How do I set up Kerberos with NFSv4.1 datastores in ESXi 6.5?

I have gotten this question enough now (and from important folks like Cormac Hogan) to write up an end to end guide on how to do this. I had a shorter version in TR-4073 and then a Linux-specific version in TR-4616, but admittedly, it wasn’t really enough to help people get the job done. I also wrote up some stuff on ESXi Kerberos in a previous blog post that wasn’t nearly as in-depth called How to set up Kerberos on vSphere 6.0 servers for datastores on NFS.

Cormac also wrote up one of his own:

https://cormachogan.com/2017/10/12/getting-grips-nfsv4-1-kerberos/

I will point out that, in general, NFS Kerberos is a pain in the ass for people who don’t set it up on a regular basis and understand its inner workings, regardless of the vendor you’re interacting with. The reason is that there are multiple moving parts involved, and support for various portions of Kerberos (such as encryption types) vary. Additionally, some hosts automate things better than others.

We’re going to set it all up as if we only have created a basic SVM with data LIFs and some volumes. If you have an existing SVM configured with NFS and such, you can retrofit as needed. While this blog covers only NFS Kerberos using ONTAP as the NFS server, the steps for AD and ESXi would apply to other NFS servers as well, in most cases.

Here’s the lab setup:

ONTAP 9.3 (but this works for ONTAP 9.0 and onward) SVM is SVM1

Windows 2012R2 (any Windows KDC that supports AES will work)/Active Directory DNS, KDC Domain is core-tme.netapp.com

ESXi 6.5 Hostname is CX400S1-GWNSG6B



ONTAP Configuration

While there are around 10 steps to do this, keep in mind that you generally only have to configure this once per SVM.

We’ll start with ONTAP, via the GUI. I’ll also include a CLI section. First, we’ll start in the SVM configuration section to minimize clicks. This is found under Storage -> SVMs. Then, click on the SVM you want to configure and then click on the NFS protocol.

1. Configure DNS

We need this because Kerberos uses DNS lookups to determine host names/IPs. This will be the Active Directory DNS information. This is found under Services -> DNS/DDNS.

2. Enable NFSv4.1

NFSv4.1 is needed to allow NFSv4.1 mounts (obviously). You don’t need to enable NFSv4.0 to use NFSv4.1. ESXi doesn’t support v4.0 anyway. But it is possible to use v3.0, v4.0 and v4.1 in the same SVM. This can be done under “Protocols -> NFS” on the left menu.

3. Create an export policy and rule for the NFS Kerberos datastore volume

Export policies in ONTAP are containers for rules. Rules are what defines the access to an exported volume. With export policy rules, you can limit the NFS version allowed, the authentication type, root access, hosts, etc. For ESXi, we’re defining the ESXi host (or hosts) in the rule. We’re allowing NFS4 only and Kerberos only. We’re allowing the ESXi host to have root access. If you use NFSv3 with Kerberos for these datastores, be sure to adjust the policy and rules accordingly. This is done under the “Policies” menu section on the left.

4. Verify that vsroot has an export policy and rule that allows read access to ESXi hosts

Vsroot is “/” in the namespace. As a result, for clients to mount NFS exports, they must have at least read access via vsroot’s export policy rule and at least traverse permissions (1 in mode bits) to navigate through the namespace. In most cases, vsroot uses “default” as the export policy. Verify whichever export policy is being used has the proper access.

If a policy doesn’t have a rule, create one. This is an example of minimum permissions needed for the ESXi host to traverse /.

5. Create the Kerberos realm

The Kerberos realm is akin to /etc/krb5.conf on Linux clients. It tells ONTAP where to look to attempt the bind/join to the KDC. After that, KDC servers are discovered by internal processes and won’t need the realm. The realm domain should be defined in ALL CAPS. This is done in System Manager using “Services -> Kerberos Realm” on the left.

6. Enable Kerberos on your data LIF (or LIFs)

To use NFS Kerberos, you need to tell ONTAP which data LIFs will participate in the requests. Doing this specifies a service principal for NFS on that data LIF. The SVM will interact with the SVM defined in the Kerberos realm to create a new machine object in AD that can be used for Kerberos. The SPN is defined as nfs/hostname.domain.com and represents the name you want clients to use to access shares. This FQDN needs to exist in DNS as a forward and reverse record to ensure things work properly. If you enable Kerberos on multiple data LIFs with the same name, the machine account gets re-used. If you use different SPNs on LIFs, different accounts get created. You have a 15 character limit for the “friendly” display name in AD. If you want to change the name later, you can. That’s covered in TR-4616.

