Why configure a "loopback" VIP (virtual IP) on servers load balanced by Sun Fire[TM] B10n?

Asset ID:	1-71-1001899.1
Update Date:	2016-04-20
Keywords:

Solution Type Technical Instruction Sure

Solution 1001899.1 : Why configure a "loopback" VIP (virtual IP) on servers load balanced by Sun Fire[TM] B10n?

Applies to:

Sun Fire B100s Blade Server - Version Not Applicable and later
Sun Fire B100x Blade Server - Version Not Applicable and later
Sun Fire B200x Blade Server - Version Not Applicable and later
All Platforms

Goal

Why does the VIP need to be configured on the loopback interface of the servers in a B10n load balancing server group?

Why not configure the VIP on the physical interface?

Solution

Traffic from client systems must first reach the B10n load balancer via the VIP address -- that's all they know about.

The clients (or more likely the router on the B10n subnet) must associate the MAC of the B10n with this VIP to insure traffic is sent to the B10n load balancer.

The B10n load balances this traffic to one of the servers. Its configuration (load balancing service & server group) determines what server to contact, via the server's physical interface.

A proprietary load balancing protocol handles B10n <-> server communications. This protocol (as implemented by the clbmod streams module residing on the server between the interface and IP module) sends the original client IP packet upstream to the server's IP layer, hence the need for a VIP on the server blade.

If the VIP is associated with a physical (not loopback) interface, clients (or the client-facing router) will receive ARP replies from the server(s), leading to the possibility that traffic will be sent directly to a server.

References

<NOTE:1017704.1> - What protocol does the B10n blade use for communication with its servers?
<NOTE:1449976.2> - Information Center: Sun Fire B100s Blade Server
<NOTE:1449975.2> - Information Center: Sun Fire B200x Blade Server

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