RX load balancing on SG200-18

[pcmdinc.com]

Hi guys,

I put this question on Spiceworks and someone chimed in and said it wasn't possible due to the nature of how etherchanel balances, but I wanted to double check.  Here is my question:

I have a cisco SG200-18 managed switch configured with LAG with LACP and a new Supermicro X9SCM-F motherboard that uses two Intel NICs (82579LM & 82574L).  The server is running Server 2012 r2 standard and I'm teaming the NICs via intel's driver.  The team type is set to IEEE 802.3ad Dynamic Link Aggregation.  From my understand that means that inbound and outbound packets should be able to utilize the increased bandwidth (thus the dynamic part).  So far in my testing coping files to and from the server from multiple PCs at the same time only files being copied from the server utilize the increased bandwidth. I can see in task manager on the server that the ethernet is using over 1 Gbps.  However, files going TO the server from multiple computers at the same time max out at 1Gbps.

Any insight on why this would be?

Edit: Also want to note that the switch is running the most recent version of the firmware.

Attached you'll find some screen setups of the different windows on the server & the switch.  Thanks!

[chrebert]

Hello,

This is a common question with LACP and LAGs in general.

It all comes down to this.  Any single connection will only ever be able to use a single member of the LAG.  Meaning that whatever the maximum speed (1Gbps) of one physical link is, that is the limit of the transfer.

It is because of how the load balancing algorithm works.  When a packet comes in, the switch hashes either the IP or MAC address of the source and destination, and comes up with a number.  If your LAG has 4 links, it is a number from 1-4.  That determines which link in the LAG gets used in that connection.  That connection will only ever use that LAG member, and cannot spill over, even if the link it is using gets full.

The load balancing algorithm can be changed to better utilize the links, however the test of a single computer transferring to another computer will always give the results you saw.

There are several enterprise level Cisco switches which can load balance based on source and destination port number, which could enable two computers to utilize multiple links, if they were transferring data on different TCP ports.  However the small business switches are only able to load balance by MAC/IP.  You can experiment with the load balancing setting to see which setting optimizes your link usage. You may also be able to tweak this setting on the server side, but that one is up to you.

Hope that helps a bit, you've done some nice testing already, so I'm really just confirming what you've already seen.

Thank you for choosing Cisco,

Christopher Ebert

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Network Support Engineer - Cisco Small Business Support Center