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Understanding NIC Bonding with Linux

Dec 02, 2009, 22:02 (0 Talkback[s])
(Other stories by Charlie Schluting)

[ Thanks to Michael Hall for this link. ]

"Most administrators assume that bonding multiple network cards together instantly results in double the bandwidth and high-availability in case a link goes down. Unfortunately, this is not true. Let's start with the most common example, where you have a server with high network load, and wish to allow more than 1Gb/s.

"Bonding With 802.3Ad

"You connect two interfaces to your switch, enable bonding, and discover half your packets are getting lost. If Linux is configured for 802.3ad link aggregation, the switch must also be told about this. In the Cisco world, this is called an EtherChannel. Once the switch knows those two ports are actually supposed to use 802.3ad, it will load balance the traffic destined for your attached server.

"This works great if a large number of network connections from a diverse set of clients are connecting. If, however, the majority of the throughput is coming from a single server, you won't get better than the 1Gb/s port speed. Switches are load balancing based on the source MAC address by default, so if only one connection takes place, it always gets sent down the same link. Many switches support changing of the load balancing algorithm, so if you fall into the single server-to-server category, make sure you allow it to round-robin the Ethernet frames."

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