[PATCH] selftests/net: add test for IPv4-in-IPv6 tunneling

[PATCH] selftests/net: add test for IPv4-in-IPv6 tunneling

[Linus Heckemann]

81c734dae203757fb3c9eee6f9896386940776bd was fine in and of itself, but
its backport to 6.12 (and 6.6) broke IPv4-in-IPv6 tunneling, see [1].
This adds a self-test for basic IPv4-in-IPv6 functionality.

[1]: https://lore.kernel.org/all/CAA2RiuSnH_2xc+-W6EnFEG00XjS-dszMq61JEvRjcGS31CBw=g@mail.gmail.com/
---
 tools/testing/selftests/net/Makefile      |  1 +
 tools/testing/selftests/net/ip6_tunnel.sh | 41 +++++++++++++++++++++++
 2 files changed, 42 insertions(+)
 create mode 100644 tools/testing/selftests/net/ip6_tunnel.sh

diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index 45c4ea381bc36..5037a344ad826 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -43,6 +43,7 @@ TEST_PROGS := \
 	io_uring_zerocopy_tx.sh \
 	ioam6.sh \
 	ip6_gre_headroom.sh \
+	ip6_tunnel.sh \
 	ip_defrag.sh \
 	ip_local_port_range.sh \
 	ipv6_flowlabel.sh \
diff --git a/tools/testing/selftests/net/ip6_tunnel.sh b/tools/testing/selftests/net/ip6_tunnel.sh
new file mode 100644
index 0000000000000..366f4c06cd6a3
--- /dev/null
+++ b/tools/testing/selftests/net/ip6_tunnel.sh
@@ -0,0 +1,41 @@
+#!/bin/bash
+# Test that IPv4-over-IPv6 tunneling works.
+
+set -e
+
+setup_prepare() {
+  ip link add transport1 type veth peer name transport2
+
+  ip netns add ns1
+  ip link set transport1 netns ns1
+  ip netns exec ns1 bash <<EOF
+  set -e
+  ip address add 2001:db8::1/64 dev transport1 nodad
+  ip link set transport1 up
+  ip link add link transport1 name tunnel1 type ip6tnl mode ipip6 local 2001:db8::1 remote 2001:db8::2
+  ip address add 172.0.0.1/32 peer 172.0.0.2/32 dev tunnel1
+  ip link set tunnel1 up
+EOF
+
+  ip netns add ns2
+  ip link set transport2 netns ns2
+  ip netns exec ns2 bash <<EOF
+  set -e
+  ip address add 2001:db8::2/64 dev transport2 nodad
+  ip link set transport2 up
+  ip link add link transport2 name tunnel2 type ip6tnl mode ipip6 local 2001:db8::2 remote 2001:db8::1
+  ip address add 172.0.0.2/32 peer 172.0.0.1/32 dev tunnel2
+  ip link set tunnel2 up
+EOF
+}
+
+cleanup() {
+  ip netns delete ns1
+  ip netns delete ns2
+  # in case the namespaces haven't been set up yet
+  ip link delete transport1
+}
+
+trap cleanup EXIT
+setup_prepare
+ip netns exec ns1 ping -W1 -c1 172.0.0.2
-- 
2.52.0

Re: [PATCH] selftests/net: add test for IPv4-in-IPv6 tunneling

[Hangbin Liu]

Hi Linus
On Sun, Feb 08, 2026 at 03:46:04PM +0100, Linus Heckemann wrote:
> 81c734dae203757fb3c9eee6f9896386940776bd was fine in and of itself, but

Please use git commit description style 'commit <12+ chars of sha1> ("<title line>")'

