Re: [PATCH net v2] Revert "ipv6: preserve insertion order for same-scope addresses"

Once upon a time, Stefano Brivio [off-list ref] said:

On Fri, 29 May 2026 13:23:57 +0200
Fernando Fernandez Mancera [off-list ref] wrote:

quoted

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.

quoted

This reverts commit cb3de96eea66f5e4a580086c6a1be46e765f97f4.

Fixes: cb3de96eea66 ("ipv6: preserve insertion order for same-scope addresses")
Reported-by: Chris Adams <redacted>
Closes: https://lore.kernel.org/netdev/20260521135310.GC977@cmadams.net/ (local)
Signed-off-by: Fernando Fernandez Mancera <redacted>
---
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 [off-list ref]