Failover and Redunancy Ideas?

[Paul Smith]

Hi Guys,

I have a Cisco 2901 router that is supporting around 200 users. It has a 100Mbps fibre WAN interface and multiple VLANS internally. It has two Azure tunnels and two AWS tunnels.

I have been asked to create a failover solution, however the decision was made from above to supplky a second 2901 but with a 4G card and SIM.

I have managed to get traffic going across the 4G but the big question is;

How do I get these two routers to work effectively in an automatic failover solution? eg HSRP, IP SLA?

[Julio E. Moisa · Accepted solution]

Hi

You can use SLA and EEM script to create an automatic failover, please let me share an example.

This script will be checking the response from the ip 8.8.8.8 frecuently, once the SLA is not receiving answer it will generate a message, this message will trigger the script to execute what you want. 

track 10 ip sla 10 reachability
delay down 10

ip sla 10
icmp-echo 8.8.8.8 source-ip 1.1.1.2
frequency 5

ip sla schedule 10 life forever start-time now
ip sla enable reaction-alerts

event manager applet FAILOVER-INTERNET

 event tag prim syslog occurs 1 pattern "%TRACKING-5-STATE: 10 rtr 10 state Up->Down"

 event tag sec syslog occurs 1 pattern "%TRACKING-5-STATE: 10 rtr 10 reachability Up->Down"

 trigger

  correlate event prim or event sec

 action 1.0 cli command "enable"

 action 2.0 cli command "no ip route 0.0.0.0 0.0.0.0 1.1.1.1 track 10"  <--remove the current default route.
 action 3.0 cli command "ip route 0.0.0.0 0.0.0.0 2.2.2.2 "   <--create a new default route pointing to other next hop

 action 4.0 cli command "exit"

 action 5.0 cli command "write memory"

*HSRP could be useful if you are connecting to devices working as active/standby like some cases with the firewalls. 

Hope it is useful

:-)

[Paul Smith]

Thank you, I love it. In this situation would you recommend a third router in case the router with SLA fails?

[Julio E. Moisa]

Hi

Thanks Paul, No, You don't need a third router, 2 routers are enough for high availability. Just a couple of questions, Will the routers be connected directly to different ISP's, and will they be receiving the Internet access directly?

:-)

[Paul Smith]

Hi Julio,

Yes they will be connected to two different ISP's. One will be fibre and the other will be 4G (LTE). Although in saying that, it is actually the same ISP (Tesltra). The only thing that is not desirable is that the LTE connection can't have static IP, according to Telstra.

Thanks again.

[Julio E. Moisa]

Hi

Thank you Paul,

You will configure static default route on both routers and interconnect them, If the second router will be getting random public IP (by dhcp I guess). Im assuming the 4G LTE Internet will work as backup access, is that correct?

So you could create a script to remove the default route on the primary router once the primary internet fails and say to the script create a default route pointing to the second router. So the traffic will be moved to the secondary router to get Internet access through the 4G LTE access.

Do you have a diagram how it will be implemented?