I took a step back from doing bisecting and focussed on creating a replication scenario, which I've done successfully.
ipconfig is struggling to handle things when two interfaces are present and sending out DHCP requests, even if one interface doesn't get a response. Here's what I've done: Using virt-manager I created a bridge, bridge1, with no IP range associated with it (I want dnsmasq on a host to handle IP). I created a second, bridge2, likewise with no IP range associated with it ready for later use. $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ I created an instance, named primary, with two NICs, one doing the usual NAT stuff so it has internet access. One hooked up to bridge1. I gave it two storage devices, 1 (sda) at 15Gb in size to act as local storage, 1 (sdb) 40Gb in size to be hosted over iSCSI (in hindsight, no reason for it not to be 15Gb too). Install Ubuntu 16.04.1 LTS on the primary instance, pretty much following through with defaults, but leaving the second hard drive unused. Reboot and bring up the instance. In my case I end up with ens3 being the NATing interface, ens9 being hooked up to the bridge interface. ########################## sudo apt update sudo apt upgrade ########################## Add to /etc/network/interfaces: auto ens9 iface ens9 inet static address 192.168.0.1/24 ########################## Then: sudo apt install open-iscsi targetcli dnsmasq ########################## dnsmasq config: log-queries log-dhcp interface=ens9 dhcp-range=192.168.0.50,192.168.0.150,12h dhcp-boot=script.ipxe enable-tftp tftp-root=/tftpd tftp-no-fail ########################## Then run targetcli and do the following commands: backstores/iblock create uefi /dev/sdb /iscsi create iqn.2015-02.oracle.boot:uefi cd iqn.2015-02.oracle.boot:uefi/tpg1 luns/ create /backstores/block/uefi portals/ create 0.0.0.0 set attribute authentication=0 demo_mode_write_protect=0 generate_node_acls=1 cache_dynamic_acls=1 exit ########################## sudo mkdir /tftpd sudo chown dnsmasq: /tftpd ########################## /tftpd/script.ipxe: #!ipxe set initiator-iqn iqn.2015-02.oracle.boot:uefi sanboot iscsi:192.168.0.1::::iqn.2015-02.oracle.boot:uefi ########################## This gets the host pretty much ready to be an iscsi target for a host. The host has been patched etc, so reboot. You may want to set up ip forwarding etc on this instance. $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ Second host: No storage. Attach Ubuntu 16.04.1 LTS iso to the instance to boot from initially. Two NICs, first attached to bridge1. Second attached to bridge2. Go through the installation procedure, logging in to the iscsi endpoint on 192.168.0.1, using the details above (no username/password necessary with this configuration) and install to the iSCSI target. At the end, detach the CD-ROM and ensure everything is set up to network boot. On start-up you should see it network boot happily, everything is awesome. Do a "sudo apt update" and "sudo apt upgrade". Then reboot. On start-up you should see the bug happening. ipconfig is sending out DHCP requests on both interfaces and failing to accept any responses it is being sent ("journalctl -xef -u dnsmasq" on primary shows it is sending them). If you remove that second NIC, you'll see that the instance is able to boot happily. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1652348 Title: initrd dhcp fails / ignores valid response Status in linux package in Ubuntu: Incomplete Bug description: Between kernel versions 4.4.0-53 and 4.4.0-57 a bug has been (re?)introduced that is breaking dhcp booting in the initrd environment. This is stopping instances that use iscsi storage from being able to connect. Over serial console it outputs: IP-Config: no response after 2 secs - giving up IP-Config: ens2f0 hardware address 90:e2:ba:d1:36:38 mtu 1500 DHCP RARP IP-Config: ens2f1 hardware address 90:e2:ba:d1:36:39 mtu 1500 DHCP RARP IP-Config: no response after 3 secs - giving up with increasing delays until it fails. At which point a simple ipconfig -t dhcp -d "ens2f0" works. The console output is slightly garbled but should give you an idea: (initramfs) ipconfig -t dhcp -[ 728.379793] ixgbe 0000:13:00.0 ens2f0: changing MTU from 1500 to 9000 d "ens2f0" IP-Config: ens2f0 hardware address 90:e2:ba:d1:36:38 mtu 1500 DHCP RARP IP-Config: ens2f0 guessed broadcast address 10.0.1.255 IP-Config: ens2f0 complete (dhcp from 169.254.169.254): addres[ 728.980448] ixgbe 0000:13:00.0 ens2f0: detected SFP+: 3 s: 10.0.1.56 broadcast: 10.0.1.255 netmask: 255.255.255.0 gateway: 10.0.1.1 [ 729.148410] ixgbe 0000:13:00.0 ens2f0: NIC Link is Up 10 Gbps, Flow Control: RX/TX dns0 : 169.254.169.254 dns1 : 0.0.0.0 rootserver: 169.254.169.254 rootpath: filename : /ipxe.efi tcpdumps show that dhcp requests are being received from the host, and responses sent, but not accepted by the host. When the ipconfig command is issued manually, an identical dhcp request and response happens, only this time it is accepted. It doesn't appear to be that the messages are being sent and received incorrectly, just silently ignored by ipconfig. I was seeing this behaviour earlier this year, which I was able to fix by specifying "ip=dhcp" as a kernel parameter. About a month ago that was identified as causing us other problems (long story) and we dropped it, at which point we discovered the original bug was no longer an issue. Putting "ip=dhcp" back on with this kernel no longer fixes the problem. I've compared the two initrds and effectively the only thing that has changed between the two is the kernel components. Ubuntu kernel bisect offending commit: # first bad commit: [fd4b5fa6e3487d15ede746f92601af008b2abbc0] mnt: Add a per mount namespace limit on the number of mounts Ubuntu kernel bisect offending commit submission: https://lkml.org/lkml/2016/10/5/308 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1652348/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp