IP SLA Group Schedule Query

[CSCO12348032]

We have a MPLS connection between sites and we also have a National Ethernet connection between the remote sites and HQ.

My Query is If I configure IP SLA on our switches like this:

ip sla 1
icmp-echo 192.168.121.153
timeout 1000
threshold 2
frequency 2
ip sla schedule 1 life forever start-time now
ip sla enable reaction-alerts

track 1 ip sla 1 reachability

ip route 0.0.0.0 0.0.0.0 192.168.121.153 track 1
ip route 0.0.0.0 0.0.0.0 192.168.121.74 100

Then it will fail over to use the National Ethernet connection (192.168.121.74) if the link between the switch and the router (192.168.121.153) is down, but doesn't fail over to use the National Ethernet connection if the link between the switch and the router is up but the MPLS WAN connection is down. 

Do I need to do something along the lines of the following to get this to work, If the Link between the switch and the router is up, but the WAN connection is down:

ip sla 2
icmp-echo 192.168.121.153
timeout 1000
threshold 2
frequency 2

ip sla 3
icmp-echo 8.8.8.8
timeout 1000
threshold 2
frequency 2

ip sla group schedule 1 2,3 life forever start-time now
ip sla enable reaction-alerts

track 1 ip sla 1 reachability

ip route 0.0.0.0 0.0.0.0 192.168.121.153 track 1
ip route 0.0.0.0 0.0.0.0 192.168.121.74 100

I am making an assumption (correct or not) that because I have grouped the IP SLA ICMP-ECHO statements then If either of them fails it will fail over to using the National Ethernet connection instead of trying to use the MPLS connection.

[Georg Pauwen]

Hello,

ip sla 1
icmp-echo 192.168.121.153
timeout 1000
threshold 2
frequency 2
ip sla schedule 1 life forever start-time now
ip sla enable reaction-alerts

track 1 ip sla 1 reachability

ip route 0.0.0.0 0.0.0.0 192.168.121.153 track 1
ip route 0.0.0.0 0.0.0.0 192.168.121.74 100

With this configuration, you are tracking the National Ethernet connection. If IP 192.168.121.153 is not reachable, the route the MPLS connection will be installed.

So it looks to me like you have to reverse your configuration and track the MPLS:

ip sla 1
icmp-echo x.x.x.x --> next hop of the MPLS
timeout 1000
threshold 2
frequency 2
ip sla schedule 1 life forever start-time now
ip sla enable reaction-alerts

track 1 ip sla 1 reachability

ip route 0.0.0.0 0.0.0.0 192.168.121.74 track 1
ip route 0.0.0.0 0.0.0.0 192.168.121.153 100

[CSCO12348032]

Apologies Georg, I had the MPLS router IP Address in against the National Ethernet connection.  I have now edited the query above.

[Georg Pauwen]

Hello,

what is your physical setup ? Can you post a brief schematic drawing ?

[CSCO12348032]

I have attached a image which gives you an idea of how this is connected.

I have left off the other three satellite sites as this would just confuse matters.

[Jon Marshall]

Just to clarify, are you using static routing on both links or more importantly on your MPLS network ?

Jon

[CSCO12348032]

There are two OSPF instances.

One which is tagged and the MPLS router propagates that and another one that will propagate over the National Ethernet link.

[Jon Marshall]

So why are you running IP SLA or are the switches not participating in OSPF ?

Jon

[CSCO12348032]

So I should remove the IP SLA configuration and simply add something like 

ip ospf cost 150 to the National Ethernet Interface instead.

[Jon Marshall]

IP SLA is usually used when you are using static routing. However if your switch is receiving OSPF routes from both networks then yes the easiest solution is simply to modify the cost of the link(s)  so that MPLS is preferred.

If the MPLS circuit goes down then your switch will no longer receive the OSPF routes and so failover to the other link. So if your switch is participating in OSPF I cannot see at the moment what benefit IP SLA gives you.

That said your jpg has not come out so it's difficult to be sure.

Jon