Problem after Linux Server Upgrade to Bullseye

uweT

Hi,
i use openvpn now for any years.
now i have a problem.
my computer (debian bullseye) can connect to debian Buster.
after connect, i can ssh to the Destination

Now i changed the Destination from buster to bullseye.
i copied the whole config
But after succesfull openvpn connect i do not see any ip on the destination
i can not ssh into the destination.
i can not ping to destination 10.0.0.1
i can not ping to destination 192.168.100.110

i use "dev tap" to connect and i have a iptables rule
iptables -t nat -A POSTROUTING -s 10.0.0.0/24 -d 192.168.100.0/24 -j MASQUERADE

From win 10 i can connect over openvpn to Bullseye and see the whole lan eg printers + routers
No Problem.

i dont know, what is different from buster to bullseye ?
i have the same configs.

any idea ?

TinCanTech

You probably forgot too enable IP Forwarding and then setup iptables.

uweT

i sure enabled ip forwarding.

normally at minimum i must see / ping the servers ip (without forwarding)

cat /proc/sys/net/ipv4/ip_forward
1

i also tried this:
https://linuxhint.com/enable_ip_forwarding_ipv4_debian_linux/

cat /etc/systemd/network/tun0.network
[Match]
Name=tap0
[Network]
IPForward=ipv4

 cat /etc/systemd/network/tap0.network
[Match]
Name=tap0
[Network]
IPForward=ipv4

i found this post from a user having vpn problems on bullseye.
But i dont know, does it belong to my problem
https://blog.emeidi.com/2021/09/19/von-stretch-nach-bullseye-mit-gravierenden-problemen/

TinCanTech

Please see https://forums.openvpn.net/viewtopic.php?t=22603

uweT

one additional question.
if i enter ip addr
i have the same mac address on both machines

 12: tap0: <BROADCAST,MULTICAST,DYNAMIC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 1000
    link/ether 6a:67:34:c4:fa:ca brd ff:ff:ff:ff:ff:ff
    inet 10.0.0.2/24 scope global tap0

7: tap0: <BROADCAST,MULTICAST,DYNAMIC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 1000
    link/ether 6a:67:34:c4:fa:ca brd ff:ff:ff:ff:ff:ff
    inet 10.0.0.1/24 scope global tap0

is it possible my Problem ?
if yes, what can i do ?

TinCanTech

Why do both machines have the same MAC address ?

uweT

It is a copy of my hard disk.
i made a copy of my disc and changed hostname + ip and put all in an other computer.

i tried

apt remove --purge openvpn 
apt install openvpn

i tried

ip link delete tap0
openvpn --mktun --dev tap0

Still the same Mac Adress

TinCanTech

uweT wrote i use openvpn now for any years.

<snip>

i use "dev tap" to connect and i have a iptables rule
iptables -t nat -A POSTROUTING -s 10.0.0.0/24 -d 192.168.100.0/24 -j MASQUERADE

This is left as an exercise to be solved.

uweT

Solved.
macchanger installed.
now it works