How to configure IP SLA for failover in Cisco 1841?

[deepthirajt]

Should I configure a IP SLA responder?

If yes, How can I do that?

[cadet alain]

Hi,

you don't need a responder for simple failover scenario. just create a sla object of type echo and track it and associate the track object with a static route or a PBR depending on what you want to do.

Regards.

Alain.

[tommyboay]

Hi,

IP SLA responder is only needed on IP SLA destination devices where certains statistics are required (MOS, UDP jitter).

In your case, simple reachability operations are good enough and won't need no responders.

Just create your operation :

ip sla 1

icmp-echo x.x.x.x source-ip x.x.x.x

timeout 500

frequency 1

ip sla schedule 1 life forever start-time now

Create a track operation to control reachability :

track 1 ip sla 1 reachability

Create your conditional static route :

ip route 0.0.0.0 0.0.0.0 x.x.x.x track 1

Important note : When dealing with failover on dual ISP (supposing it is not dual homing), you should be aware that monitoring the next hop is not sufficient to guarantee the sanity of your access. You should have a pool of destinations where a majority should stay reachable before removing the route.

HTH

Tom

[deepthirajt]

Thanks Alain and Tom.

I have configured the below scenario.

When I remove the route with the red X, the track reachability goes down (which is correct).

When I ping the device 192.168.20.254, I get a reply.

How so I verify that the router is learning that the link is down using the IP SLA? This setup can be implemented using a simple static route as well isn't?

I have configured IP SLA 1 & 2 for ISP A only.

IP SLA 1 - 172.16.1.1 to 172.16.1.3

IP SLA 2 - 172.16.1.1 to 172.16.1.2

     172.17.0.0/24 is subnetted, 1 subnets

C       172.17.1.0 is directly connected, FastEthernet0/1

     172.16.0.0/24 is subnetted, 1 subnets

C       172.16.1.0 is directly connected, FastEthernet0/0

S    192.168.21.0/24 [1/0] via 172.17.1.3

                     [1/0] via 172.16.1.3

S    192.168.20.0/24 [1/0] via 172.17.1.2

                     [1/0] via 172.16.1.2

[tommyboay]

I do not understand your question : What exactly is your goal ? Being informed that an IP SLA operation failed ? That your routing table has changed ? I'm unsure on what exactly you're trying to achieve.

Tom

[deepthirajt]

Sorry Tom, should have been clearer.

Goal is to achieve failover when the primary link goes down.

I have done the following:

Assigned 2 static routes to each site via ISP A and B.

ISP A being the primary link.

Configured IP SLA 1 to monitor the connectivity between the Cisco 1841 ISP A interface (172.16.1.1) and  WAN1 (172.16.1.3) interface on the firewall 192.168.21.254

Similarily, I have Configured IP SLA 2 to monitor the connectivity between the Cisco 1841 ISP A interface (172.16.1.1) and  WAN1 (172.16.1.2) interface on the firewall 192.168.20.254

Now, when I unplug the cable connecting the Firewall 192.168.20.254 and the switch, the reachability goes down as expected, and I am able to ping the device even though the primary link is down.

My queston is: Is the router learning that the track 1 is down and switching over the link OR is it sending the ping request using the static route using ISP B.

[cadet alain]

hi,

My queston is: Is the router learning that the track 1 is down and  switching over the link OR is it sending the ping request using the  static route using ISP B.

a traceroute will tell you that as well as a sh ip route and you should have a log message saying the track object is down.

Regards.

Alain.

[cadet alain]

Hi,

the second static route pointing to backup ISP must have an AD > 1 so it is not installed in the routing table when the track object linked to first static route is up and only when this track object is down will the floating static route be installed in the routing table to still get connectivity to distant subnet.

eg: ip route x.x.x.x y.y.y.y  track 1

     ip route x.x.x.x y.y.y.y  2

You had left the default AD for both routes so they get both installed into rib and the switching process will do load balancing

Regards.

Alain.

[deepthirajt]

When I define a static route as "IP route192.168.20.0 255.255.255.0  172.17.1.2 10" and unplug the cable, I am unable to ping the device 192.168.20.254.

Traceroute command has no entries for all 30 hops.

Also, when I define routes with AD, they don't reflect when I do a show ip route or show IP route static.

[cadet alain]

if a  static route with  higher AD for the same prefix is not installed in the RIB when the route with lower AD goes down then there is a problem with the tracking.

Do you see  a log message about the track object? do debug track and debug ip routing to see if it is working right.

Regards.

Alain.

[Bharat Sharma]

Thanks

[Georg Pauwen]

Hello,

post the configs of both routers and indicate which interfaces are connected to the firewall...

[Bharat Sharma]

Kindly check & suggest solution for same.

[Georg Pauwen]

Great, thanks, I'll have a look...

[Georg Pauwen]

Hello,

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