From: Thomas Lamprecht <t.lamprecht@proxmox.com>
To: Proxmox VE development discussion <pve-devel@lists.proxmox.com>,
Stefan Hanreich <s.hanreich@proxmox.com>
Subject: Re: [pve-devel] [PATCH docs/manager/qemu-server v2 0/3] Make VirtIO network devices always inherit MTU from bridge
Date: Fri, 18 Apr 2025 09:46:15 +0200 [thread overview]
Message-ID: <9ecdfff3-7458-4c37-a153-dce43a9ff93e@proxmox.com> (raw)
In-Reply-To: <20250417104855.144882-1-s.hanreich@proxmox.com>
Am 17.04.25 um 12:48 schrieb Stefan Hanreich:
> The current default behavior for VirtIO network devices is to default to 1500
> MTU, unless otherwise specified. This is inconvenient in cases where the MTU is
> not the default value (e.g. for VXLAN VNets or bridges with jumbo frames).
> Containers already inherit the MTU of the bridge, if not set, so change the
> behavior of VMs to be more in line with containers. This also makes using
> non-standard MTUs more convenient and less error-prone since users do not have
> to remember setting the MTU everytime they configure a network device on such a
> brige.
Hmm, does this have regression potential for bridges with a too high MTU?
I.e., one where the MTU works for LAN but not for anything going beyond that,
which is odd but can be working fine I think? At least as long as no host and
no CT uses this bridge for communicating with endpoints outside the LAN.
FWIW, we could also tie this behavior to a machine version to avoid changing
the behavior for any existing VM. But I would be fine with applying this only
for PVE 9 then and add a notice to the pve8to9 checker script that lists all
VMs that will change their MTU including the respective value.
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next prev parent reply other threads:[~2025-04-18 7:46 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-04-17 10:48 Stefan Hanreich
2025-04-17 10:48 ` [pve-devel] [PATCH qemu-server v2 1/1] net: pass host_mtu parameter when mtu is unset in netdev config Stefan Hanreich
2025-04-17 10:48 ` [pve-devel] [PATCH pve-manager v2 1/1] qemu: network: adjust MTU emptyText to match new default behavior Stefan Hanreich
2025-04-17 10:48 ` [pve-devel] [PATCH pve-docs v2 1/1] qm: document new default behavior for mtu setting Stefan Hanreich
2025-04-18 7:46 ` Thomas Lamprecht [this message]
2025-04-22 11:33 ` [pve-devel] [PATCH docs/manager/qemu-server v2 0/3] Make VirtIO network devices always inherit MTU from bridge Stefan Hanreich
2025-04-22 14:48 ` Thomas Lamprecht
2025-04-23 11:52 ` Stefan Hanreich
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