IPv6 Compliance RFC4861: Prefix Information Option Processing, On-link Flag (Hosts Only) [v6LC.2.1.3]

[LiveFreeAndRoam]

systemd version the issue has been seen with

250

Used distribution

Embedded Linux - Debian-based

Linux kernel version used

5.15.71-rt51+gc36e774d0d9a

CPU architectures issue was seen on

aarch64

Component

systemd-networkd

Expected behaviour you didn't see

Networkd MUST NOT interpret the Prefix Information OnLink (L) flag when it is clear.

RFC4861 - Extract from Page 54-55:

   Prefix Information options that have the "on-link" (L) flag set
   indicate a prefix identifying a range of addresses that should be
   considered on-link.  Note, however, that a Prefix Information option
   with the on-link flag set to zero conveys no information concerning
   on-link determination and MUST NOT be interpreted to mean that
   addresses covered by the prefix are off-link.  The only way to cancel
   a previous on-link indication is to advertise that prefix with the
   L-bit set and the Lifetime set to zero.

Unexpected behaviour you saw

Networkd interpreted the Prefix Information with a cleared OnLink (L) flag, when it MUST ignore i t.

Steps to reproduce the problem

The attached file contains a replay folder. You can replay those protocol exchanges using:

$ sudo /usr/local/bin/tcpreplay -o -i ens224 v6LC_2_1_03.pcapng 

After each protocol exchange, you can examine the routing table.

Packet 1: Router LL: RA Prefix: 2001:2:1000 (On-Link=1)

$ ip -6 r get 2001:2:0:1000::
2001:2:0:1000:: dev eno0 proto ra src 2001:2:0:1000:9640:c9ff:fed6:dcd7 metric 10 pref medium

Packet 2: Router LL: RA Prefix: 2001:2:1000 (On-Link=0)

$ ip -6 r get 2001:2:0:1000::
2001:2:0:1000:: via fe80::200:10ff:fe10:1060 dev eno0 proto ra src 2001:2:0:1000:9640:c9ff:fed6:dcd7 metric 10 pref medium

According to RFC 4861, section 6.3.4, Packet 2 ought not have affected the routing table, but clearly it has.

2_1_3 - Prefix Information Option Processing, On-link Flag.zip

Additional program output to the terminal or log subsystem illustrating the issue

No response

[yuwata]

Fix is waiting in #31177.

[LiveFreeAndRoam]

I'll be able to validate this on Tuesday, next week.

[LiveFreeAndRoam]

I retested this on 253.5 and also from ToT. I see it passing with both builds. So, this one was fixed sometime between 250 and 253.5. This one is verified.

[yuwata]

It seems I did something wrong in #31177...