Network Slowdown Due to Multicasting Malfunction

An unknown malfuction in multicast routing caused a network slowdown (and failure in some areas of campus). Multicast routing was disabled to solve the problem.

Late in the afternoon of the previous day, certain network switches began malfunctioning causing intermittent printing failures and other connectivity problems. This morning, a genral network slowdown was observed, and the Network Manager noticed that the core router was operating at 95% CPU capacity. Further investigation revealed that the most heavily loaded ports were those servicing the Internet connection, McIntyre Hall, and the Library. The Wyatt Hall port was also affected to a lesser extent. Analysis of ethernet frames on the Internet connection revealed a high percentage (ca. 99%) of what appeared to be IPv6 ICMP packets. This high percentage of IPv6 packets was also detected by analysis of traffic in McIntyre Hall. In order to simplify troubleshooting efforts, multicast routing was disabled, which caused the network to recover. The odd traffic pattern remain a mystery.