Mailinglist Archive: opensuse (621 mails)

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Re: [opensuse] How to connect two servers through an Ethernet A/B switch and not change the upstream MAC addy?
On 06/09/2019 10:58 PM, Lew Wolfgang wrote:
Hi Folks,

I've got an interesting network configuration problem that I'd
like to run by you all.

At this time I've got a server that connects to a switch at 1GbE
over Cat-6 copper with RJ-45 connections. I don't have admin
rights on the switch and it uses MAC address authentication
to turn on the port.

The server is rather important and contains about 400-TB of
data in multiple RAID-6 arrays.  I've received authorization
to purchase a second "mirror" server to act as a warm spare.
They will have a private 192.168 subnet via second Ethernet
ports, maybe 10GbE, to synchronize the data on a regular
basis between the servers.

What's the best way to hook these up?

I'm thinking of something like an RJ-45 A/B switch to manually
connect one or the other server to the upstream switch.  But
then, it looks like simple switches just pass through the two back
MAC addresses, and I need the A/B switch to present the
same MAC to upstream at all times.  Could I use macchanger
on each of the servers to keep the same MAC presented
through the switch?

Or is there a better way?

I am no network export, so take this for what it is worth, but from a couple
of decades of playing with a number of switches, DNS, etc.., I would think
something like the following would be possible in this situation.

+-------------------------+
| switch you can't change |
+-------------------------+
|
+--------------------+--------------------+
| | |
| +-------------------------+ |
| | smart switch providing | |
| | port aggregation with | | Seen as single
| | mac address cloning | | unit with
| | from server A | | failover
| +-------------------------+ | between A -> B
| | | | to upstream
| +------------+ +------------+ | switch
| | server A | | server B | |
| +------------+ +------------+ |
+-----------------------------------------+


The port aggregation can make A / B be treated as a single unit even though
they have independent IP address at the aggregating switch. It should be able
to clone the Mac address from A and put that forward as the Mac for that link.
The failover from A / B can be done several ways, either the switch will be
smart enough to handle a primary/backup role for A / B and handle it there,
some type of old box DNS between A / B and the aggregating switch handling
failover for IPs in the aggregated link should work.

What I don't know is how expensive a switch it will take to do it. Some of
the $120-$150 consumer grade models can do the link aggregation and IIRC
limited failover. If the switch can't handle failover, putting a box running
bind between A / B and the switch that can do it for you at that level.

I'm sure your higher-end switch/router hardware provides a lot more
capability that I haven't even run across yet.

The bigger challenge would seem to be replication between A / B in near
real-time to B so B can pickup from A on failover without much if any loss of
data. (open/temporary documents might be a problem, but hardware raid with
battery powered write-back cache that can be replicated on B may be a way to
mitigate against that to some extent)

That about exhausts the educated guess I would have as a way to research
putting the puzzle together. Remember, it's all elementary until you pull the
power cord on A to see if it works :)

--
David C. Rankin, J.D.,P.E.

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