net: NET_CONN_CACHE relevant

[zephyrbot]

Reported by Likai Liu:

Find in v1.8.0, not sure it exists in new version .
Set NET_CONN_CACHE y
When we do not have a connection to a host , we can only set the hash value to negative_cache when conn_cache has no free position.
Why not set it to negative_cache when the first time we find no match connection ? Then drop the later packets in negative_cache.

(Imported from Jira ZEP-2616)

[zephyrbot]

by Jukka Rissanen:

The connection cache is not enabled by default so it is not extensively tested thus there might be issues in it.
Anyway, from the bug description it is not clear what is the issue. Could you describe what kind of issue you are seeing, and what is the expected outcome?

[zephyrbot]

by Likai Liu:

Jukka Rissanen On memory and cpu constrained devices ,when we do not have a connection to a host ,I want to drop the received packets immediately, and skip the ICMP destination unreachable which affecting the efficiency.

I want to use negative_cache to drop the received packets . But it seems that it does not work.

[nashif]

@jukkar is this still an issue? Can you please take a look or close if not relevant anymore.

[jukkar]

Sure, I will do some more testing for this later this week.

[jukkar]

This works now as expected, if the connection entry is in negative cache, it is dropped immediately.