Date: Wed, 04 Jun 2025 18:36:39 +0200 From: "Dave Cottlehuber" <dch@skunkwerks.at> To: "Christos Chatzaras" <chris@cretaforce.gr>, questions@freebsd.org Cc: freebsd-net <freebsd-net@freebsd.org> Subject: Re: Problem with net.inet.tcp.path_mtu_discovery=1 Message-ID: <bf557c42-625f-4b8a-b5df-7a45c84e40ee@app.fastmail.com> In-Reply-To: <9728060D-2C02-426B-BACE-F2D2F651A62F@cretaforce.gr> References: <9728060D-2C02-426B-BACE-F2D2F651A62F@cretaforce.gr>
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On Wed, 4 Jun 2025, at 16:36, Christos Chatzaras wrote: > Hello, > > I manage some servers hosting websites. What does tcpdump/wireshark show for traffic, particularly icmp? Wireshark is very helpful in explaining some issues. What is the actual MTU on the working net vs the failing one? Is there a local MTU where the failing websites start working again? see ping(8) and use -v -D -s …. together to find a working MTU and cross check with tcpdump to find where things seem to break. On a recent cloud environment I needed to add ‘ set reassemble yes no-df’ to my pf.conf to address MTU issues between VNET jails and the internet. Happy hunting Dave
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