Etherchannel mixed-speed backup

[usige]

Has anyone had any experience using mixed-speed adapters with EtherChannel backup adapters?

I have a p570 that was built with 2 LPARs. Each lpar has a single Gig-E fiber card with no backup adapters. We are out of slots in all 4 building blocks and I have been asked to fix the single point of failure. We were just going to use one of the dual port copper adapters in the building blocks, but I have just been told that this system is in a switch network with no copper in it at all. The network guys might be able to scrounge up a 10/100 switch module, but what issues has anyone seen with this config (i.e. 1 Gb primary w/ 100 Mb backup). I know IBM says it's not supported, but likely will work.

Any help appreciated.

Usige

 

[DukeSSD]

It won't work for at least the two following reasons:
1. The adapters MUST be the same speed / duplex.
2. THE switch - note the use of THE, as in one, you cannot connect your fibre AND copper adapters to ONE switch - must be etherchanel capable.

Where to go from here?

You could investigate etherchannel on VIO.
Create two (no single point of failure) VIO servers, with one Gigabit adapter in each.
Serve the (now virtual) adapters to each of your LPARs.
Etherchannel the two virtual adapters on each LPAR.

NB: I have no idea if you can etherchannel virtual ethernets but it is the only way I can think of to have no single point of failure with two LPARs requiring Gigabit ethernet and only two adapters to play with.

 

[p5wizard]

The adapters in an etherchannel group must be on the same switch (link aggregation), the backup adapter, which IMHO is configured in case all the etherchannel ports fails (e.g. the switch the ports are on is dead) should NOT be on that same switch for obvious reasons.

I'm not sure if the backup adapter has to be the same type or speed as the link-aggregation ports, but falling back from two aggregated gigabit ports to one 100mbit port is quite a leap!

The VIO solution is valid also, but you need to be able to run an extra two LPARs (CPU, memory, disk adapter...)


HTH,

p5wizard

 

[DukeSSD]

Sorry, didn't read you post while I was awake ;-)

Good job p5wizard is on the ball again.

As you say, IBM say it is not supported but they also say "Important: Mixing adapters of different speeds in the same EtherChannel, even if one of them is operating as the backup adapter, is not supported. This does not mean that such configurations will not work. The EtherChannel driver makes every reasonable attempt to work even in a mixed-speed scenario." at the bottom of this page:

http://publib.boulder.ibm.com/infoc...mn/doc/commadmndita/etherchannel_adapters.htm

IBM "do not support" a lot of things that seem to work perfectly well, it just meant they have not considered them worth testing to the same vigorus level as the things they do support.

I found the above from a link on this page:

http://publib.boulder.ibm.com/infoc...madmn/doc/commadmndita/etherchannel_intro.htm

However this page suggests the etherchannel will not failback when the primary adapter connection problem is resolved if the failover was due to a ping failure:

http://publib.boulder.ibm.com/infoc...oc/commadmndita/etherchannel_backupconfig.htm

Makes you wonder if the ping test is worth configuring. I guess you need to test it in your environment to decide if you want to use it as a solution, you'll probably need to test for both ping failures and connectivity problems, I guess failing adapters is a bit harder to test though.

 

[sbix]

I am not sure to have catched the problem... but:
As wisely p5wizard wrote, if you would like to have 2 or more adapters in the primary channel THEY should run at the same speed.
If you don't need link aggregation but you only need to fix up the SPOF so you should add a backup channel to the etherchannel.
The backup adapter should reside on a different switch (otherwise you aren't solving the SPOF problem) and could run a different speed.

 

[unixfreak]

usige: Which version of AIX? From 5.2 I believe, AIX no longer does etherchannel backup but instead has a fall-back channel for the primary etherchannel.

I don't understand why IBM says it's not supported as it will definately work and I would even have thought taht IBM changed the setup for this exact reason.

Go ahead and set it up, connect it to two different switches and it will work

Cheers