We recommend that all PROD sites deploy switches in redundant fail-over pairs. However, even if the switches fail over, the servers connected to any single switch will not.
Unless we deploy Linux Ethernet bonding as summarized below.
We use "active-backup" mode. This requires that two of the the server's Ethernet interfaces are connected to two separate switches on the same VLAN, and that those switches are connected via a valid Inter Switch Link (ISL). We typically use IEEE 802.1q trunking for the ISL because it is a standard which is portable among different switch vendors.
Once the bonding module is loaded and properly configured the host has a new logical interface, bond0. bond0 has two slave interfaces, eth0 and eth1. One of those two interfaces is active at any given point in time, and the other only takes over if the kernel detects a failure in the active interface. When it does detect such a failure, it begins using the other interface, and it sends a gratuitous ARP out the other interface, so that upstream switching devices can update their MAC address tables. This covers many -- but not all -- possible network failure scenarios.
The Linux kernel documentation has a fairly good technical document about bonding, which you can find here: http://www.mjmwired.net/...bonding.txt
In an upcoming blog post, we will describe how to configure the servers and switches to support Linux Ethernet Bonding.
- Dave Pierce, VP Engineering
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