A question about static and default routes

[joch2joch]

Hi!

We currently have a WAN set up in the manner depicted in the attached diagram. For traffic between the 2 sites, we have designed it such that the private MPLS link will be the preferred route, by adding static routes into the each site's main routers (A-R1 and B-R1). Therefore, in case the MPLS link fails, the main site routers should forward the packets out through the Internet.

But after a little bit more thought, I am having doubts as to whether the fault-tolerant design works.

For example, assuming the link between the main router and MPLS router at B-R1 and B-R2 fails..how will A-R1 or A-R2 know?

A-R1 -> A-R2 -> B-R2 -> cannot reach B-R1

Would B-R2 push the packets back to A-R2 using its own default route? But what about the default route of A-R2? Will this result in a infinite ping pong between A-R2 and B-R2?

Need enlightenment! :)

Thank you!!

Joe

[wrockall]

Hey Joe,

I am afraid from the info you have given I really don't think your configuration will work in a failure situation.

In order to let routers B1 and A1 know that the link between B2 and A2 is down, or even the link between A1 and A2 or B1 and B2, you will need to use a dynamic routing protocol like RIP or OSPF (RIP is much simpler to understand but much less feature reach).

Perhaps something that concerns me more is that if your MPLS is down you will be dumping all of your traffic onto the Internet, how are they to find their way to the other network or have you configured a tunnel over the Internet that you have not shown?

Regards

Wil

[tdeadman]

You could try a GRE tunnel between AR1 and BR1 going via the MPLS. That way if you loose the MPLS the tunnel will go "hard" down...

But Wil is right....you need to do something with the internet routers.

Tim

[wrockall]

I would set the tunnel over the Internet rather than over the MPLS, and set a floating static towards that. I would then run RIP over the MPLS. That way there will be the fail over your require.

[joch2joch]

Hi Will, yes u r right..there was something else that i didn't illustrate. Actually, the both sides have a VPN tunnel running. I've updated the diagram now.

Well, believe it or not, this particular service provider told us that they cannot run routing protocols through their MPLS backbone...so, had to use static routes.

Joe

[wrockall]

Now I am really confused. Does the tunnel run from the two firewalls on the LANs? Does this normally run across the MPLS? What reason did your ISP give for not letting you run an IGP over the MPLS?

As always, more questions that answers!

[rrijk]

Joe,

Ever thought about "PBR Support for Multiple Tracking Options". It is like an IF THEN ELSE statement. You can ping router B and if router B answers THEN route traffic to router B. IF router B will NOT answer THEN route traffic through the internet. See: http://www.cisco.com/en/US/products/sw/iosswrel/ps5207/products_feature_guide09186a00801d1e95.html

regards,

RdR