Experimental Physics and
Industrial Control System

I'm a bit confused here.

I run multiple IOCs on my Linux server all the time, without doing
anything special with the ports.  I do see this message after iocInit()
when starting IOCs after the first one:

**********************************
cas warning: Configured TCP port was unavailable.
cas warning: Using dynamically assigned TCP port 58629,
cas warning: but now two or more servers share the same UDP port.
cas warning: Depending on your IP kernel this server may not be
cas warning: reachable with UDP unicast (a host's IP in
EPICS_CA_ADDR_LIST)
**********************************

However, channel access clients have no trouble connecting to PVs in any
of those IOCs.

This is Fedora Core 9.

Do more recent Linux kernels have a problem with this?

Mark


-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Claude Saunders
Sent: Tuesday, May 17, 2011 9:02 AM
To: [email protected]
Subject: Re: Channel Access not connecting

Hi Bruce,

 From your first sentence, I see "IOC's" (plural) and "linux". I 
recently had what I believe is the same problem, which Andrew Johnson 
kindly helped me understand. If you are running two iocs on one linux 
host, using default ports, you wind up with two processes listening on 
the same udp port. I gather with linux, the network stack will only 
deliver an incoming (pv search) broadcast UDP packet to one of those 
processes. If it happens to be the one without the PV you're looking 
for, then the ca_search fails, even though the other IOC process 
contains the PV.

    - Claude

On 05/17/2011 12:12 AM, Bruce Hill wrote:
  

I've been having trouble with one linux machine where my IOC's appear
to be running correctly, dbgf works from iocsh, but caget from another
window on the same machine fails to connect.     I suspect it has 
something
to do with how the multiple interfaces on this machine are configured,
    

but
so far have been unable to find a solution.

# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:1E:68:79:5C:4E          inet 
addr:134.79.32.161  Bcast:134.79.35.255  Mask:255.255.252.0
         inet6 addr: fe80::21e:68ff:fe79:5c4e/64 Scope:Link
         UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
         RX packets:190759 errors:0 dropped:0 overruns:0 frame:0
         TX packets:43567 errors:0 dropped:0 overruns:0 carrier:0
         collisions:0 txqueuelen:1000
         RX bytes:18427912 (17.5 MiB)  TX bytes:9772031 (9.3 MiB)
         Interrupt:19

eth2      Link encap:Ethernet  HWaddr 00:1E:68:79:5C:50          inet 
addr:192.168.254.2  Bcast:192.168.254.255  Mask:255.255.255.0
         inet6 addr: fe80::21e:68ff:fe79:5c50/64 Scope:Link
         UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
         RX packets:1238443 errors:0 dropped:0 overruns:0 frame:0
         TX packets:879202 errors:0 dropped:0 overruns:0 carrier:0
         collisions:0 txqueuelen:1000
         RX bytes:80539799 (76.8 MiB)  TX bytes:64420869 (61.4 MiB)
         Interrupt:20 Base address:0x4000

Gateway is 134.79.35.1

I'm running with defaults for the EPICS_CA* and EPICS_CAS* env
    

variables,
  

but have also played with EPICS_CA_ADDR_LIST, EPICS_CA_AUTO_ADDR_LIST,
and EPICS_CA_INTF_ADDR_LIST with no success.

See attached files for casr, epicsEnvShow, ifconfig, and netstat
    

output
  

for more configuration details.     We're running base 3.14.9 
everywhere, but this
is the only machine showing this problem.

The casr output includes:
UDP Server:
UDP 0.0.0.0:0(): User="", V4.0, 0 Channels, Priority=0

This looks wrong to me, as my working IOC's show a valid UDP addr, but
    

I'm
not sure how to fix this, or even if this is the root problem.

Any suggestions would be appreciated.
Thanks,
- Bruce

P.S.  When I run caget, tcpdump shows:
# /usr/sbin/tcpdump -i eth0  -n -nn udp dst portrange 5064-5065
tcpdump: verbose output suppressed, use -v or -vv for full protocol 
decode
listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
21:46:55.934345 IP 192.168.254.2.54260 > 134.79.35.255.5065: UDP, 
length 16
21:46:57.179960 IP 134.79.32.161.43268 > 134.79.35.255.5064: UDP, 
length 48
21:46:57.211939 IP 134.79.32.161.43268 > 134.79.35.255.5064: UDP, 
length 48
21:46:57.275932 IP 134.79.32.161.43268 > 134.79.35.255.5064: UDP, 
length 48
21:46:57.403935 IP 134.79.32.161.43268 > 134.79.35.255.5064: UDP, 
length 48

    

-- 
Bruce Hill
Member Technical Staff
SLAC National Accelerator Lab
2575 Sand Hill Road M/S 10
Menlo Park, CA  94025