[Beowulf] split traffic to two interfaces for two "subnets"

Yaroslav Halchenko list-beowulf at onerussian.com
Wed May 10 20:47:55 PDT 2006

Hi Robert,

Thank you for sharing this fun with me :-)

On Wed, 10 May 2006, Robert G. Brown wrote:
> Since you have an "infinite" IP space it seems like there are several
> ways to skin this cat.
sharpening my knife already! ;-)

> For example you might use 10.0.0.x for 13 nodes
> + eth0 and 10.0.1.x for 12 nodes + eth1 and route accordingly.  It's the
> routing (mostly from the server to the nodes) that is the tricky part,
> not the two interfaces per se.  This might make it a bit easier to
> segregate the broadcasts.
not a bad idea, sir... 
if I understand correctly, you are suggesting to create two /24 networks
(not a single /23); since they all will be routed by the same switch anyway, I
think that routing should not be an issue, nor bottleneck...

and what do you mean by segregating broadcasts? shouldn't it be simple
DNAT from lets say to so it gets heard?

> >Or may be there is a more elegant solution? (virtual server...)
> If you have a smart enough switch maybe.  Or if you have e.g. myrinet
> for IPCs and are using the ethernet only for shell and nfs type services
> you can just split the two interfaces (and their nodes) and put them on
> two different switches as well as use two class C subnets.  That will
> REALLY split the traffic -- broadcasts and so on will be appropriately
> segregated by the switch boundaries.  This is "bad" as far as node
> talking to node (on two different switches) -- they
> would have to talk through e.g. the server configured to route/forward
> the packets.  But if you never need for a node on one switch to talk
> efficiently to a node on the other switch via TCP/IP, why not?
unfortunately that would not fly since the older switch (I am about to
substitute with a new 44 ports DLink) doesn't support jumbo frames which
from my experiments on a new switch help a lot in terms of throughput
and CPU load.

>   rgb

> >Thank you in advance
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Yaroslav Halchenko              /(   )\               ICQ#: 60653192
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