Informing the IBM Community

Aggregated Ethernet – Faster and more resilient networking


Have any of you ever lost connectivity to your server because someone accidentally disconnected the wrong cable? It is so annoying as in many cases even if the cable was plugged back in you still had to answer a message on QSYSOPR to tell your system that it’s OK to start using the network connection again.

IBM has had a solution for this since v5.4 called Virtual Ethernet but this was not ideal for everyone as you had to allocate three IP addresses (one for each of the physical ports and one for the virtual port they were pretending to be). This made routing more complex as you could get packets addressed from either of the physical ports. Routers don’t like that especially when neither of these match the address the original packet was sent to.

Resilient networking made easy

IBM addressed this back in 7.1 TR3 and since then we have had the option to use Aggregated Ethernet which allows us to set up the resilience in the Ethernet line description, you simply tell it to use more than one Ethernet port in the resource section.

That’s it, no extra IP addresses, no need to configure it via a GUI or special API, just create a new line description, allocate the IP address to it and VOILA!

Now when someone unplugs the wrong cable your IBM i server simply shrugs and sends the network traffic down another Ethernet port.  Better yet, when the other cable is plugged back in, it automatically comes back online, no messages to answer.

ProTip:  If you have redundant Ethernet switches in your rack, plug one of these into each switch and then you are protected against switch failures as well.

Networking just got faster

Another bonus is that just as the name “aggregated” implies, these lines are used in tandem. IBM i automatically load balances between the ports (Virtual Ethernet did not do this, it was a failover technology at best) this means that if you use two Ethernet ports then you just got a 2Gbit Ethernet link instead of a 1Gbit.

In my experience, most companies buy a server with two Ethernet cards (just in case one of them has an issue) and these Ethernet cards usually have four ports on them.  This means you could configure all 8 ports and you just got an 8Gbit Ethernet connection to your server for free!

How do you configure it?

As I mentioned earlier, you do this in the Ethernet Line Description, so you start by creating a new Ethernet Line using a command like:
AGGRSCL(CMN03 CMN04) TEXT(‘Ethernet using top (T1) ports of both cards’)              

Once you have created it, you need to vary it on with a command like:

Then use the configure TCP command CFGTCP to allocate this IP address to your new Ethernet line.

NOTE:  If you plan to reuse your existing IP address, you will need a little downtime while you reassign the IP address from the other Ethernet line to the new aggregated one.

How do you know your Ethernet resource names?

The resource names for the Ethernet ports vary from system to system but it is easy enough to find them using the work with hardware resource command:

In the example below we can see that the system has two four port Ethernet cards.
CMN04, 06, 07 & 10 belong to one card and CMN03, 05, 08 & 09 to the other.

Protip: If you want to know which card and port number each of these CMN resources physically belongs to then place a 7 next to them to display the resource details.

In the example above we can see that CMN04 is T1 (top) port of the Ethernet card in slot C11

How can you tell which ports are up?

One of the problems with any resilience technology is that you cannot easily tell whether one part of it is broken. Just by using it, it still works, that is the point.

So, if you want to check that all the ports in your aggregated link are up you need to display the Ethernet Line Description’s status, you can do this with a command like:


In this case we can see that CMN03 is UP and working fine but CMN04 is down and it is time for you to go and check the cables!


Nice to see you

Please come and join us at our main event of the year,
i-UG’s International i-Power Show at the MK Dons Stadium in Milton Keynes on Tuesday 13th & Wednesday 14th June.We will then be back in my home town of Wolverhampton on Thursday 2nd November.

More details and a booking form are available at our website


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