Configuration Guide User guide

FastIron Configuration Guide 849
53-1002494-02
Layer 2 behavior with MCT
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Syntax: show mac mdup-stats
Syncing router MAC addresses to peer MCT devices
The MCT cluster device uses a router MAC address to identify the packets that are addressed to the
switch. Such packets may be received by a peer cluster device. The peer device switches packets
over the ICL to the local MCT device to be routed properly.
Dynamic trunks
MCT client creates a single dynamic trunk group towards the MCT cluster devices. The dynamic
trunk group consists of two trunk groups, each of which is configured on one of the MCT devices. A
dynamic trunk group runs Link Aggregation Control Protocol (LACP).
For the two dynamic trunk groups of the MCT to behave as a single trunk group from the MCT
client’s perspective, both of the dynamic trunk groups should have the same LACP system ID and
key, referred to as the MCT system ID and MCT key.
The LACP system ID in the FSX product normally comes from the port MAC address. To support
LACP over MCT, it is necessary to obtain the ID in another way. To do so, MCT uses a pre-defined
algorithm.
NOTE
Each MCT cluster device has a unique cluster ID, and one MCT client ID. The LACP key is predefined
from the client ID and cluster ID. The user cannot change the key.
MCT does not involve stacking, and control protocol synchronization is minimal. The LACP runs
independently on the cluster devices.
Port loop detection
Loop detection can be used in an MCT topology to detect Layer 2 loops due to misconfigurations,
for example, on the client side when MCT links are not configured as trunk links on the
MCT-unaware client.
In MCT, the ICL link should be up at all times to prevent the cluster from going down. They should
not be shut down when a loop is detected in a network. Instead other available ports (CCEPs)
should be shut down. If loop detection BDPUs are received on the ICL port, then instead of shutting
down the ICL links, all the CCEPs will be error-disabled and the user will be notified with the
following log message.
Loop-detection:Packet received on ICL port <port_number> for vlan
<vlan_id>.Errdisable CCEPs.
Strict mode loop detection can be enabled on ICL ports. This is because in strict mode, a port is
disabled only if a packet is looped back to that same port. Strict mode overcomes specific
hardware issues where packets are echoed back to the input port. This process assists in detecting
hardware faults on ICL ports.
Loop-detection can be enabled on MCT and non-MCT VLANs simultaneously. There is no change in
loop detection behavior when enabled on non-MCT VLANs.