subnet, Tun questions

Ryan Lovett ryan at stat.Berkeley.EDU
Fri Oct 29 00:53:06 BST 2004


                                         clients
                                            |
                                        internet
                                            |
                                        gateway (G)
                                            |
     _______________________________________|________________________
     |         |         |         |                      | | | | | |
   __|_|__   __|_|__   __|_|__   __|_|__                  | | | | | |
   |     |   |     |   |     |   |     |                 other clients
   |  A  |   |  B  |   |  C  |   |  D  |
   |_____|   |_____|   |_____|   |_____|


I'd like to setup an LVS for the above where A, B, C, and D are all on the
same subnet and have two NICs. The only port I need setup is ssh. I was
wondering if the following is feasible:

 - A, B, C, D are realservers.

 - Any client can directly access A, B, C, D.

 - A is the director.

 - When any client connects to the second interface on A, they could be
   sent to B, C, or D depending on load and all LVS traffic is sent to the
   second interfaces on B, C, and D.

 - B is a director failover.

What has tripped me up is not understanding the same-subnet issue. As the
very first step toward implementing this, I initially raised the second
interface on A (different IP, same subnet) and was then able to connect to
it via either interface. When I then lowered the second interface, I was
still able to connect to A on either interface. (the hostnames given to
eth0 and eth1 were both responsive even though the cable was physically
unplugged from eth1.)

I believe LVS-Tun is what I should use since it fits the above contraints
in the HOWTO. (no port remapping, *realserver network is on internet*,
realserver default gw (g) is own router) A, B, C, and D all happen to be
running Linux.

Is it required that the second interfaces on A, B, C, and D be on a
different (local) subnet? Otherwise, I don't see how LVS traffic can be
managed since A, B, C, and D already have a default gateway set to G.

There are clearly some larger network issues that I don't understand so I'd
appreciate any guidance on what direction to look into.  

Thanks for your time,
Ryan


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