VMs not reachable via IPv6 sometimes

[Ketanest]

Hi together,

I have an interesting thing. From time to time, the VMs are not reachable via IPv6. Services are then falling back to IPv4 which takes some time and should not be. After restarting a VM it works again. Concerns Linux KVM VMs and Windows KVM VMs (as I do not have LXC containers I can't test). It is independent of VLAN config of the VMs.

Network configuration is:

# network interface settings; autogenerated
# Please do NOT modify this file directly, unless you know what
# you're doing.
#
# If you want to manage parts of the network configuration manually,
# please utilize the 'source' or 'source-directory' directives to do
# so.
# PVE will preserve these directives, but will NOT read its network
# configuration from sourced files, so do not attempt to move any of
# the PVE managed interfaces into external files!

auto lo
iface lo inet loopback

auto eno1
iface eno1 inet manual

auto eno2
iface eno2 inet manual

auto bond0
iface bond0 inet manual
        bond-slaves eno1 eno2
        bond-miimon 100
        bond-mode 802.3ad
        bond-xmit-hash-policy layer3+4

auto vmbr0
iface vmbr0 inet static
        address 192.168.10.13/24
        gateway 192.168.10.1
        bridge-ports bond0
        bridge-stp off
        bridge-fd 0
        bridge-vlan-aware yes
        bridge-vids 2-4094

iface vmbr0 inet6 auto
        accept_ra 2
        autoconf 1

qm config of one of these VMs:

agent: 1
bios: ovmf
boot: order=scsi0;ide0;net0
cores: 2
cpu: x86-64-v2-AES
efidisk0: SSD-1TB-01:113/vm-113-disk-0.qcow2,efitype=4m,pre-enrolled-keys=1,size=528K
ide0: none,media=cdrom
machine: pc-i440fx-8.1
memory: 4096
meta: creation-qemu=8.1.5,ctime=1712501728
name: TFD-FS01
net0: virtio=BC:24:11:02:4E:86,bridge=vmbr0,tag=1
numa: 0
ostype: win11
scsi0: SSD-1TB-01:113/vm-113-disk-1.qcow2,iothread=1,size=40G
scsi1: SSD-1TB-01:113/vm-113-disk-3.qcow2,iothread=1,size=50G
scsihw: virtio-scsi-single
smbios1: uuid=4acdd49a-6cab-4299-9c9a-683efc443599
sockets: 1
tpmstate0: SSD-1TB-01:113/vm-113-disk-2.raw,size=4M,version=v2.0
vmgenid: 4598082e-b42b-49ec-a3d6-de1460a1d0ad

pveversion -v:

proxmox-ve: 8.1.0 (running kernel: 6.5.13-3-pve)
pve-manager: 8.1.10 (running version: 8.1.10/4b06efb5db453f29)
proxmox-kernel-helper: 8.1.0
proxmox-kernel-6.5.13-3-pve-signed: 6.5.13-3
proxmox-kernel-6.5: 6.5.13-3
proxmox-kernel-6.5.11-4-pve-signed: 6.5.11-4
ceph-fuse: 18.2.2-pve1
corosync: 3.1.7-pve3
criu: 3.17.1-2
glusterfs-client: 10.3-5
ifupdown2: 3.2.0-1+pmx8
ksm-control-daemon: 1.4-1
libjs-extjs: 7.0.0-4
libknet1: 1.28-pve1
libproxmox-acme-perl: 1.5.0
libproxmox-backup-qemu0: 1.4.1
libproxmox-rs-perl: 0.3.3
libpve-access-control: 8.1.3
libpve-apiclient-perl: 3.3.2
libpve-cluster-api-perl: 8.0.5
libpve-cluster-perl: 8.0.5
libpve-common-perl: 8.1.1
libpve-guest-common-perl: 5.0.6
libpve-http-server-perl: 5.0.6
libpve-network-perl: 0.9.6
libpve-rs-perl: 0.8.8
libpve-storage-perl: 8.1.4
libspice-server1: 0.15.1-1
lvm2: 2.03.16-2
lxc-pve: 5.0.2-4
lxcfs: 5.0.3-pve4
novnc-pve: 1.4.0-3
proxmox-backup-client: 3.1.5-1
proxmox-backup-file-restore: 3.1.5-1
proxmox-kernel-helper: 8.1.0
proxmox-mail-forward: 0.2.3
proxmox-mini-journalreader: 1.4.0
proxmox-offline-mirror-helper: 0.6.5
proxmox-widget-toolkit: 4.1.5
pve-cluster: 8.0.5
pve-container: 5.0.9
pve-docs: 8.1.5
pve-edk2-firmware: 4.2023.08-4
pve-firewall: 5.0.3
pve-firmware: 3.10-1
pve-ha-manager: 4.0.3
pve-i18n: 3.2.1
pve-qemu-kvm: 8.1.5-4
pve-xtermjs: 5.3.0-3
qemu-server: 8.1.1
smartmontools: 7.3-pve1
spiceterm: 3.3.0
swtpm: 0.8.0+pve1
vncterm: 1.8.0
zfsutils-linux: 2.2.3-pve1

Anyone an idea?

Thanks!
Ketanest

 

[Ketanest]

Sorry for posting that early. Found this thread:
https://forum.proxmox.com/threads/ipv6-connection-lost.62932/

Is working now with adding

iface vmbr0 inet static
    post-up echo -n 0 > /sys/class/net/vmbr0/bridge/multicast_snooping
    post-up echo -n 1 > /sys/class/net/vmbr0/bridge/multicast_querier

to /etc/network/interfaces

Greetings
Ketanest