MAC address conflict since v25

[adamenhance]

Description

I understand that, unless --mac-address is specified when calling docker run that a MAC address will be generated on container start with the prefix 02:42:ac and then the last 3 components being the container's ipv4 address in hex notation.

Since v25.0.0 (using the official docker-ce Ubuntu package for 22.04) it seems that "docker start" retains the previous MAC address even when the IP is changed and that this can cause a MAC address conflict.

This behaviour does not occur on 24.x.

Reproduce

docker network create test-network
docker run -d --name server1 --network test-network httpd
docker stop server1
docker run -d --name server2 --network test-network httpd
docker start server1

Now if you “docker inspect” for server1 and server2 they will have the same MAC address but a different IP. Connectivity will be intermittent for both containers.

Expected behavior

Starting a container should assign a unique MAC address if no MAC address was specified when the container was created.

docker version

Client: Docker Engine - Community
 Version:           25.0.0
 API version:       1.44
 Go version:        go1.21.6
 Git commit:        e758fe5
 Built:             Thu Jan 18 17:09:49 2024
 OS/Arch:           linux/amd64
 Context:           default

Server: Docker Engine - Community
 Engine:
  Version:          25.0.0
  API version:      1.44 (minimum version 1.24)
  Go version:       go1.21.6
  Git commit:       615dfdf
  Built:            Thu Jan 18 17:09:49 2024
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.6.27
  GitCommit:        a1496014c916f9e62104b33d1bb5bd03b0858e59
 runc:
  Version:          1.1.11
  GitCommit:        v1.1.11-0-g4bccb38
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

docker info

Client: Docker Engine - Community
 Version:           25.0.0
 API version:       1.44
 Go version:        go1.21.6
 Git commit:        e758fe5
 Built:             Thu Jan 18 17:09:49 2024
 OS/Arch:           linux/amd64
 Context:           default

Server: Docker Engine - Community
 Engine:
  Version:          25.0.0
  API version:      1.44 (minimum version 1.24)
  Go version:       go1.21.6
  Git commit:       615dfdf
  Built:            Thu Jan 18 17:09:49 2024
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.6.27
  GitCommit:        a1496014c916f9e62104b33d1bb5bd03b0858e59
 runc:
  Version:          1.1.11
  GitCommit:        v1.1.11-0-g4bccb38
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0
root@containering:~# docker info
Client: Docker Engine - Community
 Version:    25.0.0
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc.)
    Version:  v0.12.1
    Path:     /usr/libexec/docker/cli-plugins/docker-buildx
  compose: Docker Compose (Docker Inc.)
    Version:  v2.24.1
    Path:     /usr/libexec/docker/cli-plugins/docker-compose

Server:
 Containers: 2
  Running: 0
  Paused: 0
  Stopped: 2
 Images: 1
 Server Version: 25.0.0
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Using metacopy: false
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: systemd
 Cgroup Version: 2
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: a1496014c916f9e62104b33d1bb5bd03b0858e59
 runc version: v1.1.11-0-g4bccb38
 init version: de40ad0
 Security Options:
  apparmor
  seccomp
   Profile: builtin
  cgroupns
 Kernel Version: 5.15.0-91-generic
 Operating System: Ubuntu 22.04.3 LTS
 OSType: linux
 Architecture: x86_64
 CPUs: 1
 Total Memory: 1.918GiB
 Name: containering
 ID: 172a9933-7614-4ae1-a496-3f40c37b45c7
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

Additional Info

No response

[robmry]

@adamenhance - thank you for reporting ... this was a nasty bug, we'll get it patched.

[saltydk]

Any ETA on a build with this fix as it kind of renders v25 kind of useless with bridge networks?

[akerouanton]

@saltydk No firm ETA, but we're going to release a minor version in the upcoming hours / days to fix all the issues found v25.0.