Communication between the Orc-fortifications scattered across the Mirk-eaves are handled by goblin-runners who rush messages from one to another. The defeat of these runners not only would cut the encampments off from each other, but may result in the interception of important information about the Enemy's movements.
'I have a little challenge for you, ${PLAYER}! Do you see all of those Orc-fortifications out there? They communicate with each other through trained runners -- goblins, usually -- who carry messages from one to another. Defeat those messengers, and their communication will be disrupted.
'If you are fortunate, you might even capture a message or two from them, though they usually memorize the information they are supposed to deliver to avoid such issues.
'When you have done as I have asked, return to me here.'
Goblin-runners can be found throughout the Mirk-eaves.
Ivorel has asked you to intercept and defeat the goblin-runners that carry messages from camp to camp in the Mirk-eaves.
Ivorel is at Echad Sirion, on the eastern banks of the Anduin.
You should return to Ivorel with news of your success.