Design Reference

end-to-end perspective. If a particular link does not receive VLACP PDUs, the platform shuts
the link down after the expiry time-out occurs (time-out scale x periodic time). As a result of this
action the ports stay in a disabled state.
MultiLink Trunking
Use MLT to provide link-layer redundancy. You can use MLT to provide alternate paths around
failed links. When you configure MLT links, consider the following information:
• The device supports 24 MLT aggregation groups.
• Up to 8 ports can belong to a single MLT group.
MLT and LACP groups and port speed
Ensure that all ports that belong to the same MLT or LACP group use the same port speed, for
example, 1 Gbps, even if you use Auto-Negotiation. The software does not enforce this requirement.
Avaya recommends that you use Custom Auto-Negotiation Advertisement (CANA) to ensure proper
speed negotiation in mixed-port-type scenarios.
To maintain Link Aggregation Group (LAG) stability during failover, use CANA: configure the
advertised speed to be the same for all LACP links. For 10/100/1000 ports, ensure that CANA uses
one particular setting, for example, 1000-full or 100-full. Otherwise, a remote device can restart
Auto-Negotiation and the link can use a different capability.
Each port must use only one speed and duplex mode; all links in the up state are guaranteed to
have the same capabilities. If you do not use Auto-Negotiation and CANA, you must use the same
speed and duplex mode settings on all ports of the MLT.
Platform-to-platform MLT link recommendations
Avaya recommends that you connect physical connections in platform-to-platform MLT and link
aggregation links in a specific order. To connect an MLT link between two platforms, connect the
lower number port on one platform with the lower number port on the other platform. For example, to
establish an MLT platform-to-platform link between ports 1/1 and 1/4 on platform A with ports 1/1
and 1/4 on platform B, do the following:
• Connect port 1/1 on platform A to port 1/1 on platform B
• Connect port 1/4 on platform A to port 1/4 on platform B
In VSP 4000, brouter ports do not support MLT. You cannot use brouter ports to connect two
platforms with an MLT. An alternative is to use a Virtual Local Area Network (VLAN). This
configuration option provides a routed VLAN with a single logical port or MLT. For more information
about MLT configuration, see Avaya Virtual Services Platform 4000 Series Configuration — Link
Aggregation and MLT, NN46251–503.
MLT and spanning tree protocols
The implementation of 802.1w (Rapid Spanning Tree Protocol—RSTP) and 802.1s (Multiple
Spanning Tree Protocol—MSTP), provides a path cost calculation method. The following table
provides the path costs associated with each interface type:
Link redundancy
42 Network Design Reference for Avaya VSP 4000 Series January 2015
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