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<== Date ==> <== Thread ==>
Subject: RE: no channel access to IOC
From: [email protected] (Jeff Hill)
To: <[email protected]>, "Andrew Johnson" <[email protected]>, "Bob Dalesio" <[email protected]>, "tech-talk" <[email protected]>
Date: Wed, 20 Oct 1999 17:49:30 -0600
Andreas,
 
Channel access does not hard code the subnet mask. It obtains the broadcast
address by querying all of the network interface cards during initialization and
asking for the broadcast address that was configured for the network interface.
 
The address range 192.168.10.n is in a class C network. Therefore, the subnet mask
0xffff0000 can not be used. Instead it must be 0xffffff00 or some more restrictive subnet
mask with more least significant bits set.
 
I am surprised that the Linux machine has allowed its net mask to be set to 0xffff0000
when it is in this IP address range. You will probably need to configure the Linux box so
that its network interface is properly configured for your network.
 
Jeff
 
PS:
To avoid subnetting annoyances on our project we placed our controls
network behind a firewall with network address translation (NAT) capabilities, and
allocated an entire class B network for our control system from the address
ranges which are reserved for private  internets. There  are 64,000
host IP addresses in a class B network.
 
PPS:
Configuring different subnet masks on the same network frequently results in
ICMP storms which can impact the performance of broadcast based
communication.
 
 -----Original Message-----
From: [email protected] [mailto:[email protected]]
Sent: Wednesday, October 20, 1999 1:20 PM
To: Andrew Johnson; Bob Dalesio; tech-talk
Subject: Re: no channel access to IOC

Hi Andrew, hi Bob,
actually I tried to set the netmask this way to :ffff0000, but the UDP of the IOC was still the same
192.168.10.255... Is the subnetmask somehow hardcoded in channel access? As I pointed out, the netmask is arbitrary in this system, because it consist only of one (or two) PCs and one IOC, no connection to the outer world. So we tried both, to set it to a B-class subnet or to a C-class subnet on both machines. None of this worked.
I will try it again tomorrow, maybe we missed something. Do you have a link to the debugging tools at LANL, the link to the LANL site from http://www.cebaf.gov/accel/documents/epics_doc.html is not valid anymore (requires authentication).

Thanks,
- Andreas 

Hi Andreas,
        Are the net masks the same? Look at the debugging IOC slides on
the LANL web site for finding the netmask - if you need to.
        Bob

Andrew Johnson wrote:

Hi Andreas,

Luedeke Andreas wrote:
>
> [...] linboot.ioc.1066 > 192.168.255.255.5064: udp 32 (ttl 64, id [...])
...
> [...] iocLin.ioc.1031 > 192.168.10.255.5065: udp 16 (ttl 30, id [...])

These are broadcast addresses on two different subnets which is usually
why they can't communicate - you either need to set their subnet masks to
be the same on both machines, or if your network topology won't allow this
you'll need to set the EPICS_CA_ADDR_LIST environment variable to the
broadcast address of the other subnet (see the Channel Access reference
manual for details).  On an ioc use putEnv("VAR=value") to set this any
time before iocInit.

You can see the subnet mask by using ifShow at the vxWorks shell, and set
it by adding ":ffffff00" (without the quotes) after the target's IP
address in its boot parameters.  Replace the ffffff00 with whatever the
mask should be for its subnet.

- Andrew
--
Complexity comes for free, Simplicity you have to work for.

-- 
Andreas Luedeke, Controls Group, Swiss-Light-Source, PSI
mailto:[email protected], tel:+41-(0)56-310-4002, fax:-3351
 
References:
Re: no channel access to IOC Luedeke Andreas
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