netdev - Re: [PATCH V2 09/12] net/eipoib: Add main driver functionality

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Date:	Sun, 12 Aug 2012 17:05:12 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Or Gerlitz <or.gerlitz@...il.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Ali Ayoub <ali@...lanox.com>,
	David Miller <davem@...emloft.net>, ogerlitz@...lanox.com,
	roland@...nel.org, netdev@...r.kernel.org, sean.hefty@...el.com,
	erezsh@...lanox.co.il, dledford@...hat.com
Subject: Re: [PATCH V2 09/12] net/eipoib: Add main driver functionality

On Thu, Aug 09, 2012 at 07:06:46AM +0300, Or Gerlitz wrote:
> Eric W. Biederman <ebiederm@...ssion.com> wrote:
> > Or Gerlitz <or.gerlitz@...il.com> writes:
> 
> >> To put things in place, DHCPv4 is supported with eIPoIB, the DHCP
> >> UDP/IP payload  isn't touched, only need to set the BOOTP broadcast
> >> flag in the dhcp server config file.
> 
> > Wrong.  DHCPv4 is broken over eIPoIB. Coming from ethernet
> > htype == 1 not 32 as required by RFC4390
> > hlen == 6 not 0 as required by RFC4390
> > The chaddr field is has 6 bytes of the ethernet mac address not the
> > required 16 bytes of 0. The client-identifier field is optional over ethernet.
> > An ethernet DHCPv4 client simply does not generate a dhcp packet that
> > conforms to RFC4390.
> >
> > Therefore DHCPv4 over eIPoIB is broken, and a dhcp server or relay
> > may reasonably look at the DHCP packet and drop it because it is garbage.
> >
> > You might find a forgiving dhcp server that doesn't drop insane packets
> > on the floor and tries to make things work.
> 
> Under the eIPoIB design, the VM DHCP interaction follows
> Ethernet DHCP, and not the IPoIB DHCP (RFC 4390).
> 
> The DHCP server has no reason to drop such packets.
> 
> DHCP is a L7 (L5 to be precise) construct, I don't see
> why that the fact IPoIB DHCP RFC exists, means/mandates
> the DHCP server to care on the link layer type.
> 
> Or.

For example DHCP server could be configured with
HW address/IP address table.

-- 
MST
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