Help with a packet loop and static routes on packet tracer lab

[ThomasD86]

Hi,
I've started yesterday the Module 2 of CCNA Routing and switching and, after reading about static route, I was given a packet tracer lab with a list of requisites to satisfy. I've done the most but there's a part that I can't just figure out.

This is the topology of the network I am working with:

The exercise asks that traffic originating from the network on Router0, gets routed through the main route through Router2 before reaching Router1 and any traffic directed to the network behind Router0, should follow the same path backwards. I've achieved that with static routing.

The problem originates with the second half of this lab, the lab also asks that every device should be accessible even in the case the main route cable gets unplugged by using the Route going from Router0 to Router1 labeled as "backup" in the picture. This is where I can't figure out what I am missing.

If, I set up a static route on Router1 telling it to route traffic directed to Router0 through the backup route, it works with the main route unplugged but, when I plug the cable, the Router1 will still direct traffic towards Router0 on the backup route, rather than sending it to Router2

If I remove the static route towards the Router0 network on Router1, it will work as intended while the main route cable is plugged but, when I unplug it, if I try to ping from a pc on the Router0 network a pc on the Router2 network, the echo packet will bounce until it expires between Router 2 and 1.

I get why this is happens, the Router2 has a static route with a higher administrative distance I've set that tells it to route packets through Router1 should the direct connection not be available with Router0 and, it does so. However, not to make Router1 route traffic towards Router0 through the backup route, I've specified a route that tells it to use Router2 as next hop to reach that network. So when Router1 gets that packet it obviously sends it back towards Router2.

Admin distance seems not to help me because the Router1 has no way of knowing that the cable between Router2 and Router0 has been unplugged and thus he will just try to send it through the route I told him to. If I remove the static route on Router1, it will stop the loop but, when I plug the cable back in, all the traffic from Router1 to Router0 will go through the "backup" path rather than going through Router2.

I am at a loss on how to solve this, could anyone give me some tips? Thanks

[Deepak Kumar]

Hi,
You can archive the same with increasing the AD value of default route.
as
on Router0
ip route 0.0.0.0 0.0.0.0 <Router 1 Interface IP> 2 <AD value>

the same setting you can apply on router1 for default route toward to router0.

So this path will become a backup path and will initialize after down the network between R0 to R2.  

Regards,

Deepak Kumar

[ThomasD86]

Hi Deepak, thanky you for helping me.
I've tried the solution you suggest but the behaviour stays the same, when the network between 0 and 2 is down, everything works, but when the link between 0 and 2 is up, router1 still routes packets for 0 directly to it rather than going through 2. For instance with the network up, if I ping a pc on the router 0 network, the ping will go through router 2, then 1, then to the pc, but when the reply reaches router 1, rather than going through 2, it goes straight back to router 0

The Ip routes are the following

Router0:

ip route 172.16.44.0 255.255.255.0 192.168.20.2

ip route 172.16.44.0 255.255.255.0 192.168.30.2 2

ip route 10.0.0.0 255.255.255.0 192.168.20.2

ip route 10.0.0.0 255.255.255.0 192.168.30.2 2

ip route 0.0.0.0 0.0.0.0 192.168.30.2 2

ip route 0.0.0.0 0.0.0.0 192.168.20.2

Router2:

ip route 10.10.10.0 255.255.255.0 192.168.20.1

ip route 10.10.10.0 255.255.255.0 192.168.10.2 2

ip route 172.16.44.0 255.255.255.0 192.168.10.2

ip route 0.0.0.0 0.0.0.0 192.168.10.2 2

Router1:

ip route 10.0.0.0 255.255.255.0 192.168.10.1

ip route 10.10.10.0 255.255.255.0 192.168.30.1 2

ip route 0.0.0.0 0.0.0.0 192.168.30.1 2

The extra 0's in router 0 and 1 are because the pc need to be able to ping what is labeled as ISP on the topology (209.96.23.1)

[chrihussey]

Does this specifically say to use only static routing? The problem is that R0 will never know when the connection between R2 and R1 is up or down. The same holds true in that R1 will never know when the link between R2 and R0 is down.

If that is the case you could create two static routes in each of the routers with various administrative distances and track the far end IPs for the main routes. For example:

R0

ip sla 1

icmp-echo 192.168.10.x (R1 IP) source-interface (R0 interface to R2)

timeout 2000

frequency 5

threshold 250

!

ip sla schedule 1 start-time now life forever

!

track 10 ip sla reachability

!

! (Create primary static route give it an admin distance of 100 and track the reachability from R2 to R1)

ip route 0.0.0.0 0.0.0.0 192.168.20.x (R2 IP) 100 track 10

!

!(Create backup static route to R1 with a higher admin distance)

ip route 0.0.0.0 0.0.0.0 192.168.30.x (R1 IP) 255

!

So in this case if R0 cannot ping the R1 interface that connects to R2, it will withdraw the primary static and route to R1. You would need to configure this appropriately with the other routers. Here a link I referenced:

https://www.grandmetric.com/knowledge-base/design_and_configure/ip-sla-config-and-static-route-tracking/

This is a bit convoluted and others may have better ideas.

Finally, this could be accomplished so much easier if you implement a dynamic routing protocol such as EIGRP or OSPF and simply adjust route metrics.

Anyway, hope this is of some help.