WISP Design – OSPF “Leapfrog” path for traffic engineering

Introduction

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.

ospf-leapfrog-pic1

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.

ospf-leapfrog-pic2

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.

opsf-leapfrog-pic3

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.

opsf-leapfrog-pic4

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.

 

Read More

Cisco to MikroTik – MPLS

About the Cisco to MikroTik series

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

MPLS-Cisco-to-MikroTik

Cisco commandMikroTik Command
show mpls ldp neighbormpls ldp neighbor print
show mpls interfacesmpls ldp interface print
show mpls forwarding-tablempls forwarding-table print
show mpls bindingmpls remote-bindings print
sh mpls ip binding localmpls local-bindings print
sh mpls label rangempls print
sh mpls ldp parametersmpls ldp print
interface GigabitEthernet0/1
mpls ip
/mpls ldp interface
add interface=ether1
mpls ldp router-id Loopback0/mpls ldp
set enabled=yes lsr-id=10.1.1.3

Examples of the MikroTik RouterOS commands from the table above


[admin@MikroTik] > mpls ldp neighbor print

This command will show LDP neighbors and detail on whether they are Dynamic, Targeted, Operational or using VPLS

mpls-ldp-neighbor-print

[admin@MikroTik] > mpls ldp interface print

This command will list the interfaces that LDP is enabled on

mpls-ldp-interface-print

[admin@MikroTik] > mpls forwarding-table print

Use this command to display the MPLS forwarding table which shows what labels are assigned, the interface used and the next hop.

mpls-forwarding-table-print

[admin@MikroTik] > mpls remote-bindings print

This is a quick way to show remote bindings which displays the labels desired and used by the next hop routers for each prefix.

mpls-remote-bindings-print

[admin@MikroTik] > mpls local-bindings print

This is a quick way to show local bindings which displays the labels desired and used by the local router – in this case R3.

mpls-local-bindings-print

[admin@MikroTik] > mpls print

This is a quick way to show basic mpls settings for RouterOS which includes the label range and whether or not to propagate TTL which affects what a traceroute looks like over an MPLS network.

mpls-print

[admin@MikroTik] > mpls ldp print

This is a quick way to show mpls ldp settings for Router-OS including whether or not LDP is enabled.

mpls-ldp-print

Configurations

R1

R2

R3

R4

 

 

 

Read More