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ONTAP Discussions

What needs to be done on cDOT to use UDP in DNS queries


We were told that we should use UDP instead of TCP in DNS queries, but, what needs to be done on the storage to achieve that?



Hello Friend,


I perform transition consulting for NetApp.


If you are running 8.2.3 or 8.3, UDP is used by default if the lookup results are less than 512 bytes.   See this excerpt from the Name Services Best Practices TR-4379:


In the clustered Data ONTAP 8.2.3 operating system, UDP support for DNS was added for hostname

lookups. Both UDP and TCP can be used for DNS lookups in 8.2.3 and later. UDP will be used for

smaller lookups, while TCP will be used if the UDP response is truncated because of the size of the



skynet::> system image show -iscurrent true -fields version
node      image  version
--------- ------ -------
skynet-01 image2 8.3
skynet-02 image2 8.3
2 entries were displayed.

skynet::> nfs server show -vserver hadrian_skyvs1 -fields name-service-lookup-protocol
vserver        name-service-lookup-protocol
-------------- ----------------------------
hadrian_skyvs1 udp



Enjoy!  If this helped out, please hit the Kudos button and mark as Answered.







We happened to be runing 8.2.1. So, what do i need to do on the storage, in order to use UDP?


The provided command doesn't work on this cluster:

Error: invalid argument "name-service-lookup-protocol"



Looking forward to hear you again.




Hello Friend,


Perform the upgrade to 8.2.3P3 and it will be turned on by default and is not tunable, so the command still won't return.


See the 8.2.3 download page and read the Upgrade Guide and run an upgrade advisor:


In 8.3, that command becomes available in order to let you force TCP instead of UDP for lookup results under 512 bytes.  



If this helped out, please hit the Kudos button and accept as Answered.









OK. Then anything we could do now for this issue on 8.2.1P1? You know, upgrading is not something we could do immediately.


Hello Heights,


Until your Data ONTAP upgrade window is available, take a read through section 5.3 on TR-4379 for workarounds to ensure better performance when dealing with huge amounts of TCP DNS traffic. 







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