7. Create local UNIX group and users

For Kerberos authentication, a krb-unix name mapping takes place, where the incoming SPN will attempt to map to a UNIX user that is either local on the SVM or in external name service servers. You always need the “nfs” user, as the nfs/fqdn SPN will map to “nfs” implicitly. The other user will depend on the user you specify in ESXi when you configure Kerberos. That UNIX user will use the same user name. In my example, I used “parisi,” which is a user in my AD domain. Without these local users, the krb-unix name mapping would fail and manifest as “permission denied” errors when mounting. The cluster would show errors calling out name mapping in “event log show.”

Alternatively, you can create name mapping rules. This is covered in TR-4616. UNIX users and groups can be created using the UNIX menu option under “Host Users and Groups” in the left menu.

The numeric GID and UID can be any unused numeric in your environment. I used 501 and 502.

First, create the primary group to assign to the users.

Then, create the NFS user with the Kerberos group as the primary group.

Finally, create the user you used in the Kerberos config in ESXi.

Failure to create the user would result in the following similar error in ONTAP. (In the below, I used a user named ‘vsphere’ to try to authenticate):

**[ 713] FAILURE: User 'vsphere' not found in UNIX authorization source LDAP. [ 713] Entry for user-name: vsphere not found in the current source: LDAP. Ignoring and trying next available source [ 715] Entry for user-name: vsphere not found in the current source: FILES. Entry for user-name: vsphere not found in any of the available sources [ 717] Unable to map SPN 'vsphere@CORE-TME.NETAPP.COM' [ 717] Unable to map Kerberos NFS user 'vsphere@CORE-TME.NETAPP.COM' to appropriate UNIX user

8. Create the volume to be used as the datastore

This is done from “Storage -> Volumes.” In ONTAP 9.3, the only consideration is that you must specify a “Protection” option, even if it’s “none.” Otherwise, it will throw an error.

Once the volume is created, it automatically gets exported to /volname.

9. Verify the volume security style is UNIX for the datastore volume

The volume security style impacts how a client will attempt to authenticate into the ONTAP cluster. If a volume is NTFS security style, then NFS clients will attempt to map to Windows users to figure out the access allowed on an object. System Manager doesn’t let you define the security style at creation yet and will default to the security style of the vsroot volume (which is / in the namespace). Ideally, vsroot would also be UNIX security style, but in some cases, NTFS is used. For VMware datastores, there is no reason to use NTFS security style.

From the volumes screen, click on the newly created volume and click the “Edit” button to verify UNIX security style is used.

10. Change the export policy assigned to the volume to the ESX export policy you created

Navigate to “Storage -> Namespace” to modify the export policy used by the datastore.

11. Configure NTP

This prevents the SVM from getting outside of the 5 minute time skew that can break Kerberos authentication. This is done via the CLI. No GUI support for this yet.

cluster::> ntp server create -server stme-infra02.core-tme.netapp.com -version auto

12. Set the NFSv4 ID domain

While we’re in the CLI, let’s set the ID domain. This ID domain is used for client-server interaction, where a user string will be passed for NFSv4.x operations. If the user string doesn’t match on each side, the NFS user gets squashed to “nobody” as a security mechanism. This would be the same domain string on both ESX and on the NFS server in ONTAP (case-sensitive). For example, “core-tme.netapp.com” would be the ID domain here and users from ESX would come in as user@core-tme.netapp.com. ONTAP would look for user@core-tme.netapp.com to exist.

In ONTAP, that command is:

cluster::> nfs modify -vserver SVM1 -v4-id-domain core-tme.netapp.com

13. Change datastore volume permissions

By default, volumes get created with the root user and group as the owner, and 755 access. In ESX, if you want to create VMs on a datastore, you’d need either root access or to change write permissions. When you use Kerberos, ESX will use the NFS credentials specified in the configuration as the user that writes to the datastore. Think of this as a “VM service account” more or less. So, your options are:

Change the owner to a different user than root

Use root as the user (which would need to exist as a principal in the KDC)

