[BUG] gw_priority has no effect if IPv6 is enabled on a network #13599
Description
Description
I have a service defined like this:
networks:
localnet:
ipv4_address: 192.168.3.2
localnet_vlan101:
gw_priority: 20
ipv4_address: 192.168.101.2
networks:
localnet:
external: true
localnet_vlan101:
external: true
inspect localnet:
[
{
"Name": "localnet",
"Id": "fba84ec49d6e562a8728e377ddf571c4f67ec731a7ed015acec984d88e83e2f7",
"Created": "2025-11-22T16:13:57.561394744+08:00",
"Scope": "local",
"Driver": "macvlan",
"EnableIPv4": true,
"EnableIPv6": true,
"IPAM": {
"Driver": "default",
"Options": {},
"Config": [
{
"Subnet": "192.168.3.0/24",
"IPRange": "192.168.3.208/28",
"Gateway": "192.168.3.1"
},
{
"Subnet": "fd00:a:b:c::/64",
"IPRange": "fd00:a:b:c:1000::/72",
"Gateway": "fd00:a:b:c::1"
}
]
},
"Internal": false,
"Attachable": false,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Options": {
"parent": "XXX"
},
"Labels": {},
"Containers": {
"933d24f5f1d288f0d0a57082cee201e89945ac7914eabced58edfb36b366c487": {
"Name": "XXXXX",
"EndpointID": "28a20bfc4846d475a16ea4adcb914193626d6161248f4dc206420933822cdadf",
"MacAddress": "XXXXXX",
"IPv4Address": "192.168.3.2/24",
"IPv6Address": ""
}
},
"Status": {
"IPAM": {
"Subnets": {
"192.168.3.0/24": {
"IPsInUse": 4,
"DynamicIPsAvailable": 16
},
"fd00:a:b:c::/64": {
"IPsInUse": 2,
"DynamicIPsAvailable": 72057594037927936
}
}
}
}
}
]
inspect localnet_vlan101:
[
{
"Name": "localnet_vlan101",
"Id": "b71bf134bd7c5efce4af3c5c39243f31a99b24e326ee009be748f72ab77d87ae",
"Created": "2026-01-05T12:02:48.380234715+08:00",
"Scope": "local",
"Driver": "macvlan",
"EnableIPv4": true,
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": {},
"Config": [
{
"Subnet": "192.168.101.0/24",
"Gateway": "192.168.101.1"
}
]
},
"Internal": false,
"Attachable": false,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Options": {
"parent": "enp0s31f6.101"
},
"Labels": {},
"Containers": {
"933d24f5f1d288f0d0a57082cee201e89945ac7914eabced58edfb36b366c487": {
"Name": "XXXXX",
"EndpointID": "a986032a336513f14e762df7a62643fe5dbc9c8c4c3443e7a56a3b57e4b05088",
"MacAddress": "XXXXX",
"IPv4Address": "192.168.101.2/24",
"IPv6Address": ""
}
},
"Status": {
"IPAM": {
"Subnets": {
"192.168.101.0/24": {
"IPsInUse": 5,
"DynamicIPsAvailable": 251
}
}
}
}
}
]
Steps To Reproduce
- use the network config above
- start the service container
- exec shell in the container
- check default gateway with
ip route show
In the above configuration, I expect the gateway to be set to 192.168.101.1 , since the network has higher gw_priority of 20 (vs 0, which is the default). However, the actual observed gateway is 192.168.3.1.
I tried replacing the localnet network with a non-IPv6 network, and the gateway is correctly set to 192.168.101.1
I suspect it might be NDP router advertisements influencing the container? but I thought they would only affect the IPv6 options?
Compose Version
Docker Compose version v5.0.2
Docker Environment
Client: Docker Engine - Community
Version: 29.2.0
Context: default
Debug Mode: false
Plugins:
buildx: Docker Buildx (Docker Inc.)
Version: v0.31.1
Path: /usr/libexec/docker/cli-plugins/docker-buildx
compose: Docker Compose (Docker Inc.)
Version: v5.0.2
Path: /usr/libexec/docker/cli-plugins/docker-compose
Server:
Containers: 32
Running: 17
Paused: 0
Stopped: 15
Images: 77
Server Version: 29.2.0
Storage Driver: overlay2
Backing Filesystem: zfs
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
CDI spec directories:
/etc/cdi
/var/run/cdi
Swarm: inactive
Runtimes: io.containerd.runc.v2 runc
Default Runtime: runc
Init Binary: docker-init
containerd version: dea7da592f5d1d2b7755e3a161be07f43fad8f75
runc version: v1.3.4-0-gd6d73eb8
init version: de40ad0
Security Options:
apparmor
seccomp
Profile: builtin
cgroupns
Kernel Version: 6.8.0-94-generic
Operating System: Ubuntu 24.04.3 LTS
OSType: linux
Architecture: x86_64
CPUs: 12
Total Memory: 38.79GiB
Name: XXXX
ID: XXXXX
Docker Root Dir: /var/lib/docker
Debug Mode: false
Experimental: false
Insecure Registries:
127.0.0.0/8
::1/128
Live Restore Enabled: false
Firewall Backend: iptables
Anything else?
No response