Docker Container Has No Internet: Diagnose the Outbound Bridge Path

Outbound container connectivity and inbound published-port access are opposite directions. Establish the failing direction first.[1][3]

• Container cannot reach outside → Does the container stay running?
• LAN cannot reach a published port → This is a published-port observation, not outbound failure
• I have not established this → Establish the failing direction

Record whether the failing request travels from the container toward the outside world or from a LAN client toward a published host port.[1][3]

Only outbound container failures continue on this page.[1]

• Container cannot reach outside → Does the container stay running?
• LAN cannot reach a published port → This is a published-port observation, not outbound failure

A service reachable locally but not from another LAN device needs the published-port diagnosis, which compares the working local endpoint with the failing LAN endpoint. Do not apply outbound bridge repair paths to it.[3]

A container that does not stay running never reaches network-path diagnosis.[1]

• Yes, it runs but reaches nothing outside → Which network mode does the container use?
• No, it does not stay running → This is a container lifecycle problem, not a network path
• I have not checked → Check the container running state

Record whether the container starts and stays running before any network observation.[1]

Only a running container continues on this page.[1]

• It runs but reaches nothing outside → Which network mode does the container use?
• It does not stay running → This is a container lifecycle problem, not a network path

A container that does not stay running needs lifecycle diagnosis, not bridge or gateway checks. Preserve the state and log output and use the matching workflow.[1]

Establish the network mode before any bridge-specific conclusion. A container can attach to multiple networks, including networks using different drivers, so record every attachment; the effective outbound path is established at the egress gate later. Non-bridge modes follow different connectivity models.[1][5]

• Bridge (default or user-defined) → Is the container attached to the expected bridge network?
• Host, none, or another driver → Non-bridge modes need their own diagnosis
• I have not checked → Record the container network mode

Record the network mode from Docker-side inspection before any bridge-specific step.[9][5]

Only bridge attachments continue on this page.[1]

• Bridge (default or user-defined) → Is the container attached to the expected bridge network?
• Host, none, or another driver → Non-bridge modes need their own diagnosis

Host, none, macvlan, ipvlan, overlay, rootless, and Docker Desktop networking do not share the rootful bridge masquerading path. Record the mode and use the matching diagnosis; do not apply bridge repair steps and never change the network mode as a test.[1][5]

Compare the intended bridge network against the actual attachment, recording every attachment because a container can use several networks. The effective outbound path is established at the egress gate later, not here.[1][6]

• Yes, attached as intended → Does the container have a live address?
• No, wrong network or no attachment → Resolve the attachment gap with the deployment owner
• I have not checked → Compare intended and actual attachment

Record the intended bridge network and the actual container attachment side by side.[6]

A wrong or missing attachment is an assignment gap, not an upstream outage.[6]

• Attached as intended → Does the container have a live address?
• Wrong network or no attachment → Resolve the attachment gap with the deployment owner

Without the intended attachment, gateway and external tests cannot localize the fault. Record the intended network, the actual attachment, and the live address state, and hand those observations to the deployment owner. Do not connect, disconnect, or recreate networking as a probe.[6]

Compare the attachment with live address state. A present address continues to path checks; it never by itself declares external connectivity healthy.[6][9]

• Yes, an address is present → Which design provides the default outbound path?
• No, no address is present → Resolve address assignment before path checks
• I have not checked → Compare attachment with live addressing

Record the network attachment and the live address state side by side.[6]

A configured attachment that yields no live address is an assignment gap, not an upstream outage.[6]

• An address is present → Which design provides the default outbound path?
• No address is present → Resolve address assignment before path checks

Without a live container address, gateway and external tests cannot localize the fault. Investigate attachment and address assignment first; do not change filtering, forwarding, or upstream configuration yet.[6][2]

Establish the intended and effective egress network and the applicable gateway or default path, and record whether that evidence is known or unknown. An internal network intentionally restricts external access; multiple attachments select a default gateway that may change when attachments change. Bridge masquerading is default behavior, but user-defined external-connectivity options can alter the expected model, so bridge driver presence never proves masqueraded egress is intended. Do not change gateway priority as a probe.[1][2][8][6]

• Single bridge, external access expected → Can the container reach an external destination by IP?
• Internal network by design → Internal isolation may be intentional — not a fault
• Multiple networks, bridge egress established → Can the container reach an external destination by IP?
• Effective egress unclear or unknown → Establish the egress design before any verdict
• Effective egress is non-bridge → Non-bridge modes need their own diagnosis

A network created as internal intentionally restricts external access while containers on it can still communicate inside that network. Missing Internet here reflects the documented design, not a broken bridge path. Do not diagnose this as filtering or upstream failure, and do not remove the internal restriction as a diagnostic test.[8][1]

With multiple attachments or a custom design, the effective default outbound path cannot be established from the available evidence. Record every attachment, the applicable gateway or default path, and the intended design, and hand those observations to the deployment or network owner. Do not guess which network should provide egress and do not apply bridge repair steps.[1][6]

With a supported bridge egress design established, test an external destination by IP before any hostname. IP success with failing hostnames isolates the DNS layer; IP failure keeps the investigation at gateway, filtering, or upstream layers.[1]

• No, external IPs fail → Continue at gateway, filtering, and upstream layers
• IPs work, hostnames fail → IP path works — continue with DNS diagnosis
• Everything works now → Record the evidence while the path works
• I have not tested it → Test an external destination by IP

Test an external destination by IP from the container context, using only utilities present in the image. A missing utility is not a network failure.[1]

Separate IP reachability from name resolution before any conclusion.[1]

• External IPs fail → Continue at gateway, filtering, and upstream layers
• IPs work, hostnames fail → IP path works — continue with DNS diagnosis
• Everything works now → Record the evidence while the path works

With a supported bridge egress design established, the container attached and addressed, but external IPs failing, continue at gateway behavior, packet-filtering and forwarding evidence, and the upstream path. This conclusion is only valid because the egress gate confirmed external access is expected. The host having Internet access never proves the container forwarding path works. Collect evidence without changing policy, and distinguish the filtering backend in use.[4][2]

Reachable external IPs with failing hostnames isolate the DNS layer. Continue with the container DNS diagnosis, which separates default-bridge and user-defined-bridge resolver behavior. Do not treat this as a general connectivity failure.[1]

A currently working path cannot confirm the earlier failure is resolved. Record attachment, addressing, gateway behavior, and the exact test that failed before, and monitor for recurrence instead of changing configuration.[6]