When you have an internal Veeam-backup-server and you want to backup external linux-servers you need to create a destination NAT on the linux-server. Remember to add that line after every reboot if you do not save/restore iptables-rules during boot. You can choose the line with port-definition or just translate everything. Replace 127.0.0.1 with your external IP on your site.
iptables -t nat -I OUTPUT -d 10.10.10.100/32 -p tcp -m multiport --dports 2500:3300 -j DNAT --to-destination 127.0.0.1
iptables -t nat -I OUTPUT -d 10.10.10.100/32 -p tcp -j DNAT --to-destination 127.0.0.1