gNMI gRPC dial fails for IPv6 link-local address with zone index (%eth0) due to URL re-encoding

[ruchakulkarni11]

gNMIc fails to connect to targets using IPv6 link-local addresses that include a zone index (e.g. %eth0). Although address resolution appears correct in gRPC logs, the connection fails during transport creation because the zone index is URL-reencoded and passed incorrectly to the OS socket layer.

This results in network is unreachable errors even when the address and interface are valid and reachable (e.g. ping6 fe80::…%eth0 succeeds).

If I explicitly try with passthrough, I am getting the error:

Attempt 1: without adding scope identifier before network interface name

gnmic -a "passthrough:///[fe80::xxxx%eth0]:9339" --mode stream --stream-mode sample --sample-interval 30s sub --path :/interfaces/interface[name=eth0]/state --insecure --debug

2026/02/10 00:24:00.023698 /home/runner/work/gnmic/gnmic/pkg/app/subscribe.go:254: [gnmic] starting target "passthrough:///[fe80::xxxx%eth0]:9339" listener
2026/02/10 00:24:00.023782 /home/runner/work/gnmic/gnmic/pkg/app/gnmi_client_subscribe.go:207: [gnmic] failed to initialize target "passthrough:///[fe80::xxxx%eth0]:9339": [passthrough:///[fe80::xxxx%eth0]:9339]:57400: parse "passthrough:///[passthrough:///[fe80::xxxx%eth0]:9339]:57400": invalid URL escape "%et"

Attempt 2: with scopr identifier before network interface name

gnmic -a "passthrough:///[fe80::xxxx%25eth0]:9339" --mode stream --stream-mode sample --sample-interval 30s sub --path :/interfaces/interface[name="eth0"]/state --insecure --debug

2026/02/10 00:25:21.615469 /home/runner/work/gnmic/gnmic/pkg/app/subscribe.go:313: [gnmic] target "passthrough:///[fe80::xxxx%25eth0]:9339": subscription default-1770683120 rcv error: failed to create a subscribe client, target='passthrough:///[fe80::xxxx%25eth0]:9339', retry in 10000000000. err=rpc error: code = Unavailable desc = connection error: desc = "transport: Error while dialing: dial tcp: address [passthrough:///[fe80::xxxx%25eth0]:9339]:57400: too many colons in address"

[karimra]

what error do you get without the scheme: -a [fe80::xxxx%eth0]:9339 ?

[ruchakulkarni11]

gnmic fails to establish a gRPC connection to a link-local IPv6 address and enters TRANSIENT_FAILURE with the error:
dial tcp [fe80::x:x:x:x%25eth0]:9339: connect: network is unreachable

Debug logs:

gnmic -a fe80::x:x:x:x%25eth0 --port 9339 --mode stream --stream-mode sample --sample-interval 30s sub --path :/interfaces/interface/state --insecure --debug
.
.
.
.
.

