iCan Blog Archive

Support for Ethernet Link Aggregation, as previously featured in the i Can blog “Ethernet Link Aggregation in IBM i” and the tip IBM i Aggregate Ethernet Lines on IBM developerWorks was added to IBM i in the 7.1 release. An aggregate line description combines multiple physical Ethernet ports. The line description can then be used for TCP/IP configuration just like any other line description, but the incoming and outgoing traffic will be spread among the available ports. As a side benefit, the line description will remain active as long as any of the aggregated ports are available.

Link aggregation is a great redundancy solution for IBM i partitions that have multiple physical Ethernet ports available, all of which can be connected to a single Ethernet switch that has support for link aggregation. However, as some have commented on those articles, link aggregation does not work with virtual Ethernet ports that are connected to the internal Ethernet switch of the Power Hypervisor. This means that it is not useful to partitions that connect to the network via a Shared Ethernet Adapter (SEA) in a Virtual I/O Server (VIOS) partition or via an Ethernet layer-2 bridge provided by an IBM i partition.

SEA Failover

One solution is to use a pair of VIOS partitions, each with an SEA bridged to the physical network, and to have the Shared Ethernet Adapters configured for failover, which provides redundancy without any additional configuration in the bridged partitions.

Virtual IP Addressing

Bridged IBM i partitions can get Ethernet redundancy from the existing Virtual IP Address (VIPA) support provided by IBM i. Specifically, I will describe solutions based on VIPA Proxy ARP.

Unlike other IP interfaces, a VIPA is not bound to a line description. Instead, the user chooses a list of existing IP interfaces that will serve as proxies to connect the VIPA to the network; these are called its preferred interfaces. They are kept in priority order, and the VIPA will be serviced by the first active interface in the list.

Physical Interface With Virtual Backup

Given this, we can build a setup that will default to using a physical Ethernet port but will use a virtual Ethernet port instead if the physical port becomes unavailable. For this example, we assume that the IP addresses below are all available and appropriate to the system’s network, the physical Ethernet port is managed by line description PHYSETH, the virtual Ethernet port is managed by line description VIRTETH, and that VIRTETH is bridged to the physical network by a VIOS SEA or IBM i layer-2 bridging. We create an IP interface on each port, then create a VIPA, preferring the physical interface over the virtual Ethernet interface.


Once all three interfaces are started, the VIPA should be accessible from the network via PHYSETH; if PHYSETH fails, then VIRTETH will take over.

When each partition has a physical interface available, this can be a great solution. Each partition has control over its own physical Ethernet resource, and a single bridging support partition can provide a backup for all of the other partitions simultaneously.

For direct use, this requires that the first line description in the preferred interface list will fail if it can’t access the network (for example, if the cable is pulled or the Ethernet adapter or switch fails for some reason). This is true for IBM i physical Ethernet ports (and for aggregate line descriptions) but not true for bridged virtual Ethernet ports (which are not connected directly to the network). Thus, this solution requires changes if we want to support failover between two virtual Ethernet ports.

Virtual Interface With Virtual Backup

This can be done by writing a program that does some level of direct health check for each preferred interface and rearranges the preferred interfaces so that the first is always working. Attached below is an example CL script that monitors each preferred interface to see that it can ping a specific remote IP address, and changes the priority order if the first interface becomes unavailable while the second is available.   Download 121912 monitor.

Given this, we can fail over between two virtual Ethernet ports. This enables more complicated configurations that provide Ethernet redundancy for the clients without setting up any failover between bridging partitions.

For example, consider a system with several IBM i partitions, two of which have physical Ethernet resources. In each of those partitions, we configure a layer-2 bridge: the first bridge through one Power Hypervisor virtual LAN (VLAN), and the second through a different VLAN. Then, in each of the other IBM i partitions, we configure two virtual Ethernet interfaces and VIPA as above, with a virtual-to-virtual failover script. In half of those partitions, we choose the first bridge as primary; in the other half, we make the second bridge primary.

In this system, all of the physical Ethernet resources are being used, and the physical network is unaware of anything in the configuration. If one bridge stops working for any reason, the half of the partitions that were using it will start using the other bridge. This can provide acceptable service on systems with several IBM i partitions but not a lot of available physical Ethernet resources, at the cost of some additional configuration work.

In short, IBM i and Power Systems network and virtualization technologies give users the tools they need to meet their performance and redundancy targets. We are always looking for ways to improve our networking options as well.

This week’s blog was written by Colin DeVilbiss. Colin develops Communications and Virtual I/O support for IBM i in Rochester, MN. Thanks, Colin!

This blog post was edited to correct broken links on March 2, 2020.

This blog post was originally published on IBMSystemsMag.com and is reproduced here by permission of IBM Systems Media.