* Re: [PATCH net v2] Revert "ipv6: preserve insertion order for same-scope addresses"
2026-05-29 11:41 ` Stefano Brivio
@ 2026-05-29 11:45 ` Fernando Fernandez Mancera
2026-05-29 12:06 ` Chris Adams
2026-06-01 2:03 ` Matthieu Baerts
2 siblings, 0 replies; 6+ messages in thread
From: Fernando Fernandez Mancera @ 2026-05-29 11:45 UTC (permalink / raw)
To: Stefano Brivio
Cc: netdev, yuhuang, justin.iurman, horms, pabeni, kuba, edumazet,
davem, idosch, dsahern, Chris Adams, David Gibson,
Beniamino Galvani, Thorsten Leemhuis, Andrew Lunn, ihuguet,
regressions
On 5/29/26 1:41 PM, Stefano Brivio wrote:
> On Fri, 29 May 2026 13:23:57 +0200
> Fernando Fernandez Mancera <fmancera@suse.de> wrote:
>
>> Chris Adams reported that preserving insertion order for same-scope
>> addresses is causing SSH connections to be dropped after stopping a VM
>> while running NetworkManager.
>>
>> NetworkManager caches the IPv6 address configuration, when a RA arrives,
>> it determines the list of addresses to configure and checks if the
>> addresses are already in the right order in the kernel. If they aren't,
>> NetworkManager removes and re-adds them to achieve the desired order.
>>
>> As the order changes, NetworkManager is confused and reconfigures the
>> addresses on every update. In addition, this would also affect to cloud
>> tooling that relies on IPv6 addresses order to identify primary and
>> secondaries addresses.
>
> By the way, I'm still looking into this part, trying to find
> "problematic" examples.
>
> And I couldn't find any, yet, because it looks like there's always a
> _single_ IPv6 address being used as a secondary for a primary IPv4
> address.
>
IIRC, Azure cloud should be one of them. I do not have an account there
to test it.. but some years ago I did some work supporting configuring
IPV6 primary and secondary addresses via IMDSv2.
If someone with an account could test it I would appreciate it.
>>
>> This reverts commit cb3de96eea66f5e4a580086c6a1be46e765f97f4.
>>
>> Fixes: cb3de96eea66 ("ipv6: preserve insertion order for same-scope addresses")
>> Reported-by: Chris Adams <linux@cmadams.net>
>> Closes: https://lore.kernel.org/netdev/20260521135310.GC977@cmadams.net/
>> Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
>> ---
>> v2: updated commit description to make it more accurate
>> ---
>> net/ipv6/addrconf.c | 2 +-
>> tools/testing/selftests/net/ioam6.sh | 2 +-
>> 2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
>> index 5476b6536eb7..bb84a78b80f6 100644
>> --- a/net/ipv6/addrconf.c
>> +++ b/net/ipv6/addrconf.c
>> @@ -1013,7 +1013,7 @@ ipv6_link_dev_addr(struct inet6_dev *idev, struct inet6_ifaddr *ifp)
>> list_for_each(p, &idev->addr_list) {
>> struct inet6_ifaddr *ifa
>> = list_entry(p, struct inet6_ifaddr, if_list);
>> - if (ifp_scope > ipv6_addr_src_scope(&ifa->addr))
>> + if (ifp_scope >= ipv6_addr_src_scope(&ifa->addr))
>> break;
>> }
>>
>> diff --git a/tools/testing/selftests/net/ioam6.sh b/tools/testing/selftests/net/ioam6.sh
>> index b2b99889942f..845c26dd01a9 100755
>> --- a/tools/testing/selftests/net/ioam6.sh
>> +++ b/tools/testing/selftests/net/ioam6.sh
>> @@ -273,8 +273,8 @@ setup()
>> ip -netns $ioam_node_beta link set ioam-veth-betaR name veth1 &>/dev/null
>> ip -netns $ioam_node_gamma link set ioam-veth-gamma name veth0 &>/dev/null
>>
>> - ip -netns $ioam_node_alpha addr add 2001:db8:1::2/64 dev veth0 &>/dev/null
>> ip -netns $ioam_node_alpha addr add 2001:db8:1::50/64 dev veth0 &>/dev/null
>> + ip -netns $ioam_node_alpha addr add 2001:db8:1::2/64 dev veth0 &>/dev/null
>> ip -netns $ioam_node_alpha link set veth0 up &>/dev/null
>> ip -netns $ioam_node_alpha link set lo up &>/dev/null
>> ip -netns $ioam_node_alpha route add 2001:db8:2::/64 \
>
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH net v2] Revert "ipv6: preserve insertion order for same-scope addresses"
2026-05-29 11:41 ` Stefano Brivio
2026-05-29 11:45 ` Fernando Fernandez Mancera
@ 2026-05-29 12:06 ` Chris Adams
2026-06-01 2:03 ` Matthieu Baerts
2 siblings, 0 replies; 6+ messages in thread
From: Chris Adams @ 2026-05-29 12:06 UTC (permalink / raw)
To: Stefano Brivio
Cc: Fernando Fernandez Mancera, netdev, yuhuang, justin.iurman, horms,
pabeni, kuba, edumazet, davem, idosch, dsahern, David Gibson,
Beniamino Galvani, Thorsten Leemhuis, Andrew Lunn, ihuguet,
regressions
Once upon a time, Stefano Brivio <sbrivio@redhat.com> said:
> On Fri, 29 May 2026 13:23:57 +0200
> Fernando Fernandez Mancera <fmancera@suse.de> wrote:
>
> > Chris Adams reported that preserving insertion order for same-scope
> > addresses is causing SSH connections to be dropped after stopping a VM
> > while running NetworkManager.
> >
> > NetworkManager caches the IPv6 address configuration, when a RA arrives,
> > it determines the list of addresses to configure and checks if the
> > addresses are already in the right order in the kernel. If they aren't,
> > NetworkManager removes and re-adds them to achieve the desired order.
> >
> > As the order changes, NetworkManager is confused and reconfigures the
> > addresses on every update. In addition, this would also affect to cloud
> > tooling that relies on IPv6 addresses order to identify primary and
> > secondaries addresses.
>
> By the way, I'm still looking into this part, trying to find
> "problematic" examples.
>
> And I couldn't find any, yet, because it looks like there's always a
> _single_ IPv6 address being used as a secondary for a primary IPv4
> address.
I hit two cases that triggered the behavior:
- after an overnight suspend/resume cycle (not sure if there's a minimum
time suspended)
- with a bridge NIC, after stopping a VM with a NIC on the bridge (which
removed an fe80:: link-local address); this is the case I used to
bisect since it was easy to script
In both cases, the next IPv6 router-advertisement received was what
triggered NetworkManager to replace the current privacy addresses. This
could be 2-3 minutes after the trigger.
> > This reverts commit cb3de96eea66f5e4a580086c6a1be46e765f97f4.
