Multipathing Daemon

The in.mpathd multipathing daemon detects failures and repairs by sending out probes on all the interfaces that are part of a group. When an interface is part of a group and has a test address, the daemon starts sending out probes for determining failures on that interface. If there are no replies to five consecutive probes, the interface is considered as having failed. The probing rate depends on the failure detection time. By default, failure detection time is 10 seconds. Thus, the probing rate is one probe every two seconds. To avoid synchronization in the network, probing is not periodic. If five consecutive probes fail, in.mpathd considers the interface as failed and performs a failover of the network access from the failed interface to another interface in the group that is functioning properly. If a standby interface is configured, it is chosen for failover of the IP addresses, and broadcasts and multicast memberships. If no standby interface exists, the interface with the least number of IP addresses is chosen. Refer to the man page in.mpathd(1M) for more information.

The following two examples show a typical configuration and how the configuration automatically changes when an interface fails. When the hme0 interface fails, notice that all addresses move from hme0 to hme1.

Example 1–1 Interface Configuration Before an Interface Failure

hme0: flags=9000843<UP,BROADCAST,RUNNING,MULTICAST,IPv4> mtu 1500 index 2
     inet 19.16.85.19 netmask ffffff00 broadcast 19.16.85.255
     groupname test
hme0:1: flags=9000843<UP,BROADCAST,RUNNING,MULTICAST,DEPRECATED,IPv4,NOFAILOVER> mtu 1500 
     index 2 inet 19.16.85.21 netmask ffffff00 broadcast 129.146.85.255
hme1: flags=9000843<UP,BROADCAST,RUNNING,MULTICAST,IPv4> mtu 1500 index 2
     inet 19.16.85.20 netmask ffffff00 broadcast 19.16.85.255
     groupname test
hme1:1: flags=9000843<UP,BROADCAST,RUNNING,MULTICAST,DEPRECATED,IPv4,NOFAILOVER> mtu 1500 
     index 2 inet 19.16.85.22 netmask ffffff00 broadcast 129.146.85.255
hme0: flags=a000841<UP,RUNNING,MULTICAST,IPv6,NOFAILOVER> mtu 1500 index 2
     inet6 fe80::a00:20ff:feb9:19fa/10
     groupname test
hme1: flags=a000841<UP,RUNNING,MULTICAST,IPv6,NOFAILOVER> mtu 1500 index 2
     inet6 fe80::a00:20ff:feb9:1bfc/10
     groupname test

Example 1–2 Interface Configuration After an Interface Failure

hme0: flags=19000842<BROADCAST,RUNNING,MULTICAST,IPv4,NOFAILOVER,FAILED> mtu 0 index 2
        inet 0.0.0.0 netmask 0 
        groupname test
hme0:1: flags=19040843<UP,BROADCAST,RUNNING,MULTICAST,DEPRECATED,IPv4,NOFAILOVER,FAILED> 
        mtu 1500 index 2 inet 19.16.85.21 netmask ffffff00 broadcast 129.146.85.255
hme1: flags=9000843<UP,BROADCAST,RUNNING,MULTICAST,IPv4> mtu 1500 index 2
        inet 19.16.85.20 netmask ffffff00 broadcast 19.16.85.255
        groupname test
hme1:1: flags=9000843<UP,BROADCAST,RUNNING,MULTICAST,DEPRECATED,IPv4,NOFAILOVER> mtu 1500 
        index 2 inet 19.16.85.22 netmask ffffff00 broadcast 129.146.85.255
hme1:2: flags=1000843<UP,BROADCAST,RUNNING,MULTICAST,IPv4> mtu 1500 index 6
        inet 19.16.85.19 netmask ffffff00 broadcast 19.16.18.255
hme0: flags=a000841<UP,RUNNING,MULTICAST,IPv6,NOFAILOVER,FAILED> mtu 1500 index 2
        inet6 fe80::a00:20ff:feb9:19fa/10 
        groupname test
hme1: flags=a000841<UP,RUNNING,MULTICAST,IPv6,NOFAILOVER> mtu 1500 index 2
        inet6 fe80::a00:20ff:feb9:1bfc/10 
        groupname test

You can see that the FAILED flag is set on hme0 to indicate that hme0 has failed. You can also see that hme1:2 is now created. hme1:2 was originally hme0. The address 19.16.85.19 then becomes accessible through hme1. Multicast memberships associated with 19.16.85.19 can still receive packets, but now through hme1. When the failover of address 19.16.85.19 from hme0 to hme1 took place, a dummy address 0.0.0.0 was created on hme0. The dummy address is removed when a subsequent failback takes place. The dummy address is created so that hme0 can still be accessed. hme0:1 cannot exist without hme0.

Similarly, failover of the IPv6 address from hme0 to hme1 took place. In IPv6, multicast memberships are associated with interface indexes. They also failover from hme0 to hme1. All the addresses that in.ndpd configures also move (this is not shown in the examples).

The in.mpathd daemon continues to probe through the failed NIC, hme0. After it receives 10 consecutive replies (for a default failure detection time of 10 seconds), it considers the interface repaired and invokes the failback. After failback, the original configuration is re-established.

See in.mpathd(1M) man page for a description of all error messages logged on the console during failures and repairs.