IN.MPATHD(8) Maintenance Commands and Procedures IN.MPATHD(8)

NAME

in.mpathd - IP multipathing daemon

SYNOPSIS

/usr/lib/inet/in.mpathd

DESCRIPTION

The in.mpathd daemon performs failure and repair detection for IP
interfaces that have been placed into an IPMP group (or optionally, for
all IP interfaces on the system). It also controls which IP interfaces in
an IPMP group are "active" (being used by the system to send or receive
IP data traffic) in a manner that is consistent with the administrator's
configured policy.


The in.mpathd daemon can detect IP interface failure and repair through
two methods: by monitoring the IFF_RUNNING flag for each IP interface
(link-based failure detection), and by sending and receiving ICMP probes
on each IP interface (probe-based failure detection). Link-based failure
detection is instantaneous and is always enabled (provided the network
driver supports the feature); probe-based failure detection must be
enabled through the configuration of one or more test addresses
(described below), but tests the entire IP interface send and receive
path. The ipmpstat(8) utility can be used to check which failure
detection methods are enabled.


If only link-based failure detection is enabled, then the health of the
interface is determined solely from the state of the IFF_RUNNING flag.
Otherwise, the interface is considered failed if either of the two
methods indicate a failure, and repaired once both methods indicate the
failure has been corrected. Not all interfaces in a group need to be
configured with the same failure detection methods.


As mentioned above, to perform probe-based failure detection in.mpathd
requires a test address on each IP interface for the purpose of sending
and receiving probes. Each address must be marked NOFAILOVER (see
ifconfig(8)) and in.mpathd will be limited to probing targets on the same
subnet. Each address may be configured statically or acquired by means of
DHCP. To find targets, in.mpathd first consults the routing table for
routes on the same subnet, and uses the specified next-hop. If no routes
match, it sends all-hosts ICMP probes and selects a subset of the systems
that respond. Thus, for probe-based failure detection to operate, there
must be at least one neighbor on each subnet that responds to ICMP echo
request probes. The ipmpstat(8) utility can be used to display both the
current probe target information and the status of sent probes.


Both IPv4 and IPv6 are supported. If an IP interface is plumbed for IPv4
and an IPv4 test address is configured then in.mpathd will start sending
ICMPv4 probes over that IP interface. Similarly, if an IP interface is
plumbed for IPv6 and an IPv6 test address is configured, then in.mpathd
will start sending ICMPv6 probes over that IP interface. However, note
that in.mpathd will ignore IPv6 test addresses that are not link-local.
If both IPv4 and IPv6 are plumbed, it is sufficient to configure only one
of the two, that is, either an IPv4 test address or an IPv6 test address.
If both IPv4 and IPv6 test addresses are configured, in.mpathd probes
using both ICMPv4 and ICMPv6.


As mentioned above, in.mpathd also controls which IP interfaces in an
IPMP group are "active" (used by the system to send and receive IP data
traffic). Specifically, in.mpathd tracks the administrative configuration
of each IPMP group and attempts to keep the number of active IP
interfaces in each group consistent with that configuration. Therefore,
if an active IP interface fails, in.mpathd will activate an INACTIVE
interface in the group, provided one exists (it will prefer INACTIVE
interfaces that are also marked STANDBY). Likewise, if an IP interface
repairs and the resulting repair leaves the IPMP group with more active
interfaces than the administrative configuration specifies, in.mpathd
will deactivate one of the interfaces (preferably one marked STANDBY),
except when the FAILBACK variable is used, as described below. Similar
adjustments will be made by in.mpathd when offlining IP interfaces (for
instance, in response to if_mpadm(8)).


The in.mpathd daemon accesses three variable values in
/etc/default/mpathd: FAILURE_DETECTION_TIME, FAILBACK and
TRACK_INTERFACES_ONLY_WITH_GROUPS.


The FAILURE_DETECTION_TIME variable specifies the probe-based failure
detection time. The shorter the failure detection time, the more probe
traffic. The default value of FAILURE_DETECTION_TIME is 10 seconds. This
means that IP interface failure will be detected by in.mpathd within 10
seconds. The IP interface repair detection time is always twice the value
of FAILURE_DETECTION_TIME. Note that failures and repairs detected by
link-based failure detection are acted on immediately, though in.mpathd
may ignore link state changes if it suspects that the link state is
flapping due to defective hardware; see DIAGNOSTICS.


By default, in.mpathd limits failure and repair detection to IP
interfaces that are configured as part of a named IPMP group. Setting
TRACK_INTERFACES_ONLY_WITH_GROUPS to no enables failure and repair
detection on all IP interfaces, even if they are not part of a named IPMP
group. IP interfaces that are tracked but not part of a named IPMP group
are considered to be part of the "anonymous" IPMP group. In addition to
having no name, this IPMP group is special in that its IP interfaces are
not equivalent and thus cannot take over for one another in the event of
an IP interface failure. That is, the anonymous IPMP group can only be
used for failure and repair detection, and provides no high-availability
or load-spreading.