> >
> > Fixes: cb3de96eea66 ("ipv6: preserve insertion order for same-scope addresses")
> > Reported-by: Chris Adams <linux@cmadams.net>
> > Closes: https://lore.kernel.org/netdev/20260521135310.GC977@cmadams.net/
> > Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
> > ---
> > v2: updated commit description to make it more accurate
> > ---
> > net/ipv6/addrconf.c | 2 +-
> > tools/testing/selftests/net/ioam6.sh | 2 +-
> > 2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> > index 5476b6536eb7..bb84a78b80f6 100644
> > --- a/net/ipv6/addrconf.c
> > +++ b/net/ipv6/addrconf.c
> > @@ -1013,7 +1013,7 @@ ipv6_link_dev_addr(struct inet6_dev *idev, struct inet6_ifaddr *ifp)
> > list_for_each(p, &idev->addr_list) {
> > struct inet6_ifaddr *ifa
> > = list_entry(p, struct inet6_ifaddr, if_list);
> > - if (ifp_scope > ipv6_addr_src_scope(&ifa->addr))
> > + if (ifp_scope >= ipv6_addr_src_scope(&ifa->addr))
> > break;
> > }
> >
> > diff --git a/tools/testing/selftests/net/ioam6.sh b/tools/testing/selftests/net/ioam6.sh
> > index b2b99889942f..845c26dd01a9 100755
> > --- a/tools/testing/selftests/net/ioam6.sh
> > +++ b/tools/testing/selftests/net/ioam6.sh
> > @@ -273,8 +273,8 @@ setup()
> > ip -netns $ioam_node_beta link set ioam-veth-betaR name veth1 &>/dev/null
> > ip -netns $ioam_node_gamma link set ioam-veth-gamma name veth0 &>/dev/null
> >
> > - ip -netns $ioam_node_alpha addr add 2001:db8:1::2/64 dev veth0 &>/dev/null
> > ip -netns $ioam_node_alpha addr add 2001:db8:1::50/64 dev veth0 &>/dev/null
> > + ip -netns $ioam_node_alpha addr add 2001:db8:1::2/64 dev veth0 &>/dev/null
> > ip -netns $ioam_node_alpha link set veth0 up &>/dev/null
> > ip -netns $ioam_node_alpha link set lo up &>/dev/null
> > ip -netns $ioam_node_alpha route add 2001:db8:2::/64 \
>
> --
> Stefano
--
Chris Adams <linux@cmadams.net>
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH net v2] Revert "ipv6: preserve insertion order for same-scope addresses"
2026-05-29 11:41 ` Stefano Brivio
2026-05-29 11:45 ` Fernando Fernandez Mancera
2026-05-29 12:06 ` Chris Adams
@ 2026-06-01 2:03 ` Matthieu Baerts
2 siblings, 0 replies; 6+ messages in thread
From: Matthieu Baerts @ 2026-06-01 2:03 UTC (permalink / raw)
To: Stefano Brivio, Fernando Fernandez Mancera
Cc: netdev, yuhuang, justin.iurman, horms, pabeni, kuba, edumazet,
davem, idosch, dsahern, Chris Adams, David Gibson,
Beniamino Galvani, Thorsten Leemhuis, Andrew Lunn, ihuguet,
regressions
Hi Stefano,
On 29/05/2026 21:41, Stefano Brivio wrote:
> On Fri, 29 May 2026 13:23:57 +0200
> Fernando Fernandez Mancera <fmancera@suse.de> wrote:
>
>> Chris Adams reported that preserving insertion order for same-scope
>> addresses is causing SSH connections to be dropped after stopping a VM
>> while running NetworkManager.
>>
>> NetworkManager caches the IPv6 address configuration, when a RA arrives,
>> it determines the list of addresses to configure and checks if the
>> addresses are already in the right order in the kernel. If they aren't,
>> NetworkManager removes and re-adds them to achieve the desired order.
>>
>> As the order changes, NetworkManager is confused and reconfigures the
>> addresses on every update. In addition, this would also affect to cloud
>> tooling that relies on IPv6 addresses order to identify primary and
>> secondaries addresses.
>
> By the way, I'm still looking into this part, trying to find
> "problematic" examples.
>
> And I couldn't find any, yet, because it looks like there's always a
> _single_ IPv6 address being used as a secondary for a primary IPv4
> address.
FYI, the order change also affected some specific scripts, e.g. here
with MPTCP and packetdrill:
https://github.com/multipath-tcp/packetdrill/commit/1b7cd4482ce8
Because the order was not "natural" before, and different from IPv4, a
workaround was needed to keep the same order. I was happy to remove it,
but now it looks like I need to re-apply it :)
It would be nice to get the "natural" order back without breaking the
userspace (or with a way to choose the order).
Cheers,
Matt
--
Sponsored by the NGI0 Core fund.
^ permalink raw reply [flat|nested] 6+ messages in thread