Re: [Xen-users] ifup fails on CentOS 4

[Tim Post <tim.post@xxxxxxxxxxxxxxx>]

> if  ! arping -q -c 2 -w 3 -D -I ${REALDEVICE} ${IPADDR} ; then
>         echo $"Error, some other host already uses address ${IPADDR}."
>         echo "Real device is: $REALDEVICE"
>         exit 1
> fi
> 
> I guess this isn't an issue with Xen so I'll have to submit a bug report 
> to CentOS.
> 

Does this per chance clear up if you alter (or manually specify) the mac
of the device? Was the IP in use by another machine or bridge with a
different mac within 15 or so minutes of you trying to bring up the
device?

This *could* be due to a router taking up to ~10 minutes to arp new
changes when IP's re-appear only with different macs. I've run into this
a few times with older 3400 series with a more or less out of the box
vanilla configuration.

arping is just saying "Yes, this IP is already related to another mac
(and host)", but it doesn't take a 10 - 15 minute lag from the router
into consideration. If the IP you are using was broadcast by another
ethernet device with a different mac in the last 15 minutes .. it
[arping] would still think the IP was in use because so does the router
(again depending on your router).

Cisco (and others) say the maximum time it should take for the router to
pick up that kind of change and arp it is about 9 minutes. I've found
its sometimes double that, depending on the setup. 

Very frustrating, you could be working with a good config and are being
shot in the foot upstream.. Worth checking into anyway :)

HTH
-Tim

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