Blocking Outbound Packets

The recommended default rule for outbound UDP packets from the local system is to block the packets. If you do not follow this recommendation, port usage may, at first sight, appear to violate the firewall's inbound rules.

An example will help illustrate this situation. Suppose that in the example in the previous section:

  • The local node is the SNODE.
  • The default outbound rule allows all outbound UDP packets from the local system.
  • The “SNODE session” rule is accidently omitted.

Because of the callback feature of UDT session establishment, SNODE sessions are still likely to succeed on ports 2000–2200. This may cause confusion because ports 2000–2200 are blocked to inbound UDP packets.

If you use the recommended default outbound rule and apply the PNODE and SNODE rules described in the previous section, there will be no confusion about which port to use, and the UDT callback feature will function as designed, thus supporting reliability.