[PATCH] bonding: Validate probe replies in ARP monitor

	Add logic to check ARP request / reply packets used for ARP
monitor link integrity checking.

	The current method simply examines the slave device to see if it
has sent and received traffic; this can be fooled by extraneous traffic.
For example, if multiple hosts running bonding are behind a common
switch, the probe traffic from the multiple instances of bonding will
update the tx/rx times on each other's slave devices.

Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

1 files changed, 59 insertions, 0 deletions

diff --git a/Documentation/networking/bonding.txt b/Documentation/networking/bonding.txt
index afac780..dc942ea 100644
--- a/Documentation/networking/bonding.txt
+++ b/Documentation/networking/bonding.txt
@@ -192,6 +192,17 @@ or, for backwards compatibility, the option value.  E.g.,
 arp_interval
 
 	Specifies the ARP link monitoring frequency in milliseconds.
+
+	The ARP monitor works by periodically checking the slave
+	devices to determine whether they have sent or received
+	traffic recently (the precise criteria depends upon the
+	bonding mode, and the state of the slave).  Regular traffic is
+	generated via ARP probes issued for the addresses specified by
+	the arp_ip_target option.
+
+	This behavior can be modified by the arp_validate option,
+	below.
+
 	If ARP monitoring is used in an etherchannel compatible mode
 	(modes 0 and 2), the switch should be configured in a mode
 	that evenly distributes packets across all links. If the
@@ -213,6 +224,54 @@ arp_ip_target
 	maximum number of targets that can be specified is 16.  The
 	default value is no IP addresses.
 
+arp_validate
+
+	Specifies whether or not ARP probes and replies should be
+	validated in the active-backup mode.  This causes the ARP
+	monitor to examine the incoming ARP requests and replies, and
+	only consider a slave to be up if it is receiving the
+	appropriate ARP traffic.
+
+	Possible values are:
+
+	none or 0
+
+		No validation is performed.  This is the default.
+
+	active or 1
+
+		Validation is performed only for the active slave.
+
+	backup or 2
+
+		Validation is performed only for backup slaves.
+
+	all or 3
+
+		Validation is performed for all slaves.
+
+	For the active slave, the validation checks ARP replies to
+	confirm that they were generated by an arp_ip_target.  Since
+	backup slaves do not typically receive these replies, the
+	validation performed for backup slaves is on the ARP request
+	sent out via the active slave.  It is possible that some
+	switch or network configurations may result in situations
+	wherein the backup slaves do not receive the ARP requests; in
+	such a situation, validation of backup slaves must be
+	disabled.
+
+	This option is useful in network configurations in which
+	multiple bonding hosts are concurrently issuing ARPs to one or
+	more targets beyond a common switch.  Should the link between
+	the switch and target fail (but not the switch itself), the
+	probe traffic generated by the multiple bonding instances will
+	fool the standard ARP monitor into considering the links as
+	still up.  Use of the arp_validate option can resolve this, as
+	the ARP monitor will only consider ARP requests and replies
+	associated with its own instance of bonding.
+
+	This option was added in bonding version 3.1.0.
+
 downdelay
 
 	Specifies the time, in milliseconds, to wait before disabling