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Mon, 16 Jun 2025 13:18:34 GMT (envelope-from bugzilla-noreply@freebsd.org) X-Authentication-Warning: kenobi.freebsd.org: www set sender to bugzilla-noreply@freebsd.org using -f From: bugzilla-noreply@freebsd.org To: net@FreeBSD.org Subject: [Bug 287229] IP reassembly issue in FreeBSD 14.1 Date: Mon, 16 Jun 2025 13:18:31 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: Base System X-Bugzilla-Component: kern X-Bugzilla-Version: 14.2-STABLE X-Bugzilla-Keywords: X-Bugzilla-Severity: Affects Some People X-Bugzilla-Who: timo.voelker@fh-muenster.de X-Bugzilla-Status: Open X-Bugzilla-Resolution: X-Bugzilla-Priority: --- X-Bugzilla-Assigned-To: tuexen@freebsd.org X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: cc Message-ID: In-Reply-To: References: Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="UTF-8" X-Bugzilla-URL: https://bugs.freebsd.org/bugzilla/ Auto-Submitted: auto-generated List-Id: Networking and TCP/IP with FreeBSD List-Archive: https://lists.freebsd.org/archives/freebsd-net List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-net@FreeBSD.org MIME-Version: 1.0 https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D287229 Timo Voelker changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |timo.voelker@fh-muenster.de --- Comment #10 from Timo Voelker --- Hi Lucas, In cooperation with Michael, I built a setup for your minimal testing tool.= I executed a couple of runs and saw the same issue: the results of the runs differ. It looks like the FreeBSD machine is running against an IP fragment limit. For IP reassembly, FreeBSD uses a hash table. For each hash value (bucket),= it holds a list of reassembly entries. In each entry, it holds the fragments of one packet until all data has arrived (and reassembly can be completed) or a timeout (after 30s by default). The number of list entries (net.inet.ip.maxfragbucketsize) seems relevant h= ere. Out of the box, your FreeBSD VM has set maxfragbucketsize=3D1. This means i= f the FreeBSD VM must insert a new entry (i.e., when the first fragment of a pack= et has been received) in a bucket that already contains an entry, it removes t= his one first. In consequence, FreeBSD is probably unable to reassemble that pa= cket with the removed fragments. The value for maxfragbucketsize is set based on the available memory. Usual= ly on a 2 GB machine, like your FreeBSD VM, this value is set to 7, which seems enough to not run into this issue. However, in /boot/loader.conf of your FreeBSD VM, the size of the kernel memory is reduced: vm.kmem_size=3D"200M" vm.kmem_size_max=3D"200M" After commenting out these two lines and a reboot, maxfragbucketsize is 7 a= nd the results of multiple runs are the same. For the sake of completeness, these are other limits that might be relevant here: net.inet.ip.maxfragpackets=20 net.inet.ip.maxfrags Timo --=20 You are receiving this mail because: You are on the CC list for the bug.=