FreeRadius PAP Authentication Issue : WARNING: Unprintable characters in the password. Double-check the shared secret on the server and the NAS! Using Post-Auth-Type Reject ().[pap] Passwords don't match

If you are seeing this in radius log

WARNING: Unprintable characters in the password.  Double-check the shared secret on the server and the NAS! Using Post-Auth-Type Reject ([pap] Passwords don't match).

 [pap] login attempt with password "5?q¦¦?!##+Y?E¦¦"
[pap] Using clear text password "mypassword"

Do nothing until this warning is disappeared. To troubleshoot this use following

1) Match your key as described in warning .(NAS shared secret and shared secret on other Service like VPN in my case )

2) If keys are same and still FreeRadius is NOT Authenticating then change your secret to some simple secret like ("mysecret"). This may be due to too long shared secret or data type conversion mismatch between your Radius server and Service Shared Secret.

NOTE: You have to change shared secret on three locations.

1) Radcheck database table in Radius Server
2) /etc/raddb/clients.conf (In case of CentOS)
3) /etc/openvpn/radiusplugin.cnf

This will solve your issue. For more understanding you can see Defining Shared Secret on official documentation of Radius Server. link

how to configure pptp and freeradius

pptp authentication using freeradius you can following tutorials.

For freeradius setup : http://safesrv.net/install-and-setup-freeradius-on-centos-5/
For pptpd setup      : http://safesrv.net/setup-pptp-and-freeradius-on-centos-5/

After radius server installation test radius server locally and remote server. If response is positive then you are done with radius server. Else add nas table to radius server if is it is already not included or not already configured.

Try not to jump on another server deployment util you are not completely deployed previous one.

If you are unable to communicate between user , VPN server and freeRADIUS server then check IPTABLES and port forwarding. And also check that in VPN server configuration ,  radius server ip is defined.
Also confirm that in freeRADIUS configuaration ,   VPN server ip is listed in clients.
After successfull setup of these two servers following are possible issues you may face.

Possible issue :
Issue 1 : Carefully read tutorial and do configuration of right files. Because some directories contains file names with little difference for example options.pptpd and options-pptpd.

Issue 2 : User requires some authentications like pap , chap , mschap etc. User sends authentication requests to VPN server and VPN sever forward this request to freeRADIUS server to authenticate user.

Authentication will only be successfull if user's required authentications matches with /etc/ppp/pptpd-options configuration. In /etc/ppp/options-pptpd  authentications are written like this require-pap refuse-pap etc.

Still having problem please read this freeradius official tutorial http://wiki.freeradius.org/guide/PopTop-HOWTO   .

pptp Unknown attribute 47. Modem hang up

You are setting up PPTP Using freeRADIUS server.

freeRADIUS server is ready to process requests. And PPTP is accepting connections.

Windows clients are working fine and browsing successfully.

Ubuntu PPTP clients connect to server but in less than 10 sec they disconnect.

Server logs:
Server log is showing modem hangup.
Unknown attribute 47.
Unknown attribute 48.

Solution:
This is client side error. The server is working fine. There is no need to check server.

We found the solution in the following link.
http://ubuntuforums.org/showthread.php?t=1479655&p=9279383#post9279383

This is maximum transmission unit error on client side. (MTU , the size of largest protocol data unit)

To solve this issue only change MTU of interface through which you are connected to internet.
Enter following command in terminal.

sudo ifconfig eth0 mtu 1400

Change eth0 to interface from which you are connected to internet. MTU value of 1400 at client side. PPTP is connected and not disconneting any more. No modem hang up error on client side.

openVPN Bad LZO decompression header byte

Scenario:
You have successfully deployed freeRADIUS and openVPN.
OpenVPN client successfully connects to openVPN server
Windows openVPN client can seccessfully connect to the server and can brwose sites successfully.

Issue:
But ubuntu clients can not browse sites successfully.
And also disconnects in less than 30 seconds.

Logs:
Used logs are
/var/log/messages
/etc/openvpn/1194.logs

/var/log/openvpn.log shows the basic issue.
*Bad LZO decompression header byte: 69*

Solution:
Before connecting openVPN client correct the openVPN configuration.
Check (Tick) lozo compression in advanced settings of vpnClient configuration in Ubuntu client.

Client can browse site successfully but IP of client not changing. L2TP

You have successfully deployed freeRADIUS and L2TP.
Windows L2TP client successfully connects to L2TP server

Issue:
Client can browse site successfully but IP of client not changing.

Solution
In /etc/racoon/psk.txt
There is given ( * ) which mentioned for Iphone or android clients. Give both l2tp server ip and * with secret key also.

Now connect to server. It should work now. :)