VS/TUN, VS/DR response problem

Graeme Fowler graeme at graemef.net
Sun Jan 8 21:25:21 GMT 2006


On Sun, 2006-01-08 at 19:37 +0530, Paresh Bafna wrote:
> But packet doesn't contain all the information required for TCP protocol
> to work completely, viz RTT, MTU are not present in packet.

...RTT & MTU? TCP works perfectly well for me without having to carry
additional variable payload which would get changed from hop to hop. In
fact, unless you're talking about some application payload, TCP does not
normally carry such information. It isn't necessary.

> Also initially client will create connection with VIP, then will send
> request for particular data or service...
> So there will be connection establishment bewtween client and VIP (SYN,
> ACK-SYN and ACK)

Correct. Remember that the director is simply a router - all it does is
sends packets on to the next hop (more below).

> Then VIP (load balancing) will choose one of the server to cater this
> request, then does VIP simulate conn. establishment with real server,
> because for server to accept request (forwarded from VIP) initial
> handshake has to take place somehow. It is after this handshake server
> will allocate socket (port) for connection with client
> Is my understanding of working of LVS right or is there any basic
> mis-understanding?


Again, the director is a router, but it makes routing decisions on which
realserver to forward a given packet to based on LVS parameters - the
scheduler determines this, whether it's simple round-robin (a-b-c-a-b-c
etc) or something more complicated.
The packets are matched according to the destination VIP and service
port (which defines the virtual server instance), and then forwarded
according to the scheduler method and some in-service parameters
(weight, load, delay) to a realserver. The realserver then communicates
with the client without being aware of the director, in much the same
way as a standalone server isn't really aware of its' default router.

I hope that's a bit clearer - and I'd recommend following Joe's advice
to read the HOWTO.


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