Hello fellow WISPers,

We have a scenario that we have been hashing out the engineering of, and we thought would be good to get the communities thoughts. Please see the attached diagram for reference (I understand its simplicity, please forgive). The example diagram is not our specific setup, but is a simplified version of what we have.

The Scenario:
Currently running OSPF
QRT-6 and QRT-7 are different paths that eventually lead to separate upstream providers, each of which by default have the same path costs.
With OSPF, we can only send all of the downstream networks over one of the paths at any given time by raising the costs of one of the links.
We do not want to employ EqualCostMultiPath routing, as we do not want to load balance the links.

Goal:
To route traffic from QRT-8's networks to the QRT-6 Path, while the remaining networks route to QRT7's path, while maintaining OSPF and a dynamically changing network.

Obstacles:
#1 - These networks are downstream from many other paths and routers. At any time, the path costs to QRT-6 and QRT-7 could become unequal, and skew one direction, however the traffic of QRT-8 should only flow through QRT-6 unless that route fails.
#2 - If using marks to create routing policies, and the path cost out QRT-6 dynamically increases large enough over the path out QRT-7, the traffic will flow from QRT-8 out QRT-6 but then loop back on the next hop router to ultimately head out QRT-7.

Is this an instance that would be served well with a MPLS 'Tunnel'?

This will not be a one-off configuration, but will be implemented similarly at a few dozen locations. So from a management standpoint, a significant amount of static configuration could be a nightmare. Also, solutions that do not provide an easy method to identify and isolate problems could also prove to be problematic (aka- no way to tell without a torch which way traffic is actually flowing)

You can use traffic engineering tunnels for this.. you can either get those to use a dynamic path, which assigns tunnels to paths automatically based on which paths have enough remaining capacity for bandwidth for the tunnel, or you can configure a manual path. The dynamic option allows you to 'load balance' the links by placing some tunnels over one and some over the other, so it is not traditional load balancing, it may work OK for your situation. By default it will place the tunnels over the link that gives the shortest path to the destination that still provides the required bandwidth to the destination.

I would suggest trying out the solution first with dynamic tunnel paths and see if you can coax those into the configuration you want. Go to manual tunnel paths if that doesn't work out.