Most of the Linux distributions specify local port range from 16384 to 65536 and this may be too low for very high bandwidth and busy boxes, let’s say SMTP, Hosting, POP3/Imap and Proxy servers.
You can adjust this setting by editing /etc/sysctl.conf file and replacing the default:

net.ipv4.ip_local_port_range = 16384 65536

with

net.ipv4.ip_local_port_range = 1024 65536