System Administration Guide: IP Services

IPMP and Dynamic Reconfiguration

The dynamic reconfiguration (DR) feature enables you to reconfigure system hardware, such as interfaces, while the system is running. This section explains how DR interoperates with IPMP.

On a system that supports DR of NICs, IPMP can be used to preserve connectivity and prevent disruption of existing connections. You can safely attach, detach, or reattach NIC's on a system that supports DR and uses IPMP. This is possible because IPMP is integrated into the Reconfiguration Coordination Manager (RCM) framework. RCM manages the dynamic reconfiguration of system components.

You typically use the cfgadm command to perform DR operations. However, some platforms provide other methods. Consult your platform's documentation for details. You can find specific documentation about DR from the following resources.

Table 30–1 Documentation Resources for Dynamic Reconfiguration


For Information 

Detailed information on the cfgadm command

cfgadm(1M) man page

Specific information about DR in the Sun Cluster environment 

Sun Cluster 3.1 System Administration Guide

Specific information about DR in the Sun Fire environment 

Sun Fire 880 Dynamic Reconfiguration Guide

Introductory information about DR and the cfgadm command

Chapter 6, Dynamically Configuring Devices (Tasks), in System Administration Guide: Devices and File Systems

Tasks for administering IPMP groups on a system that supports DR 

Replacing a Failed Physical Interface on Systems That Support Dynamic Reconfiguration

Attaching NICs

You can add interfaces to an IPMP group at any time by using the ifconfig command, as explained in How to Configure an IPMP Group With Multiple Interfaces. Thus, any interfaces on system components that you attach after system boot can be plumbed and added to an existing IPMP group. Or, if appropriate, you can configure the newly added interfaces into their own IPMP group.

These interfaces and the data addresses that are configured on them are immediately available for use by the IPMP group. However, for the system to automatically configure and use the interfaces after a reboot, you must create an /etc/hostname.interface file for each new interface. For instructions, refer toHow to Configure a Physical Interface After System Installation.

If an /etc/hostname.interface file already exists when the interface is attached, then RCM automatically configures the interface according to the contents of this file. Thus, the interface receives the same configuration that it would have received after system boot.

Detaching NICs

All requests to detach system components that contain NICs are first checked to ensure that connectivity can be preserved. For instance, by default you cannot detach a NIC that is not in an IPMP group. You also cannot detach a NIC that contains the only functioning interfaces in an IPMP group. However, if you must remove the system component, you can override this behavior by using the -f option of cfgadm, as explained in the cfgadm(1M) man page.

If the checks are successful, the data addresses associated with the detached NIC fail over to a functioning NIC in the same group, as if the NIC being detached had failed. When the NIC is detached, all test addresses on the NIC's interfaces are unconfigured. Then, the NIC is unplumbed from the system. If any of these steps fail, or if the DR of other hardware on the same system component fails, then the previous configuration is restored to its original state. You should receive a status message regarding this event. Otherwise, the detach request completes successfully. You can remove the component from the system. No existing connections are disrupted.

Reattaching NICs

RCM records the configuration information associated with any NIC's that are detached from a running system. As a result, RCM treats the reattachment of a NIC that had been previously detached identically as it would to the attachment of a new NIC. That is, RCM only performs plumbing.

However, reattached NICs typically have an existing /etc/hostname.interface file. In this case, RCM automatically configures the interface according to the contents of the existing /etc/hostname.interface file. Additionally, RCM informs the in.mpathd daemon of each data address that was originally hosted on the reattached interface. Thus, once the reattached interface is functioning properly, all of its data addresses are failed back to the reattached interface as if it had been repaired.

If the NIC being reattached does not have an /etc/hostname.interface file, then no configuration information is available. RCM has no information regarding how to configure the interface. One consequence of this situation is that addresses that were previously failed over to another interface are not failed back.

NICs That Were Missing at System Boot

NICs that are not present at system boot represent a special instance of failure detection. At boot time, the startup scripts track any interfaces with /etc/hostname.interface files that cannot be plumbed. Any data addresses in such an interface's /etc/hostname.interface file are automatically hosted on an alternative interface in the IPMP group.

In such an event, you receive error messages similar to the following

moving addresses from failed IPv4 interfaces: hme0 (moved to hme1)
moving addresses from failed IPv6 interfaces: hme0 (moved to hme1)

If no alternative interface exists, you receive error messages similar to the following:

moving addresses from failed IPv4 interfaces: hme0 (couldn't move; 
   no alternative interface) 
 moving addresses from failed IPv6 interfaces: hme0 (couldn't move; 
   no alternative interface) 

Note –

In this instance of failure detection, only data addresses that are explicitly specified in the missing interface's /etc/hostname.interface file move to an alternative interface. Any addresses that are usually acquired through other means, such as through RARP or DHCP, are not acquired or moved.

If an interface with the same name as another interface that was missing at system boot is reattached using DR, RCM automatically plumbs the interface. Then, RCM configures the interface according to the contents of the interface's /etc/hostname.interface file. Finally, RCM fails back any data addresses, just as if the interface had been repaired. Thus, the final network configuration is identical to the configuration that would have been made if the system had been booted with the interface present.