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Authenticating PPP users while keeping them out of IOS on a Cisco router

Posted on 2008-10-23
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Last Modified: 2013-12-14
We authenticate PPP users on a Cisco router using a local username and password list. To my horror, recently I realized that any PPP user could could open an SSH or telnet session to the router with full administrative privileges using their PPP username and password.

As a temporary fix I have put in some ACL's to prevent access to port 22 and 23 from anywhere except admin IP addresses. However obviously now I am looking to put in a more permanent and secure solution without the hassle of having to install a separate RADIUS authentications server. I would like to keep maintaining a PPP username and password list on the router without compromising security.

The relevant router config sections is attached

!                                                                               
line con 0                                                                      
line aux 0                                                                      
line vty 0 4                                                                    
 privilege level 15                                                             
 transport input telnet ssh                                                     
!                                                                               
 
!                                                                               
aaa new-model                                                                   
!                                                                               
!                                                                               
aaa authentication ppp default local                                               
!                                     
 
!                                                                               
username admin secret 5 $8$NCxxxxxxxxxxxx
username pppuser1 password 0 secret123                             
archive                                                                         
 log config                                                                     
  hidekeys                                                                      
!

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Question by:Fo_Shizzle
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by:kyleb84
ID: 22792510
Local RADIUS server...

The Cisco itself can be the RADIUS server as well...

aaa new-model
aaa authentication login default radius local
aaa authentication login no_radius enable
aaa authentication ppp default if-needed radius
aaa authorization network radius
aaa accounting exec start-stop radius
aaa accounting network start-stop radius
---
radius-server local
 nas [VLAN1IP] key [key]
 group usersgrp
  user user1 nthash password1 group usersgrp
  user user2 nthash password2 group usersgrp
!
radius-server host [VLAN1IP] auth-port 1812 acct-port 1813 key [key]
radius-server retransmit 3
radius-server attribute 32 include-in-access-req format %h
radius-server authorization permit missing Service-Type
radius-server vsa send accounting

-------------

The above authenticates ppp users via RADIUS username/passwords, and console access by the local password database.

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kyleb84 earned 500 total points
ID: 22792570
Hmm should change the line:

"aaa authentication login default radius local"
to
"aaa authentication login default local"

and:
line vty 0 4
 login authentication default
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