> For the complete documentation index, see [llms.txt](https://notes.joeir.net/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://notes.joeir.net/system-administration/networking-cheatsheet.md).

# Networking cheatsheet

## Get DNS records

Using default DNS resolvers:

```bash
nslookup google.com
```

Using Cloudflare (`1.1.1.1`) DNS resolver:

```bash
nslookup google.com 1.1.1.1
```

## Setup HTTP server with netcat

Run the following to start a HTTP responder on port `5555`:

```bash
while :; do echo -e "HTTP/1.1 200 OK\nContent-Length: 3\n\n ok" | nc -l -p 5555; done
```

To verify TCP connectivity, run the above and then:

```bash
curl localhost:5555
# or
wget -qO - localhost:5555
```

## Verifying port connectivity

To verify that port `443` is open on `google.com`, use:

```bash
nc -zv google.com 443
```

Generic structure of command:

```bash
nc -zv ${HOSTNAME} ${PORT}
```