Is it normal to have thousand of open UDP ports on a high trafficated website when you are using the RemoteEventListner (for chache handling)?It seems like the ports remains until the next application pool recycling.
Are you running CMS 5 SP2 by any chance? There is this known issue there:
#10566 EPiServer Events System consumes all UDP ports after is has been running for several hours
This issue is fixed in SP3 and later.
I am running CMS 5 SP1 (5.1.422.122), so upgrading to SP3 will fix it?
The bug was found in SP2 but it's entirely possible that it was existing in SP1 aswell.
I can't say for sure if upgrading to SP3 will fix it but I would try upgrading and test if that helps resolve the issue.
There are no changes made to the database when upgrading from SP2 to SP3. But since you're using SP1 you're going to have to upgrade the database as well.
The UDP problem is gone after upgrading to CMS 5 SP3 so I'll guess the UDP bug exists in SP1 aswell.