> its backport to 6.12 (and 6.6) broke IPv4-in-IPv6 tunneling, see [1].
> This adds a self-test for basic IPv4-in-IPv6 functionality.
> 
> [1]: https://lore.kernel.org/all/CAA2RiuSnH_2xc+-W6EnFEG00XjS-dszMq61JEvRjcGS31CBw=g@mail.gmail.com/
> ---
>  tools/testing/selftests/net/Makefile      |  1 +
>  tools/testing/selftests/net/ip6_tunnel.sh | 41 +++++++++++++++++++++++
>  2 files changed, 42 insertions(+)
>  create mode 100644 tools/testing/selftests/net/ip6_tunnel.sh
> 
> diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
> index 45c4ea381bc36..5037a344ad826 100644
> --- a/tools/testing/selftests/net/Makefile
> +++ b/tools/testing/selftests/net/Makefile
> @@ -43,6 +43,7 @@ TEST_PROGS := \
>  	io_uring_zerocopy_tx.sh \
>  	ioam6.sh \
>  	ip6_gre_headroom.sh \
> +	ip6_tunnel.sh \
>  	ip_defrag.sh \
>  	ip_local_port_range.sh \
>  	ipv6_flowlabel.sh \
> diff --git a/tools/testing/selftests/net/ip6_tunnel.sh b/tools/testing/selftests/net/ip6_tunnel.sh
> new file mode 100644
> index 0000000000000..366f4c06cd6a3
> --- /dev/null
> +++ b/tools/testing/selftests/net/ip6_tunnel.sh
> @@ -0,0 +1,41 @@
> +#!/bin/bash
> +# Test that IPv4-over-IPv6 tunneling works.

Maybe tests IPv6-over-IPv6 as well?

> +
> +set -e
> +
> +setup_prepare() {
> +  ip link add transport1 type veth peer name transport2
> +
> +  ip netns add ns1

net lib has a helper setup_ns()

> +  ip link set transport1 netns ns1
> +  ip netns exec ns1 bash <<EOF
> +  set -e
> +  ip address add 2001:db8::1/64 dev transport1 nodad
> +  ip link set transport1 up
> +  ip link add link transport1 name tunnel1 type ip6tnl mode ipip6 local 2001:db8::1 remote 2001:db8::2
> +  ip address add 172.0.0.1/32 peer 172.0.0.2/32 dev tunnel1
> +  ip link set tunnel1 up
> +EOF

You can use ip -n $ns_name address/link other than put all the cmds in a inner
bash.


> +
> +  ip netns add ns2
> +  ip link set transport2 netns ns2
> +  ip netns exec ns2 bash <<EOF
> +  set -e
> +  ip address add 2001:db8::2/64 dev transport2 nodad
> +  ip link set transport2 up
> +  ip link add link transport2 name tunnel2 type ip6tnl mode ipip6 local 2001:db8::2 remote 2001:db8::1
> +  ip address add 172.0.0.2/32 peer 172.0.0.1/32 dev tunnel2
> +  ip link set tunnel2 up
> +EOF

Same here

> +}
> +
> +cleanup() {
> +  ip netns delete ns1
> +  ip netns delete ns2

At the same time cleanup_all_ns() help could be used.

> +  # in case the namespaces haven't been set up yet
> +  ip link delete transport1
> +}
> +
> +trap cleanup EXIT
> +setup_prepare
> +ip netns exec ns1 ping -W1 -c1 172.0.0.2
> -- 
> 2.52.0
> 

Thanks
Hangbin

Re: [PATCH] selftests/net: add test for IPv4-in-IPv6 tunneling

[Ricardo B. Marlière]

On Sun Feb 8, 2026 at 11:46 AM -03, Linus Heckemann wrote:
> 81c734dae203757fb3c9eee6f9896386940776bd was fine in and of itself, but
> its backport to 6.12 (and 6.6) broke IPv4-in-IPv6 tunneling, see [1].
> This adds a self-test for basic IPv4-in-IPv6 functionality.
>
> [1]: https://lore.kernel.org/all/CAA2RiuSnH_2xc+-W6EnFEG00XjS-dszMq61JEvRjcGS31CBw=g@mail.gmail.com/

