NSX-T: Clear NSX-T DNS Forwarder Cache


[Update: NSX-T ingests negative SOA TTL from myDNS server in this example.  Microsoft DNS defaults this to 1 hour.  So NSX-T will cache the negative result for an hour.
To combat this behavior, you can set your source DNS server to a lower TTL so that cache in NSX-T clear quicker.  Valid records in this setup will still cache for 1 hour or whatever you have your DNS server set to.]
To determine TTL value for the negative record:
nslookup -type=a -nosearch -d2 brokenaka.ninja.corp

Summary:

Ran into an interesting behavior w/ NSX-T's DNS forwarder service.  Basically, if I queried for an invalid DNS name, NSX-T's DNS caching appears to capture that invalid query for an undetermined amount of time.

So what does this do?  Basically, if I queried for ninja.naka.corp w/o creating the entry on my DNS server, NSX-T caches that invalid record.  If I then registered ninja.naka.corp on my DNS server, NSX-T will continue to tell me that the record is invalid even though does now exist in my DNS server.

Verified this behavior occurs w/ NSX-T 2.5.2.  It 'might' occur in 3.x, but unsure.  What I am aware of is that there still does not appear to be a UI method to flush this service's cache.

Workaround:

The only way around this problem appears to either wait for the cache to time out or force flushing of cache via API.  Below are curl and powershell examples of how to do this:

Curl Method:


Powershell Method:

Comments

Post a Comment

Popular posts from this blog

NSX-T: Release associated invalid node ID from certificate

Image
Summary: Basically had an expiring certificate registered in NSX-T that was associated to a node_id that is no longer valid.  Long story short, there wasn't anything obvious in API to delete or disassociate a certificate from a node_id for 3.2.2.  Not sure how things got in this state, but annotating for future reference.  This may change in future revisions, so always check API for latest. Details: Effectively had a stale node associated w/ a certificate that was expiring.  Could not delete certificate until that node was disassociated from the certificate. To get certificate details and associated node_id's, you can use the following curl call (UI works too): curl -k -X GET -H "Content-Type: application/json" -u admin https://<manager ip>/api/v1/trust-management/certificates/<cert UUID> Above will return something like this: Below must be run from one of the manager nodes via elevation to root: ONLY RUN THIS IF YOU ARE ABSOLUTELY SURE OF WHAT YOU ARE DO...
Read more

NSX-T: vCenter and NSX-T Inventory out of Sync (Hosts in vSphere not showing up in NSX-T)

Image
Summary: NSX-T loses synch w/ vCenter inventory, but statuses don't appear to show an issue.  Basically, you add a host to a vCenter cluster, NSX-T bits should start to automatically installing on new host.  Assuming you've created a Transport Node Profile and associated w/ the cluster.  The problem is that NSX-T doesn't see the new host and its link to the compute manager (vCenter) looks fine. Looks fine, Y U NO WORK!? So what's going on here?  This appears to affect NSX-T 2.5 and 2.5.1.  Cause is unknown. Workaround: Restart the cm-inventory service on each NSX-T mgmt/controller node using API or CLI. Details: If you were to query the status of the cm-inventory via API or CLI, you could query all 3 manager/controller nodes and get a status of running.  Even if the primary node associated w/ the VIP, if configured, is not necessarily in charge of inventory.  So you could restart the cm-inventory service till you are blue in the face ...
Read more

MacOS: AnyConnect VPN client was unable to successfully verify the IP forwarding table modifications.

Image
The VPN client was unable to successfully verify the IP forwarding table modification.  A VPN connection will not be established. Summary: I started running into issue utilizing Cisco AnyConnect on my Mac basically complaining about not able to overwrite IP forwarding tables.  This was on 4.6.x.  Since my VPN endpoints were not providing me w/ an updated client and w/ no access to Cisco Anyconnect downloads, my only option was to try openconnect.  It was totally worth it, here is why and how to set it up. PreReqs: Homebrew Installing OpenConnect: Launch MacOS Terminal brew install openconnect Getting VPN IP's/DNS Endpoints from AnyConnect: The information is typically located in your profile xml files located here: /opt/cisco/anyconnect/profile/somethingsomething.xml In the xml file, you are looking for "<HostAddress>typicallyaDNSName.com</HostAddress>" entry.  These are your VPN endpoints that you would need to pass to openconnec...
Read more