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B.Carpenter and J.M.Gerard CN/CS
For another year or two, most of the CERN Ethernets will be bridged together, which means that problems created anywhere may be felt everywhere. The long-term solution is the sub-division of the network using routers, but at present we have to cope with mutual interference between several thousand computers.
In some cases, such interference is stopped by automatic blocking of the traffic from a faulty system. Other cases escape automatic blocking, but are still serious enough to cause continued CERN-wide disruption of network services. These cases are stopped by manual blocking, when we notice the pattern of faulty traffic (usually continuous broadcasting). We always attempt to contact and advise the person responsible, but often this is simply not possible due to lack of information. We also always attempt to refer the problem to the competent support service in CN (or in AS for Macintosh problems). However, in the case of a device or operating system that enjoys no support at CERN, it is very difficult for us to do more than signal the problem to the user, and leave the system blocked until the problem is solved. This is clearly very frustrating for all concerned, but seems to be one of the penalties of such a wide variety of network hardware and software on a very large shared network.
We also monitor the networks for traffic patterns which are not annoying enough for immediate action, but which still cause intermittent disturbance to network services. In these cases we always attempt to contact the person(s) responsible for the systems concerned. We explain the problems being caused and suggest what needs to be done. In fairness to other users, in the last resort even these systems have to be manually blocked.
The list of blocked systems is always available via Mosaic, Netscape or any other Web browser on the Networks Status page accessed via http://wwwcs.cern.ch/. We always try to unblock systems as soon as it is safe to do so.
As the network is progressively divided up with routers, the global aspect of this problem will disappear, and cases of interference between computers should mainly become local.