Today I have encountered an extremely weird thing.
I own a dedicated server which runs several CSGO servers, I haven't modified any of them for almost a year. Last night I've noticed that one of the servers is lagging horribly, even though CPU load barely hits 50%. After spending 12 hours doing voodoo stuff (including clean reinstalls), I found out that it only lags on a certain combination of IP and port (the one that it's been using for over a year). Switching to a different IP or a different port completely eliminates any lags, however when using its usual IP, the server suffers from severe lag spikes (red sv and nasty var). The other servers are totally fine too.
I'm not that good at Linux, but from what I've gathered, there are no signs of a ddos attack and no suspicions connections.
Can anyone explain this?