Tracking Attacks

I think I’m being attacked, I have a network monitor and it monitored hundreds of attacks to the same port per second!

I launched a packet sniffer to extract packets and compared them to each other, exactly the same 1k worth of text, reads like bits and pieces of a book.

The problem is that the IP’s are spoofed so I can’t just to to they’re ISP. What can I do? Anyways to block them without closing up the port(needed for mud services)?