Thanks. That looks like what we need.

But I do have a further query. For historical reasons which I won't go
into, the production server has on 4-port NIC. Each port on the NIC is
patched individually into a switch with two going to the primary and two
going to the secondary. They all have different IP's Then the four IP's are
bound to one virtual IP address which matches the servers DNS. I am told
the reason for this setup is we could stand a failure on up to 3 of the
switch ports but of course we would be toast if the NIC failed.

Anyway that requires some additional configuration of course. And since
each server is behind an application firewall and sends traffic to other
systems behind other firewalls we have to make sure outbound traffic has
the DNS IP else it will be blocked by the firewalls.

The DR site is similarly setup except of course all the IP addresses are in
a different subnet and behind different firewalls with rules based on the
primary IP there.

So we would create two IP interfaces setup as above with on interface as
primary and one as secondary and name them accordingly.

Then the startup program would interrogate the serial number and start the
appropriate interface.

Sounds like the perfect solution. I might get our tech guys to try it on
one of our test LPARs which we can IPL at will and access via the console
to check IP configuration has been done.


On Sat, Oct 30, 2021 at 10:42 PM Marc Rauzier <marc.rauzier@xxxxxxxxx>

Le 30/10/2021 à 11:13, Laurence Chiu a écrit :
It was mentioned that the production LPAR could have two IP stacks
one for the production site and one for the DR site. Then on IPL the
startup script could interrogate the serial number of the server it was
running on and implement the appropriate IP stack. That sounds like the
right answer but we don't have the expertise or knowledge to know how to

First of all set up IP interfaces (not stacks) not to automatically
start. Review AUTOSTART parameter of CHG(ADD)TCPIFC command.

You can setup gateways to specify preferred interfaces, so that they are
used only when on the appropriate site. Review CHG(ADD)TCPRTE command
and its BINDIFC parameter.

Then, in the startup program (the one in QSTRUPPGM system value), before
starting any service of sub-system, add a couple of lines as below:

Retrieve serial number from QSRLNBR system value (RTVSYSVAL command)

If serialnumber = siteone, start IP interface of siteone with STRTCPIFC
command (I would suggest to use an alias here in place of the IP itself)

if serialnumber = sitetwo, start IP interface of sitetwo still with

if serialnumber = an unexpected value, do nothing and report a message

Another approach would be to use a dhcp server to provide IP address
(review *IP4DHCP special value of INTNETADR parameter of CHG(ADD)TCPIC
command), and make sure that the dhcp and dns servers of the enterprise
are properly set so that dns is updated on an automatic way from dhcp.

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