Change permissions

In my opinion, changing the owner is the best, most secure choice here. To do that:

cluster::> volume modify -vserver SVM1 -volume kerberos_datastore -user parisi

That’s all from ONTAP for the GUI. The CLI commands would be (all in admin priv):

cluster::> dns create -vserver SVM1 -domains core-tme.netapp.com -name-servers 10.193.67.181 -timeout 2 -attempts 1 -skip-config-validation true cluster::> nfs modify -vserver SVM1 -v4.1 enabled cluster::> export-policy create -vserver SVM1 -policyname ESX cluster::> export-policy rule create -vserver SVM1 -policyname ESX -clientmatch CX400S1-GWNSG6B.core-tme.netapp.com -rorule krb5* -rwrule krb5* -allow-suid true -ruleindex 1 -protocol nfs4 -anon 65534 -superuser any cluster::> vol show -vserver SVM1 -volume vsroot -fields policy cluster::> export-policy rule show -vserver SVM1 -policy [policy from prev command] -instance cluster::> export-policy rule modify or create (if changes are needed) cluster::> kerberos realm create -vserver SVM1 -realm CORE-TME.NETAPP.COM -kdc-vendor Microsoft -kdc-ip 10.193.67.181 -kdc-port 88 -clock-skew 5 -adminserver-ip 10.193.67.181 -adminserver-port 749 -passwordserver-ip 10.193.67.181 -passwordserver-port 464 -adserver-name stme-infra02.core-tme.netapp.com -adserver-ip 10.193.67.181 cluster::> kerberos interface enable -vserver SVM1 -lif data -spn nfs/ontap9.core-tme.netapp.com cluster::> unix-group create -vserver SVM1 -name kerberos -id 501 cluster::> unix-user create -vserver SVM1 -user nfs -id 501 -primary-gid 501 cluster::> unix-user create -vserver SVM1 -user parisi -id 502 -primary-gid 501 cluster::> volume create -vserver SVM1 -volume kerberos_datastore -aggregate aggr1_node1 -size 500GB -state online -policy kerberos -user 0 -group 0 -security-style unix -unix-permissions ---rwxr-xr-x -junction-path /kerberos_datastore

ESXi Configuration

This is all driven through the vSphere GUI. This would need to be performed on each host that is being used for NFSv4.1 Kerberos.

1. Configure DNS

This is done under the “Hosts and Clusters -> Manage -> Networking -> TCP/IP config.”

2. Configure NTP

This is found in “Hosts and Clusters -> Settings -> Time Configuration”

3. Join the ESXi host to the Active Directory domain

Doing this automatically creates the machine account in AD and will transfer the keytab files between the host and KDC. This also sets the SPNs on the machine account. The user specified in the credentials must have create object permissions in the Computers OU in AD. (For example, a domain administrator)

This is found in “Hosts and Clusters -> Settings -> Authentication Services.”

4. Specify NFS Kerberos Credentials

This is the user that will authenticate with the KDC and ONTAP for the Kerberos key exchange. This user name will be the same as the UNIX user you used in ONTAP. If you use a different name, create a new UNIX user in ONTAP or create a name mapping rule. If the user password changes in AD, you must also change it in ESXi.

With NFS Kerberos in ESX, the ID you specified in NFS Kerberos credentials will be the ID used to write. For example, I used “parisi” as the user. My SVM is using LDAP authentication with AD. That user exists in my LDAP environment as the following:

cluster::*> getxxbyyy getpwbyuid -node ontap9-tme-8040-01 -vserver SVM1 -userID 3629 (vserver services name-service getxxbyyy getpwbyuid) pw_name: parisi pw_passwd: pw_uid: 3629 pw_gid: 512 pw_gecos: pw_dir: pw_shell: /bin/sh

As a result, the test VM I create got written as that user:

drwxr-xr-x 2 3629 512 4096 Oct 12 10:40 test

To even be able to write at all, I had to change the UNIX permissions on the datastore to allow write access to “others.” Alternatively, I could have changed the owner of the volume to the specified user. I mention those steps in the ONTAP section.

If you plan on changing the user for NFS creds, be sure to use “clear credentials,” which will restart the service and clear caches. Occasionally, you may need to restart the nfsgssd service from the CLI if something is stubbornly cached:

[root@CX400S1-03003-B3:/] /etc/init.d/nfsgssd restart watchdog-nfsgssd: Terminating watchdog process with PID 33613 Waiting for process to terminate... nfsgssd stopped nfsgssd started

In rare cases, you may have to leave and re-join the domain, which will generate new keytabs. In one particularly stubborn case, I had to reboot the ESX server after I changed some credentials and the Kerberos principal name in ONTAP.

