What Ports Are Blocked?
Published on March 14, 2022•Updated on November 21, 2023
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)