Do Zen block any ports?

Zen only block the ports between 135-139 on UDP and TCP, at the outside of our ADSL gateways.  This means traffic on these ports between our ADSL gateways, other Zen servers and the global Internet, would be blocked.

This block is in place because Microsoft Software uses these ports to broadcast packets of information.  If they were not blocked they could potentially add a large number of un-necessary packets to our network, which are intended for use on a private network.

The ports also present a potential security risk to customers - from viruses which might seek access to a system through these ports (for example, Blaster and Welchia) to a malicious Internet user who could use the information made public by these ports in an attempt to gain access or control of other computers.  The block operated by Zen should NOT be considered an alternative to running your own firewall software or hardware.

If you require these ports for an application - e.g. a Microsoft service running between two sites - you are advised to configure VPN access between the sites.  This will allow traffic on ports 135-139 to be carried over the VPN tunnel.