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Bronze

Switch-independent load-balancing NIC teaming on server-side and MAC/ARP flapping on L2/L3 switches

Since active deployment of Windows Server 2012, our servers support team began to utilize new feature - switch-independent load-balancing NIC teaming. At first look it seems great - no additional network configuration is required and load balancing is performed by server itself by sending frames in round-robin or some hash algorithm out from different NICs (say two for simplicity) but with same MAC address. Theoretical bandwith is now grown up to 2Gbps (if we have two 1G NICs per server) against failover NIC teaming configuration, when one of two adapters is always down.

But how does this affect (if does) switching and routing performance of network equipment? From point of view of L2 switch - it has to rewrite its CAM table each time a server sends frame from different NIC. Isn't it expensive operation? Won't it affect switching in a bad way? We see in our logs that same server make switches to change mac-to-port associations several times per second.

Well, and how does it affect routing, if the switch to which server is connected is L3 switch an performs routing for the subnet server connected to? Will CEF operate well if ARP entry chages several times per second?

Thank you.

1 REPLY
Bronze

Since nobody answered here,

Since nobody answered here, we created service request and got the following answer (in short):

L2 MAC flapping between ports is very bad and you must avoid such configurations as much as possible. There is one possible variant that can be considered in your situation - use port-channel (either L2 or L3), in this configuration port-channel will be treted as single port and there won't be flapping.

Conversation example is here: https://ramazancan.wordpress.com/tag/best-practice/

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