I''m using bonding in active-fallback mode to guarantee maximum
availability on some critical servers.
The mii mode is active so I can detect things like dead card and/or
unplugged cable even on the inactive slave.
But how do I check that the inactive slave is properly
configured/connected to the switch/vlan?
I ask this question because it has just bitten me in a part I''ll keep
undisclosed.
Scenario:
your bond0 is running fine. it uses eth0 as active slave and eth2 as
inactive slave (different cards/ different driver to be safe)
some bozo reconfigures the switch port where your eth2 is plugged in and
you don''t notice it (the crucial point here)
later on, your eth0 dies (or is unplugged by the brother of the first bozo)
and bamm... your nice HA node is off-line.
note: eth2 is still plugged and fine at the mii level.
even an arp would return OK so going from mii to arp for the bond is not
the right option.
So. How could I check that an IP packet send via eth2 would really reach
its vlan?
I tried a probably naive thing:
ifenslave -d bond0 eth2
ifconfig eth2 $ip netmask 255.255.255.255
route add -host $target eth2
ping $target
(target is the gateway, ip is a reserved IP used only on this server to
do that check)
but it does not work as I hopped. Sometimes the ping is OK (but goes
thru bond0) sometimes it blocks...
The real question is How to do it properly (rather than how to fix my
naive try).
Thank you for your help.
Olivier
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olivier arsac <oliv@arsac.org> wrote: [...]>Scenario: >your bond0 is running fine. it uses eth0 as active slave and eth2 as inactive >slave (different cards/ different driver to be safe) >some bozo reconfigures the switch port where your eth2 is plugged in and you >don''t notice it (the crucial point here) >later on, your eth0 dies (or is unplugged by the brother of the first bozo) >and bamm... your nice HA node is off-line. >note: eth2 is still plugged and fine at the mii level. >even an arp would return OK so going from mii to arp for the bond is not the >right option. > >So. How could I check that an IP packet send via eth2 would really reach its >vlan?One obvious remedy is better bozo control, but for purposes of discussion, let''s look at this as simply a question about assurance of the inactive path. The short answer to you question is that you can''t do what you''re trying to do. The bonding driver itself, as you''ve noted, is reasonably good at detecting link state, and connectivity to local network peers (via the ARP monitor), but doesn''t provide full end-to-end path validation for all active and inactive slaves. The long answer is that end-to-end validation of the inactive path is fairly complicated, and can be tricky to do correctly. If an inactive slave transmits something, it may cause updating of forwarding tables on the network (either because ARP probes have this effect, or because many switches snoop traffic to determine which destination is reachable via which port), which is undesirable. Inactive slaves, at least in recent versions of bonding, also drop all incoming traffic to prevent the same packet from being delivered multiple times (if, e.g., a switch is flooding traffic to all ports of the bond for whatever reason). The ideal case is to issue, e.g., a ping (ICMP Echo Request) to some IP address on the desired destination. An IP-level probe is better in the grand scheme of things because an IP packet is routable and can reach off the local network (which an ARP cannot). If we move up to IPv6, this becomes more complicated, as the "inactive" slave would have to participated in the IPv6 stateless address autoconfiguration independently from the master, which also causes headaches for IPv6 snooping switches. So, to achieve an actual end to end test from the "inactive" slave to the peer of choice, it''s necessary to isolate this traffic so that it properly returns to the "inactive" slave (and isn''t routed back to the master). This separate communication needs to take place on a logically discrete network (which may also be physically discrete, as appears to be the case in your situation). If the "probe" network isn''t separate from the "real" network, then intermediate routers may send the probes or replies over the wrong path, or improperly update forwarding tables and so on. The bonding driver today doesn''t support this type of "independent" slave activity; all slaves are considered to be minions of the master, and aren''t allowed to operate independently. I will point out that the ARP monitor, for a subset of cases, can come close to what you want. The current versions of the bonding driver support an "arp_validate" option, and can validate that the ARP probes (which are broadcasts) sent out over the active slave actually reach the inactive slave. It doesn''t validate the ARP replies, as those are only received by the active slave, and it doesn''t attempt to transmit on the inactive slave.>I tried a probably naive thing: >ifenslave -d bond0 eth2 >ifconfig eth2 $ip netmask 255.255.255.255 >route add -host $target eth2 >ping $target >(target is the gateway, ip is a reserved IP used only on this server to do that >check) >but it does not work as I hopped. Sometimes the ping is OK (but goes thru >bond0) sometimes it blocks... >The real question is How to do it properly (rather than how to fix my naive >try).I would hazard to guess that your problem here is likely one of routing. Maybe on the sender end, maybe on the reply end, maybe both. On the sender end, you can force ping to use a particular interface via the "-I" option, which will assure you that you''re using the eth2 for the transmission. The question is going to be which path the reply packet takes to get back to the sender. The other problem, of course, is that you''ve removed your backup link from the bond, so if the primary should fail while you''ve got it running this ping test, you''ll lose all connectivity. One perhaps cheap and easy, but not 100% reliable, method would be for you to periodically manually fail over the bond to whichever link is inactive (via ifenslave -c bond0 ethX, cycling X through your set of slave interfaces). The up side of this is that you''ll exercise both paths regularly, so any bozo induced nonsense should become visible sooner rather than later; the precise interval for "sooner" depending upon how often the failover is induced. The down side is that a failover will probably lose at least a few packets, and you''ll have to arrange your script or whatever to stop if you experience an actual failure. -J --- -Jay Vosburgh, IBM Linux Technology Center, fubar@us.ibm.com
Thank you for this very complete answer.