That’s the extent of the ESXi host configuration for now. We’ll come back to the host to mount the datastore once we make some changes in Active Directory.

Active Directory Configuration

Because there are variations in support for encryption types, as well as DNS records needed, there are some AD tasks that need to be performed to get Kerberos to work.

1. Configure the machine accounts

Set the machine account attributes for the ESXi host(s) and ONTAP NFS server to only allow AES encryption. Doing this avoids failures to mount via Kerberos that manifest as “permission denied” on the host. In a packet trace, you’d potentially be able to see the ESXi host trying to exchange keys with the KDC and getting “unsupported enctype” errors if this step is skipped.

The exact attribute to change is msDS-SupportedEncryptionTypes. Set that value to 24, which is AES only. For more info on encryption types in Windows, click to view this blog.

You can change this attribute using “Advanced Features” view with the attribute editor. If that’s not available or it’s not possible to use, you can also modify using PowerShell.

To modify in the GUI:

To modify using PowerShell:

PS C:\> Set-ADComputer -Identity [NFSservername] -Replace @{'msDS-SupportedEncryptionTypes'=24}

2. Create DNS records for the ESXi hosts and the ONTAP server

This would be A/AAAA records for forward lookup and PTR for reverse. Windows DNS let’s you do both at the same time. Verify the DNS records with “nslookup” commands.

This can also be done via GUI or PowerShell.

From the GUI:

From PowerShell:

PS C:\Users\admin>Add-DnsServerResourceRecordA -IPv4Address 10.193.67.220 -CreatePtr core-tme.netapp.com -Name ontap9 PS C:\Users\admin>Add-DnsServerResourceRecordA -IPv4Address 10.193.67.35 -CreatePtr core-tme.netapp.com -Name cx400s1-gwnsg6b

Mounting the NFS Datastore via Kerberos

Now, we’re ready to create the datastore in ESX using NFSv4.1 and Kerberos.

Simply go to “Add Datastore” and follow the prompts to select the necessary options.

1. Select “NFS” and then “NFS 4.1.”

VMware doesn’t recommend mixing v3 and v4.1 on datastores. If you have an existing datastore that you were mounting via v3, VMware recommends migrating VMs using storage vmotion.

2. Specify the name and configuration

The datastore name can be anything you like. The “folder” has to be the junction-path/export path on the ONTAP cluster. In our example, we use /kerberos_datastore.

Server(s) would be the data LIF you enabled Kerberos on. ONTAP doesn’t support NFSv4.1 multi-pathing/trunking yet, so specifying multiple NFS servers won’t necessarily help here.

4. Check “Enable Kerberos-based authentication”

Kind of a no-brainer here, but still worth mentioning.

5. Select the hosts that need access.

If other hosts have not been configured for Kerberos, they won’t be available to select.

6. Review the configuration details and click “Finish.”

This should mount quickly and without issue. If you have an issue, review the “Troubleshooting” tips below.

This can also be done with a command from ESX CLI:

esxcli storage nfs41 add -H ontap9 -a SEC_KRB5 -s /kerberos_datastore -v kerberosDS

Troubleshooting Tips

If you follow the steps above, this should all work fine.

But sometimes I make mistakes. Sometimes YOU make mistakes. It happens. 🙂

Some steps I use to troubleshoot Kerberos mount issues…

Review the vmkernel logs for vcenter

Review “event log show” from the cluster CLI

Ensure the ESX host name and SVM host name exist in DNS (nslookup)

Use packet traces from the DC to see what is failing during Kerberos authentication (filter on “kerberos” in wireshark)

Review the SVM config: Ensure NFSv4.1 is enabled Ensure the SVM has DNS configured Ensure the Kerberos realm is all caps and is created on the SVM Ensure the desired data LIF has Kerberos enabled (from system manager of via “kerberos interface show” from the cli) Ensure the export policies and rules allow access to the ESX datastore volume for Kerberos, superuser and NFSv4. Ensure the vsroot volume allows at least read access for the ESX host. Ensure the SVM has the appropriate UNIX users and group created (nfs user for the NFS SPN; UNIX user name that matches the NFS user principal defined in ESX) or the users exist in external name services

From the KDC/AD domain controller: Ensure the machine accounts created use AES only to avoid any weird issues with encryption type support Ensure the SPNs aren’t duplicated (setspn /q {service/fqdn} Ensure the user defined in the NFS Kerberos config hasn’t had a password expire