I used this script to test the regression in a clean v6.12 tree with
commit 81c734dae203 ("ip6_tunnel: use skb_vlan_inet_prepare() in
__ip6_tnl_rcv()") applied on top:


# ../ip6_tunnel.sh
PING 172.0.0.2 (172.0.0.2) 56(84) bytes of data.

--- 172.0.0.2 ping statistics ---
1 packets transmitted, 0 received, 100% packet loss, time 0ms


dropwatch shows:

1 drops at __ip6_tnl_rcv+74 (0xffffffffc05c7064) [software]


Now, when also applying commit 4b406f814817 ("net: tunnel: make
skb_vlan_inet_prepare() return drop reasons") on top of that, the issue
goes away. Is there a way to trigger stable to pick this up?

> ---
>  tools/testing/selftests/net/Makefile      |  1 +
>  tools/testing/selftests/net/ip6_tunnel.sh | 41 +++++++++++++++++++++++
>  2 files changed, 42 insertions(+)
>  create mode 100644 tools/testing/selftests/net/ip6_tunnel.sh
>
> diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
> index 45c4ea381bc36..5037a344ad826 100644
> --- a/tools/testing/selftests/net/Makefile
> +++ b/tools/testing/selftests/net/Makefile
> @@ -43,6 +43,7 @@ TEST_PROGS := \
>  	io_uring_zerocopy_tx.sh \
>  	ioam6.sh \
>  	ip6_gre_headroom.sh \
> +	ip6_tunnel.sh \
>  	ip_defrag.sh \
>  	ip_local_port_range.sh \
>  	ipv6_flowlabel.sh \
> diff --git a/tools/testing/selftests/net/ip6_tunnel.sh b/tools/testing/selftests/net/ip6_tunnel.sh
> new file mode 100644
> index 0000000000000..366f4c06cd6a3
> --- /dev/null
> +++ b/tools/testing/selftests/net/ip6_tunnel.sh
> @@ -0,0 +1,41 @@
> +#!/bin/bash
> +# Test that IPv4-over-IPv6 tunneling works.
> +
> +set -e
> +
> +setup_prepare() {
> +  ip link add transport1 type veth peer name transport2
> +
> +  ip netns add ns1
> +  ip link set transport1 netns ns1
> +  ip netns exec ns1 bash <<EOF
> +  set -e
> +  ip address add 2001:db8::1/64 dev transport1 nodad
> +  ip link set transport1 up
> +  ip link add link transport1 name tunnel1 type ip6tnl mode ipip6 local 2001:db8::1 remote 2001:db8::2
> +  ip address add 172.0.0.1/32 peer 172.0.0.2/32 dev tunnel1
> +  ip link set tunnel1 up
> +EOF
> +
> +  ip netns add ns2
> +  ip link set transport2 netns ns2
> +  ip netns exec ns2 bash <<EOF
> +  set -e
> +  ip address add 2001:db8::2/64 dev transport2 nodad
> +  ip link set transport2 up
> +  ip link add link transport2 name tunnel2 type ip6tnl mode ipip6 local 2001:db8::2 remote 2001:db8::1
> +  ip address add 172.0.0.2/32 peer 172.0.0.1/32 dev tunnel2
> +  ip link set tunnel2 up
> +EOF
> +}
> +
> +cleanup() {
> +  ip netns delete ns1
> +  ip netns delete ns2
> +  # in case the namespaces haven't been set up yet
> +  ip link delete transport1
> +}
> +
> +trap cleanup EXIT
> +setup_prepare
> +ip netns exec ns1 ping -W1 -c1 172.0.0.2

Re: [PATCH] selftests/net: add test for IPv4-in-IPv6 tunneling

[Ricardo B. Marlière]

