HyperV Gen2 VM not booting over PXE - hyper-v

Question

I have two VMs in HyperV, both on the same virtual switch (internal), on the same subnet. I am trying to set up one as a DHCP and TFTP server for PXE boot. With Gen1 machine, it's working fine with pxelinux. Gen2 with UEFI does not unfortunately work.
DHCP & TFTP Server
IP 192.168.1.2
VLAN identification is disabled
DHCP - ISC DHCP Server running in a docker container with "host" network type with the following configuration:
set vendorclass = option vendor-class-identifier;
option pxe-system-type code 93 = unsigned integer 16;
set pxetype = option pxe-system-type;
authoritative;
default-lease-time 7200;
max-lease-time 7200;
option tftp-server-name "192.168.1.2";
option bootfile-name "efi/core.efi";
subnet 192.168.1.0 netmask 255.255.255.0 {
interface "eth0:0";
option routers 192.168.1.1;
option subnet-mask 255.255.255.0;
range 192.168.1.100 192.168.1.150;
option broadcast-address 192.168.1.255;
option domain-name-servers 8.8.8.8, 8.8.4.4;
option domain-name "ad.lholota.net";
option domain-search "ad.lholota.net";
if substring(vendorclass, 0, 9)="PXEClient" {
if pxetype=00:06 or pxetype=00:07 {
filename "efi/core.efi";
} else {
filename "pxelinux/pxelinux.0";
}
}
next-server 192.168.1.2;
}
TFTP - tftp-hpa running in a docker container on a "host" type network. I can download the efi files manually through a standard tftp client.
Booting machine
HyperV Gen2
No virtual HDD or DVD
Firmware tab has only one item in the boot sequence - network
Secure boot is disabled
VLAN identification is disabled
Network adapter pointing into the same internal switch as the first VM
Enable virtual machine queue - checked
Enable IPsec task offloading - checked, maximum number: 512
MAC Address dynamic
Enable DHCP guard - NOT checked
Enable router advertisement guard - NOT checked
Procted network - NOT checked
Mirroring mode - None
Enable device naming - NOT checked
The trouble is that the machine doesn't even get to the TFTP server because it doesn't finish the DHCP Discover-Offer-Request-Ack flow. It gets stuck on offer as shown in the dhcpdump below. The booting machine never sends the request message. Funny enough, BIOS based Gen1 HyperV machine boots without any issue so the DHCP flow works there.
Can you please give me a hint of what might be wrong?
TIME: 2018-07-11 19:49:37.641
IP: 0.0.0.0 (0:15:5d:0:50:d0) > 255.255.255.255 (ff:ff:ff:ff:ff:ff)
OP: 1 (BOOTPREQUEST)
HTYPE: 1 (Ethernet)
HLEN: 6
HOPS: 0
XID: 8bf1c250
SECS: 0
FLAGS: 7f80
CIADDR: 0.0.0.0
YIADDR: 0.0.0.0
SIADDR: 0.0.0.0
GIADDR: 0.0.0.0
CHADDR: 00:15:5d:00:50:d0:00:00:00:00:00:00:00:00:00:00
SNAME: .
FNAME: .
OPTION: 53 ( 1) DHCP message type 1 (DHCPDISCOVER)
OPTION: 57 ( 2) Maximum DHCP message size 1472
OPTION: 55 ( 35) Parameter Request List 1 (Subnet mask)
2 (Time offset)
3 (Routers)
4 (Time server)
5 (Name server)
6 (DNS server)
12 (Host name)
13 (Boot file size)
15 (Domainname)
17 (Root path)
18 (Extensions path)
22 (Maximum datagram reassembly size)
23 (Default IP TTL)
28 (Broadcast address)
40 (NIS domain)
41 (NIS servers)
42 (NTP servers)
43 (Vendor specific info)
50 (Request IP address)
51 (IP address leasetime)
54 (Server identifier)
58 (T1)
59 (T2)
60 (Vendor class identifier)
66 (TFTP server name)
67 (Bootfile name)
97 (UUID/GUID)
128 (???)
129 (???)
130 (???)
131 (???)
132 (???)
133 (???)
134 (???)
135 (???)
OPTION: 97 ( 17) UUID/GUID 008c0c7ab81331a0 ...z..1.
4297445b2e41610e B.D[.Aa.
a8 .
OPTION: 94 ( 3) Client NDI 010300 ...
OPTION: 93 ( 2) Client System 0007 ..
OPTION: 60 ( 32) Vendor class identifier PXEClient:Arch:00007:UNDI:003000
---------------------------------------------------------------------------
TIME: 2018-07-11 19:49:37.641
IP: 0.0.0.0 (0:15:5d:0:50:12) > 255.255.255.255 (ff:ff:ff:ff:ff:ff)
OP: 2 (BOOTPREPLY)
HTYPE: 1 (Ethernet)
HLEN: 6
HOPS: 0
XID: 8bf1c250
SECS: 0
FLAGS: 7f80
CIADDR: 0.0.0.0
YIADDR: 192.168.1.105
SIADDR: 192.168.1.2
GIADDR: 0.0.0.0
CHADDR: 00:15:5d:00:50:d0:00:00:00:00:00:00:00:00:00:00
SNAME: .
FNAME: efi/core.efi.
OPTION: 53 ( 1) DHCP message type 2 (DHCPOFFER)
OPTION: 51 ( 4) IP address leasetime 7200 (2h)
OPTION: 1 ( 4) Subnet mask 255.255.255.0
OPTION: 3 ( 4) Routers 192.168.1.1
OPTION: 6 ( 8) DNS server 8.8.8.8,8.8.4.4
OPTION: 15 ( 14) Domainname ad.lholota.net
OPTION: 28 ( 4) Broadcast address 192.168.1.255

Answer 1

I have had what i believe is the same issue when booting HyperV virtual machines on win10 2004(19041.685): gen 1 works, gen 2 times out without ever asking for the boot file.
I strongly suspect this is an issue with the GEN2 UEFI PXE implementation. Because as soon as I have at least two entries to choose from in the pxe boot menu it requests files and downloads as expected.
I run dnsmasq for tftp and DHCP and my config file below works if and only if at least one of the last two rows are uncommented. (pxe-service=x86-64_EFI and pxe-service=7 are equal)
config context: https://linuxconfig.org/how-to-configure-a-raspberry-pi-as-a-pxe-boot-server
# /etc/dnsmasq.d/03-tftpboot.conf
enable-tftp
tftp-lowercase
tftp-root=/mnt/data/netboot
pxe-prompt="Choose:"
pxe-service=x86PC,"PXELINUX (BIOS)",bios/pxelinux.0
pxe-service=x86PC,"WinPE (BIOS)",boot/pxeboot.n12
pxe-service=x86-64_EFI,"PXELINUX (EFI)",efi64/syslinux.efi
pxe-service=x86-64_EFI,"winpe (EFI)",boot/wdsmgfw.efi
#pxe-service=7,"PXELINUX (EFI-7)",efi64/syslinux.efi

Answer 2

I think I am experiencing the same problem when using digital rebar provisioner. Works great on Gen 1 but not on Gen 2. Have followed the same configuration as well.
Looking at the digital rebar code it seems like it should work but does not: https://github.com/digitalrebar/provision/blob/8269e1c7ff12a82854c19eccd114d064e2278211/midlayer/pxe.go#L252
I think this could be related:
https://wiki.fogproject.org/wiki/index.php/BIOS_and_UEFI_Co-Existence
https://serverfault.com/questions/739138/hyper-v-2016-gen2-vm-pxe-dhcp-timeout-wireshark-dhcp-discover-offer