Nexus 3064PQ mac address hash collision

[vpluto]

Hello!

On our 3064PQ we have just a few features activated:

Software
BIOS: version 4.5.0
NXOS: version 7.0(3)I7(6)

csw-c3064-kir58-1# sh feature | i enabled
interface-vlan         1          enabled
lacp                   1          enabled
lldp                   1          enabled
sshServer              1          enabled
telnetServer           1          enabled
vtp                    1          enabled

So, vPC is not activated and we shouldn't have a 40K MAC-addresses limit.

But having just 37K MACs, we already have a lot of hash collisions, for example:

2019 May 19 22:09:56 csw-c3064-kir58-1 %-SLOT1-5-BCM_L2_HASH_COLLISION: L2 ENTRY unit=0 mac=20:89:84:f6:c2:69 vlan=417 port=0x0800081c
2019 May 19 22:09:57 csw-c3064-kir58-1 last message repeated 13 times

Maybe there is an option we need to configure to expand the hash calculation formula and prevent the hash collisions?

[maksim8]

Hi
did you find solution?

[jingt0829]

Found this from configuration doc:

In releases prior to Release 7.0(3)I2(1), there was no syslog message indicating the MAC collision events. Starting 7.0(3)I2(1) there is a new syslog on Cisco Nexus 3000 Series platforms to indicate the MAC collision events. The syslog message has the details, for example, the source MAC address, the VLANs, and the internal port number information. MAC collisions are normal and they are expected if the table usage crosses about 75% as observed on various setups. See the following example of the syslog: 2015 Mar 26 06:20:37 switch%-SLOT1-5-BCM_L2_HASH_COLLISION: L2 ENTRY unit=0 mac=00:11:11:f7:46:40 vlan=1998 port=0x0800082e.

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus3000/sw/system_mgmt/7_x/b_Cisco_Nexus_3000_Series_NX-OS_System_Management_Configuration_Guide_7x/b_Cisco_Nexus_3000_Series_NX-OS_System_Management_Configuration_Guide_7x_chapter_01011.htm...

[f00z]

What is output of show hardware capacity forwarding?

[maksim8]

# show hardware capacity forwarding

L2 table utilization on Module = 1

Asic Max Count Used Count
-----+---------+---------
0 131072 32356

[jingt0829]

Hi Maksim8,

I suppose you still get the 'hash collision' erros logs? Did you run into any issue with 32K mac addresses on your switch? 

[f00z]

Hmm, interesting. I tested the 3064 and also the 3100's and the nexus 9332 by generating random MAC addresses and all of them had collisions around 80% usage but not before. Possibly a bug, or if the addresses are mostly virtual machines which generate MAC addrs in  a strange way that it makes a collision earlier.

I'd update to the 7.0.3.I7.8 , this 7.0.3.I7 train has fixed a lot of issues we had previously in the 7.x code