On 1/3/26 8:23 PM, Yumei Huang wrote:
> IPv6 addresses with the same scope are returned in reverse insertion
> order, unlike IPv4. For example, when adding a -> b -> c, the list is
> reported as c -> b -> a, while IPv4 preserves the original order.
>
> This behavior causes:
>
> a. When using `ip -6 a save` and `ip -6 a restore`, addresses are restored
> in the opposite order from which they were saved. See example below
> showing addresses added as 1::1, 1::2, 1::3 but displayed and saved
> in reverse order.
>
> # ip -6 a a 1::1 dev x
> # ip -6 a a 1::2 dev x
> # ip -6 a a 1::3 dev x
> # ip -6 a s dev x
> 2: x: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default
> qlen 1000
> inet6 1::3/128 scope global tentative
> valid_lft forever preferred_lft forever
> inet6 1::2/128 scope global tentative
> valid_lft forever preferred_lft forever
> inet6 1::1/128 scope global tentative
> valid_lft forever preferred_lft forever
> # ip -6 a save > dump
> # ip -6 a d 1::1 dev x
> # ip -6 a d 1::2 dev x
> # ip -6 a d 1::3 dev x
> # ip a d ::1 dev lo
> # ip a restore < dump
> # ip -6 a s dev x
> 2: x: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default
> qlen 1000
> inet6 1::1/128 scope global tentative
> valid_lft forever preferred_lft forever
> inet6 1::2/128 scope global tentative
> valid_lft forever preferred_lft forever
> inet6 1::3/128 scope global tentative
> valid_lft forever preferred_lft forever
> # ip a showdump < dump
> if1:
> inet6 ::1/128 scope host proto kernel_lo
> valid_lft forever preferred_lft forever
> if2:
> inet6 1::3/128 scope global tentative
> valid_lft forever preferred_lft forever
> if2:
> inet6 1::2/128 scope global tentative
> valid_lft forever preferred_lft forever
> if2:
> inet6 1::1/128 scope global tentative
> valid_lft forever preferred_lft forever
>
> b. Addresses in pasta to appear in reversed order compared to host
> addresses.
>
> The ipv6 addresses were added in reverse order by commit e55ffac60117
> ("[IPV6]: order addresses by scope"), then it was changed by commit
> 502a2ffd7376 ("ipv6: convert idev_list to list macros"), and restored by
> commit b54c9b98bbfb ("ipv6: Preserve pervious behavior in
> ipv6_link_dev_addr()."). However, this reverse ordering within the same
> scope causes inconsistency with IPv4 and the issues described above.
>
> This patch aligns IPv6 address ordering with IPv4 for consistency
> by changing the comparison from >= to > when inserting addresses
> into the address list. Also updates the ioam6 selftest to reflect
> the new address ordering behavior. Combine these two changes into
> one patch for bisectability.
>
> Fixes: e55ffac60117 ("[IPV6]: order addresses by scope")
> Link: https://bugs.passt.top/show_bug.cgi?id=175
> Suggested-by: Stefano Brivio <[email protected]>
> Signed-off-by: Yumei Huang <[email protected]>
> ---
> net/ipv6/addrconf.c | 2 +-
> tools/testing/selftests/net/ioam6.sh | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
>
I am ok with the change, but I will not be surprised if someone
complains about a change in behavior.
Reviewed-by: David Ahern <[email protected]>
