Port Monitoring with PRTG

A port is a part of the network address and ensures the proper distribution of connections and data packets. Valid port numbers range from 0 to 65535. Many applications use typical or standardized ports like FTP (port 20), SMTP (port 25), and SNMP (port 161). These ports are used primarily by protocols such as the Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).

The Transmission Control Protocol (TCP) is the most commonly used protocol to send packets. It operates in a connection-oriented manner and requires the establishment of a connection between a client and server before any data can be sent. The server needs to be in a listening state (referred to as passive open) to accept connection requests from clients. the resulting load is higher than with UDP. There are standardized ports for TCP.

The User Datagram Protocol (UDP) is a connectionless protocol. There is no sequential numbering and it generates much less load. Therefore, UDP is more economical, but also more prone to errors. The UDP protocol is often used for applications where packet loss is not that important. There are also standardized ports for UDP.

Paessler PRTG is a comprehensive network and port monitoring tool that helps administrators keep an eye on the health and performance of their networks. In the context of port monitoring, PRTG can monitor the status and activity of network ports on various devices, helping to identify potential issues such as traffic bottlenecks, unauthorized access, or malfunctioning ports. It can monitor ports on switches, routers, and other network devices to ensure optimal network performance.

Port monitoring is a network management technique that is used to analyze traffic on specific ports and to determine whether ports are open or closed for maintaining network security and performance.

A port sniffer is a tool or software that captures and analyzes data on network ports. It is commonly used for network diagnostics and troubleshooting. While port monitoring offers a broader range of functionalities including security features, a port sniffer focuses more on detailed data packet analysis and can be used for specific investigations or audits.

Port mirroring is a network technique that allows you to copy or mirror the network traffic from one network port (or multiple ports) and send that copy to another port on the same network switch. In PRTG, port mirroring is used by the Packet Sniffer sensor to monitor header traffic.

PRTG requires several ports to be open and reachable on your system for full functionality. Here you can find a first overview:

• LDAP port for Active Directory integration: 389 (unsecure), 636 (secure)
• Auto-update and activation: 443
• Communication between cluster nodes: 23570
• Incoming remote probe connections: 23560
• Notifications: 443 (push), 25 (SMTP), 162 (SNMP trap), 514 (Syslog)
• PRTG application server and PRTG core server: 23580
• PRTG web server: 443 (secure), 80 (unsecure); fallbacks: 8443 and 8443+ (secure), 8080+ (unsecure)
• Report generation (PDF): 8085
• Update check and download: 80

In PRTG, “sensors” are the basic monitoring elements. One sensor usually monitors one measured value in your network, for example the traffic of a switch port, the CPU load of a server, or the free space on a disk drive. On average, you need about 5-10 sensors per device or one sensor per switch port.