Remote Access VPN on ASA - Authentication using LDAP Server

[minkumar]

Introduction

This document provides an example on how to Configure Remote Access VPN on ASA and do the Authentication using LDAP server

Prerequisites

ASA and LDAP server both should be reachable.

Components Used

1. ASA 8.2

2. LDAP (Microsoft)

Configuration Remote Access VPN on ASA

interface configuration:

hostname(config)# interface ethernet0
hostname(config-if)# ip address 10.10.4.200 255.255.0.0
hostname(config-if)# nameif outside
hostname(config)# no shutdown

Configuring ISAKMP Policy and Enabling ISAKMP on the Outside Interface

hostname(config)# isakmp policy 1 authentication pre-share
hostname(config)# isakmp policy 1 encryption 3des
hostname(config)# isakmp policy 1 hash sha 
hostname(config)# isakmp policy 1 group 2
hostname(config)# isakmp policy 1 lifetime 43200
hostname(config)# isakmp enable outside

Configuring an Address Pool

hostname(config)# ip local pool testpool 192.168.0.10-192.168.0.15

Adding a User

hostname(config)# username testuser password 12345678

Creating a Transform Set

hostname(config)# crypto ipsec transform-set FirstSet esp-3des esp-md5-hmac

Creating a Tunnel group

hostname(config)# tunnel-group testgroup type ipsec-ra
hostname(config)# tunnel-group testgroup general-attributes
hostname(config-general)# address-pool testpool
hostname(config)# tunnel-group testgroup ipsec-attributes
hostname(config-ipsec)# pre-shared-key 44kkaol59636jnfx

Creating a Dynamic crypto map

hostname(config)# crypto dynamic-map dyn1 1 set transform-set FirstSet
hostname(config)# crypto dynamic-map dyn1 1 set reverse-route

Creating a Crypto Map Entry to Use the Dynamic Crypto Map

hostname(config)# crypto map mymap 1 ipsec-isakmp dynamic dyn1
hostname(config)# crypto map mymap interface outside

Configuring LDAP server on the ASA

ciscoasa(config-aaa-server-group)#aaa-server LDAP (inside) host 192.168.1.2
ciscoasa(config-aaa-server-host)#ldap-base-dn dc=ftwsecurity, dc=cisco, dc=com
ciscoasa(config-aaa-server-host)#ldap-login-dn cn=admin, cn=users, dc=ftwsecurity, dc=cisco, dc=com
ciscoasa(config-aaa-server-host)#ldap-login-password **********
ciscoasa(config-aaa-server-host)#ldap-naming-attribute sAMAccountName
ciscoasa(config-aaa-server-host)#ldap-scope subtree
ciscoasa(config-aaa-server-host)#server-type microsoft
ciscoasa(config-aaa-server-host)#exit

Assigning LDAP server under tunnel group

ciscoasa(config)#tunnel-group testgroup general-attributes
ciscoasa(config-tunnel-general)#authentication-server-group LDAP

Verifcation

Test with CLI:

You can use the test command on the command line in order to test your AAA setup. A test  request is sent to the AAA server, and the result appears on the command line.

ciscoasa#test aaa-server authentication LDAP host 192.168.1.2
   username cisco password cisco123INFO: Attempting Authentication test to IP address <192.168.1.2>
   (timeout: 12 seconds)
INFO: Authentication Successful

Troubleshoot

If unsure of the current DN string to use, you can issue the dsquery command on a Windows Active Driectory server from a command prompt in  order to verify the appropriate DN String of a user object.

C:\Documents and Settings\Administrator>dsquery user -samid cisco!--- Queries Active Directory for samid id "cisco""CN=cisco,CN=Users,DC=ftwsecurity,DC=cisco,DC=com"

The debug ldap 255 command can help to troubleshoot authentication problems in this  scenario. This command enables LDAP debugging and allows you to watch  the process that the ASA uses to connect to the LDAP server.

Debug - Successful authentication

ciscoasa#debug ldap 255[7] Session Start
[7] New request Session, context 0xd4b11730, reqType = 1
[7] Fiber started
[7] Creating LDAP context with uri=ldap://192.168.1.2:389
[7] Connect to LDAP server: ldap://192.168.1.2:389, status = Successful
[7] defaultNamingContext: value = DC=ftwsecurity,DC=cisco,DC=com
[7] supportedLDAPVersion: value = 3
[7] supportedLDAPVersion: value = 2
[7] supportedSASLMechanisms: value = GSSAPI
[7] supportedSASLMechanisms: value = GSS-SPNEGO
[7] supportedSASLMechanisms: value = EXTERNAL
[7] supportedSASLMechanisms: value = DIGEST-MD5

