Use the information in this section to understand the considerations and guidelines while configuring link aggregation into your network.
Note
Static MAC is not supported against SMLT.
After you configure MLT with LACP, you must enable the aggregation parameter. After you enable the aggregation parameter, the LACP aggregator maps one-to-one to the specified multilink trunk.
The following lists the steps that are involved to configure MLT with LACP:
Assign a numeric key to the ports you want to include.
Configure the LAG for aggregation.
Enable LACP on the port.
Create an MLT and assign to it the same key as in step 1.
The multilink trunk with LACP only aggregates ports whose key matches its own.
The newly created MLT with LACP adopts the VLAN membership of its member ports after the first port is attached to the aggregator associated with this LAG. After a port detaches from an aggregator, the associated LAG port deletes the member from its list.
After a multilink trunk is configured with LACP, you cannot add or delete ports manually without first disabling LACP. You can add or remove VLANs to an MLT without manually disabling LACP.
The following list identifies expected configuration behavior for all platforms when you add VLANs to an LACP-enabled MLT:
If only one port is part of the MLT/LAG, use the vlan members add <1-4059> {slot/port[/sub-port][-slot/port[/sub-port]] [,...]} command to add newer VLANs to the LAG.
If two or more ports with several VLANs are active members of the MLT/LAG, you must use the mlt <1-512> vlan <1-4059> command to add new VLANs.
If at least one port is active on the MLT/LAG (LACP), and you need to add a second port that is physically up and has the same key, you must use the mlt <1-512> vlan <1-4059> command. The port values must match otherwise the new port enters the churn condition.
If the switch displays a persistent error that you cannot change the port VLAN membership, you must correct the configuration during a maintenance window:
Shutdown the ports.
Disable LACP on the ports.
Add all VLANs to the port members being aggregated.
Enable LACP on the ports.
Enable the ports.
To enable tagging on ports belonging to a LAG, disable LACP on the port, and then enable tagging and LACP on the port.
If you enable Open Shortest Path First (OSPF) routing on a port, do not set the LACP periodic transmission timer to less than 1 second.
You can configure Split MultiLink Trunking (SMLT) with MLT, or with MLT with LACP. Follow these guidelines while you configure SMLT with LACP:
If you configure LACP for SMLT, you must configure the same LACP smlt-sys-id on both sides. After you configure the LACP system ID for SMLT, configure the same LACP smlt-sys-id on both aggregation switches to avoid loss of data. Configure the LACP smlt-sys-id to be the base MAC address of one of the aggregate switches, and include the MLT-ID. Configure the same system ID on both of the SMLT core aggregation switches.
If you use LACP in an SMLT square configuration, the LACP ports must have the same keys for that SMLT LAG; otherwise, the aggregation can fail if a switch fails.
If an SMLT aggregation switch has LACP enabled on some of its multilink trunks, do not change the LACP system priority.
After you configure SMLT links, set the multicast packets per-second value to 6000 pps.
To avoid traffic loss when an SMLT goes down during a CP switchover, distribute multiple SMLT links across different slots.
To avoid unnecessary processing, do not enable LACP on vISTs . Use VLACP if an optical network between the SMLT core switches requires a failure detection mechanism.
Using the LACP smlt-sys-id enables you to use a third-party switch as a wiring closet switch in an SMLT configuration. This enhancement provides an option for the administrator to configure the SMLT Core Aggregation Switches to always use the system ID. In this way, the SMLT Core Aggregation Switch always uses the same LACP key regardless of the state of the SMLT Core Aggregation Switch neighbor (or the vIST link). Therefore no change in LAGs must occur on the attached device regardless of whether the device is a server or a third-party switch. This situation does not affect edge switches used in SMLT configurations. The actor system priority of LACP_DEFAULT_SYS_PRIO, the actor system ID the user configures, and an actor key equal to the MLT-ID are sent to the wiring closet switch. Configure the system ID to be the base MAC address of one of the aggregate switches along with its MLT-ID. The administrator must ensure that the same value for the system ID is configured on both of the SMLT Core Aggregation Switches.
You can configure the LACP smlt-sys-id used by SMLT core aggregation switches. After you set the LACP system ID for SMLT, configure the same LACP smlt-sys-id on both aggregation switches to avoid the loss of data.
The LACP System ID is the base MAC address of the switch, which is carried in Link Aggregation Control Protocol Data Units (LACPDU). If two links interconnect two switches that run LACP, each switch knows that both links connect to the same remote device because the LACPDUs originate from the same System ID. If you enable the links for aggregation using the same key, LACP can dynamically aggregate them into an MLT LAG.
If SMLT is used between the two switches, they act as one logical switch. Both aggregation switches must use the same LACP System ID over the SMLT links so that the edge switch sees one logical LACP peer, and can aggregate uplinks towards the SMLT aggregation switches. This process automatically occurs over the vIST connection, where the base MAC address of one of the SMLT aggregation switches is chosen and used by both SMLT aggregation switches.
However, if the switch that owns that Base MAC address restarts, the vIST goes down, and the other switch reverts to using its own Base MAC address as the LACP System ID. This action causes all edge switches that run LACP to think that their links are connected to a different switch. The edge switches stop forwarding traffic on their remaining uplinks until the aggregation can reform (which can take several seconds). Additionally, after the restarted switch comes back on line, the same actions occur, thus disrupting traffic twice.
The solution to this problem is to statically configure the same LACP smlt-sys-id MAC address on both aggregation switches.
Note
The SMLT ID is always the same as the MLT ID. For instance, both sides can have an MLT 10, but once SMLT is enabled on both sides it will function as an SMLT. Until SMLT is enabled on both peers however, it will function as a normal MLT.
Only the physical link state or its LACP peer status affects LACP module operation. After a link is enabled or disabled, an LACP module is notified. The MSTP or RSTP forwarding state does not affect LACP module operation. LACPDUs can be sent if the port is in an MSTP or RSTP blocking state.
Unlike legacy MultiLink trunks, configuration changes (such as speed and duplex mode) to a LAG member port are not applied to all member ports in the multilink trunks. The changed port is removed from the LAG and the corresponding aggregator, and the user is alerted that the configuration is created.
Important
Link Aggregation Control Protocol, as defined by IEEE, is a protocol that exists between two bridge endpoints; therefore, the LACP PDUs are terminated at the next Server Provider (SP) interface.
Use Virtual Link Aggregation Control Protocol (VLACP) for all SMLT access links configured as MultiLink Trunks to ensure both end devices can communicate. The switch does not support LACP and VLACP on the same links simultaneously.
VLACP for SMLT also protects against CPU failures by causing traffic to switch or reroute to the SMLT peer if the CPU fails or stops responding.
The following table provides the values for VLACP in an SMLT environment:
|
Parameter |
Value |
|---|---|
|
SMLT access |
|
|
Timeout |
Short |
|
Timer |
500ms |
|
Timeout scale |
5 |
|
VLACP MAC |
01:80:C2:00:00:0F |
|
SMLT core |
|
|
Timeout |
Short |
|
Timer |
500ms |
|
Timeout scale |
5 |
|
VLACP MAC |
01:80:C2:00:00:0F |
|
vIST |
|
|
Timeout |
Long |
|
Timer |
10000 |
|
Timeout scale |
3 |
|
VLACP MAC |
01:80:C2:00:00:0F |
If you want to modify SMLTs that contain network-to-network interface (NNI) ports, do the modification during maintenance windows. Otherwise, if you create or delete SMLTs that contain NNI ports running MSTP, IS-IS adjacencies that connect to those ports can bounce even if the SMLT is not used.