Hello,
I am facing problem with ip sla track mechanism.
I have two ISPs connected to my router C881.
- ISP1 = primary (connected to FastEthernet4)
- ISP2 = backup (connected to FastEterhet3/Vlan20)
I am using ISP1 as primary ISP and tracking reachability of IP address 8.8.4.4 through ip sla track 200:
!
ip sla 200
icmp-echo 8.8.4.4
request-data-size 200
timeout 3000
threshold 1000
owner SYSADMIN
frequency 5
history hours-of-statistics-kept 25
history distributions-of-statistics-kept 20
history lives-kept 2
history buckets-kept 60
history filter all
!
ip sla schedule 200 life forever start-time now
ip sla enable reaction-alerts
!
track 200 ip sla 200 reachability
delay down 30 up 180
!
Default-route to ISP1 is tracked and second default-route is configured with higher value of metric.
This is how my static routing looks like:
!
ip route 0.0.0.0 0.0.0.0 FastEthernet4 1.1.1.1 name ISP1 track 200
ip route 0.0.0.0 0.0.0.0 Vlan20 2.2.2.2 250 name ISP2
ip route 8.8.4.4 255.255.255.255 FastEthernet4 1.1.1.1 name force-ISP1
ip route 8.8.4.4 255.255.255.255 Null0 250 name deny-via-ISP2
!
It works almost as expected:
- when ISP1 is going down (i mean if 8.8.4.4 becomes unreachable via ISP1), after 30 seconds, default route is pointing to ISP2
- also when ISP1 is going up (8.8.4.4 becomes reachable again via ISP1), after 180 seconds, default route is pointing back to ISP1
*Mar 14 14:09:52.034: %TRACKING-5-STATE: 200 ip sla 200 reachability Up->Down
*Mar 14 14:12:57.039: %TRACKING-5-STATE: 200 ip sla 200 reachability Down->Up
...but
In some cases (I believe that it may be in situation, that ISP1 is down for longer time), ip sla/track is unable to detect that ISP1 becomes UP again and the default route is pointing to ISP2 forever (at least until FastEthernet4 is disconnected/connected again, or shut/no shut command is applied).
*Mar 17 14:18:13.019: %TRACKING-5-STATE: 200 ip sla 200 reachability Up->Down
This is how some show command outputs looks like:
ROUTER-MD#show ip route static
8.0.0.0/32 is subnetted, 2 subnets
S 8.8.4.4 [1/0] via 1.1.1.1, FastEthernet4
S* 0.0.0.0/0 [250/0] via 2.2.2.2, Vlan20
ROUTER-MD#show ip sla statistics 200 details
IPSLAs Latest Operation Statistics
IPSLA operation id: 200
Latest RTT: NoConnection/Busy/Timeout
Latest operation start time: *12:17:51.494 MET Wed Mar 18 2015
Latest operation return code: Timeout
Over thresholds occurred: FALSE
Number of successes: 0
Number of failures: 31
Operation time to live: Forever
Operational state of entry: Active
Last time this entry was reset: Never
ROUTER-MD#show track 200
Track 200
IP SLA 200 reachability
Reachability is Down
42 changes, last change 22:00:06
Delay up 180 secs, down 30 secs
Latest operation return code: Timeout
Tracked by:
STATIC-IP-ROUTING 0
But as you can see here, 8.8.4.4 is reachable from the router:
ROUTER-MD#show ip route 8.8.4.4
Routing entry for 8.8.4.4/32
Known via "static", distance 1, metric 0
Routing Descriptor Blocks:
* 1.1.1.1, via FastEthernet4
Route metric is 0, traffic share count is 1
ROUTER-MD#ping 8.8.4.4
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 8.8.4.4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 40/41/44 ms
During that behavior, I see no icmp traffic destined to 8.8.4.4 with "debug ip icmp" command enabled.
Debug IP sla & track results are here:
ROUTER-MD#show debug
Track debugging is on
IP SLAs:
TRACE debugging is on for entries:
200
ERROR debugging is on for entries:
200
*Mar 18 12:40:16.530: IP SLAs(200) Scheduler: saaSchedulerEventWakeup
*Mar 18 12:40:16.530: IP SLAs(200) Scheduler: Starting an operation
*Mar 18 12:40:16.530: IP SLAs(200) echo operation: Sending an echo operation - destAddr=8.8.4.4, sAddr=1.1.1.2
*Mar 18 12:40:16.530: IP SLAs(200) echo operation: Sending ID: 27
*Mar 18 12:40:19.530: IP SLAs(200) echo operation: Timeout - destAddr=8.8.4.4, sAddr=1.1.1.2
*Mar 18 12:40:19.530: IP SLAs(200) Scheduler: Updating result
*Mar 18 12:40:19.530: IP SLAs(200) Scheduler: start wakeup timer, delay = 2000
*Mar 18 12:40:21.530: IP SLAs(200) Scheduler: saaSchedulerEventWakeup
*Mar 18 12:40:21.530: IP SLAs(200) Scheduler: Starting an operation
*Mar 18 12:40:21.530: IP SLAs(200) echo operation: Sending an echo operation - destAddr=8.8.4.4, sAddr=1.1.1.2
*Mar 18 12:40:21.530: IP SLAs(200) echo operation: Sending ID: 27
*Mar 18 12:40:24.530: IP SLAs(200) echo operation: Timeout - destAddr=8.8.4.4, sAddr=1.1.1.2
*Mar 18 12:40:24.530: IP SLAs(200) Scheduler: Updating result
*Mar 18 12:40:24.530: IP SLAs(200) Scheduler: start wakeup timer, delay = 2000
...etc
I would appreciate any help.
Thank you,
MB
