Thank you Spirit.
I finally found a part of the problem. On this promox node, I have one CT which seems to consume all bandwidth intermittently (>100Mbps) and froze all the node. I migrated all other CT on another nodes except the one with the bandwidth problem. Problem still here. I'm trying to found where come from this. May be the CT is infected with a virus or something like this. Normally, this CT do not have to consume bandwidth as the web sites on it are only used for extranet services.
Do we have a easy way to limit Network Bandwidth Usage for a specific CT?