WARFRAME USES UDP PORTS 4950 AND 4955 (or whichever ports are set at the in-game options)
in order to let you join games. If you have more than one PC/Console playing Warframe these ports might conflict and the second PC/Console may be unable to communicate

Note: The Xbox One's network protocols are different and shouldn't need this workaround.

To fix this issue, change the network ports used by the second PC/Console.

1. Open the Main Menu ([ESC] on PC), select OPTIONS, then GAMEPLAY.

2. Change the Network Ports [UDP] to another range of numbers (first PC/Console will be using 4950 & 4955 so pick another pair)