This week’s blog was written by Colin DeVilbiss, an IBM software engineer. He works mostly on communications device drivers for IBM i in the development lab in Rochester, Minn. Thanks, Colin.
In 7.1 Technology Refresh 3, IBM i added the capability to aggregate multiple Ethernet ports in one Ethernet line description. An aggregated line description offers two significant benefits over a single-resource line description: improved reliability and parallel throughput.
An aggregate line description stays available as long as at least one of its aggregated Ethernet ports is working; for example, if four Ethernet ports are aggregated in one line description, the line description will remain active even if three of those Ethernet ports lose their link, and all of the workloads will continue running.
In addition, workloads with multiple parallel TCP connections or with multiple remote clients will be able to take advantage of having multiple physical connections to the same IP address, increasing throughput with each available resource. For example, if four Ethernet ports are aggregated, each running at one gigabit per second, the aggregate could support up to four gigabits of throughput across multiple connections.
Link aggregation gives IBM i administrators a new tool to improve their network configurations, taking advantage of underutilized resources and adapting to meet new demands in the business.
For example, if a partition has a two-port Ethernet adapter, but IBM i is only using one port, it's straightforward to aggregate the two ports together and have additional protection against a failure in a cable, switch port, or port on the adapter, while potentially doubling throughput on some workloads, potentially with no additional hardware cost.
Likewise, if an IP interface is getting close to saturating its capacity, link aggregation lets the administrator scale the underlying line description's capacity incrementally, without changing technology for the individual links. That is, if one gigabit per second isn't enough, link aggregation can provide two gigabits per second of potential throughput without needing to jump to 10-gigabit-per-second infrastructure.
Creating an Aggregate Line Description
The main requirements for creating an aggregate line description are:
- An IBM i partition at 7.1 with Technology Refresh 3 and its PTF group loaded
- Two or more gigabit-capable physical Ethernet resources in the partition
- A switch that supports link aggregation (sometimes under the names “trunking” or “teaming”)
At the switch, the corresponding ports must be configured into a static aggregate; switches vary, and each manufacturer has its own configuration commands and interfaces, so check there.
Assuming that the desired Ethernet resources are CMN02 and CMN03, creating the aggregate line description is as simple as:
CRTLINETH LIND(ETHAGG) RSRCNAME(*AGG) AGGPCY(*ETHCHL *SRCDESTP) AGGRSCL(CMN02 CMN03)
That is, create a new Ethernet line description
- named ETHAGG
- using link aggregation instead of a single hardware resource
- using static assignment of resources (the only supported policy in TR3)
- assigning outgoing frames to ports based on the source and destination IP addresses and TCP ports (which is likely to provide the best “spreading” of traffic across the ports)
- aggregating CMN02 and CMN03
Varying the line description on will bring all of the ports active, and DSPLIND can be used to see the status of each port. TCP/IP can use the line description just like any other Ethernet line description.
For more details, see the Ethernet on System i topic in the IBM Information Center.
In short, Ethernet Link Aggregation lets 7.1 TR3 users make better use of their Ethernet resources, potentially improving the reliability and performance of their network workloads without purchasing any additional hardware.