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Re: network setup question

On Wed, 2010-05-05 at 21:06 -0400, Miles Fidelman wrote: 
> Not sure if this is the right list, sort of a general linux networking 
> question (pointers to a more appropriate list welcomed)....
> Setup:
> - I have two servers in a datacenter, currently used for different things
> - I have one gigE cable coming in from one of the datacenter's big 
> routers - that goes into a simple gigE switch - each box is plugged into 
> that switch
> - I have two network /27 network blocks that are NOT contiguous - I use 
> one for each box
> - as I understand the basic setup, any traffic from one of my boxes to 
> the other (one netblock to the other) end up going to the datacenter's 
> router and back (and the traffic gets accounted for in our bill)
> Up to now, I haven't been routing any traffic between boxes, but I'm 
> getting ready to install some cluster software and I expect there to be 
> a lot of inter-box traffic.  So....
> I'm now looking for a way to have the inter-box traffic go directly 
> through the gigE switch, and not reach the datacenter's router.  Which 
> leaves me with some questions that are just a bit beyond my general 
> network setup knowledge:
> 1. Yes, I have a cross-over cable plugged directly between the 2nd 
> ethernet card in each box.  I plan to dedicate that for disk mirroring 
> traffic; but I expect I'll end up with things running on one box that 
> need to talk to the other, that may go through the primary ethernet ports.
> 2. Is there a way to use ARP and/or set up routing tables so that 
> inter-box traffic simply goes through the bridge?
> 3. If not, is this something I can do with a simple Linksys switch/router?
> Any guidance would be much appreciated.

if the 2 servers are in the same ethernet broadcast domain - just
because they are in the same switch doesn't mean they can talk directly
- they could be vlan'ed apart. 

Presuming they are then

for example
if server a has ip on eth0  - belongs to
192.168.0/ network
and server b has on eth0 - belongs to

then what you can do is (iproute package is your friend)
on server A
ip r a dev eth0 src

on server B
ip r a dev eth0 serc

that should work for you.

you could add these to post-up instructions in /etc/network/interfaces
for eth0


> Miles Fidelman
> -- 
> In theory, there is no difference between theory and practice.
> In<fnord>  practice, there is.   .... Yogi Berra

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