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IP SLA design for VSAT Links


Hi all,

     We added following config to track VSAT links. But the problem is whenever VSAT bandwidth is FULL, track is getting failed automatically and automatically default route switching over to dialup.

    Once the traffic is started to flow though dialup link VSAT bandwidth is coming to low and track will get success. Then default route is switching over to VSAT.

     This happening again and agin. please guide me to resolve this track flapping issue.

SLA config :

ip sla 109

icmp-echo source-interface Tunnel10

timeout 6000

frequency 10

ip sla schedule 109 life forever start-time now

Track config :

track 109 ip sla 109 reachability

route config :

ip route Tunnel10 track 109

ip route tunnel5 50

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3 Replies 3

cadet alain


Maybe you could shape traffic going over VSAT so bandwidth is never FULL.



Don't forget to rate helpful posts.



I get this a lot too. What I did in the end was configure the IP SLA to use a TOS (Type of Service ) value. You configure it under the ip sla object itself. e.g.

ip sla 109

icmp-echo source-interface Tunnel10

tos 184

timeout 6000

frequency 10

ip sla schedule 109 life forever start-time now

There is a matrix for TOS values and how it is respresented in DSCP etc. 184 is basically DSCP 46 or Expedited Forwarding. By setting the TOS value on the IP SLA packets it'll now get expeditited out of the router faster. Crucially of course you ALSO need to create a QOS framework on your router to manage the packets so that your SLA gets pushed out above all the others.

So a basic MQC might look like this (forgive me I'm writing this from my head). Basically I'll be permitting the SLA traffic 8kbps (which is more than enough) as priority traffic and then shaping all other traffic to 98% of the line rate. You'll need to set the correct 'bandwidth' statement under the interface facing the VSAT (i've suggested 2Mbps). I noticed you are using a tunnel interface in your statement so you'll also need to use the 'qos pre-classify' statement in that logical interface.

class-map SLA

match dscp ef

policy-map SHAPER

class SLA

  priority 8

class class-default

   shape average 98%

interface G0/0

service-policy output SHAPER

bandwidth 2048000

interface tu10

qos pre-classify

Hope this helps


Alteranitely if you do not want to configure qos to the router you can use to the static route a track with multiple sla.

So, the static route will removed if all the sla (so all the packets) fail on the same time.

You can achieve this if you configure a Tracked List and Boolean Expression.

A tracked list contains one or more objects. The Boolean expression enables two types of calculation by using either "and" or "or" operators.In your case you need to use "and" and as many sla as you think are needed in order to overcome your problem

You can find detailed examples to the next link:

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