Masquerade not working

[hexblot]

Hello,
have a root server with one nic and public dual stack ip, trying to configure NAT (maasquerade) as per docs, however the container seems unable (?) to reach out.

PVE has the following "/etc/network/interfaces" (have also tried using the interface directly instead of vmbr1):

source /etc/network/interfaces.d/*

auto lo
iface lo inet loopback
iface lo inet6 loopback

auto enp7s0
iface enp7s0 inet manual

auto vmbr1
iface vmbr1 inet static
        address a.b.c.245/26
        gateway a.b.c.193
        bridge-ports enp7s0
        bridge-stp off
        bridge-fd 0
        up route add -net a.b.c.192 netmask 255.255.255.192 gw a.b.c.193 dev enp7s0
        # route a.b.c.192/26 via a.b.c.193
        post-up echo 1 > /proc/sys/net/ipv4/ip_forward

iface vmbr1 inet6 static
        address x:y:z:w::2/64
        gateway fe80::1

auto vmbr0
iface vmbr0 inet static
  address 10.42.100.1/24
  bridge-ports none
  bridge-stp off
  bridge-fd 0
#  post-up   echo 1 > /proc/sys/net/ipv4/ip_forward
  post-up   iptables -t nat -A POSTROUTING -s '10.42.100.0/24' -o vmbr1 -j MASQUERADE
  post-down iptables -t nat -D POSTROUTING -s '10.42.100.0/24' -o vmbr1 -j MASQUERADE

The VM (LXC) itself has the following networking:


the container has Alpine Linux (for tests), which seems to be able to ping but not actually use it:



Any insight would be extremely helpful. Thank you in advance!