Subject: |
Re: CA WAN/gateway extensions notes |
From: |
[email protected] (Steve Lewis) |
Date: |
Mon, 11 Apr 94 09:59:04 PDT |
Chip Watson comments on extending the broadcasts beyond the local subnet...
Some of the functionality mentioned can be realized with Cisco routers.
They can be configured with UDP broadcast forwarding lists. The
granularity is not as fine as suggested, that is, such broadcasts would
not be restricted to "nth" time. However, in many circumstances this
would be an easy fix and involves no EPICS code. Even with the full EPICS
implementation, some routers might need to be configured to support
"directed broadcasts": where the destination IP address is the broadcast
address of another network and the last IP entity in the IP forwarding
chain, which is usually a router, must turn the IP packet into a medium
broadcast packet. (A Sun workstation would do this by default if configured
as usual.)
At LBL at ALS we have a prototype of such a forwarder, but are going to
try using the built-in capability of the Cisco routers within a few weeks.
Note that for connection management to work correctly when an IOC is
restarted, broadcasts must propagate in the reverse direction so the IOC
"beacons" can reach all their potential clients. Our prototype does *NOT*
have this capability and its lack is obvious: All the clients have to be
manually restarted or they never reconnect. The prototype does have a
simple filter.
The restrictions appear to be completely handled by the access control
mechanisms coming in the CA-server with 3.12. So any restrictions built
beyond that would mostly serve restrict broadcast traffic (and hence workload
on the CA UDP server)--still worthwhile in some situations. However 3.12
does not meet CEBAF's June 1 deadline. Thus even if the routers could be
set up, there would be no access protection for awhile, unless you wanted to
temporarily use the LBL forwarders. The author is Al Robb.
In about 18-24 months ATM switches will make all of this even more
feasible and eliminate bandwidth issues for all practical purposes. I
have found funds to buy a small ATM switch to experiment with this fall.
Steve Lewis
PS: Yes, I want that collaboration-wide status display!
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