[ipxe-devel] Curious routing problem with iPXE

[Andrew Bobulsky]

Hello Lee, Michael,

The issue you're seeing here is, most unfortunately, expected
behavior.  You can read up on it here:
http://support.microsoft.com/kb/960104

As I recall it, this behavior is seen in pretty much every NT 5.1 OS,
including WinPE 3.0, Windows 7, and 2008 R2.  Microsoft basically made
the executive decision that placing your network traffic and iSCSI
traffic on the same NIC is insane, and decided that the only reason
you'd have a gateway on your iSCSI NIC would be if that gateway were
actually required to route traffic to and from your SAN.  I wish I
knew why they thought this was a good idea, because all it seems to
really accomplish in my experience with it is to stifle iSCSI booting
in low-cost setups.  Take that with however many grains of salt you
desire :P

The only workaround I'm aware of is to establish a default gateway
sometime *after* the iSCSI connection is in place and the client's
routing table is initially populated.  If you boot with no default
gateway, you can then add one once the OS is online, and the
trickle-down from the iBFT won't occur.

Curious though, Lee, for your solution, what exactly did you do and
what are the results?  I've never configured option 249, so I'm
puzzled :)

Cheers,
Andrew Bobulsky



On Wed, Feb 9, 2011 at 7:52 PM, Michael Brown <mbrown at fensystems.co.uk> wrote:
> On Wednesday 09 Feb 2011 23:25:18 Lee Bradshaw wrote:
>> I've now set up a native Windows iSCSI server and am booting from it. All
>>  is working fine, except that the routing to the server is odd. My PC is
>>  .244; the server is .2. When I list the routing table I get:
>>
>> IPv4 Route Table
>>
> ===========================================================================
>> Active Routes:
>> Network Destination        Netmask          Gateway       Interface  Metric
>>           0.0.0.0          0.0.0.0       10.10.10.1     10.10.10.244    266
>>        10.10.10.0    255.255.255.0         On-link      10.10.10.244    266
>>        10.10.10.2  255.255.255.255       10.10.10.1     10.10.10.244    266
>> ...
>>
>> You will notice the curious route to the server via a gateway at
>> 10.10.10.1. This seems to be caused by iPXE not correctly processing the
>> subnet from DHCP, which was 255.255.255.0. I know this is what it read
>> from the DHCP server because it says so during the boot.
>
> Interesting.  I'm pretty sure if you type "route" at the iPXE command line,
> you'll find that iPXE's routing table doesn't include a dedicated host route to
> 10.10.10.2, if only because iPXE doesn't even support a concept of routing
> beyond a simple "network address, subnet mask, gateway address" triplet. :)
>
> iPXE passes IP configuration information to Windows via the iBFT, which can
> contain only a local IP address, subnet prefix, and gateway address; there's no
> way that iPXE could pass host-specific routes to Windows even if it wanted to.
>
>> In many installations this wouldn't be a problem - although it's an
>> unnecessary overhead - but in my case the gateway at 10.10.10.1 is on a
>> 100Mb connection to the switch, whereas the rest of the network is 1000Mb.
>> As you can imagine, this means the performance of my disks is not what it
>> should be.
>>
>> I've been able to work around it by adding a static route (DHCP 249) to
>> override the errant entry, but it would be nice if I didn't have to do
>>  this. Any ideas?
>
> I vaguely (and quite possibly inaccurately) remember that Shao Miller has
> encountered this problem before.  Shao: any thoughts?
>
> Michael
> _______________________________________________
> ipxe-devel mailing list
> ipxe-devel at lists.ipxe.org
> https://lists.ipxe.org/mailman/listinfo/ipxe-devel
>