Teaming Concepts, Teaming and Network Addresses

4.3Teaming Concepts

Storage devices use RAID technology to group individual hard drives. Switch ports can be grouped together using technologies such as Cisco Gigabit EtherChannel, IEEE 802.3ad Link Aggregation, Bay Network Multilink Trunking, and Extreme Network Load Sharing. Network interfaces on servers can be grouped together into a team of physical ports called a virtual adapter.

4.3.1Teaming and Network Addresses

Network Addressing

To understand how teaming works, it is important to understand how node communications work in an Ethernet network. This Section is based on the assumption that the reader is familiar with the basics of IP and Ethernet network communications. The following information provides the concepts of network addressing used in an Ethernet network.

Every Ethernet network interface in a host platform, such as a computer system, requires a globally unique Layer 2 address and at least one globally unique Layer 3 address. Layer 2 is the Data Link Layer, and Layer 3 is the Network layer as defined in the OSI model. The Layer 2 address is assigned to the hardware and is often referred to as the MAC address or physical address. This address is pre- programmed at the factory and stored in NVRAM on a network interface card or on the system motherboard for an embedded LAN interface. The Layer 3 addresses are referred to as the protocol or logical address assigned to the software stack. IP and IPX are examples of Layer 3 protocols. In addition, Layer 4 (Transport Layer) uses port numbers for each network upper level protocol such as Telnet or FTP. These port numbers are used to differentiate traffic flows across applications. The combination of the IP address and the TCP port number is called a socket.

Ethernet devices communicate with other Ethernet devices using the MAC address, not the IP address. However, most applications work with a host name that is translated to an IP address by a Naming Service such as WINS and DNS. Therefore, a method of identifying the MAC address assigned to the IP address is required. The Address Resolution Protocol for an IP network provides this mechanism. For IPX, the MAC address is part of the network address and ARP is not required. ARP is implemented using an ARP Request and ARP Reply frame. ARP Requests are typically sent to a broadcast address while the ARP Reply is typically sent as unicast traffic. A unicast address corresponds to a single MAC address or a single IP address. A broadcast address is sent to all devices on a network.

Teaming and Network Addresses

A team of adapters will function as a single virtual network interface, and do not appear to be any different than a non-teamed adapter to other network devices. A virtual network adapter advertises a single Layer 2, and one or more Layer 3 addresses. When the teaming driver initializes, it selects one MAC address from one of the physical adapters that make up the team to be the Team MAC address. This address is typically taken from the first adapter that gets initialized by the driver. When the system hosting the team receives an ARP request, it selects one MAC address from among the physical adapters in the team to use as the source MAC address in the ARP Reply. In Windows operating systems, the IPCONFIG /all command shows the IP and MAC address of the virtual adapter and not the individual physical adapters. The protocol IP address is assigned to the virtual network interface and not to the individual physical adapters.

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