On Mon, Sep 28, 2009 at 16:33:56 -0400, Jason Frisvold wrote:
> On Sep 28, 2009, at 12:25 PM, Nathan Stratton Treadway wrote:
> >I haven't tried running Amanda on a host with two IP numbers on the  
> >same
> >subnet, but another possibility is that the routing configuration on  
> >the
> >backup server host have been changed somewhat during the loss and
> >re-creation of the "eth0" config file.  Given the right sort of  
> >change,
> >that might result in that the kernel is now choosing a different  
> >"route"
> >for communicating with the client hosts, which in turn might lead to  
> >it
> >to assign a different source IP to the outgoing packets.
> 
> Aha !  This was the problem.  I'm curious as to why it decided to  
> change the default src IP though ...  The server was rebooted  

Well, as I understand it, the kernel uses the source IP that matches the
outgoing route entry that it has selected for sending the packet in
question.  When the routes are choosing between interfaces on separate
subnets, this generally does exactly what you want, since it means the
source IP of the outgoing packet is the one assigned to the interface
actually used to send the packet, and a return packet would thus come
back in via that same interface.

I haven't investigated this as closely in the context of two IP numbers
assigned to the same physical interface, but by analogy it would seem
that if the kernel it choosing the other IP, it's now choosing a
different route entry for sending the packet.  Since both entries point
to the same subnet, it might be making the selection using some very
minor criteria.  (For example, if both routes have the same netmask, it
might be as simple as which route appears first in the routing table.)



> recently, and that's about it ..  I'll have to dig more, but this  
> solves my problem for the moment.  Thanks !

(When you say "this solves my problem", what exactly did you do to get
things working?)

                                                Nathan

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Nathan Stratton Treadway  -  nathanst AT ontko DOT com  -  Mid-Atlantic region
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