Chapter 27

IP Network Multipathing (Overview)

IP Network Multipathing provides both load spreading and failover when you have multiple network interface cards that are connected to the same IP link (for example, Ethernet).

This chapter contains the following information:

• "Introduction"

• "IP Network Multipathing Features"

• "Communication Failures"

• "IP Network Multipathing Components"

• "Solaris Network Multipathing"

• "Administering Multipathing Groups With Multiple Physical Interfaces"

• "Administering Multipathing Groups With a Single Physical Interface"

• "Removing Network Adapters From Multipathing Groups"

• "Detached Network Adapters"

• "Multipathing Daemon"

• "Multipathing Configuration File"

Introduction

IP Network Multipathing provides your system with the following capabilities:

• Recovery from single-point failures with network adapters

• Increased traffic throughput

If a failure occurs in the network adapter, and if you have an alternate adapter connected to the same IP link, the system switches all the network accesses automatically from the failed adapter to the alternate adapter. This process ensures uninterrupted access to the network. Also, when you have multiple network adapters that are connected to the same IP link, you achieve increased traffic throughput by spreading the traffic across multiple network adapters.

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Note - Other IP-related documents, such as RFC 2460, use the term link instead of IP link. This document uses the term IP link to avoid confusion with IEEE 802. In IEEE 802, link refers to a single wire from an Ethernet NIC to an Ethernet switch.

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See IP link definition in the Glossary or refer to Table 27-1.

IP Network Multipathing Features

The Solaris implementation of IP Network Multipathing provides the following features:

• Failure Detection - Ability to detect when a network adapter has failed and automatic switching (failover) of the network access to an alternate network adapter. This assumes that you have configured an alternate network adapter. See "Detecting Physical Interface Failures" for more information.

• Repair Detection - Ability to detect when a network adapter that failed previously has been repaired and automatically switching back (failback) of the network access to an alternate network adapter. This assumes that you have enabled failbacks. See "Detecting Physical Interface Repairs" for more information.

• Outbound Load Spreading - Outbound network packets are spread across multiple network adapters without affecting the ordering of packets in order to achieve higher throughput. Load spreading occurs only when the network traffic is flowing to multiple destinations that use multiple connections.

Communication Failures

Communication failures can occur in the following ways:

1. Transmit/receive path of the NIC can stop transmitting packets.

2. Attachment of the NIC to the link is down.

3. Port on the switch does not transmit/receive packets.

4. Physical interface in a group not present at system boot.

5. Host on the other end is not responding or the router that is forwarding the packets is not responding.

The Solaris implementation of IP Network Multipathing addresses the first four types of communication failures.

IP Network Multipathing Components

The following table identifies and describes the components that compose IP Network Multipathing.

Table 27-1 IP Network Multipathing Components

Component	Description
IP Link	A communication facility or medium over which nodes can communicate at the link layer. The link layer is the layer immediately below IPv4/IPv6. Examples include Ethernets (simple or bridged) or ATM networks. One or more IPv4 subnet numbers/prefixes are assigned to an IP link. A subnet number/prefix cannot be assigned to more than one IP link. In ATM LANE, an IP link is a single emulated LAN. When using ARP, the scope of the ARP protocol is a single IP link.
Network Interface Card (NIC)	Network adapter that is either internal or a separate card that serves as an interface to a link.
Physical interface	A node's attachment to a link. This attachment is often implemented as a device driver plus a network adapter. Some network adapters can have multiple points of attachment, for example, qfe. The usage of Network adapter in this document refers to a "Single Point of Attachment."
Physical interface group	The set of physical interfaces on a system that are connected to the same link. They are identified by assigning the same (non-null) character string name to all the physical interfaces in the group.
Physical interface group name	A name that is assigned to a physical interface that identifies the group. The name is local to a system. Multiple physical interfaces, sharing the same group name, form a physical interface group.
Failure detection	The process of detecting when a NIC or the path from the NIC to some layer 3 device no longer works.
Repair detection	The process of detecting when a NIC or the path from the NIC to some layer 3 device starts operating correctly after a failure.
Failover	The process of switching network access from a failed interface to a good physical interface. Network access includes IPv4 unicast, multicast, and broadcast traffic, as well as IPv6 unicast and multicast traffic.
Failback	The process of switching back network access to an interface that is detected to have been repaired.
Standby Interface	A physical interface that is not used to carry data traffic unless some other physical interface in the group has failed.