Hi, All

I did recursive query capacity test.   I used traffic generator to place 15K 
QPS traffic to DNS 1 with FQDN1 (Note, FQDN1 can't be resolve by DNS1, it need 
to forward it to DNS2  and TTL is set to 0)

But during the test , I found lots of failure , the successful rate is not high 
(85%).   Then I used TCPdump commands to capture logs in DNS1 , I found the 
following things:

Thing 1.  DNS query number is larger than response number between traffic 
generator and DNS1 .  About 15% traffic are dropped by DNS1 . 

Thing 2. DNS recursive query number between DNS1 and DNS2  is far less than 
query number between traffic generator and DNS1   

I want to confirm DNS behavior here: 

DNS1 will initiate a recursive query  towards DNS2 when first query is coming . 
 transaction time between DNS1 and DNS2 is about 3 miliseconds.  If in these 3 
miliseconds, there are other queries with same FQDN are coming, whether all 
these queries will be lined up in DNS1 because DNS1 has initiated the same FQDN 
resolve request to DNS2 ? if yes, which will explain thing 2  I observed during 
the test.    After DNS1 gets response from DNS2, then DNS1 will send response 
to the all the requests from traffic generator lined up in DNS1 , but 
unfortunately ,  DNS1 seems drop some packets here. There are 15% packet 
without response .

Besides, CPU usage is not high in DNS1 , only 30%

Is my understanding correct ?   Which parameters in DNS will impact the 
performance significantly ?   How to do further troubleshooting ?

Thank you very much!!


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