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Questions regarding LVS-DR

To: lvs-users@xxxxxxxxxxxxxxxxxxxxxx
Subject: Questions regarding LVS-DR
From: Dan Trainor <dan@xxxxxxxxxxxxxx>
Date: Thu, 20 Oct 2005 18:03:48 -0600
Hello, all -

I have been doing some research on LVS-DR, and I think this is the
method for which I want to go ahead with, but first, I had some questions.

Looking at the LVS-HOWTO, I see the first example under chapter 6, at
http://www.austintek.com/LVS/LVS-HOWTO/HOWTO/LVS-HOWTO.LVS-DR.html.  The
first example explains a sample setup, with a client, a director, and
various realservers.

My question is, when using the following diagram (taken from the HOWTO):

Host                    IP
client                  CIP=192.168.1.254
director                DIP=192.168.1.1
virtual IP (VIP)        VIP=192.168.1.110 (arpable)
realserver1             RIP1=192.168.1.2
                        VIP=192.168.1.110 (lo:0, not arpable)
realserver2             RIP2=192.168.1.3
                        VIP=192.168.1.110 (lo:0, not arpable)
realserver3             RIP3=192.168.1.4
                        VIP=192.168.1.110 (lo:0, not arpable)
.
.
realserver-n            192.168.1.n+1


...does this imply that the realservers and the director share a common
IP that needs to be on a routable network, or were nonroutable networks
used here just for the sake of example?  If the realservers need to
respond the client directly in an LVS-DR setup, do they need to be made
aware of which netwrk they're on, to grab a default gateway and such to
appropriately map a request back to a client?  If we're not using ARP
for these VIP interfaces, wouldn't this be a problem?  I wouldn't call
myself a networking newbie by any means, but this is something that I
don't quite understand.  If the opposite were true, and the realservers'
VIPs were routable IPs, then I suppose it would not be much of a
problem?  I'm not sure, this is where I'm hoping you guys step in and
teach me a lesson :)

My understanding is that the director and realservers share a VIP, which
should/may/can be a non-routable IP, which would open up some IP space
for other network services to use the same network or subnetwork.  In
fact, if this is the case, then I think the setup I want to work with,
will work appropriately.

Regardless, I am a bit confused, and would very mcuh appreciate it if
someone were to straighten things out for me.

Thanks!
-dant





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