Fix: DCNM Fabric Update Failure For Specific Parameters

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Troubleshooting DCNM Fabric Update Failures for Specific Parameters

Hey guys! Ever run into a snag where your DCNM fabric update just refuses to cooperate with certain parameters? It's a head-scratcher, but let's dive into this issue and figure out what's going on. This article will walk you through a specific problem encountered while trying to update fabric parameters using Ansible with Cisco DCNM (Data Center Network Manager). We'll break down the error, explore the potential causes, and discuss how to troubleshoot and resolve it. So, buckle up, and let's get started!

The Problem: DCNM Fabric Update Failing

The core issue revolves around the dcnm_fabric module in Ansible failing to update specific fabric parameters. When attempting to apply changes to a fabric, DCNM throws a 500 Internal Server Error, citing "invalid fields." This is super frustrating, especially when you're trying to automate your network configurations. Here’s a breakdown of the situation:

  • The Setup: We're using Ansible to manage a Cisco DCNM environment.
  • The Goal: Update specific parameters of an existing fabric.
  • The Issue: The dcnm_fabric module fails with a 500 Internal Server Error.
  • The Error Message: The error message indicates "invalid fields" in the JSON response, but it's not always clear which fields are the real culprits. It often suggests that certain fields should be empty, which doesn't make a whole lot of sense.

Let's dig deeper into the specifics. The error messages point to discrepancies between what DCNM expects and what the Ansible module is sending. For instance, in a BGP Fabric type, you might see errors related to fields like L3VNI_MCAST_GROUP, ADVERTISE_PIP_ON_BORDER, and ENABLE_NXAPI_HTTP. Similarly, for an EVPN VXLAN fabric type, the errors might revolve around fields like USE_LINK_LOCAL, ISIS_OVERLOAD_ENABLE, and ISIS_P2P_ENABLE. The kicker? DCNM is asking for these fields to be empty, even if they have valid configurations.

Why does this happen?

Well, there could be a few reasons, and pinpointing the exact cause is key to fixing this. One common reason is inconsistencies or bugs in how the DCNM API handles updates for certain parameters. Another potential cause could be the way the dcnm_fabric module constructs the payload for the PUT request. It's also worth considering whether the DCNM version itself has any known issues related to fabric updates. Understanding the root cause is crucial, guys, because it dictates the troubleshooting steps and the eventual solution.

Diving into the Details: Ansible, DCNM, and the Error

To really understand what's going on, we need to look at the specifics of the Ansible playbook, the DCNM version, and the error messages themselves. The Ansible playbook provides the desired state of the fabric, and the dcnm_fabric module is responsible for translating that into API calls to DCNM. Let's break down each component:

Ansible Playbook

The playbook is the heart of our automation efforts. It defines the desired configuration for the DCNM fabric. Here’s a snippet of the playbook that triggers the error:

---

- name: Debug Fabric Update
  hosts: marehler_vnd1
  any_errors_fatal: true
  gather_facts: no

  tasks:

