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On Fri, Dec 05, 2003 at 03:40:01PM +0530, SAMPATHKUMAR KISHORE KANIYAR wrote:
> LVS folks,
>
> I am new to LVS, and have been configuring and using LVS and learning
> how LVS works.
>
> I have a question about LVS-DR. Look at the following configuration:
>
> A ---------------
> ------------------| LOAD BALANCER |
> | ---------------
> | | A'
> | |
> | |
> | --------
> | --------| Switch |-------
> | | -------- |
> | | |
> | | B' | C'
> | ---------- ----------
> | | SERVER 1 | | SERVER 2 |
> | ---------- ----------
> | | B | C
> _____ | |
> / \ | |
> -------- / \ | |
> | CLIENT |----| Gateway |---------------------------------
> -------- \ /
> \_____/
>
>
> I have indicated the N/W inteface cards for the Load balancer and
> the Servers by A, A', B, B' and C, C' respectively.
>
> Also, let us say the IP address for N/W interface card A on Load
> balancer is configured to the Virtual IP: VIP.
>
> When the Client request to VIP is directed by the load balancer to
> Server 1 (say), my understanding is that it is received by
> Server 1 on N/W interface card B', which will have a loopback
> alias interface configured with IP address VIP.
>
> I have 2 questions about Server 1 "responding" to the "client":
> 1) Server 1 responds to the CLIENT on N/W interface card B, right?
> 2) If so, what is the IP address returned in the response packet?
> Isn't it the IP address configured for N/W interface card B,
> which is -not- VIP? But, the client knows/expects only VIP.
>
> Can someone clarify?
No it is the VIP. The destination address of the packet recieved
from the end-user (client) via the linux director (load balancer)
will be the VIP. Thus the source address in the reply packet from
the real server (server) to the end-user will be the VIP.
Think of it like this. A host can have more than one IP address
(e.g. 10.0.0.1 and 127.0.0.1) and when a connection is made
to one of these addresses the reply always comes back from
that addresss. This is the same mechanism that is at play in LVS-DR.
As an asside, it is not neccessary to have two NIC's in
each of the real-servers. One is fine. Though your topology
should work.
--
Horms
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