added description of CA repeater
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Jeff Hill
+70
-34
@@ -46,10 +46,11 @@ height="31" width="88"></a></p>
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Information</a></li>
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<li><a href="#port">IP port numbers</a></li>
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<li><a href="#Environmen">WAN Environment</a></li>
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<li><a href="#Dynamic">Disconnect Time Out Interval / Server Beacon
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<li><a href="#Disconnect">Disconnect Time Out Interval / Server Beacon
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Period</a></li>
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<li><a href="#Dynamic">Dynamic Changes in the CA Client Library Search
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Interval</a></li>
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<li><a href="#Repeater">The CA Repeater</a></li>
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<li><a href="#Configurin">Configuring the Time Zone</a></li>
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<li><a href="#Configurin1">Configuring the maximum array size</a></li>
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<li><a href="#Configurin2">Configuring a CA server</a></li>
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@@ -425,6 +426,18 @@ number will default to EPICS_CA_SERVER_PORT.</p>
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</tbody>
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</table>
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<h4><a name="Routing">Routing restiction on vxWorks systems</a></h4>
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<p>Frequently vxWorks systems boot by default with routes limiting access
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only to the local subnet. If a EPICS system is operating in a WAN environment
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it may be necessary to configure routes into the vxWorks system which enable
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a vxWorks based CA server to respond to requests originating outside it's
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subnet. These routing restrinctions can also apply to vxWorks base CA clients
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communicating with off subnet servers. An EPICS system manager can implemnt
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an rudamentary, but robust, form of access control for a particular host by
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not providing routes in that host that reach outside of a limited set of
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subnets. See "routeLib" in the vxWorks reference manual.</p>
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<h3><a name="Disconnect">Disconnect Time Out Interval</a></h3>
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<p>If the CA client library does not see a beacon from a server that it is
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@@ -487,6 +500,28 @@ EPICS_CA_ADDR_LIST was modified to include a destination address for the
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server, but the server's beacon address list was not modified so that it's
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beacons are received by the client.</p>
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<h3><a name="Repeater">The CA Repeater</a></h3>
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<p>When several client processes run on the same host it is not possible for
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all of them to all directly receive a copy of the server beacon messages when
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the beacon messages are sent to unicast addresses, or when legacy IP kernels
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are still in use. To avoid confusion over these restrictions a special UDP
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server, the CA Repeater, is auotomatically spawned by the CA client library
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when it is not found to be running. This program listens for server beacons
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sent to the UDP port specified in the EPICS_CA_REPEATER_PORT parameter and
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fans any beacons received out to any CA client program running on the same
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host that have registered themselves with the CA Repeater. If the CA Repeater
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is not already running on a workstation, then the "caRepeater" program must
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be in your path before using the CA client library for the first time. If a
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host based IOC is run on the same workstation with standalone CA client
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processes, then it is probably best to start the caRepeater process when the
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workstation is booted. Otherwise it is possible for the standalone CA client
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processes to become dependent on a CA repeater started within the confines of
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the host based IOC. As long as the host based IOC continues to run there is
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nothing wrong with this situation, but problems could arise if this host
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based IOC process exits before the standalone client processes which are
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relying on its CA repeater for services exit.</p>
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<h3><a name="Configurin">Configuring the Time Zone</a></h3>
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<p><em>Readers Note: Starting with EPICS R3.14 all of the libraries in the
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@@ -580,7 +615,7 @@ request transportation of large arrays.</p>
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<tr>
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<td>EPICS_CAS_BEACON_ADDR_LIST</td>
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<td>{N.N.N.NN.N.N.N:P...}</td>
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<td>EPICS_CA_ADDR_LIST</td>
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<td>EPICS_CA_ADDR_LIST<sup>1</sup></td>
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</tr>
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<tr>
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<td>EPICS_CAS_BEACON_PERIOD</td>
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@@ -600,55 +635,56 @@ request transportation of large arrays.</p>
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</tbody>
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</table>
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<h4>Server Port</h4>
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<p>The server configures its port number from the EPICS_CAS_SERVER_PORT
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environment variable if it is specified. Otherwise the EPICS_CA_SERVER_PORT
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environment variable determines the server's port number. Two servers can
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share the same UDP port number on the same machine, but there are
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restrictions - see a <a href="#Unicast">discussion of unicast addresses and
