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Only one of the two physical slave interfaces in 802.3ad Load Sharing Bond handles most of the traffic Technical Level
Symptoms
  • Output of "netstat -ni" command and traffic capture show that only one of the two physical slave interfaces in 802.3ad Load Sharing Bond interface handles most of the traffic.

Cause

Since Bond interface inherits its MAC address from one of the physical slave interfaces, this MAC address will be static for the session.

Default Transmit Hash Policy for 802.3ad Load Sharing Bond is "Layer 2", which uses XOR of hardware MAC addresses - i.e., [[(Source_MAC) XOR (Destination_MAC)] % 2].
All variables in the above formula are constants, because MAC addresses between the links do not change.
As a result, most packets will be distributed via the same physical slave interface of the Bond.

The bond mechanism will dispatch the traffic among the slaves, based on the transmit policy. If the transmit policy is changed to layer 3 for example, the decision will be made based on the IP addresses of incoming packets, which in case of layer 3 devices usage, could be a lot and contribute to the load distribution between the slaves.

In a scenario that we are using Layer 2 policy, and we have many layer 2 devices in the network, users will benefit from layer 2 Transmit Hash Policy, as the incoming traffic will be forwarded from multiple layer 2 sources.


Solution
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