Comment 4 for bug 1805920

I agree this may not be a MAAS bug specifically but I'm not sure where else to seek assistance.

You say MAAS doesn't support PXE booting over VLANs but vlan 0 is special: https://en.wikipedia.org/wiki/IEEE_802.1Q#Frame_format
"The reserved value 0x000 indicates that the frame does not carry a VLAN ID"

Here is the relevant portion of the switch config that the customer has shared with me. The ports are configured to vlan 17 as native (untagged) and to only allow vlan 17 at all. Note that this is not vlan 0.

  interface Vethernet2424
    description server 1/3, VNIC eth0
    switchport mode trunk
    no lldp transmit
    no lldp receive
    no pinning server sticky
    pinning server pinning-failure link-down
    switchport trunk native vlan 17
    switchport trunk allowed vlan 17
    bind interface port-channel1287 channel 2424
    no shutdown

  interface Vethernet2426
    description server 1/2, VNIC eth0
    switchport mode trunk
    no lldp transmit
    no lldp receive
    no pinning server sticky
    pinning server pinning-failure link-down
    switchport trunk native vlan 17
    switchport trunk allowed vlan 17
    bind interface port-channel1286 channel 2426
    no shutdown

  interface Vethernet2428
    description server 1/1, VNIC eth0
    switchport mode trunk
    no lldp transmit
    no lldp receive
    no pinning server sticky
    pinning server pinning-failure link-down
    switchport trunk native vlan 17
    switchport trunk allowed vlan 17
    bind interface port-channel1285 channel 2428
    no shutdown

1. On all 3 MAAS nodes, the physical interface enp6s0 is the sole member of bondm which is in bride broam. The vnet interfaces of VMs show up under broam as well. The physical interfaces are not vlan tagged.
2. The netplan on each machine looks like this (with differing addresses and customer specific nameserver info):

  network:
      ethernets:
          enp6s0:
              dhcp4: false
      version: 2
      bonds:
          bondm:
              interfaces: [ enp6s0 ]
              parameters:
                  mode: active-backup
                  primary: enp6s0
      bridges:
          broam:
              addresses: [ 10.17.101.10/22 ]
              gateway4: 10.17.100.1
              interfaces: [ bondm ]
              nameservers:
                  addresses: [ 123.123.123.1, 123.123.123.2 ]
                  search: [ unicloud1.example.net ]

3. The command-line for dhcpd doesn't show an interface:

  vernhart@infra1:~$ ps fuax | grep dhcpd
  vernhart 24086 0.0 0.0 13136 1100 pts/8 S+ 20:25 0:00 \_ grep --color=auto dhcpd
  dhcpd 8794 0.0 0.0 45964 16976 ? Ss Nov29 0:11 dhcpd -user dhcpd -group dhcpd -f -q -4 -pf /run/maas/dhcp/dhcpd.pid -cf /var/lib/maas/dhcpd.conf -lf /var/lib/maas/dhcp/dhcpd.leases broam
  vernhart@infra1:~$ sudo netstat -nlp | grep dhcp
  tcp 0 0 10.17.101.10:647 0.0.0.0:* LISTEN 8794/dhcpd
  tcp 0 0 0.0.0.0:7911 0.0.0.0:* LISTEN 8794/dhcpd
  udp 5120 0 0.0.0.0:67 0.0.0.0:* 8794/dhcpd
  udp 0 0 0.0.0.0:7309 0.0.0.0:* 8794/dhcpd
  udp6 0 0 :::27481 :::* 8794/dhcpd
  raw 0 0 0.0.0.0:1 0.0.0.0:* 7 8794/dhcpd

4. The VMs inside all the pods can communicate with each other.

  root@fce:~/fibernet-fcb# juju machines -m controller
  Machine State DNS Inst id Series AZ Message
  0 started 10.17.101.23 p6aaff bionic default Deployed
  1 started 10.17.101.25 84gxpn bionic zone2 Deployed
  2 started 10.17.101.24 bqfy3m bionic zone3 Deployed

  root@fce:~/fibernet-fcb# juju ssh -m controller 0
  Welcome to Ubuntu 18.04.1 LTS (GNU/Linux 4.15.0-39-generic x86_64)

   * Documentation: https://help.ubuntu.com
   * Management: https://landscape.canonical.com
   * Support: https://ubuntu.com/advantage

    System information as of Fri Nov 30 22:29:54 UTC 2018

    System load: 0.06 Processes: 138
    Usage of /: 13.2% of 91.17GB Users logged in: 0
    Memory usage: 2% IP address for ens6: 10.17.101.23
    Swap usage: 0%

    Get cloud support with Ubuntu Advantage Cloud Guest:
      http://www.ubuntu.com/business/services/cloud

   * Canonical Livepatch is available for installation.
     - Reduce system reboots and improve kernel security. Activate at:
       https://ubuntu.com/livepatch

  33 packages can be updated.
  0 updates are security updates.

  Last login: Fri Nov 16 20:17:20 2018 from 10.17.101.10
  ubuntu@juju-1:~$ ping 10.17.101.25 -c 1
  PING 10.17.101.25 (10.17.101.25) 56(84) bytes of data.
  64 bytes from 10.17.101.25: icmp_seq=1 ttl=64 time=0.534 ms

  --- 10.17.101.25 ping statistics ---
  1 packets transmitted, 1 received, 0% packet loss, time 0ms
  rtt min/avg/max/mdev = 0.534/0.534/0.534/0.000 ms
  ubuntu@juju-1:~$ ping 10.17.101.24 -c 1
  PING 10.17.101.24 (10.17.101.24) 56(84) bytes of data.
  64 bytes from 10.17.101.24: icmp_seq=1 ttl=64 time=0.653 ms

  --- 10.17.101.24 ping statistics ---
  1 packets transmitted, 1 received, 0% packet loss, time 0ms
  rtt min/avg/max/mdev = 0.653/0.653/0.653/0.000 ms
  ubuntu@juju-1:~$

Your final two asks:

1. Is STP enabled? I don't believe so but I can't find the response from the customer stating so. I will confirm. I don't think this would be an issue, however, because I can see the DHCP responses coming in a timely manner on the virtual interface when I tcpdump.

2. Is STP or a long forward-delay configured on the bridge?

  vernhart@infra2:~$ brctl show
  bridge name bridge id STP enabled interfaces
  broam 8000.fee6cd1cc06b no bondm
  vernhart@infra2:~$ brctl showstp broam
  broam
   bridge id 8000.fee6cd1cc06b
   designated root 8000.fee6cd1cc06b
   root port 0 path cost 0
   max age 20.00 bridge max age 20.00
   hello time 2.00 bridge hello time 2.00
   forward delay 15.00 bridge forward delay 15.00
   ageing time 300.00
   hello timer 0.00 tcn timer 0.00
   topology change timer 0.00 gc timer 136.28
   flags

  bondm (1)
   port id 8001 state forwarding
   designated root 8000.fee6cd1cc06b path cost 100
   designated bridge 8000.fee6cd1cc06b message age timer 0.00
   designated port 8001 forward delay timer 0.00
   designated cost 0 hold timer 0.00
   flags