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Ports and Protocols

Updated Jan 16, 2018 ·

Overview​

Ports

  • Logical communication endpoint that exists on a computer or server.

Protocols

  • Defined set of rules and conventions that govern device communication and data exchange.

Types of Ports​

There are physical ports that you connect wires to and logical ports that determine where the data/traffic goes.

  • Physical Ports

    • Refer to the connection points on networking devices like routers, switches, servers, and computers where various cables, such as fiber optic or Cat5 cables, are plugged in to establish a network.

  • Logical Ports

    • When establishing communication between systems, logical ports, or sockets, are used as address numbers for data transfer. Ports enable a single IP address to support multiple simultaneous communications, each using a different port number.

      ProtocolPortSecurity
      HTTP80Insecure
      HTTPS443Secure
      RADIUS auth1812-
      SQL Server1433/1434-
      Docker API2375/2376-

Secure Ports​

Based on direction:

  • Inbound Ports

    • Logical communication opening on a server that is listening for a connection from a client.

  • Outbound Ports

    • Logical communication opening created on a client in order to call out to a server that is listening for a connection.

Grouping of Ports:

  • Well-known Ports (0–1023)

    • Core protocols in the TCP/IP model, such as DNS and SMTP.
    • Assigned by IANA

  • Registered Ports (1024–49151)

    • Each vendor registers the port number (that they want to use) with IANA.
    • Associated with proprietary applications.
    • Example:
      • 1433 - Microsoft SQL Server
      • 3389 - RDP (Microsoft proprietary)

  • Dynamic or private Ports (49152–65535)

    • For sessions associated with well-known or registered ports, dynamically assigned and released.
    • Can be used by any application without the need to be registered with IANA.
    • Commonly used in gaming, instant messaging, and chat for connections.

Port Security​

Port security is a common security feature found on network switches that allows administrators to restrict which devices can connect to a specific port based on the network interface card's MAC address.

Network Switches​

Network switches make traffic switching decision based on the MAC address of the sending and receiving devices, through a process called transparent bridging.

  • Switches prevent collisions by ensuring each port is its own collision domain.
  • This allows switches to operate in full duplex mode.

Concepts:

  • Full duplex

    • This means a port can both receive and send data at the same time.

  • CAM Table

    • Content Address Memory (CAM) Table
    • Stores information about the MAC addresses available on any given port.

  • MAC Flooding

    • Randomized MAC addresses are sent to the network switch.
    • When this happens, the network switch will simply fail open.
    • When it fail-open, the switch begins to rebroadcast all traffic out to every port.
    • For more information, please see MAC Address Flooding

Implementing Port Security​

Port security works in two modes:

  • Static Port Security

    • Manually link MAC addresses of devices to specific network interfaces for enhanced security.
    • Any other unregistered device that tries to plug to the switchport will be rejected.
    • Can be a lengthy process because each MAC address needs to be determined.
    • To simplify the process, we can use "sticky MAC"

  • Dynamic Port Security

    • Also known as Persistent MAC Learning and Sticky Mode
    • Dynamically associate the first MAC address connected to switchport as authorized.
    • Switches memorize the first MAC address they see on each port and limit access to the port.
    • This prevents other MAC addresses from connecting to the specific switch port.
    • Can still be bypassed through MAC spoofing or resetting MAC Addresses.

IEEE 802.1X Protocol​

802.1x is a standardized framework that controls access to networks by verifying devices before they connect.

  • Port-based network access control
  • Requires devices to authenticate before using the network
  • Works with wired and wireless networks
  • This ensures only trusted devices can connect.

For more information, please see IEEE 802.1X Protocol

Components of 802.1X​

  • Supplicant

    • Client device trying to connect.

  • Authenticator

    • Device through which supplicant will go through
    • Network switch or access point

  • Authentication Server

    • Usually RADIUS, performs authentications

Authentication Mechanisms​

  • RADIUS

    • Cross-platform
    • Does NOT support remote access protocol, NetBIOS, or X.25 PAD connections
    • Ideal for mixed network infrastructure.
    • For more information, please see RADIUS

  • TACACS+

    • Cisco-proprietary protocol
    • Slower, relies on TCP, but adds security
    • Supports all networking protocols
    • For more information, please see TACACS+

EAP​

EAP (Extensible Authentication Protocol) is a versatile authentication framework that supports multiple methods for secure access to network resources.

  • A flexible authentication framework supporting methods like EAP-TLS, EAP-TTLS, and PEAP.
  • Commonly used in wireless networks (e.g., Wi-Fi) and secure network access setups.
  • Provides strong security through certificate-based authentication.

For more information, please see EAP

Transport Method​

The transport method refers to the protocols used to move data across networks, primarily TCP and UDP, each serving different purposes based on their characteristics.

TCP​

TCP (Transmission Control Protocol) is a reliable, connection-oriented protocol that ensures data is transferred accurately and in order between devices on a network.

  • Provides reliable, ordered, and error-checked delivery of data.
  • Ensures complete data transfer between sender and receiver.
  • Utilizes handshakes to establish a connection before data transfer.
  • Suitable for applications where data integrity is crucial, e.g. web browsing, email, file transfers.

UDP​

UDP (User Datagram Protocol) is a connectionless protocol that offers fast transmission by not guaranteeing the delivery of packets, often used in real-time communications.

  • Does not guarantee delivery, order, or error checking
  • Has lower overhead compared to TCP, leading to faster data transmission
  • Preferred for real-time applications where speed is critical, e.g. streaming, VoIP, online gaming.