What Ports Are Blocked?

We block several outbound ports for network security.

Blocked by default

You may request these blocks be removed by opening a support ticket.

• TCP port 25 (SMTP)
• TCP & UDP port 137 (NetBIOS Name Service)
• TCP & UDP port 138 (NetBIOS Datagram)
• TCP & UDP port 139 (NetBIOS Session)
• TCP & UDP port 445 (SMB over TCP)
• TCP port 1688 (Microsoft Key Management Server, inbound only)

Permanently blocked

These ports are commonly abused for DDOS attacks. These blocks are permanent and cannot be removed.

• TCP & UDP port 17
• TCP & UDP port 19
• TCP & UDP port 1900
• UDP port 53413
• UDP port 11211

We also filter RFC1918 address ranges on public network interfaces.

• 10.0.0.0 through 10.255.255.255 (10/8 prefix)
• 172.16.0.0 through 172.31.255.255 (172.16/12 prefix)
• 192.168.0.0 through 192.168.255.255 (192.168/16 prefix)