It's worth speaking to the network administrator - if it's only occuring on this server , it may be a cable or network card. If it's occuring across other servers - look at switches \ routers. Collect some good quality statistics , if a network person can run a trace - that can assist Netstat is a useful tool I've used - check some notes - http://www.sqlserver-dba.com/2012/03/sql-server-netstat-monitoring-and-tuning-performance.html