One challenge that every WISP owner or operator has faced is how to leverage unused bandwidth on a backup path to generate more revenue.
For networks that have migrated to MPLS and BGP, this is an easier problem to solve as there are tools that can be used in those protocols like communities or MPLS TE to help manage traffic and set policy.
However, many WISPs rely solely on OSPF and cost adjustment to attempt to influence traffic. Alternatively, trying to use policy routing can lead to a design that doesn’t failover or scale well.
Creating a bottleneck on a single path
WISPs that are OSPF routed will often have a primary path back to the Internet at one or more points in the network typically from a tower that aggregates multiple backhauls.
As more towers are added that rely on this path, it can create a bottleneck while other paths are unused.
Creating an alternate best path by leapfrogging another router
One way to solve this problem is to use VLANs to create another subnet for OSPF to form an adjacency.
By tagging the VLAN from Tower 6 through Tower 3 and into Tower 4, a new path for OSPF is created that will cause Tower 6 and Tower 7 to take an alternate path.
This allows a WISP operator to tap into unused bandwidth while still retaining a straightforward failover mechanism.
Tower 6 and 7 can now use the alternative path
Now that a lower cost path exists at Layer 3 for Tower 6 and 7, the original best path become less congested and bandwidth that was previously unused can now be used to load balance traffic.
How to build the new path?
I often recommend “switch-centric” architecture also known as “router-on-a-stick” when building a WISP – there are a number of benefits to doing this. In this case, since the switches handle all connections, it’s fairly easy to tag a VLAN from Tower 6 to Tower 4 and create the “leapfrog” path.
A few closing thoughts
This works well when the towers you need to move onto an alternate path are part of a stub network – that is, they only have one way into the aggregation point before the traffic is split.
If you were trying to do this with rings that connect to other rings and had redundant paths, there could be unintended results so you need to plan the costs and paths carefully.
Labbing the topology to see what will happen is always a good idea.
Hope this is helpful for someone looking to get just a little more bandwidth out of an OSPF based WISP network.
One of the hardest things to do quickly in network engineering, is learn a new syntax for a NOS. Especially if you have a tight deadline and need to stand up equipment you’ve never worked with before. The command structure for RouterOS can be cumbersome if you are used to the Cisco CLI.
If you’ve been in networking for a while, you probably started with learning the Cisco CLI. Therefore, it is helpful to compare the commands if you want to implement a network with a MikroTik and Cisco routers.
This is the third post in a series that creates a Rosetta stone between IOS and RouterOS. We plan to tackle other command comparisons like VLANs, QoS and basic operations to make it easier for network engineers trained in Cisco IOS to successfully implement Mikrotik / RouterOS devices.
Click here for the first article in this series – “Cisco to MikroTik BGP command translation” Click here for the second article in this series – “Cisco to MikroTik OSPF command translation”
While many commands have almost the exact same information, others are as close as possible. Since there isn’t always an exact match, sometimes you may have to run two or three commands to get the information needed.
Using EVE-NG for testing
In the last article, we began using EVE-NG instead of GNS3 to emulate both Cisco IOS and RouterOS so we could compare the different commands and ensure the translation was as close as possible. Don’t get me wrong, I like GNS3, but the web interface of EVE-NG makes it really easy to keep all the horsepower for complex labs at a central location and then VPN in to work on labs as needed.
Network for Basic mpls commands
show mpls ldp neighbor
mpls ldp neighbor print
show mpls interfaces
mpls ldp interface print
show mpls forwarding-table
mpls forwarding-table print
show mpls binding
mpls remote-bindings print
sh mpls ip binding local
mpls local-bindings print
sh mpls label range
sh mpls ldp parameters
mpls ldp print
/mpls ldp interface
mpls ldp router-id Loopback0
set enabled=yes lsr-id=10.1.1.3
Examples of the MikroTik RouterOS commands from the table above