  - name: Update the Fabric
    cisco.dcnm.dcnm_fabric:
      state: merged
      config:
        - FABRIC_NAME: VXLAN-BGP2
          FABRIC_TYPE: BGP
          DEPLOY: false
          BGP_AS: 65000.3
          SUPER_SPINE_BGP_AS: 65000.1
          BGP_AS_MODE: Multi-AS
          ALLOW_LEAF_SAME_AS: true
          UNDERLAY_IS_V6: false
          STATIC_UNDERLAY_IP_ALLOC: false
          SUBNET_TARGET_MASK: 31
          SUBNET_RANGE: 10.24.0.0/16
          LOOPBACK0_IP_RANGE: 10.22.0.0/22
          ENABLE_EVPN: true
          OVERLAY_MODE: cli
          ALLOW_L3VNI_NO_VLAN: true
          ENABLE_L3VNI_NO_VLAN: false
          ANYCAST_GW_MAC: 20:20:00:00:00:aa
          ADVERTISE_PIP_BGP: true
          ANYCAST_BGW_ADVERTISE_PIP: false
          REPLICATION_MODE: Multicast
          LOOPBACK1_IP_RANGE: 10.23.0.0/22
          RP_LB_ID: 254
          RP_COUNT: 2
          RP_MODE: asm
          ENABLE_TRM: true
          ENABLE_TRMv6: false
          ANYCAST_RP_IP_RANGE: 10.254.254.0/24
          MULTICAST_GROUP_SUBNET: 239.239.0.0/25
          L3VNI_MCAST_GROUP: 239.239.0.3
          L2_SEGMENT_ID_RANGE: 30000-49000
          L3_PARTITION_ID_RANGE: 50000-59000
          NETWORK_VLAN_RANGE: 2300-2999
          VRF_VLAN_RANGE: 2000-2299
          VPC_PEER_LINK_VLAN: 3600
          VPC_PEER_KEEP_ALIVE_OPTION: management
          VPC_AUTO_RECOVERY_TIME: 360
          VPC_DELAY_RESTORE: 150
          VPC_PEER_LINK_PO: 500
          VPC_ENABLE_IPv6_ND_SYNC: false
          ENABLE_FABRIC_VPC_DOMAIN_ID: false
          VPC_DOMAIN_ID_RANGE: 1-100
          FABRIC_VPC_QOS: false
          BGP_LB_ID: 0
          NVE_LB_ID: 1
          BGP_MAX_PATH: 4
          BFD_ENABLE: false
          BGP_AUTH_ENABLE: false
          PIM_HELLO_AUTH_ENABLE: false
          ENABLE_MACSEC: false
          GRFIELD_DEBUG_FLAG: Enable
          ENABLE_PVLAN: false
          AAA_REMOTE_IP_ENABLED: false
          FABRIC_MTU: 9100
          L2_HOST_INTF_MTU: 9000
          ENABLE_NXAPI: false
          SNMP_SERVER_HOST_TRAP: true
          FEATURE_PTP: false
          DNS_SERVER_IP_LIST: 10.200.253.13
          DNS_SERVER_VRF: management
          NTP_SERVER_IP_LIST: 10.200.253.13
          NTP_SERVER_VRF: management
          SYSLOG_SERVER_IP_LIST: 10.200.253.19
          SYSLOG_SERVER_VRF: management
          SYSLOG_SEV: 4
          ENABLE_NETFLOW: false

This playbook uses the cisco.dcnm.dcnm_fabric module to update the fabric named VXLAN-BGP2. It sets a bunch of parameters, and that's where the trouble begins. When Ansible runs this playbook, it throws the following error:

The Dreaded Error Message

fatal: [marehler_vnd1]: FAILED! => {"changed": false, "metadata": [{"action": "fabric_update", "check_mode": false, "sequence_number": 1, "state": "merged"}], "msg": "Module failed.", "response": [{"DATA": "Invalid JSON response: Failed to create the fabric, due to invalid fields [{L3VNI_MCAST_GROUP=239.239.0.3}], please provide valid fields [{L3VNI_MCAST_GROUP=}] for fabric-settings", "MESSAGE": "Internal Server Error", "METHOD": "PUT", "REQUEST_PATH": "https://[2001:420:448b:8006::7]:443/appcenter/cisco/ndfc/api/v1/lan-fabric/rest/control/fabrics/VXLAN-BGP2/Easy_Fabric_eBGP", "RETURN_CODE": 500, "sequence_number": 1}], "result": [{"changed": false, "sequence_number": 1, "success": false}]}

Notice the key part: Invalid JSON response: Failed to create the fabric, due to invalid fields [{L3VNI_MCAST_GROUP=239.239.0.3}], please provide valid fields [{L3VNI_MCAST_GROUP=}] for fabric-settings. It's saying that the L3VNI_MCAST_GROUP field is invalid and should be empty. But that doesn't make sense, right? We need that parameter set for our multicast configuration!

DCNM Version

The DCNM version in this case is ND 3.2.1(i). Knowing the DCNM version is crucial because it helps us check for known bugs or limitations in that specific release. Cisco often releases patches and updates to fix these kinds of issues, so it's always a good idea to keep your DCNM version up to date.

Troubleshooting Steps: Let's Get Our Hands Dirty

Alright, so we've identified the problem. Now, let's roll up our sleeves and get into the troubleshooting process. Here’s a step-by-step guide to help you nail down the cause and find a solution:

1. Double-Check the Obvious: Syntax and Typos

Okay, this might sound like a no-brainer, but trust me, it's worth checking. Sometimes, a simple typo in the playbook can cause the whole thing to fall apart. Carefully review your playbook, especially the config section, to ensure there are no syntax errors or typos in the parameter names or values. A misplaced colon, a misspelled parameter, or an incorrect data type can all lead to this kind of error.

2. Validate the Parameter Values

Next up, let's make sure the values you're providing for the parameters are valid according to DCNM's requirements. For example, IP addresses should be in the correct format, VLAN ranges should be within the allowed limits, and so on. Refer to the DCNM documentation for the specific requirements for each parameter.

