Linux bridge issues

interruptor.bash

while true
do
    echo "next"
    ip link add vethtest0 type veth peer name vethtest1
    brctl addif brtest vethtest0
    sleep 2
    brctl delif brtest vethtest0
    ip link del vethtest0
    sleep 1
done

setup.bash

#!/bin/bash

set -e

# teardown
function cleanup {
    set +e
    brctl delif brtest vethtest0
    ip link del vethtest0
    iptables -t nat -D POSTROUTING -j MASQUERADE -s 10.12.10.0/24 -d 0.0.0.0/0
    iptables -D FORWARD -i brtest -o enp0s31f6 -j ACCEPT
    iptables -D FORWARD -o brtest -i enp0s31f6 -j ACCEPT
    ip link delete veth0
    ip link set down brtest
    brctl delbr brtest
    ip netns del test
}
trap cleanup EXIT

ip netns add test

brctl addbr brtest
ip addr add 10.12.10.1/24 dev brtest
ip link set up dev brtest

ip link add veth0 type veth peer name veth1
ip link set veth1 netns test
brctl addif brtest veth0
ip link set up dev veth0

ip netns exec test ip addr add 10.12.10.42/24 dev veth1
ip netns exec test ip link set up dev veth1
ip netns exec test ip route add default via 10.12.10.1 dev veth1

# change external interface name
iptables -A FORWARD -o brtest -i enp0s31f6 -j ACCEPT
iptables -A FORWARD -i brtest -o enp0s31f6 -j ACCEPT
iptables -t nat -A POSTROUTING -j MASQUERADE -s 10.12.10.0/24 -d 0.0.0.0/0

while true; do ip netns exec test python3 -c "import socket; socket.gethostbyname('example.org')" && echo success; sleep 1; done