- Assuming I really have to implement some sort of inactive slave-link
check.
- Assuming it is acceptable to remove the inactive slave from the bound
for the duration of the check.
Could you help me check my script? It works well for me but as I''m
about
to deploy it for production purpose I''d rather have a double check from
you guys.
(Note: I''m not reliable when it comes to (among other things) routing
and network related topics)
Thx.
Olivier
---------------------------------------------------------------------------------------
#!/bin/bash
# Check all nics enslaved in a bond.
# This is a way to check that all nics (including inactive ones) are
working properly.
#
# Authors:
# OA: Olivier Arsac
# History:
# 19/04/2007: OA scratch
# 31/06/2007: OA better handling of "free" IPs used during test
# TODO:
# remove all TODOs from the script
#set -x
# try to be robust -> exit if a variable is not set (probably something
went wrong)
set -o nounset
trap clean INT TERM
PATH=/exploit/local/sbin:/exploit/local/bin:/usr/kerberos/sbin:/usr/kerberos/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/exploit/unix/prod/bin
com=`basename "$0"`
fullcom="$*"
usage() {
echo "Usage: $com [-q] [-i ip] [-t target] [bond]"
echo " Check all nics enslaved to a bond."
echo " This is a way to check that all nics (including inactive
ones) are working properly. You should check that periodicaly to avoid
nasty surprises when your active nic stops working and you have to
fallback to your (unchecked) slave one."
echo " exit 0 if all is OK (or if no bond is present)."
echo " -q: quiet (no verbose message for human operator)."
echo " -i: ip to use during check of inactive slaves."
echo " -t: target ip to ping during checks."
echo "eg: $com"
echo " check all nics from all bonds."
echo "eg: $com -q bond0"
echo " check silently all nics from bond0."
}
quiet=0
ip=""
target=""
while getopts "qi:t:" option
do
case $option in
q) quiet=1;;
i) ip=$OPTARG;;
t) target=$OPTARG;;
*) usage; exit 1;;
esac
done
# drop what has been parsed by getopts
shift `expr $OPTIND - 1`
# get args
if [ "$#" -ne 0 ]
then
bonds="$@"
for bond in $bonds; do
if [ ! -f /proc/net/bonding/$bond ]; then
echoe "Error: $bond is not a valid bond."