On Mon Feb 9, 2026 at 6:32 PM -03, Ricardo B. Marlière wrote:
> On Sun Feb 8, 2026 at 11:46 AM -03, Linus Heckemann wrote:
>> 81c734dae203757fb3c9eee6f9896386940776bd was fine in and of itself, but
>> its backport to 6.12 (and 6.6) broke IPv4-in-IPv6 tunneling, see [1].
>> This adds a self-test for basic IPv4-in-IPv6 functionality.
>>
>> [1]: https://lore.kernel.org/all/CAA2RiuSnH_2xc+-W6EnFEG00XjS-dszMq61JEvRjcGS31CBw=g@mail.gmail.com/
>
> I used this script to test the regression in a clean v6.12 tree with
> commit 81c734dae203 ("ip6_tunnel: use skb_vlan_inet_prepare() in
> __ip6_tnl_rcv()") applied on top:
>
>
> # ../ip6_tunnel.sh
> PING 172.0.0.2 (172.0.0.2) 56(84) bytes of data.
>
> --- 172.0.0.2 ping statistics ---
> 1 packets transmitted, 0 received, 100% packet loss, time 0ms
>
>
> dropwatch shows:
>
> 1 drops at __ip6_tnl_rcv+74 (0xffffffffc05c7064) [software]
>
>
> Now, when also applying commit 4b406f814817 ("net: tunnel: make
> skb_vlan_inet_prepare() return drop reasons") on top of that, the issue

oops, that would be 9990ddf47d41 ("net: tunnel: make skb_vlan_inet_prepare() return drop reasons")

> goes away. Is there a way to trigger stable to pick this up?
>
>> ---
>>  tools/testing/selftests/net/Makefile      |  1 +
>>  tools/testing/selftests/net/ip6_tunnel.sh | 41 +++++++++++++++++++++++
>>  2 files changed, 42 insertions(+)
>>  create mode 100644 tools/testing/selftests/net/ip6_tunnel.sh
>>
>> diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
>> index 45c4ea381bc36..5037a344ad826 100644
>> --- a/tools/testing/selftests/net/Makefile
>> +++ b/tools/testing/selftests/net/Makefile
>> @@ -43,6 +43,7 @@ TEST_PROGS := \
>>  	io_uring_zerocopy_tx.sh \
>>  	ioam6.sh \
>>  	ip6_gre_headroom.sh \
>> +	ip6_tunnel.sh \
>>  	ip_defrag.sh \
>>  	ip_local_port_range.sh \
>>  	ipv6_flowlabel.sh \
>> diff --git a/tools/testing/selftests/net/ip6_tunnel.sh b/tools/testing/selftests/net/ip6_tunnel.sh
>> new file mode 100644
>> index 0000000000000..366f4c06cd6a3
>> --- /dev/null
>> +++ b/tools/testing/selftests/net/ip6_tunnel.sh
>> @@ -0,0 +1,41 @@
>> +#!/bin/bash
>> +# Test that IPv4-over-IPv6 tunneling works.
>> +
>> +set -e
>> +
>> +setup_prepare() {
>> +  ip link add transport1 type veth peer name transport2
>> +
>> +  ip netns add ns1
>> +  ip link set transport1 netns ns1
>> +  ip netns exec ns1 bash <<EOF
>> +  set -e
>> +  ip address add 2001:db8::1/64 dev transport1 nodad
>> +  ip link set transport1 up
>> +  ip link add link transport1 name tunnel1 type ip6tnl mode ipip6 local 2001:db8::1 remote 2001:db8::2
>> +  ip address add 172.0.0.1/32 peer 172.0.0.2/32 dev tunnel1
>> +  ip link set tunnel1 up
>> +EOF
>> +
>> +  ip netns add ns2
>> +  ip link set transport2 netns ns2
>> +  ip netns exec ns2 bash <<EOF
>> +  set -e
>> +  ip address add 2001:db8::2/64 dev transport2 nodad
>> +  ip link set transport2 up
>> +  ip link add link transport2 name tunnel2 type ip6tnl mode ipip6 local 2001:db8::2 remote 2001:db8::1
>> +  ip address add 172.0.0.2/32 peer 172.0.0.1/32 dev tunnel2
>> +  ip link set tunnel2 up
>> +EOF
>> +}
>> +
>> +cleanup() {
>> +  ip netns delete ns1
>> +  ip netns delete ns2
>> +  # in case the namespaces haven't been set up yet
>> +  ip link delete transport1
>> +}
>> +
>> +trap cleanup EXIT
>> +setup_prepare
>> +ip netns exec ns1 ping -W1 -c1 172.0.0.2

