Summary
SLX 9740 or Extreme 8820 switches configured as Multi-Chassi Trunking (MCT) peers in an IP Fabric environment will incorrectly flood IGMP Multicast packets, which may cause a high CPU usage and excess traffic in the network, resulting in network impact
Impact
This can cause severe network impact.
Products Affected
SLX9740 and Extreme 8820
Software Affected
SLX-OS 20.5.3b, SLX-OS 20.6.1b, SLX-OS 20.6.2, SLX-OS 20.6.2a Releases
Symptoms
The attached downstream L2 switches may see high CPU utilization while handling received IGMP packets. The MCT peer ICL links shall be at full line rate for transmit and receive. Additionally, the downstream switch interface statistics may see an unexpectedly high rate of multicast receive packets and all Switch LEDs may flash or remain solid depending on the switch LED behavior.
Workaround
IGMP Snooping may be configured on the Leaf nodes to eliminate flooding in the Network. This will not mitigate the looping of IGMP packets on MCT ICL links. Alternatively, one of the MCT peers can be put into Maintenance Mode to break the loop on the ICL.
Below example is how to enable IGMP snooping on a particular VLAN:
Leaf2# conf t
Entering configuration mode terminal
Leaf2(config)# vlan 15
Leaf2(config-vlan-15)# ip igmp snooping enable
Leaf2(config-vlan-15)#
In lieu of these mitigations, simply running SLX-OS 20.5.3a, 20.6.1a, or earlier releases will avoid this issue.
Solution
Upgrade the SLX-OS version to 20.5.3c, 20.6.1c, or 20.6.2b when it becomes available.
Please see the full field notice article here for more information and updates.
