[PLUG] ARP black magic question

Eric Harrison eharrison at mail.mesd.k12.or.us
Tue Aug 26 18:41:02 UTC 2003


On Tue, 26 Aug 2003, Galen Seitz wrote:

>Eric Harrison <eharrison at mail.mesd.k12.or.us> wrote:
>
>> >> That is, when some random host sends out an arp query "who has serverb?",
>> >> Server A needs to respond "serverb is at 01:02:03:04:05:06", where 
>> >> "01:02:03:04:05:06" is the real MAC address for server B. 
>> 
>> >The question is, do you want to proxy an IP or a mac address?
>> 
>> I'm not trying to _proxy_ arp. The kernel doc's say that proxy_arp
>> forwards arp packets between two devices attached to different media.
>> 
>> I'm trying to get one server to respond to arp requests for another
>> server on the same physical network. Proxy arp doesn't work in this case,
>> or at least I have not figured out how to bend proxy arp in that fashion...
>
>Now I really am confused.  If serverB is on the same wire, why can't it
>respond to the ARP request?  Is serverB slow to respond to ARP requests,
>or does it not respond at all?  Is it correct to say that you want 
>something like proxy arp, but for a single segment?  Perhaps you could
>hack arpd to do what you want.

Load-balancing/fail-over can be extremely convoluted at times. I've
tried real hard not to give any details on the setup as a whole, since
it definately would not help to clarify what I'm trying to do with
this one little piece of the puzzle ;-)

Let it surfice to say that if "serverB" crashes, or is otherwise
unavailable, things will still work perfectly as long as the other
servers/routers/etc on the same physical network *think* "serverB"
is still up.

I didn't think of trying to hack arpd, but I did have a number of other
messy ideas. I was rather hoping that someone would have tried to 
do this in the past would know a simple, easy to maintain solution ;-)

-Eric





More information about the PLUG mailing list