Experimental Physics and
Industrial Control System

Ralph Lange <[email protected]> · Mon, 31 Mar 2014 17:15:41 +0200

All,

As probably many of you know, running multiple IOCs on one host has an

annoying side effect: Clients that are using that host's IP address in

their EPICS_CA_ADDR_LIST with EPICS_CA_AUTO_ADDR_LIST=NO will only reach

one of the IOCs - usually the one that was started last. All clients

have to use broadcasts to reach all IOCs.

The same is true for CA Gateway machines that are set up in a way that

makes multiple Gateway processes serve channels into the same network.

Here's a little helper (for Linux hosts) that I recently was playing

around with - based on an idea by Rodrigo Bongers (CNPEM, Brazil).

If you drop the attached script into /etc/network/if-up.d *and*

/etc/network/if-down.d, it will automatically create/delete an iptables

rule that replaces the destination address of all incoming CA UDP

traffic on each interface with the broadcast address of that interface.

Simple and effective: the kernel will see all incoming name resolution

requests as broadcasts, and delivers them to all IOCs instead of one.

Note: This will not work for clients on the same host. (Adding that

feature makes things a lot more complicated, and I like things to be

simple.)

If you need connections between IOCs on one host, I would suggest adding

the broadcast address of the loopback interface (usually

127.255.255.255) to each IOC's EPICS_CA_ADDR_LIST setting.

Enjoy!
~Ralph

#!/bin/sh -e
# Called when a new interface comes up

# Author: Ralph Lange <[email protected]>

# Make any incoming Channel Access name resolution queries go to the broadcast address
# (to hit all IOCs on this host)

# Change this if you run CA on a non-standard port
PORT=5064

[ "$METHOD" != "none" ] || exit 0
[ "$IFACE" != "lo" ] || exit 0

line=`ifconfig $IFACE | grep "inet addr"`
addr=`echo $line | sed -e 's/.*inet addr:\([0-9\.]*\).*/\1/'`
bcast=`echo $line | sed -e 's/.*Bcast:\([0-9\.]*\).*/\1/'`

if [ "$MODE" = "start" ]
then
    iptables -t nat -A PREROUTING -d $addr -p udp --dport $PORT -j DNAT --to-destination $bcast
elif [ "$MODE" = "stop" ]
then
    iptables -t nat -D PREROUTING -d $addr -p udp --dport $PORT -j DNAT --to-destination $bcast
fi

exit 0

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System