[Day 4] 7. Extra

Router can have multiple Network Interface Cards (NICs):
- A router can have multiple network interfaces to connect to different networks, allowing it to route traffic between them.
Plugins (Nagios context):
- Plugins in Nagios are scripts that execute specific commands to monitor various services or check the status of devices.
System Variables (Nagios context):
- Nagios uses system variables, called macros, that are enclosed in double dollar signs (
```
$USER$
```
  ). These macros can be used within Nagios commands to represent dynamic values (like hostnames, IP addresses, etc.).
Backup Configuration Files:
- Always take a backup of any configuration file before making changes. This is crucial to avoid losing original configurations and to easily restore them if needed. Important for exams as well!
Squid Reverse Proxy and Ports:
- By default, Squid operates on port 3128.
- When configuring Squid as a reverse proxy, you should use the
```
accel
```
  option in the
```
http_port
```
  configuration to enable reverse proxy functionality.
Internet Caching Protocol (ICP):
- ICP is used by Squid for communication between caching proxies. It helps to determine whether a cache can serve a requested resource or if it needs to fetch it from the original server.