That could be your ISP, your DSL connection, a cluster of servers en-route or a whole variety of things. Or it could be the DNS servers serving the forum.
The internet was never designed to serve the amount of traffic it does. Outages which last for minutes are nothing to worry about, unless it's mission critical and you have paid out a very big stack of money for failover. Note: mission critical on its own is not enough. You have to have the servers and software for failover back up and they are very, very expensive.