[Openstack] DHCP and kernel > 3.2

Adam Gandelman adamg at canonical.com
Thu Aug 9 22:52:43 UTC 2012


On 08/09/2012 12:13 AM, Alessandro Tagliapietra wrote:
> Hello guys,
>
> i've just installed kernel 3.4 from Ubuntu kernel PPA archive and after this upgrade VM aren't able to get the DHCP address but with tcpdump i see the request and offer on the network.
> Someone else experienced this? I've tried also with 3.3, same story. Rolling back to 3.2 and everything works fine.
>
> I've tried with both flatdhcp and vlan mode.
>
> Best
>
> Alessandro
>

Hey Alessandro-

I'm able to confirm this affects the quantal kernel (on both quantal and 
precise) and vanilla kernels since 3.2.26 (at least those available from 
http://kernel.ubuntu.com/~kernel-ppa/mainline/)  I began looking at this 
issue a while back and doing some packet dumping, but I seem to have 
misplaced those .pcaps.  IIRC, what I saw happening was the instances' 
DHCP DICOVERY makes it to the server, dnsmasq properly sends an OFFER, 
but the the instance never returns with the REQUEST.  I feel like, at 
one point, I was seeing an external DHCP server (on the public network) 
responding to the DISCOVERYs with OFFERs of addresses from the wrong 
network,  and the instance actually REQUEST'ing and getting an IP from 
the wrong server.

I will open a bug about this in Launchpad against the kernel and see if 
we can get some help bisecting and figuring out what broke.

Adam




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