Description of problem:

Adding an IPv6 only host to the engine fails. At the end of the installation the engine sends a setupNetworks() without IPv4 and without IPv6 to create the ovirtmgmt bridge, leaving the host without IP.

Version-Release number of selected component (if applicable):
ovirt-engine-4.3.8.2-0.4.el7.noarch
vdsm-4.30.40-1.el7ev.x86_64

How reproducible:
Always

Steps to Reproduce:
1. Install RHEL 7.7 host, configure IPv6 only on eth0. Other interfaces (eth1 and eth2) have no config.

PROXY_METHOD=none
BROWSER_ONLY=no
DEFROUTE=yes
IPV4_FAILURE_FATAL=no
IPV6INIT=yes
IPV6_AUTOCONF=no
IPV6_DEFROUTE=yes
IPV6_FAILURE_FATAL=no
IPV6_ADDR_GEN_MODE=stable-privacy
NAME=ethernet-eth0
UUID=f13e2615-16f4-47f5-a71b-d320dbe282b6
DEVICE=eth0
ONBOOT=yes
IPV6ADDR=2::2/64
IPV6_DEFAULTGW=2::128

2. Add Host to RHV. After ansible-deploy, the host is non-op due to missing networks. Then the engine sends this to create the ovirtmgmt bridge:

2020-02-24 09:49:34,586+10 INFO  [org.ovirt.engine.core.dal.dbbroker.auditloghandling.AuditLogDirector] (EE-ManagedThreadFactory-engine-Thread-1219) [7d6ab528] EVENT_ID: VDS_ANSIBLE_INSTALL_FINISHED(561), Ansible host-deploy playbook execution has successfully finished on host host2.kvm.

2020-02-24 09:49:34,689+10 INFO  [org.ovirt.vdsm.jsonrpc.client.reactors.ReactorClient] (SSL Stomp Reactor) [] Connecting to host2.kvm/2:0:0:0:0:0:0:2

2020-02-24 09:49:34,839+10 INFO  [org.ovirt.engine.core.bll.host.HostConnectivityChecker] (EE-ManagedThreadFactory-engine-Thread-1219) [7d6ab528] Engine managed to communicate with VDSM agent on host 'host2.kvm' with address 'host2.kvm' ('75e966fa-f19c-4e0e-981e-683eebaebda4')

2020-02-24 09:49:38,081+10 ERROR [org.ovirt.engine.core.bll.SetNonOperationalVdsCommand] (EE-ManagedScheduledExecutorService-engineScheduledThreadPool-Thread-45) [35f30b49] Host 'host2.kvm' is set to Non-Operational, it is missing the following networks: 'ovirtmgmt,san-1,san-2'

2020-02-24 09:49:38,243+10 INFO  [org.ovirt.engine.core.vdsbroker.vdsbroker.HostSetupNetworksVDSCommand] (EE-ManagedThreadFactory-engine-Thread-1219) [35e50694] START, HostSetupNetworksVDSCommand(
  HostName = host2.kvm, 
  HostSetupNetworksVdsCommandParameters:{
    hostId='75e966fa-f19c-4e0e-981e-683eebaebda4', 
    vds='Host[host2.kvm,75e966fa-f19c-4e0e-981e-683eebaebda4]', 
    rollbackOnFailure='true', 
    commitOnSuccess='false', 
    connectivityTimeout='120', 
    networks='[
      HostNetwork:{
        defaultRoute='true', 
        bonding='false', 
        networkName='ovirtmgmt', 
        vdsmName='ovirtmgmt', 
        nicName='eth0', 
        vlan='null', 
        vmNetwork='true', 
        stp='false', 
        properties='null', 
        ipv4BootProtocol='NONE', 
        ipv4Address='null', 
        ipv4Netmask='null', 
        ipv4Gateway='null', 
        ipv6BootProtocol='AUTOCONF', 
        ipv6Address='null',             <--- ??
        ipv6Prefix='null',              <--- ??
        ipv6Gateway='null', 
        nameServers='null'}
    ]', 
    removedNetworks='[]', 
    bonds='[]', 
    removedBonds='[]', 
    clusterSwitchType='LEGACY', 
    managementNetworkChanged='true'}
), log id: 24d7b4a1

Which results in this:

MainProcess|jsonrpc/7::DEBUG::2020-02-24 09:49:38,960::ifcfg::578::root::(writeConfFile) Writing to file /etc/sysconfig/network-scripts/ifcfg-ovirtmgmt configuration:
# Generated by VDSM version 4.30.40.1
DEVICE=ovirtmgmt
TYPE=Bridge
DELAY=0
STP=off
ONBOOT=yes
MTU=1500
DEFROUTE=no
NM_CONTROLLED=no
IPV6INIT=yes
IPV6_AUTOCONF=yes

MainProcess|jsonrpc/7::DEBUG::2020-02-24 09:49:38,980::ifcfg::578::root::(writeConfFile) Writing to file /etc/sysconfig/network-scripts/ifcfg-eth0 configuration:
# Generated by VDSM version 4.30.40.1
DEVICE=eth0
BRIDGE=ovirtmgmt
ONBOOT=yes
MTU=1500
DEFROUTE=no
NM_CONTROLLED=no

3. Connectivity Check of course fails, and VDSM rolls back the config:

MainProcess|jsonrpc/7::INFO::2020-02-24 09:52:40,825::connectivity::48::root::(check) Connectivity check failed, rolling back

4. Even though ifcf-eth0 was restored, it looks like roll-back did not bring the interface up, so the host is completely without network.

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 52:54:00:19:c1:02 brd ff:ff:ff:ff:ff:ff
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 52:54:00:86:31:ae brd ff:ff:ff:ff:ff:ff
4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 52:54:00:5f:79:52 brd ff:ff:ff:ff:ff:ff
5: ovs-system: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
    link/ether 3e:d0:db:db:a5:85 brd ff:ff:ff:ff:ff:ff
6: br-int: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
    link/ether 26:86:e6:f0:44:47 brd ff:ff:ff:ff:ff:ff
22: ;vdsmdummy;: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
    link/ether 96:9a:d7:92:e8:53 brd ff:ff:ff:ff:ff:ff
24: genev_sys_6081: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 65000 qdisc noqueue master ovs-system state UNKNOWN group default qlen 1000
    link/ether f2:94:10:58:80:ac brd ff:ff:ff:ff:ff:ff
    inet6 fe80::f094:10ff:fe58:80ac/64 scope link 
       valid_lft forever preferred_lft forever