Layer 2 Behavior with MCT

Layer 2 behavior when MCT is configured includes MAC operations, dynamic trunks, port loop detection, and multicast snooping over MCT.

MAC Database Update

Each MAC address is advertised with a cost. Low-cost MAC addresses are given preference over high-cost addresses. MAC addresses that are learned locally are given the highest priority, or the cost of 0, so that they are always selected as the best MAC addresses.

If a MAC address moves from a CCEP port to a CEP port, a MAC move message is sent to the peer, and the peer moves the MAC address from its CCEP ports to the ICL links.

If two MAC addresses have the same cost, the address learned from the lower RBridge ID wins and is installed in the forwarding database (FDB).

MAC addresses in MCT VLANs are updated across the cluster using MAC Database Update Protocol (MDUP) messages.

Cluster MAC types

Cluster Local MAC (CL): MAC addresses that are learned on the MCT VLAN and on CEPs locally. MAC addresses are synchronized to the cluster peer device and are subject to aging.

Cluster Remote MAC (CR): MAC addresses that are learned by way of MDUP messages from the peer device (CL on the peer). The MAC addresses are always programmed on the ICL port and do not age. The CR is deleted only when the CL is deleted from the peer. An MDB entry is created for these MAC addresses with a cost of 1 and is associated with the peer RBridge ID.

Cluster Client Local MAC (CCL): MAC addresses that are learned on the MCT VLAN and on CCEPs. The MAC addresses are synchronized to the cluster peer device and are subject to aging. An MDB entry with a cost of 0 is created for these addresses, and they are associated with the client and cluster RBridge IDs.

Cluster Client Remote MAC (CCR): MAC addresses that are learned by way of MDUP messages from the peer device (CCL on the peer). The MAC addresses are always programmed on the corresponding CCEP and do not age. The CCR is deleted only when the CCL is deleted from the peer. An MDB entry with the cost of 1 is created for the MAC addresses, and they are associated with the client and peer RBridge IDs.

Cluster Multi-Destination Local MAC (CML): A static MAC entry that is configured locally on the MCT VLAN. Any static MAC address configured on the MCT VLAN will have the ICL added by default. Consequently, the address automatically becomes a multi-destination MAC entry. The local configuration generates a local MDB. Any CML entry can still have up to two associated MDBs, one local and one remote. The remote MDB contains the remote static configuration for the same MAC and VLAN. If the dynamic MAC and static configuration coexist, the dynamic MAC address is removed, whether it is learned locally or from MDUP. The port list of a CML entry contains an ICL port, the client ports from the client list in the local configuration and the remote configuration (if it exists), and all locally configured CEPs.

Cluster Multi-Destination Remote MAC (CMR): A static MAC entry that is configured on the MCT VLAN on the peer side and has no associated local configuration. The CMR entry has only the information from the remote MDB. The port list of a CMR entry contains an ICL port and all the client ports from the client list in the remote configuration. When there is a local configuration for the same entry, the CMR is converted to the CML.

MAC aging

Only the local MAC entries are aged on a cluster device. The remote MAC address entries are aged based on explicit MDUP messages only.

The remote MAC addresses learned through MDUP messages are dynamic addresses, but they never age from the FDB.

MAC flush

If the CEP is down, the MAC addresses are flushed, and individual MAC deletion messages are sent to the peer device.

If the local CCEP is down, the MAC addresses are flushed locally, and individual MAC deletion messages are sent to the peer device.

If the clear mac command is used, the MDB and FDB are rebuilt.

If the clear mac vlan command is used, the local MDB and FDB are rebuilt for the VLAN.

MAC movement happens normally on the local device.

In cases of CEP to CCEP MAC movement, the MAC movement occurs normally on the local device, and all the other MDBs from the peer are deleted to create a new local MDB.

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.