Adding or Changing TCP/UDP Port Assignments

TCP and UDP are Transport layer protocols in the IP protocol suite. These transport layer protocols use ports to establish communication between application layer protocols. For example, all Web traffic uses the HTTP protocol. HTTP is an application layer protocol that uses the standard TCP/UDP port 80. The Internet Assigned Numbers Authority (IANA) is responsible for maintaining the list of standard port numbers and their assignments. For an up-to-date listing of all standard TCP/UDP port assignments, visit www.iana.org.

When the analyzer reads a TCP, UDP or IPX packet, it infers the upper layer protocols by using pre-defined rules of traversal. For example, if the packet has a TCP source or destination port number 80, then the upper layer protocol is HTTP. These rules, which are built in to the software, determine the upper layers of the protocol stack based on the source or destination port numbers in the packet. The built-in rules are based on the standard port assignments. However, it is quite common to come across network systems in which upper layer protocols use user-defined port numbers for both standard and custom protocols. In such cases, the analyzer users can tell the software which port numbers are assigned to which protocols.

The analyzer autotraverses the stack from TCP, UDP and IPX based on the source or destination port number. Many systems use user-defined port numbers for both standard and custom protocols. Here’s how to tell the analyzer about a custom port assignment on the system you are monitoring.

Add a New Port Assignment

1. Choose Set Initial Decoder Parameters from the Options menu on the Control window.
2. Click the TCP tab (or UDP or IPX for those protocols).
3. Choose the Single Port radio button
4. Enter the port number in the Port Number box.
5. In the Protocol drop-down list, choose the protocol to traverse to.
6. Click the Add button.

The system adds the new entry to the bottom of the port number list.

Modify an Existing Port Assignment

1. Choose Set Initial Decoder Parameters from the Options menu on the Control window.
2. Click the TCP tab (or UDP or IPX for those protocols).
3. Select (click on and highlight) the port assignment to modify.
4. Change the port number and/or choose the protocol to traverse to.
5. Select the Port Range radio button and specify the starting and ending port numbers.  The range is inclusive.
6. Click the Modify button.

The system displays the changes in port assignment.

Delete a Port Assignment

1. Choose Set Initial Decoder Parameters from the Options menu on the Control window.
2. Click the TCP tab (or UDP or IPX for those protocols).
3. Select (click on and highlight) the port assignment to delete.
4. Select Delete.

The system deletes the port assignment.

Move a Port Assignment

If you need to move an entry to ensure it is processed before or after another entry, select the entry in the list and then click the Move Up or Move Down buttons.

Port Assignment Considerations

• The analyzer traverses an entry if either the source or destination port match.
• The analyzer processes port number entries in order from top to bottom.