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z/VM Virtual Switch Link Aggregation


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Link Aggregation (LAG) support for the virtual switch was first introduced in z/VM starting with z/VM Release 5.3. The virtual switch configured in Ethernet mode supports the aggregation of multiple OSA-Express features for external LAN connectivity. By supporting IEEE 802.3ad Link Aggregation, the combination of multiple OSA-Express features appears as one large link. The deployment of this type of configuration increases the virtual switch bandwidth and provides near seamless failover in the event that a port becomes unavailable.
This support provides the ability to aggregate physical OSA-Express features for use by a single virtual switch (Exclusive mode) or to shared by multiple virtual switches (Multi-VSwitch LAG) mode.


Both Exclusive and Multi-VSwitch LAG configurations provide the same industry standard IEEE 802.3ad Link Aggregation protocol support with an external partner switch. Both of these LAG configurations are completely transparent to z/VM guest hosted by either a simulated NIC connected directly to the VSwitch or a HiperSockets Bridge NIC connection.

The primary difference between these two configurations is the LAG sharing characteristics. A LAG (Link Aggregation Group) is exclusively used by a single virtual switch or shared by multiple virtual switches. Some comparisons between the two LAG deployments:

Exclusive LAG vs Multi-VSwitch LAG
Comparison Item Exclusive LAG Multi-VSwitch LAG
Application Simpler for a single system LAG. Multiple VSwitch access to the same network.
OSA-Express Resources Dedicated networking ports service one VSwitch. Volume of network traffic requires high bandwith and throughput. Shared resources result in a reduction of physical ports that are more fully utilized.
Network Access Network access is limited to a single z/VM system and VSwitch. Access to the network can span multiple VSwitches within a z/VM system and across many z/VM systems within the CEC.
Port Group Management Must be managed (configuration) on the z/VM system that the port group was defined. Can be managed on any z/VM system within the same IVL domain.
Physical Switch Partner Each exclusive LAG requires a separate and distinct physical LAG to be configured and managed on the partner switch. Only a single LAG configuration required to support a Multi-VSwitch LAG configuration. The single physical LAG provides network connectivity and high availability for all z/VM systems within the same CEC.
z/VM Support z/VM 5.3 or higher. z/VM 6.3 with APARS VM65583 and PI21053.
Hardware Support z9 EC and z9 BC processors or higher and OSA-Express2 or higher. OSA-Express4S & OSA-Express5s support for Multi-VSwitch Link Aggregation requires an IBM z13 with Driver 22H with a minimum Bundle level of S11a with MCL N98805.007.

For more information about Link Aggregation with the z/VM Virtual Switch, see:



Hints and Tips

Here are some examples of configuration errors that may occur and how to detect and correct them:

Here are some Multi-VSwitch LAG best practices:

  • It is recommended that the IVL network bandwith match the bandwidth of the links within the LAG port group. For example, if the port group is composed of 10G OSA-Express features, then the IVL should also be deployed with 10g OSA-Express features. This will insure that the IVL network will have enough bandwith to support potential failover situations.
  • For configurations that deploy one or two VSwitches per z/VM system, the two controllers provided by z/VM will be sufficient. Even though a given controller can service more than one VSwitch, optimum operational performance is achieved when there is a one to one pairing of VSwitch to controller. For more information see z/VM Connectivity chapter "Virtual Switch Controller Configuration Strategy" in the Library.


Please direct questions, comments and feedback regarding z/VM's Link Aggregation support or any of the information on this page to either:

Sue Farrell
z/VM Development
farrells@us.ibm.com
Rick Tarcza
z/VM Development
tarcza@us.ibm.com

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