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Lars Marowsky-Bree wrote:
>
> Good morning,
>
> I have thought about how the ARP problem can occur at all with direct routing,
> because I never noticed it. Then it occured to me that your virtual IP comes
> from the same subnet as the real IP of the LVS and also all the real servers
> share this media.
>
> To avoid the "ARP problem" in this case without adding a kernel patch or
> anything else, you can just add a direct route for the VIP using the real IP
> of the LVS as a gateway address on the router in front of the LVS. ("ip route
> VIP 255.255.255.255 real_ip" on a Cisco, or "route add -host VIP gw RIP" on
> Linux)
>
For the clients who reach the virtual server through the router, there
is no problem if a static route for VIP is added.
However, fot the clients who are in the network of virtual server,
the "ARP problem" will arise. There is fight in ARP response, and
the clients don't know send the packets to the load balancer or
the real server.
In my point of view, the VIP address is shared by the load balancer
and real servers in VS-TUN or VS-DR, only the load balancer does
ARP response for VIP to accept request packets, and the real servers
has the VIP but don't, so that they can process packets destined for
VIP.
Wensong
> Since I just used 2 ethernet cards and had the LVS act as gateway/firewall
> anyway, I never noticed the ARP problem. (We have 2 LVS in a standby
> configuration to eliminate the SPOF)
>
> Just my few cents.
>
> Sincerely,
> Lars Marowsky-Brée
>
> --
> Lars Marowsky-Brée
> Network Management
>
> teuto.net Netzdienste GmbH
>
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