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 06/10/2019 12:35 AM, Per Jessen wrote:
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.
So not a hot standby, more like a backup copy, but always fairly recent?

Yes, maybe sync the deltas from the active box to the standby every six
hours or so?  Maybe even daily would work okay.  The really dynamic
function being served is Subversion.  Users would still have local
checked-out copies of their data if something went wrong.  svnserve
has a nifty script that does hot-backups of repositories, and I
think it could even be configured to automatically replicate onto
a second server.  I'd have to play around with that one.


What's the best way to hook these up?
First thought - just a cross-over cable between two interfaces. Or
multiple bonded ditto. That's how we run our storage servers with
drbd.

Yes, the servers have two Ethernet interfaces, one will connect to a
back-end subnet for syncing/backups.   There are some other servers
back there that never leave the 192.168.4.0/24 subnet.  NAT is not
used, there's no IP forwarding going on.

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.
As you have funding for purchasing a secon
d server, might it not be feasible to have the 2nd MAC authorised on the
upstream switch?

Yes, a second MAC and port could be used, but then each server
would have different IP addresses.  We've got about 100 local users
using svnserve, samba, NFS, and direct ssh logins, and we need to be
able to quickly switch between the two servers transparently.  A
DNS CNAME could be used, but the switch time would depend on
caches timing out.  I wouldn't think that switching would happen
very often, but it would be nice if it could be locally deterministic.
A smooth transition would involved shutting down the active
interface on A, then do a delta data-sync to the B via the back-end
interfaces, then switch upstream from A to B, then bring up B's interface.
I think this could be done with "macchanger", but I've never
fiddled with it.

Of course, a sudden failure of A, with subsequent switching to B, would
be messier and possibly loose data, but such is life.  At least
the whole system wouldn't be down for an extended period of
time.

Regards,
Lew


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