exit 6
fi
done
else
bonds=`ls /proc/net/bonding/ 2>/dev/null`
fi
#match a MAC address
re_mac="([a-zA-Z0-9][a-zA-Z0-9]:){5}[a-zA-Z0-9][a-zA-Z0-9]"
re_ip="(([0-9]{3}[.]){3}[0-9]{3}"
function echoe(){
echo "$@" >/dev/stderr
}
function echoq(){
if [ $quiet -eq 0 ] ; then echo "$@"; fi
}
# set a valid mac to a nic
# (must get a mac from the slaves in bond but one that is not currently
in use by the bond)
get_free_mac_ret=""
function get_free_mac(){
bond=$1
nic=$2
free_mac=""
macs=`grep "Permanent HW addr:" /proc/net/bonding/$bond | egrep -o
$re_mac| tr ''a-z'' ''A-Z''`
bond_mac=`ifconfig $bond | grep HWaddr | egrep -o $re_mac`
for mac in $macs; do
if [ "$mac" != "$bond_mac" ]; then
free_mac=$mac
fi
done
get_free_mac_ret=$free_mac
}
# ping a target using a specified nic to test for IP connectivity
check_nic_ret=0
function check_nic(){
target=$1
if [ $# -ge 2 ]; then
nic=$2
ping -n -c 3 -I $nic $target 1>/dev/null 2>/dev/null
else
ping -n -c 3 $target 1>/dev/null 2>/dev/null
fi
if [ $? -ne 0 ]; then
ma=""
if [ $# -ge 3 ]; then
ma="(using $3 as ip)"
fi
echoq " [ERROR]"
echo "$nic interface on $host is not working properly! $ma" >
/dev/stderr
check_nic_ret=1
else
echoq " [OK]"
check_nic_ret=0
fi
}
# arping a target using a specified nic to test for IP connectivity
function exercise_nic_arp(){
target=$1
nic=$2
src_ip=$3
arping -c 3 -s "$src_ip" -I "$nic" "$target"
1>/dev/null 2>/dev/null
}
# reset a properly configured bond if someone interrupts the script
clean_bond=""
clean_nic=""
function clean(){
echoq
echoq "Script interrupted, restoring bond."
if [ ! -z $clean_bond ] && [ ! -z $clean_nic ]; then
ifenslave $clean_bond $clean_nic 2>/dev/null
fi
exit 2
}
host=`hostname -s`
table=200
if [ ! -d /proc/net/bonding ]; then
echoe "Warning: Module bonding not loaded. Obviously no bond to
check."
#trying to check a bond on a server where none is present is probably
not realy an error -> exit 0 with a warning message
exit 0
fi
if [ -z $target ]; then
# no target given as parameter -> auto-detect
# get the default gateway as a ping target
target=`route -n | grep UG | awk ''{print $2}''`
if [ -z $target ]; then
echoe "Error: Unable to auto-detect the target to use during test
(use -t?)."
exit 3
fi
fi
if [ -z "$ip" ]; then
# no ip given as parameter -> auto-detect
ip_b1=`host "${host}-bond-t1" | grep -o "$re_ip"`
ip_b2=`host "${host}-bond-t2" | grep -o "$re_ip"`
if [ -z "$ip_b1" ] && [ -z "$ip_b2" ]; then
echoe "Error: Unable to auto-detect an ip to use during test (use
-i?)."
exit 4
fi
fi
error_nb=0
for bond in $bonds
do
bond=`basename $bond`
echoq "checking bond $bond"
active=`grep "Active Slave" /proc/net/bonding/$bond |cut
-d'':'' -f2`
echoq -n " active slave :$active"
check_nic $target
error_nb=$(($error_nb + $check_nic_ret))
slaves=`grep "Slave Interface:" /proc/net/bonding/$bond |cut
-d'':'' -f2`
slave_nb=0
for slave in $slaves
do
if [ $slave != $active ]; then
# this nic is enslaved but not active. we want to check if it is
ready to work (no cable or VPN trouble that will bite us only when the
active slave will change)
echoq -n " inactive slave : $slave"
# search for a free mac in this bond (ie a real phy MAC that is
not the one used by the bond)
get_free_mac $bond $slave
free_mac=$get_free_mac_ret
# store the bond/nic we are going to un-enslave (to be able de
re-enslave it in case of interrupt)
clean_bond=$bond
clean_nic=$slave
if [ -z "$ip" ]; then
ip="$ip_b1" # TODO: use a clever way to match slave and free
ip
fi
# free this nic from the bond
ifenslave -d $bond $slave
# set it up with a "free" mac
ifconfig $slave hw ether $free_mac
# set it up with a temp IP
ifconfig $slave $ip netmask 255.255.255.255
# it seems we need a small temporisation here or the rest may fail
sleep 2
exercise_nic_arp $target $slave $ip
check_nic $target $slave $ip
error_nb=$(($error_nb + $check_nic_ret))
# clean this temporary ip/route
ifconfig $slave down
# re-enslave this nic to the bond
ifenslave $bond $slave
clean_bond=""; clean_nic=""
slave_nb=$(($slave_nb + 1))
fi
done
echoq -n " bond : $bond"
check_nic $target $bond
error_nb=$(($error_nb + $check_nic_ret))
if [ $slave_nb -eq 0 ]; then
echoe "Error: No inactive slave in $bond."
exit 5
fi
done
if [ $error_nb -ne 0 ]; then
exit $((10 + $error_nb))
fi
exit 0
---------------------------------------------------------------------------------------