MultiLink Trunking

Table 1. MultiLink Trunking product support

Feature

Product

Release introduced

MultiLink Trunking (MLT) / Link Aggregation Group (LAG)

5420 Series

VOSS 8.4

5520 Series

VOSS 8.2.5

VSP 4450 Series

VSP 4000 4.0

VSP 4900 Series

VOSS 8.1

VSP 7200 Series

VOSS 4.2.1

VSP 7400 Series

VOSS 8.0

VSP 8200 Series

VSP 8200 4.0

VSP 8400 Series

VOSS 4.2

VSP 8600 Series

VSP 8600 4.5

XA1400 Series

VOSS 8.0.50

MultiLink Trunking (MLT) is a point-to-point connection that aggregates multiple ports to logically act like a single port with aggregated bandwidth. Grouping multiple ports into a logical link provides a higher aggregate on a switch-to-switch or switch-to-server application.

To include ports as trunk group members of an MLT, you must statically configure the ports.

MLT traffic distribution algorithm

You can use a multilink trunk to aggregate bandwidth between two switches. The MLT algorithm ensures that each packet in a flow does not arrive out of sequence, and that a flow always traverses the same link path.

The hashing algorithm uses the following packet fields and the incoming interface (source) port number to calculate the index to outgoing (destination) port number in an MLT:

Traffic type

Hashing algorithm

IPv4 traffic

Hash Key = [Destination IP Address (32 bits), Source IP Address (32 bits), Source TCP/UDP Port, Destination TCP/UDP port]

IPv4 traffic without TCP/UDP header

Hash Key = [Source IP Address (32 bits), Destination IP address (32 bits)]

IPv6 traffic

Hash Key = [Destination IPv6 Address (128 bits), Source IPv6 address (128 bits), Source TCP/UDP Port, Destination TCP/UDP port]

IPv6 traffic without TCP/UDP header

Hash Key = [Source IP Address (128 bits), Destination IP address (128 bits)]

Mac-In-Mac transit traffic

For VSP 7400 Series:

Hash Key = [Destination IP Address (32 bits), Source IP Address (32 bits), Source Port (8 bits), BackBone Destination MAC Address (48 bits), BackBone Source Mac Address (48 bits)]

For all other platforms:

Hash Key = [Source Port (8 bits), BackBone Destination MAC Address (48 bits), BackBone Source Mac Address (48 bits)]

Layer 2 Non-IP traffic

Hash Key = [Destination MAC Address (48 bits), Source MAC Address(48 bits)]

MultiLink trunking and autonegotiation interaction

To use MLT with the switch, you can have ports running at different speeds. After you use MLT with LACP, LACP dynamically checks for proper speed on all port members. You do not need to have similar physical connection types. After you use autonegotiation with MLT and not LACP, you need to ensure that all ports run at the same speed.

MLT configuration rules

Multilink trunks adhere to the following rules. Unless otherwise stated, these rules also apply to MLT with LACP.

Multilink trunks have the following general features and requirements:

With MSTP or RSTP enabled, ports in the same multilink trunk operate as follows:

MLT with LACP LAG rules

The Link Aggregation Group (LAG) adheres to the following rules: