ipset losing entries on its own

I am having ipset 6.32

The hash type is hash:ip

I am adding/deleting IP addresses to it dynamically using scripts.

However, it has been observed that at times few IPs (3-4 out of 4000)
are not found in the set though it was added. Also, logs show there
was not request for deletion of that IP from IPSet.

Is it a bug?

output of ipset -L -t

Name: STORE
Type: hash:ip
Revision: 4
Header: family inet hashsize 1024 maxelem 65536
Size in memory: 50480
References: 1

On 2017-09-06 13:08, Akshat Kakkar wrote:

I am having ipset 6.32

The hash type is hash:ip

I am adding/deleting IP addresses to it dynamically using scripts.

However, it has been observed that at times few IPs (3-4 out of 4000)
are not found in the set though it was added. Also, logs show there
was not request for deletion of that IP from IPSet.

Is it a bug?

I think you should try to make script to create at least reproducible 
scenario
And sure post more info about your setup (kernel version, vanilla or 
distro)

I understand that without reproducible scenarios, its hard to debug ...
But the point is, this issue is fully random and of very low frequency.

For the setup, it is CentOS 7.3 upgraded to kernel 4.4.

Whenever a system comes up on the network, he provides his credentials
and after successful authentication, his IP is added in an IPSET which
is having access to certain resources.

What I observed is rehashing of set is not happening.

When I add multiple IPs to the ipset manually on ipset v6.32,
rehashing is not happening and my hashsize remains same as 1024

but when I add to ipset 4.5 (pretty old, I know!), rehashing is
happening and my hashsize changes from 1024 to 1536 to 2304 to 3456!

Another observation :
At times rehashing happens (v6.32) and hashsize increases to 2048 from
1024. But this is at times and not always. Needless to mention, it is
for exactly same IPs added to the ipset in exactly same order.

Any more information needed?

can somebody throw more light on this? How it is possible (without a
bug) that for exactly same set of IPs, at time IPSET HASHSIZE remains
at 1024 and at times it increases to 2048?

As a workaround I am running the show setting HASHSIZE as 16384 at
times of IPSET creation itself, and till now (its more than 4 days)
the issue has not repeated.

But this need to be addressed, right?

Has anybody got any clue in this?