IP SLA

IP SLA

In IOS, IP SLA is used as a redundancy mechanism for static routes. A basic example is when two links towards the ISP are available, and therefore two static defaults routes are configured. IP SLA allows tracking the status of the main link, in order to activate the backup link when the main link goes down.

CISCO IOS

1. Configure IP SLA probe to ping a target (an Internet address, or the next-hop of the primary link)

# ip sla 1
# icmp-echo <primary-next-hop> source-interface <primary-interface>
# timeout 1000
# threshold 2
# frequency 3
# ip sla schedule 1 life forever start-time now

2. configure an IP SLA object to track the status of the probe

# track 1 ip sla 1 reachability

3 Configure the static routes, linking the primary route to the IP SLA object, so that the first route will be deactivated when the probe fails, thus activating the backup link:

# ip route 0.0.0.0 0.0.0.0 <primary-next-hop> track 1
# ip route 0.0.0.0 0.0.0.0 <secondary-next-hop> 10.

JUNOS

In Junos we can use the rpm probe service combined with the IP monitoring feature. There are the following steps to configure IP monitoring.

1. Configure the rpm probe to track the status of the primary next-hop:

# set services rpm probe Probe-Primary-NH test TEST target address <primary-next-hop>

# set services rpm probe Probe-Primary-NH test TEST probe-count 3

# set services rpm probe Probe-Primary-NH test TEST probe-interval 5

# set services rpm probe Probe-Primary-NH test TEST test-interval 5

# set services rpm probe Probe-Primary-NH test TEST thresholds successive-loss 3

# set services rpm probe Probe-Primary-NH test TEST thresholds total-loss

# set services rpm probe Probe-Primary-NH test TEST next-hop<primary-next-hop>

2. Configure the static route towards the first ISP:

# set routing-options static route 0.0.0.0/0 next-hop <primary-next-hop>

3. Configure the IP monitoring service to track the rpm probe, and to install the route towards the secondary next-hop when the primary fails:

# set services ip-monitoring policy MONITORING-POLICY match rpm-probe Probe-Primary-NH

# set services ip-monitoring MONITORING-POLICY then preferred-route route 0.0.0.0/0 next-hop <secondary-next-hop>