Experimental Physics and
Industrial Control System

Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov> · Wed, 28 Oct 2020 07:45:00 -0700

On 10/27/20 11:42 PM, Jeong Han Lee via Tech-talk wrote:
> Hi,
> 
>   I have a silly question about EPICS IOC and its client applications.
> Are they OK with IPv6 addresses only?

Sorry, but no.  The CA protocol as it exists now can only encode
IPv4 addresses in search and beacon messages.  So some extra
work would need to be done to specify a different message format
for these messages over IPv6.

PVA messages do have room, and in fact IPv4 are always encoded as IPv6.

However, both protocols suffer from the fact that existing implementations
are coded assuming AF_INET addressing.

Since my new PVXS client/server is based on libevent, which does handle
IPv6 addressing, I did look into the feasibility of supporting IPv6.

The main obstacle I found was in discovering/inspecting host network
interfaces.  With IPv6 this is both more complicated, as most interfaces
will have more than one address, and less portable.  eg. on Linux
the existing code in libCom uses an API which only returns IPv4
addresses.

In the long run I think that way forward is to move away from search
by broadcast, from which this complexity arises.  With CA we've been
able to add both unicast search over TCP (eg. to a name server) and
multicast UDP search as alternatives.  These methods still need to
be added to the various PVA implementations though.

>   If any sites or persons have some examples, please let me know.

As an aside, after reading a recent article, and finding that the
router/modem in my apartment supported IPv6, I did figure out how
to enable global IPv6 addressing on my laptop.  Mainly I needed to
allow ICMPv6 messages through the laptop firewall.

> $ ping -n google.com
> PING google.com(2607:f8b0:4000:801::200e) 56 data bytes
> 64 bytes from 2607:f8b0:4000:801::200e: icmp_seq=1 ttl=115 time=59.2 ms
...

https://blog.hansenpartnership.com/creating-a-home-ipv6-network/

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System