Tuesday, December 22, 2009

IP SLA Basic Operation - It's really not that evil :)

So...here I am ...with probably my last Tech post for year 2009...hmmm...somethings were good about this year and some were quite bad...good part was my new job...bad part was local traffic in this country and of course my Malaria infection around July this year...but in total...all is well that ends well :)

So today I am gonna show some IP SLA basics...which still looks like evil stuff to many more Network Engineers out there...My personal experience is it's neither easy nor that tough...The reason I said this because most of the IP SLA configurations are straight forward...but due to it's so many features and tools inside this cool IOS tool...sometimes it takes time to figure out what is going around...

One more thing I would like to mention before diving into configuration is that IP SLA (Service Level Agreement) was also called as SAA (Service Assurance Agent) and RTR (Response Time Reporter) in older IOS versions

Okay...in my scenario we are running HSRP between R1 and R2 with virtual ip as is the active router here with tracking enabled for it's Ethernet interface Fa1/0...now the problem with this scenario is if Ethernet interface of R3 Fa1/0 goes down...we will loose reachability to R4...but the interesting thing is than R2 will remain as Active router for HSRP instance...that's because R2's interface Fa1/0 will remain up because it's a Ethernet interface.So R1 will never take over the load....and we will end up with big mess in our network :(

So let's put IP SLA in action to fix this issue...we will use IP SLA to track reachability to R3's ethernet interface...the IP SLA instance will keep tracking this reachability and the moment it will loose reachability...it will decrement the HSRP priority for the current router by defined factor....So here is the sample config...

ip sla monitor 1
 type echo protocol ipIcmpEcho
 timeout 300
 frequency 1
ip sla monitor schedule 1 life forever start-time now

track 1 rtr 1 reachability

interface FastEthernet0/0
 ip address
 duplex auto
 speed auto
 standby 1 ip
 standby 1 priority 105
 standby 1 preempt
 standby 1 track 1 decrement 50

router ospf 1
 passive-interface FastEthernet0/0
 network area 0

So happy new year in advance to all of you

Best Regards,
Deepak Arora
CCIE#XXXXX...Oops that number is still missing :)

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