!--- The ASA connects to the LDAP server for admin bind and search for cisco.
[7] Binding as administrator
[7] Performing Simple authentication for admin to 192.168.1.2
[7] LDAP Search:
        Base DN = [dc=ftwsecurity, dc=cisco, dc=com]
        Filter  = [sAMAccountName=cisco]
        Scope   = [SUBTREE]
[7] User DN = [CN=cisco,CN=Users,DC=ftwsecurity,DC=cisco,DC=com][7] Talking to Active Directory server 192.168.1.2
[7] Reading password policy for cisco, dn:CN=cisco,CN=Users,
       DC=ftwsecurity,DC=cisco,DC=com

!--- The ASA binds to the LDAP server as cisco to test the password.
[7] Binding as user
[7] Performing Simple authentication for kate to 192.168.1.2
[7] Checking password policy for user cisco
[7] Binding as administrator
[7] Performing Simple authentication for admin to 192.168.1.2
[7] Authentication successful for kate to 192.168.1.2
[7] Retrieving user attributes from server 192.168.1.2[7] Retrieved Attributes:
[7]     objectClass: value = top
[7]     objectClass: value = person
[7]     objectClass: value = organizationalPerson
[7]     objectClass: value = user
[7]     cn: value = cisco
[7]     givenName: value = cisco
[7]     distinguishedName: value = CN=cisco,CN=Users,DC=ftwsecurity,
           DC=cisco,DC=com
[7]     instanceType: value = 4
[7]     whenCreated: value = 20070815155224.0Z
[7]     whenChanged: value = 20070815195813.0Z
[7]     displayName: value = cisco
[7]     uSNCreated: value = 16430
[7]     memberOf: value = CN=Castaways,CN=Users,DC=ftwsecurity,DC=cisco,DC=com
[7]     memberOf: value = CN=Employees,CN=Users,DC=ftwsecurity,DC=cisco,DC=com
[7]     uSNChanged: value = 20500
[7]     name: value = cisco
[7]     objectGUID: value = ..z...yC.q0.....
[7]     userAccountControl: value = 66048
[7]     badPwdCount: value = 1
[7]     codePage: value = 0
[7]     countryCode: value = 0
[7]     badPasswordTime: value = 128321799570937500
[7]     lastLogoff: value = 0
[7]     lastLogon: value = 128321798130468750
[7]     pwdLastSet: value = 128316667442656250
[7]     primaryGroupID: value = 513
[7]     objectSid: value = ............Q..p..*.p?E.Z...
[7]     accountExpires: value = 9223372036854775807
[7]     logonCount: value = 0
[7]     sAMAccountName: value = cisco
[7]     sAMAccountType: value = 805306368
[7]     userPrincipalName: value = cisco@ftwsecurity.cisco.com
[7]     objectCategory: value = CN=Person,CN=Schema,CN=Configuration,
           DC=ftwsecurity,DC=cisco,DC=com
[7]     dSCorePropagationData: value = 20070815195237.0Z
[7]     dSCorePropagationData: value = 20070815195237.0Z
[7]     dSCorePropagationData: value = 20070815195237.0Z
[7]     dSCorePropagationData: value = 16010108151056.0Z
[7] Fiber exit Tx=685 bytes Rx=2690 bytes, status=1
[7] Session End

Debug - Authentication fails - Incorrect Password

ciscoasa#debug ldap 255[8] Session Start
[8] New request Session, context 0xd4b11730, reqType = 1
[8] Fiber started
[8] Creating LDAP context with uri=ldap://192.168.1.2:389
[8] Connect to LDAP server: ldap://192.168.1.2:389, status = Successful
[8] defaultNamingContext: value = DC=ftwsecurity,DC=cisco,DC=com
[8] supportedLDAPVersion: value = 3
[8] supportedLDAPVersion: value = 2
[8] supportedSASLMechanisms: value = GSSAPI
[8] supportedSASLMechanisms: value = GSS-SPNEGO
[8] supportedSASLMechanisms: value = EXTERNAL
[8] supportedSASLMechanisms: value = DIGEST-MD5

!--- The ASA connects to the LDAP server as admin to search for cisco.
[8] Binding as administrator
[8] Performing Simple authentication for admin to 192.168.1.2
[8] LDAP Search:
        Base DN = [dc=ftwsecurity, dc=cisco, dc=com]
        Filter  = [sAMAccountName=kate]
        Scope   = [SUBTREE]
[8] User DN = [CN=cisco,CN=Users,DC=ftwsecurity,DC=cisco,DC=com][8] Talking to Active Directory server 192.168.1.2
[8] Reading password policy for cisco, dn:CN=cisco,CN=Users,
       DC=ftwsecurity,DC=cisco,DC=com
[8] Read bad password count 1

