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Date:      Mon, 26 Apr 2021 19:48:25 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 255432] pf fragment reassembly leads to invalid IP checksum since 13.0-RELEASE
Message-ID:  <bug-255432-227@https.bugs.freebsd.org/bugzilla/>

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D255432

            Bug ID: 255432
           Summary: pf fragment reassembly leads to invalid IP checksum
                    since 13.0-RELEASE
           Product: Base System
           Version: 13.0-RELEASE
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: topical@gmx.net

Scenario: I have 2 lagg interfaces: one with mtu 1500 another with mtu 9000.
Both have several VLANs.

Fragmented UDP packets are received by VLAN of first interface, reassembled=
 by
pf ("scrub in all fragment reassemble"), and then sent out as jumbo frame by
VLAN of second interface.

All networks cards are mellanox ("mce"). All H/W offload features but LRO a=
re
enabled.

Before 13.0 everything worked fine. Since 13.0, the resulting jumbo frame is
sent out with invalid IP checksum and thus discarded by receiver.

Disabling TXCSUM on outgoing VLAN interface doesn't change anything.

I tried to disable VLAN_HWCSUM on outgoing LAGG interface, but this seems t=
o be
impossible without reboot - ifconfig still shows this feature as enabled. As
this is a production system, rebooting for further tests is not an option.=
=20

But: if I decrease mtu of outgoing VLAN interface to 1500, the packet gets
fragmented again and IP checksums are correct.=20

I know that there are (cheap) network cards with broken/limited H/W offload
support and thus you should disable all these features. But AFAIK mellanox
cards are not affected by this and actually they worked until 13.0

--=20
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