Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Tue, 14 Oct 2014 11:37:19 -0500

On 10/14/2014 07:12 AM, Ryan Pierce wrote:
> I'm wondering what I think may be the same thing. Is it possible to
> tunnel EPICS over TCP? I'd like it to work between subnets without
> having to dual-home a host on both.

It is possible to tunnel the CA protocol over TCP, but it's going to be
a unidirectional connection. In the case below that should work because
there is only one CA server.

> On Oct 14, 2014, at 2:45 AM, HaveF <[email protected] wrote:

>> |              router A                          router B
>>            +-------------+                   +-------------+
>>            | 202.201.1.4 |                   | 202.201.1.5 |
>>            +-------------+                   +-------------+
>>              /                                \
>>             /                                  \
>>            /                                    \
>>        +---------------+                     +---------------+
>>        | 192.168.1.200 |                     | 192.168.1.100 |
>>        |   CAS         |                     |   camonitor   |
>>        |               |                     |               |
>>        +---------------+                     +---------------+
>> |
>>
>> Could it possible to get pv from another subnet?
>>
>> Could it possible to Set the CAS’s EPICS_CA_ADDR_LIST to 202.201.1.5,
>> and then configure router B, map the port 5065 to 192.168.1.255:5065
>> <http://192.168.1.255:5065>?

I think what you can do may depend on the capabilities of your routers,
but what you describe doesn't make much sense to me. The connection
between the two end nodes is initiated by the client, in this case the
camonitor program, so it needs to know how to connect to the CAS, not
the other way around. The fact that you are using unroutable IP
addresses and that from their addresses both the client and server nodes
appear to be living in the same IP subnet may make this tricky.

You may be able to set up a TCP tunnel from router B so that a
connection from the 192.168.1.100 node made to a specific port on router
B's internal IP address would be tunnelled through to router A and
result in a TCP connection to port 5064 on the CAS node.

If you can do that, you would configure the 192.168.1.100 node with the
environment variable EPICS_CA_NAME_SERVERS set to the IP Addr:port
number of the tunnel entrance on router B. You may also want to set its
EPICS_CA_AUTO_ADDR_LIST variable to NO if you want to suppress UDP name
search broadcasts on subnet B. The camonitor program will then make a
TCP connection through the tunnel directly to the CAS and use this for
its name searches and data connection.

HTH,

-- 
People everywhere confuse what they read in newspapers with news.
-- A. J. Liebling

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System