L2MCAST-SLOT2-2-L2MCAST_MAC_FULL_LC

campbech1 · ‎12-29-2014

Since upgrading to version 6.2(8b) on our core Nexus 7ks I'm seeing the following errors:

2014 Dec 29 08:09:22 DC7K-ADMIN_VDC %L2MCAST-SLOT2-2-L2MCAST_MAC_FULL_LC: Failed to insert entry in MAC table for FE 0 swidx 268 (0x
10c) with err (mac table full). To avoid possible multicast traffic loss, disable OMF. Use the configuration CLI: "no ip igmp snoopi
ng optimise-multicast-flood"

When this is reported to syslog, I have an alert that fires a SecureCRT script to log into the switch that reported the alert and then log to a text file how many MAC addresses it currently "sees". The number of MAC addresses normally sits around 12k, no where near the 16384 limit.

Anyone else seen this message?

module-1# show hardware internal forwarding f2 l2 table utilization instance all

L2 Forwarding Resources
-------------------------
L2 entries: Module inst   total    used   mcast   ucast   lines   lines_full
------------------------------------------------------------------------------
              1         0   16384   12368     281   12087     512            4
              1         1   16384    8862       1    8861     512            0
              1         2   16384   12384     282   12102     512            1
              1         3   16384    8857       8    8849     512            0
              1         4   16384    8997       9    8988     512            0
              1         5   16384    8861       1    8860     512            0
              1         6   16384    8847       0    8847     512            0
              1         7   16384     558       0     558     512            0
              1         8   16384     558       0     558     512            0
              1         9   16384     558       0     558     512            0
              1        10   16384     558       0     558     512            0
              1        11   16384    8849       0    8849     512            0

InayathUlla Sharieff · ‎12-29-2014

%L2MCAST-SLOT3-2-L2MCAST_MAC_FULL_LC: Failed to insert entry in MAC table for FE 7 swidx 19 (0x13) with err (mac table full). To avoid possible multicast traffic loss, disable OMF. Use the configuration CLI: "no ip igmp snooping optimise-multicast-flood"

Such messages mean that the mac address entry was not installed into the MAC table due to a hash function that is used to optimize the MAC table usage.As a consequence, the multicast traffic will be dropped when IGMP snooping is enabled. If you disable IGMP snopping, the traffic will be flooded.

You can check current resources on the card with this command:

attach module 1

show hardware internal forwarding l2 table utilization instance all

The max L2 entries(MAC address) per ASIC/Instance in the F2 module is 16K, there are totally 12 ASIC/Instance per F2 module (each ASIC controls 4 ports, for example instance 0 controls port 1-4), so theoretically, one F2 module can support up to 16k*12=192k MAC addresses. However each ASIC will synchronize the mac address table per VLAN with other ASICs with the same VLAN. For example if ports 1 and 15 both allow vlan 1000, they will both have the mac address table entries for vlan 1000. Thus, if vlan 1000 has 16K mac address table entries, no more entries will be able to be programmed into those two ASICs. You may be hitting such issues.

Therefore, it is suggested to only allow those required VLANs in the trunk port.

Following is a link for the N7K verified scalability:

http://www.cisco.com/en/US/partner/docs/switches/datacenter/sw/verified_scalability/b_Cisco_Nexus_7000_Series_NX-OS_Verified_Scalability_Guide.html#concept_1A55D144F3504CC49B22DD500E766A4E

campbech1 · ‎12-30-2014

Thank you for the information, but that's the same information I already provided in my first post. Never do we come close to the 16k MAC limit, we normally hover around 12k.

I have also gone through and limited VLANs were appropriate to limit as much as possible.

campbech1 · ‎02-10-2015

After opening a TAC case and also escalating the case we've found that the CAM tables fill much quicker than the 16384 limitation on the card. This error message will start displaying around 70 - 80% of the 16384 MAC addresses that the F2 states as a maximum.

Be careful. We thought that since the limitation documented by Cisco was 16384 we would be ok with about 12k clients on these cards, we were very wrong.