[SOLVED] Proxmox VM networking is bust after restart

May 25, 2025
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Hi all. I will preface by saying that I am not the smartest when it comes to networking. Things were working before this, I suspect the restart wiped some temporary configuration that I naturally failed to document. I recently updated from 8.2 to 8.4 and soon after did a restart of proxmox which I am now regretting. Everything used to be able to run off of a simple bridged setup and I have no clue why all traffic that isn't on the main IP is now being dropped.

It is a bit of a strange setup because these are the IPs I was assigned:
1748158058400.png

Notably, 5 different IP ranges with 5 different gateways. No CIDN will cover all of these, unfortunately. Previously, through some black magic I have long since forgotten, though, this all worked with my basic bridged network setup.


Code:
# 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

iface enp10s0f1np1 inet manual

iface enp10s0f0np0 inet manual

iface enp5s0 inet manual

iface enp6s0 inet manual

iface enxca4201690694 inet manual

auto vmbr0
iface vmbr0 inet static
        address 104.243.35.200/32
        gateway 104.243.35.1
        bridge-ports enp10s0f1np1
        bridge-stp off
        bridge-fd 0

auto vmbr1
iface vmbr1 inet static
        bridge-ports none
        bridge-stp off
        bridge-fd 0
        bridge-vlan-aware yes
        bridge-vids 2-4094

auto vmbr1.200
iface vmbr1.200 inet static
        address 192.168.69.1/24
This is my /etc/network/interfaces file. 104.243.35.200 was the IP I was using for proxmox itself.

Frankly, I feel way out of my element right now, and on the verge of tears. Any and all help is greatly appreciated, thank you.
 
Last edited:
I've solved this, and for anybody who experiences this issue in the future, the culprit was actually docker. Docker sets the default policy for FORWARD to DROP after updating it, and needs to be configured to not do that so that it doesn't interfere with VMs.

Temporary solution:
iptables -P FORWARD ACCEPT

Permanent solution:
See Docker docs
 
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