[Dnsmasq-discuss] About UEFI PXE booting in proxy mode

Steven Shiau steven at nchc.org.tw
Wed Mar 29 07:46:49 BST 2017


Hi Doug,

Thanks for your explanation. Simon also emailed me after my post and let 
me know where the problem is. The conclusion is this issue seems not be 
easily fixed.
So the patch for grub will be applied after grub 2.02. Before that, 
could you please show me the configuration file you confirmed it will 
work by using dhcp-boot strategy?
Thank you very much.

Steven


On 3/27/2017 AM 11:29, Doug Brown wrote:
> Hi Simon and Steven,
>
> I just found this recent thread while I was Googling for the exact 
> same problem (UEFI clients won't boot in PXE mode, but BIOS clients 
> will) and there was never any conclusion reached. I'm running into the 
> exact same problem, and I can provide a pcap dump, which I have 
> attached to this message. After the initial DHCP exchange, it shows 
> four DHCP packets on port 4011 sent from the client which seem to be 
> ignored by dnsmasq. Here is the configuration I am using with dnsmasq 
> 2.76, based on Steven's original third example:
>
> port=0
> log-dhcp
> dhcp-no-override
> enable-tftp
> tftp-root=/tftpboot
> dhcp-range=ens33,192.168.7.100,192.168.7.200,10h
> pxe-service=X86PC, "Boot BIOS PXE", pxelinux.0
> pxe-service=BC_EFI, "Boot UEFI BC", grubx64.efi
> pxe-service=X86-64_EFI, "Boot UEFI X86-64", grubx64.efi
>
> If I switch to using the dhcp-boot strategy, everything works great on 
> both BIOS and UEFI. But the above configuration using PXE doesn't seem 
> to work properly with UEFI clients for some reason, and it seems to be 
> a dnsmasq issue. It does work fine with BIOS clients though.
>
> I think I can answer Steven's earlier question as to why proxy PXE 
> (example config #4) doesn't work with UEFI. The problem in that case 
> is not due to dnsmasq at all -- it's correctly sending grub to the 
> client. The problem is that grub doesn't know how to detect that it 
> was loaded from a DHCP proxy, so it won't know where to download 
> grub.cfg. Shim, which you can use as a first stage bootloader to load 
> grub if you need to support Secure Boot, has the exact same problem. 
> It only knows how to look at the original DHCP ack's boot info. The 
> UEFI environment provides info about the proxy offer, but grub and 
> shim don't look at it. See the following thread where a patch was 
> submitted for grub:
>
> https://lists.gnu.org/archive/html/grub-devel/2016-04/msg00051.html
>
> I think it's probably possible to work around the proxy problem by 
> using grub-mkstandalone to create a version of grub.efi that has an 
> embedded intermediate grub.cfg that is coded to download the real 
> grub.cfg from your server, as long as you don't need Secure Boot support.
>
> Either way, I still think there's something wrong with dnsmasq's PXE 
> support because the example config above (non-proxy) doesn't work with 
> any UEFI clients that I have tested, as shown by the pcap dump 
> attached. Any ideas?
>
> Thanks,
> Doug
>
> On 1/26/2017 11:16 AM, Simon Kelley wrote:
>> There's no DHCP traffic in that capture. It appears to all be ssh.
>>
>> Wrong interface?
>>
>>
>> Cheers,
>>
>> Simon.
>>
>>
>> On 24/01/17 08:50, Steven Shiau wrote:
>> > Hi Simon,
>>
>> > Attached please find the dump file of the command "tcpdump -s 0 -w
>> > capturefile". Let me know if you need more info. Thank you very
>> > much.
>>
>> > Steven
>>
>>
>> > On 1/24/2017 AM 05:25, Simon Kelley wrote: Thanks for the reply.
>> > Please could you repeat the tcpdump using the command
>>
>> > tcpdump -s 0 -w capturefile
>>
