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Configuring TACACS+ Authentication to ACI Fabric with Cisco ACS

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This document will provide screenshots to outline the steps to setup TACACS+ configuration to ACI and also the configuration required on Cisco ACS server.

Please find the official Cisco guide for configuring TACACS+ Authentication to ACI: https://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/2-x/Security_config/b_Cisco_APIC_Security_Guide/b_Cisco_APIC_Security_Guide_chapter_0100.html

ACS Configuration

*Note only specific web browsers and version are supported on Cisco ACS, check the release notes of your ACS versions to find the supported browsers. Using unsupported browsers can lead to configuration loss in ACS.

  1. First step is to configure the APIC and fabric node devices on the ACS. Navigate to Network Resource > Network Devices Groups > Network Devices and AAA Clients

                 Specify the client name, and create a device type.

ACSClients.JPG

 ACSDevicetype1.JPGACSDeviceType.JPGACSDeviceType3.JPG

   Add the Cisco APIC and fabric node Ip Addresses (out-band or INB), ensure to select IP range to add multiple node addresses.
ACSclientIp.JPG

 Select TACACS+ under the authentication options, the shared secret will be used for the Cisproviderkey.JPGco APIC provider Keys.

Authentication options.JPG

 2. Next step is to configure users and Identity groups. Navigate to Users and Identity Stores > Identity Groups.

The identity group will group different types of users together, in the example below I have created an ADMIN Identity-group to group all users who will have admin privileges.

ACIIdentityGroup.JPG

 3. You can now configure the users, (these can be internal or external uses such as from Active Directory) navigate to Users and Identity Stores > Internal Identity Stores > Users. Create an admin user, map this user to the identity group, and configure a password.

ACIadminuser.JPG

 4. Create the policy elements, this is where we configure the Cisco AV pair, to specify the APIC required RBAC roles and privileges for different users

               The AV pair are configured in the following format:

                shell:domains = domainA/writeRole1|writeRole2|writeRole3/readRole1|readRole2,

                 domainB/writeRole1|writeRole2|writeRole3/readRole1|readRole2(16003) * Unix ID

 

Below are some examples of the av-pair strings for some different types of users:

  • For users with admin access to entire fabric:

            shell:domains = all/admin/(16002)

 

  • For users with read-only access to fabric:

            shell:domains = all//read-all (16003)

 *note readonly users do not have access to leaf’s or spines, admin write privilege is required.

 

  • For a user with admin access to tenants under security domain mydomain, and read only access to the rest of the tenants.

            shell:domains = mydomain/admin/,all//read-all(16004)

 

* As best practice, Cisco recommend that you assign a unique UNIX user id in the range 16000-23999.If the UNIX user ID is not specified, ID 23999 is applied by the APIC system. There is a known bug if unique UNIX ids are not used.

 

Navigate to Policy elements > Device Administration > Shell Profiles and create a new shell profile. Name the profile, and navigate to the ‘Custom attributes’ tab, here you can add the av-pair string.  

 Fabricadminuser.JPGavpaistring.JPG

 5. Last step is to configure the access policies, this is where you tie it all together, mapping the user to the shell profile to the AAA clients. Navigate to Access Policies > Default Device Admin > Authorization.

         Create a new Rule, mapping the identity group, the device type and shell profile.

accesspolicy.JPG

 

Configuring APIC for TACACS+ ACCESS

  1. First create the TACACS+ Provider, navigate to Admin > AAA > TACACS+ Management > TACACS+ Providers.

Here you will need to specify the ACS hostname (ensure DNS is setup in your fabric if using hostname) or IP, the port, (default is 49), the key (this should match the ‘shared secret’ configured on ACS) and also the management endpoint (Inb or OOB)
TACACS provider.JPG

 *Note if the APIC has INB management configured, choosing the OOB management EPG for the TACACS+ provider does not take effect as INB is the default preferred by APIC. In versions 2.1(1x) and higher there is an option to toggle between INB and OOB so to make OOB as the default management connectivity. Find this under Fabric > Fabric Policies > Global Policies > APIC Connectivity Preferences.

InbOOB.JPG2. Next create the TACACS+ Provider Group and map to TACACS+ provider created in step 1. Navigate to Admin > AAA > TACACS+ Management > TACACS+ Provider Groups.
TACACSproviderGroup.JPG

 3. Create the Login Domain and map to TACACS+ Provider group. Navigate to Admin > AAA > AAA Authentication > Login Domains.

TACACSLoginDomain.JPG

*You will notice a ‘fallback’ login domain is already created by default, this is the local domain to allow local authentication in case you are locked out of your fabric if the default authentication settings are changed.

Changing the Default Authentication to your fabric.

If you would like TACACS+ to be the default authentication method when accessing the fabric you can make this change under the AAA authentication tab.

AAAdefaultauth.JPG

If TACACS+ is not configured as the default authentication method, (local is the default) you will need to explicitly select the login domain when logging in via GUI, or use the below format to access nodes using TACACS+ logins via cli.

Login format: ssh apic#domain\\username@ip 

TACACSUIlogin.JPG

 

 

 

 

 

 

 

Recovering with Local Fallback User

In the event that connectivity is lost to the TACACS+ server and you are locked out of your fabric you can use the local admin fallback user. Below is the format to do this:

From the GUI, use apic:fallback\\admin.

From Cli, use ssh apic#fallback\\admin

FallbackloginUI.JPG

 

 

 

 

 

 

 

Always ensure under Default Authentication that ‘Fallback Check’ is set to false, otherwise you will not be able to recover with local login credentials. 

FallbackCheck.JPG

 

 

 

 

 

 

 

Verification

A couple of check to make sure your configuration is correct:

 

1. First check to make sure you can ping the TACACS+ Server from both Apic and Leaf nodes. This can rule out any network issues. 

 

2.  Check the configuration has been correctly pushed to the Leafs and APICs:

 Leaf101# show tacacs-server groups

total number of groups:1

following TACACS+ server groups are configured:

        group ACS_TACACS:

                server: 10.66.80.98 on port 49

                deadtime is 0

 Leaf101# show aaa authentication

         default: local

         console: local

 

  3. Check the nginx logs and search for the TACACS+ provider IP to confirm reachability, these logs can sometimes give you a clue to why TACACS connectivity is not working.  

 

leaf101# grep 10.66.80.98 /var/log/dme/log/nginx.log | less
34703||17-12-11 10:40:33.239+08:00||aaa||DBG4||||Received response from 10.66.80.98 - notifying callback handler (IPv4)||../dme/svc/extXMLApi/src/gen/ifc/app/./ping/lib_ifc_ping.cc||757
34703||17-12-11 10:40:33.239+08:00||aaa||DBG4||||Received update on status of 10.66.80.98 (DN uni/userext/tacacsext/tacacsplusprovider-10.66.80.98) - status is \ ALIVE||../dme/svc/extXMLApi/src/gen/ifc/app/./pam/PamWorker.cc||1448

Comments
Contributor

Awesome write up!

 

Contributor

Great write up!  I would have loved to have had this document when we initially set up our fabric.  Took us a while to figure out the correct av-pair.  The official docs at the time had some formatting issues that was clobbering proper whitespacing.

 

I would like to point on that the steps are the same for ISE 1.2+ instead of ACS, locations have just moved to Work Centers > Device Administration.

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