Internet Connection Restarts When I Join a Server

I’m experiencing a very strange issue which pretty much restarts my Internet connection whenever I join a server. This doesn’t happen all the time, and I can often get into one and then play with no problems, but it has gotten so bad that whenever I successfully get into a server, I lose connection after only a few seconds. I did some research online and found others with this problem, but they could only say it was my router. If there’s no way to get rid of this issue without changing my router, is there any way to decrease the chances of it happening at least? I was thinking maybe it had something to do with only allowing map files to download during server joins, but I honestly have no clue and could really use some advice.