Troubleshooting MTU and tun-mtu issues

How to do it...

1.Start the server using the configuration file, basic-udp-server.conf:

[root@server]# openvpn --config basic-udp-server.conf

2.Next, create the client configuration file by appending a line to

the basic-udp-client.conf file:

        cipher CAST5-CBC

Save it as example6-1-client.conf.

3.Start the client, after which the following message will appear in the client

log:

        [root@client]# openvpn --config example6-1-client.conf

       ... WARNING: 'cipher' is used inconsistently, local='cipher

        CAST5-CBC'', remote='cipher BF-CBC''

       ... [openvpnserver] Peer Connection Initiated with server-

        ip:1194

       ... TUN/TAP device tun0 opened

       ... /sbin/ip link set dev tun0 up mtu 1500

       ... /sbin/ip addr add dev tun0 10.200.0.2/24 broadcast

        10.200.0.255

       ... Initialization Sequence Completed

       ... Authenticate/Decrypt packet error: cipher final failed

And, similarly, on the server side:

        ... client-ip:52461 WARNING: 'cipher' is used