!--- The ASA attempts to bind as cisco, but the password is incorrect.
[8] Binding as user
[8] Performing Simple authentication for kate to 192.168.1.2
[8] Simple authentication for cisco returned code (49) Invalid credentials[8] Binding as administrator
[8] Performing Simple authentication for admin to 192.168.1.2
[8] Reading bad password count for cisco, dn: CN=cisco,CN=Users,
       DC=ftwsecurity,DC=cisco,DC=com
[8] Received badPwdCount=1 for user cisco
[8] badPwdCount=1 before, badPwdCount=1 after for cisco
[8] now: Tue, 28 Aug 2007 15:33:05 GMT, lastset: Wed, 15 Aug 2007 15:52:24 GMT,
       delta=1122041, maxage=3710851 secs
[8] Invalid password for cisco
[8] Fiber exit Tx=788 bytes Rx=2904 bytes, status=-1
[8] Session End

Debug - Authentication Fail - User not found on LDAP server

ciscoasa#debug ldap 255[9] Session Start
[9] New request Session, context 0xd4b11730, reqType = 1
[9] Fiber started
[9] Creating LDAP context with uri=ldap://192.168.1.2:389
[9] Connect to LDAP server: ldap://192.168.1.2:389, status = Successful
[9] defaultNamingContext: value = DC=ftwsecurity,DC=cisco,DC=com
[9] supportedLDAPVersion: value = 3
[9] supportedLDAPVersion: value = 2
[9] supportedSASLMechanisms: value = GSSAPI
[9] supportedSASLMechanisms: value = GSS-SPNEGO
[9] supportedSASLMechanisms: value = EXTERNAL
[9] supportedSASLMechanisms: value = DIGEST-MD5

!--- The user Minakshi is not found.
[9] Binding as administrator
[9] Performing Simple authentication for admin to 192.168.1.2
[9] LDAP Search:
        Base DN = [dc=ftwsecurity, dc=cisco, dc=com]
        Filter  = [sAMAccountName=minakshi]
        Scope   = [SUBTREE]
[9] Requested attributes not found[9] Fiber exit Tx=256 bytes Rx=607 bytes, status=-1
[9] Session End

Please post comments if there are any queries and rate if useful.

Scenario 2:

Problem:

Is it possible to strip the suffix from a username to authenticate against an active directory in ACS 5.4? I can find this when using an external proxy service, but not for network access.

Solution:

Username suffix/prefix stripping is possible when using:

LDAP

Radius Identity server

External Proxy

With AD, the option is unavailable.

Self proxy + AD is a workaround but that has some limitations and is a complex configuration.

Source Discussion:

CSC Discussion:

[deshtikypshaq]

very good document, thank you

[zr595576323]

thank you

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[ibarra083]

Excellent article. Very useful.

[nstapp]

I just wanted to add some clarity for users who see and follow this but may still  have an issue.  There are some LDAP implementations, like SUN DSEE that DO NOT return memberof by default.  They have whats called dynamic attributes (or operationsl attributes) like "ismemberof".  These are not returned when you query for a user.  It must be EXPLICITLY requested in the ldap query, and since in ASA you cannot provide a filter for the BASE BIND this is not possible with an ASA. 

     The only way to make this work is use a ROOT DN bind, or have the system operator specifically return them with a normal query.

[sergio2025]

Hello All,

I have a LDAP Server Group with three domain controllers for Remote Access VPN authentication using LDAP.

Only the first DC in the LDAP server group authenticates remote Windows users and performs a successfully Test within AAA server Groups; the others fail to test and/or authenticate.

The other DCs are up and running, respond to ping and DNS queries, ldap-service account is active. They have same setting in AAA Server dialog window. I tested ldap with a Windows computer and works well connecting to such domain controllers and the Replication between DCs appears to be working well.

Current Cisco ASDM version is 7.9 for ASA 5500 series. I realize this ASA is EOL; yet I need to see if this issue can be fix with current version?

Thanks for your input.

[sergio2025]

Test with CLI:

=> I have Cisco ASDM 7.9(2) 152 Software version to connect to ASA 5515 Security appliance; I know this is EOL. 

As part of the troubleshooting I run Tests in ASA's CLI interface which Fail with error code (DC02 and DC02):

test aaa-server authentication LDAP host 10.10.##.## username myserviceaccount password "Mypassword@890"

INFO: Attempting Authentication test to IP address (10.10.##.##) (timeout: 12 seconds)
ERROR: Authentication Rejected: Unspecified

It successful, however, with DC01 of the LDAP server group.

In Configuration, Remote Access VPN, AAA Server Groups, The AAA server settings are the same for all three DCs here; except the IP address of course. 

Base DN: 

DC=<domain>,DC=org

Login DN:

CN=LDAP Service Account,OU=Service Accounts,DC=<domain>,DC=org

Password is the same.

No LDAP attribute Map used.

Server port 389 and is not blocked by the Firewall setting on each DC, nor in the ASA.

The inbound/outbound are allowing traffic for such port on each DC.

Any suggestions in how to fix that issue?

Thank you

[Marvin Rhoads]

@sergio2025 I would suggest doing a packet capture to the DC being tested. Since LDAP is unencrypted plain text, you should be able to see whether the issue is on the ASA or DC side when you open the pcap in Wireshark.