VM can't get IP without default egress rules on OVN

[Trygve Vea]

Confirmed on:

- RDO stable/2023.1 (antelope)
- Almalinux 9, kernel 5.14.0-284.18.1.el9_2.x86_64
- Neutron 22.0.2 (RDO)
- OVN 22.12 (from CentOS SIG)

How to reproduce:

- Have a functioning instance which gets its IP address from DHCP
- Ensure that you have a user that can log in through console
- Remove default egress rules ("any" to 0.0.0.0/0)
- Reboot instance
- Watch instance not having IP

Workaround:

- Add a security group rule that allows egress udp 67:68 to 0.0.0.0/0 will ensure that the instance gets an IP.

See also: https://bugs.launchpad.net/networking-ovn/+bug/1536028

[Brian Haley (brian-haley)]

I can confirm the failure, from my test VM:

### ifconfig -a
eth0 Link encap:Ethernet HWaddr FA:16:3E:FF:E9:72
          inet addr:169.254.69.35 Bcast:169.254.255.255 Mask:255.255.0.0
          inet6 addr: fe80::f816:3eff:feff:e972/64 Scope:Link
          inet6 addr: fda3:8d6b:fd7:0:f816:3eff:feff:e972/64 Scope:Global
          UP BROADCAST RUNNING MULTICAST MTU:1442 Metric:1
          RX packets:21 errors:0 dropped:0 overruns:0 frame:0
          TX packets:66 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:2984 (2.9 KiB) TX bytes:4508 (4.4 KiB)

What is odd is that it is getting its IPv6 address.

I'll have to bug Ihar since he made a change for IPv6 that seemed similar,

https://github.com/ovn-org/ovn/commit/071cd7385f4aaf6e0e4635aa16a84e174b53d4ef

[Rodolfo Alonso (rodolfo-alonso-hernandez)]

Hello:

This OVN gap is covered in the documentation [1], section "DHCP service for instances".

This bug is a duplicate of LP#1926515.

Regards.

[1]https://github.com/openstack/neutron/blob/master/doc/source/ovn/gaps.rst