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two servers sharing the same UDP port on the same host</a>.</p>
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<h4>Server Beacons</h4>
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<p>CA servers send "beacon" messages to each address specified in
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EPICS_CAS_BEACON_ADDR_LIST, and also any addresses auto configured from
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network interfaces found if EPICS_CAS_AUTO_BEACON_ADDR_LIST is "yes" or
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"YES".</p>
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<h4>Configuring the Server's Beacon Period</h4>
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<p>The EPICS_CAS_BEACON_PERIOD parameter determines the server's beacon
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period and is specified in floating point seconds. The default is typically
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15 seconds. See also <a href="#Disconnect">EPICS_CA_CONN_TMO</a> and <a
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href="#Dynamic">Dynamic Changes in the CA Client Library Search
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Interval</a>.</p>
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<p>The server configures its port number from the EPICS_CAS_SERVER_PORT
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environment variable if it is specified. Otherwise the EPICS_CA_SERVER_PORT
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environment variable determines the server's port number. Two servers can
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share the same UDP port number on the same machine, but there are
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restrictions - see a <a href="#Unicast">discussion of unicast addresses and
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two servers shareing the same UDP port on the same host</a>.</p>
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<p>CA servers build a list of addresses to send beacons to during
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initialization. If EPICS_CAS_AUTO_BEACON_ADDR_LIST has the value "YES" then
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the beacon address list will contain at least the broadcast address of all
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LAN interfaces found in the host and the destination address of all
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point-to-point interfaces found in the host. If EPICS_CAS_BEACON_ADDR_LIST is
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defined then its contents will be used to augment this list. Individual
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entries in EPICS_CAS_BEACON_ADDR_LIST may override the destination port
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number if ":nnn" follows the host name or IP address there. Only if
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EPICS_CAS_BEACON_ADDR_LIST is not defined, EPICS_CA_ADDR_LIST is defined, and
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EPICS_CAS_INTF_ADDR_LIST is not defined, then the contents of
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EPICS_CA_ADDR_LIST will inetead be used to augment this list.</p>
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point-to-point interfaces found in the host.</p>
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<p>If EPICS_CAS_BEACON_ADDR_LIST is defined then its contents will be used to
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augment this list. Individual entries in EPICS_CAS_BEACON_ADDR_LIST may
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override the destination port number if ":nnn" follows the host name or IP
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address there. <sup>1</sup>Alternatively, if EPICS_CAS_BEACON_ADDR_LIST is
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not defined, EPICS_CA_ADDR_LIST is defined, and EPICS_CAS_INTF_ADDR_LIST is
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not defined, then the contents of EPICS_CA_ADDR_LIST will be used to augment
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the list. Otherwise, the list is not augmented.</p>
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<p>The EPICS_CAS_BEACON_PORT parameter specifies the destination port for
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server beacons. The only exception to this occurs when ports are specified
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in EPICS_CAS_BEACON_ADDR_LIST or possibly in EPICS_CA_ADDR_LIST. If
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EPICS_CAS_BEACON_PORT is not specified then beacons are sent to the port
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specified in EPICS_CA_REPEATER_PORT.</p>
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<h4>Binding a Server to a Limited Set of Network Interfaces</h4>
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<p>The parameter EPICS_CAS_INTF_ADDR_LIST allows a ca server to bind itself
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to a limited set of network interfaces (each specified by its IP address). By
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defualt, the CA server is accessible from all network interfaces configured
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into its host. <em>In R3.14 and R3.13 the CA server employed by
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iocCore does not implemet this feature</em>.</p>
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into its host. <em>In R3.14 and R3.13 the CA server employed by iocCore does
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not implemet this feature</em>.</p>
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<h4>Client Configuration that also Applies to Servers</h4>
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<p>See also <a href="#Configurin1">Configuring the Maximum Array Size</a>.</p>
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<p>Typically vxWorks hosts boot with routes configured for the host's subnet.
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If a EPICS system is operating in a WAN environment it may be necessary to
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configure routes into the vxWorks system which enable a vxWorks based CA
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server to respond to requests originating outside it's subnet. An EPICS
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system manager can implemnt an rudamentary, but robust, form of access
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control for a particular host by not providing routes in that host that reach
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outside of a limited set of subnets.</p>
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<p>See also <a href="#Routing">Routing restiction on vxWorks systems</a>.</p>
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<h2><a name="Troublesho">Troubleshooting</a></h2>
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@@ -2505,7 +2541,7 @@ and then output to the console.</p>
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<dd>write access denied</dd>
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</dl>
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<p><small>CVS Revision $Id$</small></p>
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<p><small>CVS Revision $Id: CAref.html,v 1.26 2002/08/08 15:37:05 jhill Exp
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$</small></p>
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</body>
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</html>
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