We just hit this issue in a Wallaby deployment (manual package
deployment, Ubuntu 20.04, kernel 5.4, linux bridge). Neutron-dhcp-agent
fails with the following error:
neutron.privileged.agent.linux.ip_lib.InvalidArgument: Invalid
parameter/value used on interface X, namespace qdhcp-Y"
whenever the network MTU is < 1280 bytes. Comparing the interface X of
the namespace Y to properly functioning interfaces of other namespaces
shows that IPv6 configuration is missing from the interface X.
DHCP agents remain broken globally until the network is removed or
adjusted to MTU >= 1280.
** Changed in: neutron
Status: Expired => Opinion
** Changed in: neutron
Status: Opinion => Confirmed
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https://bugs.launchpad.net/bugs/1988069
Title:
neutron-dhcp-agent fails when small tenant network mtu is set
Status in neutron:
Confirmed
Bug description:
High level description:
When a user creates a tenant network with a very small MTU (in our case 70),
neutron-dhcp-agent stops updating the dnsmasq configuration, causing DHCP
issues for all networks.
Pre-conditions:
Neutron is using the openvswitch, baremetal, and networking-generic-switch
mechanism drivers.
A physical network named `physnet1` is configured, with MTU=9000
Step-by-step reproduction steps:
As an admin user, run:
# Create "normal" network and subnet
openstack network create --provider-network-type vlan
--provider-physical-network physnet1 --mtu 1500 test-net-1500
openstack subnet create --subnet-range 10.100.10.0/24 --dhcp --network
test-net-1500 test-subnet-1500
# Create "small MTU" network and subnet
openstack network create --provider-network-type vlan
--provider-physical-network physnet1 --mtu 70 test-net-70
openstack subnet create --subnet-range 10.100.11.0/24 --dhcp --network
test-net-70 test-subnet-70
# attempt to launch an instance on the "normal" network
openstack server create --image Ubuntu --flavor Baremetal --network
test-net-1500
Expected output: what did you hope to see?
We expected to see neutron-dhcp-agent update the dnsmasq configuration, which
would then serve requests from the instances.
* Actual output: did the system silently fail (in this case log traces are
useful)?
Openstack commands complete successfully, but instance never receives a
response to its DHCP requests. Neutron-dhcp-agent logs show:
https://paste.opendev.org/show/b4r0XCu5KpguM72bnh0u/
Version:
** OpenStack version "stable/xena", hash
bc1dd6939d197d15799aaf252049f76442866c21
** Linux distro, kernel. Ubuntu 20.04
** Containers built with Kolla, and deployed via Kolla-Ansible
* Environment:
Single node deployment, all services (core, networking, database, etc.) on
one node.
All compute-nodes are baremetal via Ironic.
* Perceived severity: is this a blocker for you?
High, as non-admin users can trigger an DHCP outage affecting all users.
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