As described above, when in.mpathd detects that an IP interface has
repaired, it activates it so that it will again be used to send and
receive IP data traffic. However, if FAILBACK is set to no, then the IP
interface will only be activated if no other active IP interfaces in the
group remain. However, the interface may subsequently be activated if
another IP interface in the group fails.

FILES

/etc/default/mpathd
Contains default values used by the in.mpathd
daemon.

SEE ALSO

if_mpadm(8), ifconfig(8), ipmpstat(8), attributes(7), icmp(4P),
icmp6(4P),


System Administration Guide: IP Services

DIAGNOSTICS

IP interface interface_name has a hardware address which is not unique in
group group_name; offlining
Description:


For probe-based failure detection, load-spreading, and other code
IPMP features to work properly, each IP interface in an IPMP group
must have a unique hardware address. If this requirement is not met,
in.mpathd will automatically offline all but one of the IP interfaces
with duplicate hardware addresses.


IP interface interface_name now has a unique hardware address in group
group_name; onlining
Description:


The previously-detected duplicate hardware address is now unique, and
therefore in.mpathd has brought interface_name back online.


Test address address is not unique in group; disabling probe-based
failure detection on interface_name
Description:


For in.mpathd to perform probe-based failure detection, each test
address in the group must be unique.


No test address configured on interface interface_name disabling probe-
based failure detection on it
Description:


For in.mpathd to perform probe-based failure detection on an IP
interface, it must be configured with a test address: IPv4, IPv6, or
both.


IP interface_name in group group_name is not plumbed for IPv[4|6],
affecting IPv[4|6] connectivity
Description:


All IP interfaces in a multipathing group must be homogeneously
plumbed. For example, if one IP interface is plumbed for IPv4, then
all IP interfaces in the group must be plumbed for IPv4, or IPv4
packets will not be able to be reliably sent and received. The
STREAMS modules pushed on all IP interfaces must also be identical.


The link has come up on interface_name more than 2 times in the last
minute; disabling repair until it stabilizes.
Description:


To limit the impact of interfaces with intermittent hardware (such as
a bad cable), in.mpathd will not consider an IP interface with a
frequently changing link state as repaired until the link state
stabilizes.


Invalid failure detection time of time, assuming default 10000 ms
Description:


An invalid value was encountered for FAILURE_DETECTION_TIME in the
/etc/default/mpathd file.


Too small failure detection time of time, assuming minimum of 100 ms
Description:


The minimum value that can be specified for FAILURE_DETECTION_TIME is
currently 100 milliseconds.


Invalid value for FAILBACK value
Description:


Valid values for the boolean variable FAILBACK are yes or no.


Invalid value for TRACK_INTERFACES_ONLY_WITH_GROUPS value
Description:


Valid values for the boolean variable
TRACK_INTERFACES_ONLY_WITH_GROUPS are yes or no.


Cannot meet requested failure detection time of time ms on (inet[6]
interface_name) new failure detection time for group group_name is time
ms
Description:


The round trip time for ICMP probes is higher than necessary to
maintain the current failure detection time. The network is probably
congested or the probe targets are loaded. in.mpathd automatically
increases the failure detection time to whatever it can achieve under
these conditions.


Improved failure detection time time ms on (inet[6] interface_name) for
group group_name
Description:


The round trip time for ICMP probes has now decreased and in.mpathd
has lowered the failure detection time correspondingly.


IP interface failure detected on interface_name
Description:


in.mpathd has detected a failure on interface_name, and has set the
IFF_FAILED flag on interface_name, ensuring that it will not be used
for IP data traffic.


IP interface repair detected on interface_name
Description:


in.mpathd has detected a repair on interface_name, and has cleared
the IFF_FAILED flag. Depending on the administrative configuration,
the interface_name may again be used for IP data traffic.


All IP interfaces in group group are now unusable
Description:


in.mpathd has determined that none of the IP interfaces in group can
be used for IP data traffic, breaking network connectivity for the
group.


At least 1 IP interface (interface_name) in group group is now usable
Description:


in.mpathd has determined that at least one of the IP interfaces in
group can again be used for IP data traffic, restoring network
connectivity for the group.


The link has gone down on interface_name
Description:


in.mpathd has detected that the IFF_RUNNING flag for interface_name
has been cleared, indicating that the link has gone down.


The link has come up on interface_name
Description:


in.mpathd has detected that the IFF_RUNNING flag for interface_name
has been set, indicating that the link has come up.


May 13, 2009 IN.MPATHD(8)