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Link aggregation & spof's conversations

Trusted Contributor

Link aggregation & spof's conversations

Mike asked a fairly simple question and got a lot of great answers:






   I'm looking for some advice on whether two server links can be aggregated into a single channel with each link going to a port on a different switch (for resilience). In the past I understood that products that support link aggregation, such as HP-UX APA, required links to connect to a single switch. However I gather that some implementations, such as CISCO Etherchannel, can aggregate across switches (depending on the switch model?).


So, nowadays, can we aggregate links across switches on HP-UX? What about LINUX and Windows on ProLiant rack and blades? Are there any gotchas I should be aware of?


I know nothing about networks so apologies if the above is naive.






Some great responses:




From Thierry: 

Hi Michael,


I can answer only for HP-UX :)


This is called Split Trunking:


See "Split Trunking Support with HP Auto Port Aggregation" white paper: 



Supported on:

    - Nortel switches that support SMLT (Split Multi-Link Trunking) ie Nortel 6000 Passport

      Only LACP mode is supported.

    - Cisco StackWise cross-stack EtherChannels (ie: 3750) you can use both manual mode and LACP mode link aggregation PAgP is not supported. 

For HPN Procurve, it seems that the functionality exists but have not been tested yet with APA.


Hope this helps,


From Gergely: 

... and HP Networking, featured called IRF (can be found in almost every switch in A-series)


From Vincent: 

Let me try to paint a fuller picture...


Pretty much all HP servers and the OSes we support can do link aggregation one form or another: HP-UX has been covered already. Windows has it in HP's NIC teaming driver, Linux has bonding mode 4, vSphere has "route based on IP hash", XenServer I'm not sure but probably can benefit from the Linux bonding driver. No clue about OpenVMS or NonStop.


Then it all depends on the switches that the server connects to, whether they can act as a single logical switch from a link aggregation point of view. The goal is that the server doesn't even "know" that it's connected to different physical switches. Pretty much all major vendors have that technology nowadays (only compatible between 2 or more switches of the same brand/model). HP Networking has it as mentioned previously (IRF from the H3C side, there's also a distributed trunking feature from the ProCurve side). Cisco has 2: VSS on the Catalyst line, vPC on the Nexus line. Avaya has SMLT (from Nortel). Juniper has Virtual Chassis.


Gotchas to be aware of: not all switch models of a vendor support this. If a switch model supports it, it may be only with recent firmware versions. Do check. Then it might support static link aggregation, dynamic link aggregation, or both, which can have an influence on whether it works with the OS you're considering in the server.


And finally, specifically on c-Class blade interconnects:

Passthru: depends on the upstream switch Virtual Connect: no ProCurve 6120: no Cisco 3020: no Cisco 3120: yes, VSS

BNT: not sure. They've got something called SmartConnect that I think can do this, and they seem to sell it directly as a license upgrade for HP switches, but I don't think HP has ever offered it, and now with BNT part of IBM...

Hope that helps.


From Mark: 

Interesting discussion.


I've not kept up switch tech, but it appears things have improved. If you could have collaborative link aggregation over switches then that would be cool, although it sounds to me like you need to have the same switch infrastructure throughout the estate (where LACP was open).


So right now, without collaborative Link aggregation in Windows Teaming connected to greater than one switch unfortunately the best scenario adapter load balancing where receive constrained to one NIC's bandwidth (but it is fault tolerant) and transmit can happen on any.


Best Regards


And a response from Vincent: 

HP's NIC Teaming driver does have "802.3ad Dynamic" as one of the available team types. You still can do load balancing in both directions with the "basic" teaming driver, subject to the previous discussion about switches.




Any additional comments are most welcome. Are you using LACP or some sort of virtual switch aggregation?