of these packets is reported. This example
extends the `point-to-point-2.py` example. The main aim of this example is
to demonstrate how two networks can be interconnected by a network of routers.
Besides enabling IPv4 forwarding and setting default routes in hosts, this
example requires setting default routes in the routers.

<!-- The below snippet will render example code in docs website -->
{download}`Source code <point-to-point-3.py>`
```{literalinclude} point-to-point-3.py
---
language: python
linenos:
---
```


## 4. simple-lan.py
This program emulates a Local Area Network (LAN). Four hosts: `h1` to `h4`
are connected using a switch `s1`. Five ping packets are sent from `h1` to `h2`
and five ping packets from `h3` to `h4`. The success/failure of these packets
is reported. This example demonstrates how to use the `Switch` class in NeST to
set up a LAN.

<!-- The below snippet will render example code in docs website -->
{download}`Source code <simple-lan.py>`
```{literalinclude} simple-lan.py
---
language: python
linenos:
---
```


## 5. two-lans-connected-directly.py
This program emulates two Local Area Networks (LANs) connected directly to
each other. LAN-1 consists of three hosts `h1` to `h3` connected to switch
`s1`, and LAN-2 consists three hosts `h4` to `h6` connected to switch `s2`.
Switches `s1` and `s2` are connected to each other. Five ping packets are sent
from `h1` to `h4`, five from `h2` to `h5` and lastly, five from `h3` to `h6`.
The success/failure of these packets is reported. This program extends
`simple-lan.py`.

<!-- The below snippet will render example code in docs website -->
{download}`Source code <two-lans-connected-directly.py>`
```{literalinclude} two-lans-connected-directly.py
---
language: python
linenos:
---
```


## 6. two-lans-connected-via-router.py
This program emulates two Local Area Networks (LANs) connected via a router.
LAN-1 consists three hosts `h1` to `h3` connected to switch `s1`, and
LAN-2 consists three hosts `h4` to `h6` connected to switch `s2`. Switches
`s1` and `s2` are connected to each other via a router `r1`. Five ping
packets are sent from `h1` to `h4`, five from `h2` to `h5` and lastly, five
from `h3` to `h6`. The success/failure of these packets is reported. This
program extends `two-lans-connected-directly.py`.

<!-- The below snippet will render example code in docs website -->
{download}`Source code <two-lans-connected-via-router.py>`
```{literalinclude} two-lans-connected-via-router.py
---
language: python
linenos:
---
```