Re: [PATCH] selftests/net: add test for IPv4-in-IPv6 tunneling

[Ricardo B. Marlière]

On Sun Feb 8, 2026 at 11:46 AM -03, Linus Heckemann wrote:
> 81c734dae203757fb3c9eee6f9896386940776bd was fine in and of itself, but
> its backport to 6.12 (and 6.6) broke IPv4-in-IPv6 tunneling, see [1].
> This adds a self-test for basic IPv4-in-IPv6 functionality.
>
> [1]: https://lore.kernel.org/all/CAA2RiuSnH_2xc+-W6EnFEG00XjS-dszMq61JEvRjcGS31CBw=g@mail.gmail.com/
> ---
>  tools/testing/selftests/net/Makefile      |  1 +
>  tools/testing/selftests/net/ip6_tunnel.sh | 41 +++++++++++++++++++++++
>  2 files changed, 42 insertions(+)
>  create mode 100644 tools/testing/selftests/net/ip6_tunnel.sh

FWIW,

Tested-by: Ricardo B. Marlière <rbm@suse.com>

>
> diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
> index 45c4ea381bc36..5037a344ad826 100644
> --- a/tools/testing/selftests/net/Makefile
> +++ b/tools/testing/selftests/net/Makefile
> @@ -43,6 +43,7 @@ TEST_PROGS := \
>  	io_uring_zerocopy_tx.sh \
>  	ioam6.sh \
>  	ip6_gre_headroom.sh \
> +	ip6_tunnel.sh \
>  	ip_defrag.sh \
>  	ip_local_port_range.sh \
>  	ipv6_flowlabel.sh \
> diff --git a/tools/testing/selftests/net/ip6_tunnel.sh b/tools/testing/selftests/net/ip6_tunnel.sh
> new file mode 100644
> index 0000000000000..366f4c06cd6a3
> --- /dev/null
> +++ b/tools/testing/selftests/net/ip6_tunnel.sh
> @@ -0,0 +1,41 @@
> +#!/bin/bash
> +# Test that IPv4-over-IPv6 tunneling works.
> +
> +set -e
> +
> +setup_prepare() {
> +  ip link add transport1 type veth peer name transport2
> +
> +  ip netns add ns1
> +  ip link set transport1 netns ns1
> +  ip netns exec ns1 bash <<EOF
> +  set -e
> +  ip address add 2001:db8::1/64 dev transport1 nodad
> +  ip link set transport1 up
> +  ip link add link transport1 name tunnel1 type ip6tnl mode ipip6 local 2001:db8::1 remote 2001:db8::2
> +  ip address add 172.0.0.1/32 peer 172.0.0.2/32 dev tunnel1
> +  ip link set tunnel1 up
> +EOF
> +
> +  ip netns add ns2
> +  ip link set transport2 netns ns2
> +  ip netns exec ns2 bash <<EOF
> +  set -e
> +  ip address add 2001:db8::2/64 dev transport2 nodad
> +  ip link set transport2 up
> +  ip link add link transport2 name tunnel2 type ip6tnl mode ipip6 local 2001:db8::2 remote 2001:db8::1
> +  ip address add 172.0.0.2/32 peer 172.0.0.1/32 dev tunnel2
> +  ip link set tunnel2 up
> +EOF
> +}
> +
> +cleanup() {
> +  ip netns delete ns1
> +  ip netns delete ns2
> +  # in case the namespaces haven't been set up yet
> +  ip link delete transport1
> +}
> +
> +trap cleanup EXIT
> +setup_prepare
> +ip netns exec ns1 ping -W1 -c1 172.0.0.2