unknown protocol drops

[Eric Lindsey]

We started using Cisco 3850 switches. We are seeing unknown protocol drops on 10gb and 1gb uplinks. We have 3750x switches that have the same config. The 3750s are not showing these drops. What would cause these unknown protocol drops? It does not appear to be a fiber or SFP issue. And it does not seem to be affecting the normal traffic.

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[Leo Laohoo]

Eric,

Judging from your description, I'd recommend you raise a TAC Case.  I think this could be a "cosmetic" bug.

[Luis Villanueva]

Hello lindseye444,

Please have a look at this bug:

https://tools.cisco.com/bugsearch/bug/CSCuh47950/?reffering_site=dumpcr

Symptom:
when a routing protocol packet (such as but not limited to EIGRP) is received on a 3850 configured as an L2 device, interfaces receiving these packets will increment "unknown protocol drops" 

This is a cosmetic issue and will not affect the routing protocols involved.

Conditions:
EIGRP or other routing protocol packets are received by a Catalyst 3850 that is configured as an Layer2 switch.

Workaround:
Once an SVI (switch virtual interface: for example "interface vlan 10") with an IP address is configured on the 3850 for the vlan in question the "unknown protocol drops" counter stops incrementing

Further Problem Description:
L3 routing protocol packets might be punted to CPU received on a L2 switchport, if no SVI is presented, unknown protocol drops will increase on the physical interface.

Regards.