Hi,
search in the forum for fail2ban - if i remember right someone used this also for proxmox. I have'nt experience with fail2ban and proxmox but i used it for another server with ssh-access with good results.
fail2ban block the ip (with iptables) after three unsuccesfull logins (you can change in the configuration the fails and blocking time).
if you are unsure on how to use iptables - you might do better with something like apf and bfd to be installed
in the meantime - try this
iptables -A INPUT -s IP-ADDRESS -j DROP
Replace IP-ADDRESS with your actual IP address. For example, if you wish
to block an ip address 24.2.212.100 for whatever reason then type the
command as follows:
# iptables -A INPUT -s 24.2.212.100 -j DROP
A great application to install would be pfsense (you can do this using the ISO in fact in proxmox) or use another server if you want the best results as it can run as a transparent firewall.
I've used iptables -A INPUT -s IP-ADDRESS -j DROP and also iptables -A OUTPUT -dIP-ADDRESS -j DROP
But I can see with iftop that I've heavy traffic from that specified IP.