On Tue, Mar 02, 2021 at 08:37:02AM +0000, Lech Szychowski via IBM Community wrote:
> Two networks ie two different subnets?
Two different subnets yes. The HMC needs a 1:1 relationship between
the HMC and the FSP port (IP), and having two IPs on the same subnet
is a common problem in networking.
> But is it required to have a separate VLAN for each of this
> subnet?
No. VLANs aren't needed in this instance, just subnets. We are using
the open network with static IPs, so that's ok. The static IPs could
share a VLAN.
VLANs are mandatory if you are using a private interface with DHCP
enabled, because you are going to conflict with other DHCP services on
that VLAN.
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Russell Adams
Russell.Adams@AdamsSystems.nlPrincipal Consultant Adams Systems Consultancy
http://adamssystems.nl/
Original Message:
Sent: 3/2/2021 3:37:00 AM
From: Lech Szychowski
Subject: RE: Redundant HMCS, flat open network?
Two networks ie two different subnets? OK, seems fair enough because from the FSP network stack perspective having two different interfaces in the same subnet makes it difficult to tell which one should be used to contact each HMC. But is it required to have a separate VLAN for each of this subnet?
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Lech Szychowski
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Original Message:
Sent: Mon March 01, 2021 10:02 AM
From: Russell Adams
Subject: Redundant HMCS, flat open network?
To answer my own question for future searches, IBM has said that two HMCs on the same subnet may not manage an FSP, even on a single IP/port. They stated the HMCs will compete to manage the server, knocking the other HMC offline and causing "No connection" errors. Thus it is not a supported configuration.
This is an application topology layer issue with the HMC having a 1:1 mapping between HMCs and FSP ports extended to networking. That's not a problem, it just needs to be documented somewhere that while it may look like it's working that it is not supported.
Redundant HMCs must always have two networks for each HMC/FSP pair, open or private.
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Russell Adams
Original Message:
Sent: Wed February 24, 2021 09:11 AM
From: Russell Adams
Subject: Redundant HMCS, flat open network?
I'm well aware that the best practices for two redundant HMCs is to give each HMC a public/open network connection, and a private VLAN for FSP communication for each HMC. Then each POWER system attaches their HMC1 and HMC2 ports to the respective private VLAN. That's 3 networks total: one open, two private.
I'm in a situation where I've been asked to connect both two HMCs and the HMC ports on the FSP to the same open network. The customer doesn't want any extra VLANs at all. No problem assigning static IPs on the FSP ports, and I know a single HMC can manage FSPs on an open network on a single port.
The question is will the FSP allow both HMC ports to be on the same subnet for redundant HMCs?
I can't find this documented anywhere, and in my old notes I found a reference to B1A38B24 where the ASMI may reject IPs on the same subnet?
Does anyone else know if this is allowed?
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Russell Adams
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