2026/02/06 18:53:53.302477 /home/build/go/pkg/mod/google.golang.org/grpc@v1.76.0/grpclog/internal/logger.go:45: [gnmic] [core] [Channel #1] parsed dial target is: resolver.Target{URL:url.URL{Scheme:"passthrough", Opaque:"", User:(*url.Userinfo)(nil), Host:"", Path:"/[fe80::x:x:x:x%eth0]:9339", RawPath:"/[fe80::x:x:x:x%25eth0]:9339", OmitHost:false, ForceQuery:false, RawQuery:"", Fragment:"", RawFragment:""}}
2026/02/06 18:53:53.302499 /home/build/go/pkg/mod/google.golang.org/grpc@v1.76.0/grpclog/internal/logger.go:45: [gnmic] [core] [Channel #1] Channel authority set to "[fe80::x:x:x:x%25eth0]:9339"
2026/02/06 18:53:53.302810 /home/build/go/pkg/mod/google.golang.org/grpc@v1.76.0/grpclog/internal/logger.go:45: [gnmic] [core] [Channel #1] Resolver state updated: {
"Addresses": [
{
"Addr": "[fe80::x:x:x:x%eth0]:9339",
"ServerName": "",
"Attributes": null,
"BalancerAttributes": null,
"Metadata": null
}
],
"Endpoints": [
{
"Addresses": [
{
"Addr": "[fe80::x:x:x:x%eth0]:9339",
"ServerName": "",
"Attributes": null,
"BalancerAttributes": null,
"Metadata": null
}
],
"Attributes": null
}
],
"ServiceConfig": null,
"Attributes": null
} (resolver returned new addresses)
2026/02/06 18:53:53.302870 /home/build/go/pkg/mod/google.golang.org/grpc@v1.76.0/grpclog/internal/logger.go:45: [gnmic] [core] [Channel #1] Channel switches to new LB policy "pick_first"
2026/02/06 18:53:53.302938 /home/build/go/pkg/mod/google.golang.org/grpc@v1.76.0/grpclog/internal/logger.go:45: [gnmic] [pick-first-leaf-lb] [pick-first-leaf-lb 0xc00081f560] Received new config {
"shuffleAddressList": false
}, resolver state {
"Addresses": [
{
"Addr": "[fe80::x:x:x:x%eth0]:9339",
"ServerName": "",
"Attributes": null,
"BalancerAttributes": null,
"Metadata": null
}
],
"Endpoints": [
{
"Addresses": [
{
"Addr": "[fe80::x:x:x:x%eth0]:9339",
"ServerName": "",
"Attributes": null,
"BalancerAttributes": null,
"Metadata": null
}
],
"Attributes": null
}
],
"ServiceConfig": null,
"Attributes": null
}
2026/02/06 18:53:53.302994 /home/build/go/pkg/mod/google.golang.org/grpc@v1.76.0/grpclog/internal/logger.go:45: [gnmic] [core] [Channel #1] Channel Connectivity change to CONNECTING
2026/02/06 18:53:53.303022 /home/build/go/pkg/mod/google.golang.org/grpc@v1.76.0/grpclog/internal/logger.go:45: [gnmic] [core] [Channel #1 SubChannel #2] Subchannel created
2026/02/06 18:53:53.635018 /home/build/go/pkg/mod/google.golang.org/grpc@v1.76.0/grpclog/internal/logger.go:45: [gnmic] [core] [Channel #1] Channel exiting idle mode

2026/02/06 18:53:53.635082 /home/build/go/pkg/mod/google.golang.org/grpc@v1.76.0/grpclog/internal/logger.go:45: [gnmic] [core] [Channel #1 SubChannel #2] Subchannel Connectivity change to CONNECTING
2026/02/06 18:53:53.635216 /home/build/go/pkg/mod/google.golang.org/grpc@v1.76.0/grpclog/internal/logger.go:45: [gnmic] [core] [Channel #1 SubChannel #2] Subchannel picks a new address "[fe80::x:x:x:x%eth0]:9339" to connect
2026/02/06 18:53:53.635844 /home/build/go/pkg/mod/google.golang.org/grpc@v1.76.0/grpclog/internal/logger.go:45: [gnmic] [core] Creating new client transport to "{Addr: "[fe80::x:x:x:x%eth0]:9339", ServerName: "[fe80::x:x:x:x%25eth0]:9339", }": connection error: desc = "transport: Error while dialing: dial tcp [fe80::x:x:x:x%25eth0]:9339: connect: network is unreachable"

2026/02/06 18:53:53.635880 /home/build/go/pkg/mod/google.golang.org/grpc@v1.76.0/grpclog/internal/logger.go:60: [gnmic] [core] [Channel #1 SubChannel #2] grpc: addrConn.createTransport failed to connect to {Addr: "[fe80::x:x:x:x%eth0]:9339", ServerName: "[fe80::x:x:x:x%25eth0]:9339", }. Err: connection error: desc = "transport: Error while dialing: dial tcp [fe80::x:x:x:x%25eth0]:9339: connect: network is unreachable"

2026/02/06 18:53:53.635912 /home/build/go/pkg/mod/google.golang.org/grpc@v1.76.0/grpclog/internal/logger.go:45: [gnmic] [core] [Channel #1 SubChannel #2] Subchannel Connectivity change to TRANSIENT_FAILURE, last error: connection error: desc = "transport: Error while dialing: dial tcp [fe80::x:x:x:x%25eth0]:9339: connect: network is unreachable"

2026/02/06 18:53:53.635959 /home/build/go/pkg/mod/google.golang.org/grpc@v1.76.0/grpclog/internal/logger.go:45: [gnmic] [core] [Channel #1] Channel Connectivity change to TRANSIENT_FAILURE