>> > and send me the resulting file? That has far more information than
>> > tcpdump prints.
>>
>>
>> > Cheers,
>>
>> > Simon.
>>
>> > On 20/01/17 08:39, Steven Shiau wrote:
>> >>>> Hi Simon,
>> >>>>
>> >>>> Thanks for your reply. I am answering you in the following.
>> >>>>
>> >>>> On 2017/01/20 06:47, Simon Kelley wrote:
>> >>>>> Your example 3 - I'm confused why that shouldn't work - the
>> >>>>> PXE client seems to be making further requests which are
>> >>>>> bring ignored. Would it be possible for you to get a packet
>> >>>>> dump of that exchange using tcpdump?
>> >>>> $ sudo tcpdump -ni ens38 'udp port 67 and udp port 68'
>> >>>> tcpdump: verbose output suppressed, use -v or -vv for full
>> >>>> protocol decode listening on ens38, link-type EN10MB
>> >>>> (Ethernet), capture size 262144 bytes 16:18:33.208355 IP
>> >>>> 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from
>> >>>> 00:0c:29:1d:9a:d1, length 347 16:18:36.205647 IP
>> >>>> 192.168.22.254.67 > 255.255.255.255.68: BOOTP/DHCP, Reply,
>> >>>> length 341 16:18:36.385548 IP 0.0.0.0.68 >
>> >>>> 255.255.255.255.67: BOOTP/DHCP, Request from
>> >>>> 00:0c:29:1d:9a:d1, length 359 16:18:36.386212 IP
>> >>>> 192.168.22.254.67 > 255.255.255.255.68: BOOTP/DHCP, Reply,
>> >>>> length 341 ^C 4 packets captured 4 packets received by filter
>> >>>> 0 packets dropped by kernel
>> >>>>
>> >>>>> Example 4 looks quite hopeful - the client is
>> >>>>> succerssfully downloading the bootx64.efi file (ignore the
>> >>>>> error before, that's just testing for the existance of the
>> >>>>> file.
>> >>>>>
>> >>>>> Can you see what's displayed on the client system at this
>> >>>>> point?
>> >>>> It's blank screen due to the background_image for grub is
>> >>>> not downloaded,  and in the end the grub shows no grub.cfg
>> >>>> error, as attached. That format is from the grub prefix we
>> >>>> added by: ======================================= set
>> >>>> prefix=(tftp)/grub-efi.cfg echo "Grub CPU and platform:
>> >>>> \$grub_cpu, \$grub_platform" echo 'Network status: '
>> >>>> net_ls_cards net_ls_addr net_ls_routes
>> >>>>
>> >>>> tr --set pretty_mac x: x- \$net_default_mac
>> >>>>
>> >>>> echo "Loading config file
>> >>>> \$prefix/grub.cfg-01-\$pretty_mac..." configfile
>> >>>> \$prefix/grub.cfg-01-\$pretty_mac
>> >>>>
>> >>>> echo "Loading config file
>> >>>> \$prefix/grub.cfg-\$net_default_ip..." configfile
>> >>>> \$prefix/grub.cfg-\$net_default_ip
>> >>>>
>> >>>> echo "Loading config file: \$prefix/grub.cfg" configfile
>> >>>> \$prefix/grub.cfg
>> >>>>
>> >>>> echo "Could not find config file
>> >>>> \$prefix/grub.cfg-\$pretty_mac,
>> >>>> \$prefix/grub.cfg-\$net_default_ip or \$prefix/grub.cfg!"
>> >>>> sleep 15 ======================================= This is
>> >>>> exactly the same problem as mentioned here:
>> >>>> http://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2016q4/010
>> 931
>>
>> >>>>
>> .html
>> >>>>
>> > i.e., only grub efi is downloaded, while the rest of required files
>> > are
>> >>>> not downloaded. As I mentioned for comparison, for non-proxy
>> >>>> mode with same configuration, it works well.
>> >>>>
>> >>>> Thanks again.
>> >>>>
>> >>>> Steven
>> >>>>
>> >>>>
>> >>>>
>> >>>> _______________________________________________
>> >>>> Dnsmasq-discuss mailing list
>> >>>> Dnsmasq-discuss at lists.thekelleys.org.uk
>> >>>> http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss
>> >>>>
>> >>
>> >>
>> >>>>
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>>
>>
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Steven Shiau <steven _at_ stevenshiau org>
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