3. Experiment with Minimal Changes

This is a classic debugging technique. Try making minimal changes to the playbook and running it again. For instance, if you're updating multiple parameters, try updating just one parameter at a time. This can help you isolate which specific parameter is causing the issue. Comment out sections of your playbook and incrementally add them back in to see when the error pops up.

4. Consult the DCNM Documentation

Cisco's documentation is your best friend in these situations. Dig into the DCNM documentation for your specific version and look for any known issues or limitations related to fabric updates. Pay close attention to the parameter descriptions and any notes about specific requirements or constraints. Sometimes, there might be a particular order in which parameters need to be updated, or certain parameters might have dependencies on others.

5. Check for DCNM Bugs

It’s entirely possible that this is a bug in DCNM itself. Cisco maintains a bug tracking system, so search for any reported issues related to fabric updates and the specific error messages you're seeing. If you find a bug report that matches your issue, it might contain a workaround or a fix in a later DCNM release.

6. Try Different API Calls Directly

To rule out issues with the Ansible module, try making the API calls directly using tools like curl or Postman. This allows you to send the raw JSON payload to DCNM and see if you get the same error. If the API call fails directly, it points to an issue with DCNM's API handling. If it works, then the problem might be in how the Ansible module is constructing the payload.

7. Review DCNM Logs

DCNM logs can provide valuable insights into what's happening behind the scenes. Check the DCNM logs for any error messages or warnings that might shed light on the issue. Look for anything related to fabric updates, API calls, or parameter validation. The logs might contain more detailed information about why a particular parameter is being rejected.

8. Upgrade DCNM (If Possible)

If you're running an older version of DCNM, consider upgrading to the latest stable release. Cisco often includes bug fixes and performance improvements in newer releases, and it's possible that your issue has already been resolved. Before upgrading, make sure to review the release notes and any compatibility information.

9. Engage with the Community and Cisco TAC

If you've tried all the above steps and you're still stuck, it's time to reach out for help. Post your issue on relevant forums or communities, like the CiscoDevNet forum. There might be other users who have encountered the same problem and found a solution. You can also open a case with Cisco TAC (Technical Assistance Center). They have experts who can help you troubleshoot DCNM issues and provide guidance.

Potential Causes and Solutions: Cracking the Case

Based on the error messages and the troubleshooting steps, here are some potential causes and solutions for the DCNM fabric update failure:

1. DCNM API Bug

  • Cause: A bug in the DCNM API might be causing it to incorrectly validate certain parameters during an update.
  • Solution:
    • Check the Cisco bug tracking system for known issues.
    • Upgrade DCNM to a version with a fix (if available).
    • As a temporary workaround, try updating the fabric in smaller increments or using the DCNM GUI.

2. Ansible Module Issue

  • Cause: The cisco.dcnm.dcnm_fabric module might be constructing the payload incorrectly or not handling the API response properly.
  • Solution:
    • Try making the API calls directly to DCNM (as described above) to isolate the issue.
    • Update the cisco.dcnm collection to the latest version.
    • If the issue persists, consider opening an issue on the Ansible collection's GitHub repository.

3. Parameter Dependencies or Order

  • Cause: Certain fabric parameters might have dependencies on others, or there might be a specific order in which they need to be updated.
  • Solution:
    • Consult the DCNM documentation for parameter dependencies and update order.
    • Try updating the parameters in a different order.

4. Data Type Mismatch

  • Cause: The data type of the value you're providing for a parameter might not match what DCNM expects.
  • Solution:
    • Double-check the DCNM documentation for the expected data types of each parameter.
    • Ensure that the values in your playbook match the expected data types.

5. Missing or Incorrect Default Values

  • Cause: In some cases, DCNM might require certain parameters to be explicitly set, even if they have default values.
  • Solution:
    • Try including all relevant parameters in your playbook, even if they have default values.

Wrapping Up: Taming the DCNM Fabric Update Beast

So there you have it, guys! Troubleshooting DCNM fabric update failures can be a bit of a journey, but with a systematic approach and a good understanding of the components involved, you can conquer this beast. Remember to:

  • Isolate the issue: Use minimal changes and direct API calls to pinpoint the problem.
  • Consult the documentation: Cisco's documentation is your best friend.
  • Leverage the community: Don't be afraid to ask for help from other users and Cisco TAC.
  • Keep your software up to date: Upgrading DCNM and Ansible collections can often resolve bugs.

By following these steps, you'll be well-equipped to tackle DCNM fabric update failures and keep your network automation running smoothly. Happy networking!