問題文
A design has one router hand a label to the router below it, rather than the other way round, so that the router below looks the label up in a table tied to the tunnel it arrived over. An engineer has to record what the upstream router does about its own tables, and the condition that has to hold before such a binding is put to use at all. Which statement is correct?
選択肢
- The map of the inbound labels at the upstream device gains no entry for that value, and the binding stays unused until support at the downstream device is already known.
- The map of the outbound labels at the upstream device gains no entry for that value, and the binding stays unused until support at the downstream device is already probable.
- The map of the inbound labels at the upstream device gains no entry for that value, and the binding stays unused until support at the downstream device is already probable.
- The map of the outbound labels at the upstream device gains no entry for that value, and the binding stays unused until support at the downstream device is already known.