What Is a Shared IPv4 Port Block?

A shared IPv4 port block is a range of public ports, on an IPv4 address that several servers share, that is set aside for one server. Traffic that arrives on one of those ports is passed on to your server. Your server is reachable from the internet without needing a whole IPv4 address of its own.

How it works

IPv4 addresses are scarce, so instead of giving every server its own, a provider can give each server a block of ports on a shared address. This is port forwarding: a rule says that traffic reaching, for example, port 20001 on the shared address goes to port 8080 on your server.

You connect by naming the port as well as the address, as in ssh -p 20000 root@203.0.113.10 or http://203.0.113.10:20001. Ports outside your block belong to other servers, so the standard web ports 80 and 443 are not yours on a shared address.

When to use it

• SSH and admin access to a server.
• Apps you reach on a custom port: dashboards, APIs, game servers, development tools.
• Servers that talk out to the internet but take few incoming connections, such as workers and CI runners.

When not to use it

• A public website on its own domain over IPv4 that needs ports 80 and 443. Use managed web hosting, or give the server a dedicated IPv4 address.
• Anything that needs the address and port numbers never to change. They can change if the server moves to another host (see below).

How it works on VeloxaHost

• Included with every server. Each server gets a block of ports on the region's shared IPv4 address, 10 by default, at no extra charge.
• SSH on the first port. The first port forwards to SSH (port 22). The block and the exact ssh command are on the server's page under How to connect.
• Forward the rest. Point any other port of the block at any port on the server, over TCP or UDP, from the console or the API.
• Mail is blocked by default. Forwarding to port 25 is refused unless support has enabled mail for your organization.
• Moves with the server. If a server moves to another host in the region, for maintenance or a migration, its block moves to that host's shared address, and the address and port numbers can change. The new ones are on the server page.
• No IPv6 yet. US East does not provide IPv6, so the shared IPv4 block, or a dedicated IPv4 address, is how a server is reached.

FAQ

Can I run a website on a shared IPv4 port block?

Yes, on a port in your block, such as http://203.0.113.10:20001. For a site on your own domain on ports 80 and 443, use managed web hosting or a dedicated IPv4 address.

How many ports do I get?

10 by default. The first is used for SSH; the other 9 are yours to forward.

Does the shared block cost extra?

No. It is included with every server.

Can my ports change?

Yes, if the server is moved to another host in the region. The server's page always shows the current address and ports.