Ethernet Bonding

Ethernet Bonding Configuration

Firmware 1.3 or newer support Ethernet ports bonding, that is method for aggregating multiple network interfaces into a single logical “bonded” interface. The behavior of the bonded interfaces depends upon the mode of operation and may require support from the switch connected to the radio unit. Three modes of operation are currently supported as described in the figure below, i.e. Adaptive load balancing, Trunking/Etherchannel and IEEE 802.3ad (LACP).

1. ethernet bonding

 

The Adaptive load balancing mode does not require any special switch support.  The receive load balancing is achieved by ARP negotiation. The bonding software intercepts the ARP Replies sent by the local system on their way out and overwrites the source hardware address with the unique hardware address of one of the slaves in the bond such that different peers use different hardware addresses for the server.
Receive traffic from connections created by the server is also balanced.  When the local system sends an ARP Request the bonding software copies and saves the peer’s IP information from the ARP packet.  When the ARP Reply arrives from the peer, its hardware address is retrieved and the bonding driver initiates an ARP reply to this peer assigning it to one of the slaves in the bond.Different behavior is exhibited in this mode of operation whether the Ethernet ports are bridged or routed with the WiFi interface. Specifically, if the Ethernet ports are bridged the load balancing is enforced on the TX side because the traffic flow is identified based on the destination IP address. The figure below describes the scenario where the Base Station is bridged. Traffic flowing from the Base Station to the CPEs will NOT be load balanced.

2. balance-alb-bridge

 
Different behavior is exhibited when the Ethernet is operating in routing mode, i.e. the WiFi is on a separate IP subnet, as depicted below.

3. balance-alb-routed
 

Trunking/Etherchannel

This mode will balance the traffic such that packets destined for specific peers will always be sent over the same interface. Peers are identified by a traffic flow by hashing the tuple <IP-SRC, IP-DST, PORT-SRC, PORT-DST>. Therefore, the same pair of IP addresses can actually be allocated on separate ports depending on the specific traffic flow.With this mode of operation, the switch ports need to be configured for “etherchannel” or “trunking, which is a very common feature supported by the majority of the switches.
In this mode of operation, there is no limitation whether the Ethernet are bridged or routed with the WiFi interface.

IEEE 802.3ad (LACP)

The IEEE 802.3ad mode is a standard aggregation mode and requires that the switch have the appropriate ports configured as an 802.3ad aggregation.  The precise method used to configure this varies from switch to switch, but, for example, a Cisco 3550 series switch requires that the appropriate ports first be grouped together in a single etherchannel instance, then that etherchannel is set to mode “lacp” to enable IEEE 802.3ad (instead of standard EtherChannel). Below is reported an example configuration for a Cisco 3550 switch.

interface Port-channel5
 switchport access vlan 666
 switchport mode access
 storm-control broadcast level 20.00
 storm-control action shutdown
!
interface FastEthernet0/7
 switchport access vlan 666
 switchport mode access
 power inline never
 storm-control broadcast level 20.00
 storm-control action shutdown
 channel-protocol lacp
 channel-group 5 mode active
 spanning-tree portfast
!
interface FastEthernet0/8
 switchport access vlan 666
 switchport mode access
 power inline never
 storm-control broadcast level 20.00
 storm-control action shutdown
 channel-protocol lacp
 channel-group 5 mode active
 spanning-tree portfast

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