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Julian's posting the other day showed that the dummy0 device
on realservers does arp. This prompted me to find out why
my LVS was working, when it shouldn't
The problem: If the router which feeds the director in a VS-DR LVS gets
the wrong MAC address for the VIP the LVS does not work.
Current solutions: All involve stopping the realservers from replying to
arp requests. The realservers are patched, or hidden behind a firewall
(the director with 2 NICs), or on a separate network.
I assume that my LVS was working because the director replied to arp
requests before the realservers (the director is 3x-4x the speed of the
realservers) and the entry in the router/client's arp table was always the
VIP of the director. In this case it didn't matter that the VIP on the
realservers was on an arp'ing device (dummy0). I had erroneously concluded
that since my LVS was working, and I was using dummy0 devices on the
realservers, that the dummy0 devices were not replying to arp requests.
I didn't bother to check whether dummy0 was replying to arp requests.
New solution: hard wire the MAC address of the VIP on the director
into the router's arp table. In my case I don't have a router, and
my client connects directly to the director. I have a file /etc/ethers
with the entry
lvs.mack.net 00:A0:CC:55:7D:40
and on the client (router) I run
$arp -f /etc/ethers
to add this (permanent) entry to the router's (client's) arp table
(check content of arp table with `arp -a`).
The lvs now works without hiding the realservers, or without patching the
realservers. The range of devices for the VIP on the realservers is wider
now and can be eth0:1 on a /24 netmask (or can stay as lo:0/32).
I have checked this on 2 different lots of hardware: one in which the
director replies to arps for the VIP first and another where the same
realserver always replies to the arp for the VIP first. I will be updating
the HOWTO and configure files (will be a few days). Please regard this
approach as experimental until a few people have got it to work.
Joe
--
Joseph Mack mack@xxxxxxxxxxx
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