Collaboratory - Network Problems/Solutions
Under certain network conditions, attempts to
yield the message "Hub cannot establish back-connection to Node..."
Two potential reasons, not mutually exclusive, are discussed:
- The Collaboratory uses an implementation of the Common Object
Request Broker Architecture (CORBA) specification to communicate
between instances of Chimera.
By default, CORBA randomly allocates network ports for communication.
Clients behind firewalls may see this network traffic as a security
threat and block the connections.
- Some routers and firewalls use a process called
Network Address Translation (NAT) that enables several computers on
an intranet to be connected to the internet via a single IP address.
A computer on a network using NAT is assigned a "local" IP address,
often 192.168.1.102, that is only meaningful within the intranet
(cannot be used for messages from elsewhere on the internet).
A computer on a network using NAT may supply its local address
to the Collaboratory hub rather than the address needed
for internet communications.
These problems can be solved by designating a port number and IP
address using the
Regardless of which of the back-connection problems apply,
a specific port number should be designated for communications. The port
number must be greater than 1024, as ports up to 1024 are reserved for
use by the system. If a firewall is blocking connections, it should be
configured to allow incoming TCP traffic on the designated port.
If NAT is known to be used, or the back-connection
error message still appears after a port number has been designated,
the proper IP address should also be supplied.
The proper address is that of the router or computer
supplying the internet connection.
UCSF Computer Graphics Laboratory / December 2003