OpenStack Neutron Networking Errors
The Neutron failures that leave instances without networking: a port fails to bind, VIF plugging times out, the subnet runs out of IPs, a floating-IP pool is missing, or an OVS/DHCP/L3 agent is dead. Each guide leads with the cause and the `openstack network`, `neutron`, and `ovs-vsctl` commands to prove it. Jump to your symptom below, or hand the agent your neutron logs.
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Every guide in this cluster
13 guides-
'binding_failed' Neutron Port Binding Failed
Fix the Neutron PortBindingFailed / binding_failed error in OpenStack: diagnose ML2 mechanism drivers, dead L2 agents, physnet bridge mappings, and MTU.
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'Timeout waiting for vif plugging callback' — Fix Neutron/Nova VIF Plug
Fix Nova 'Timeout waiting for vif plugging callback' errors: diagnose the missing Neutron network-vif-plugged event, dead L2 agent, OVN chassis, RabbitMQ gaps, and timeout tuning in Kolla-Ansible.
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'No more IP addresses available on network' (Neutron IP exhaustion)
Resolve the Neutron 'No more IP addresses available' error: exhausted allocation pools, leaked ports, oversized reservations, small CIDRs, and orphaned VM ports.
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Open vSwitch agent 'XXX' dead — fix neutron-openvswitch-agent / ovs-vswitchd
Fix a dead Neutron Open vSwitch agent (alive :-() and unresponsive ovs-vswitchd: diagnose the ovsdb-server socket, agent-to-server RPC, and restart order so tenant networking recovers.
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'Failed to allocate the network(s)' in OpenStack — Fix
Fix OpenStack Nova's 'Failed to allocate the network(s), not rescheduling' error: usually a VIF plug timeout or dead L2 agent. Diagnose ports and unblock spawn.
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'Floating IP pool not found' external network failure
Allocating a floating IP and hitting Floating IP pool not found or ExternalNetworkNotReachable? Diagnose missing external networks and bad pool names step by step.
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'neutron-l3-agent router namespace missing' connectivity loss
L3 router namespace qrouter-<id> missing and tenants lost external connectivity? Diagnose dead l3-agent, OVS bridge gaps, and namespace recreation step by step.
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'SubnetInUse: One or more ports have an IP allocation' — Free the Subnet
Fix Neutron SubnetInUse when deleting a subnet or network: find the ports still holding IP allocations — router interfaces, DHCP, floating IPs, and stuck instance ports — and clear them safely.
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'agent is not alive' Neutron Agent Down (alive=XXX)
Fix Neutron's 'agent is not alive' / alive=XXX (L2/L3/DHCP) error: diagnose dead openvswitch, dhcp, and l3 agents, RabbitMQ heartbeats, and clock skew.
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'Security Group ... in use' SecurityGroupInUse on Delete
Fix Neutron's SecurityGroupInUse 'Security Group ... in use' 409 when deleting a security group: find the ports still bound to it, detach them, then delete cleanly.
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Neutron DHCP Agent Down — Instances Not Getting IP Addresses
Fix a down Neutron DHCP agent so instances get IPs again: diagnose agent alive=XXX, restart neutron-dhcp-agent, respawn dnsmasq, and rebalance networks.
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Neutron L3 HA Failover Not Switching Router Master (keepalived)
Fix Neutron L3 HA routers that won't fail over: diagnose keepalived VRRP, split-brain masters, blocked HA network multicast, and restore a single active router agent.
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Neutron Overlay MTU Mismatch Dropping/Fragmenting Tenant Traffic
Fix OpenStack Neutron overlay MTU mismatches on VXLAN/GENEVE tenant networks: diagnose black-holed large packets, set global_physnet_mtu, and align instance MTU.
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Frequently asked questions
Why does an OpenStack port fail to bind (binding_failed)?
openstack network agent list and the neutron-server log. See port binding failed."No more IP addresses available" — how do I fix it?
openstack ip availability show <network>. See no more IP addresses.A network agent shows as down — does that break everything?
openstack network agent list, and check RabbitMQ connectivity, which agents rely on.