During a project I’ve been working on, we needed to configure OTV on a Cisco ASR. I did write a blog for configuring OTV on a Nexus 7000 before (click here) but the configuration on a Cisco ASR router is a bit different. The used technologies and basic configuration steps are equal, but the syntax is different for a few configuration steps .
Unfortunately, the documentation is not as good as for the Nexus 7000. I’ve found one good configuration guide (here) but this guide isn’t covering all. So, it’s a good reason to write a blog post about the basic OTV configuration on a Cisco ASR router.
For more information about OTV, check this website.
First, the network layout for this OTV network.
As you can see in the diagram, the ASR routers are back-to-back connected. There is no guideline how to connect these routers, as long as there is IP connectivity between them with multicast capabilities and a MTU of atleast 1542 btyes.
Another post, this time about the basic OTV configuration on a Nexus 7000.
The OTV configuration has the be made on a different switch (or VDC) where no SVI’s are configured for the VLAN’s you want to extend to the other site.
First of all some terminology:
- Edge device: This device performs layer 2 activities (to the internal network) and OTV transportation to the other site(s).
- Transport network: This is the network (can be layer 3) that connects all the sites. This is your WAN connection, possible managed by your service provider.
- Join interface: This is the uplink interface on the edge device that is connected to the transport network.
- Internal interface: This is the interface on the edge device that is connected to the internal network.
- Overlay interface: This is a logical interface, with support for multi access, multicast. This interface encapsulates layer 2 frames in IP headers (also ‘MAC routing’)
- Overlay network: A logical network that connects all sites together and uses MAC routing for interconnecting the sites.
- Site: Your (layer 2) network on a location. In most cases, this is one of your datacenters.
Cisco published a configuration guide for connecting a Nexus 2248TP FEX to a Nexus 7000. I’ll explain the configuration process to configure the FEX for basic connectivity.
A FEX is a Nexus 2000 series switch. In a very high level explanation, this switch is a switchport module in a separate 1U chassis, which is configured and controlled from a Nexus 5000/7000. There is 1 drawback: the switchports on the FEX can only be used for host ports. It’s not possible to connect other switches to a FEX port because of the fact that BPDUguard is enabled by default. It’s not possible to disable BPDUguard. Switchports on the FEX can be used for layer 2 and layer 3 connections. For more information about the FEX itself I’ll refer to this link
All configuration is done on the Nexus 7000 with NX-OS 6.0(1). In this scenario, the 2248TP FEX is connected to switchport ethernet 1/1 (10GE port) of the Nexus 7000 with a twinax cable.
First, let’s configure a switchport for the FEX:
switch(config)# int ethernet 1/1
switch(config-if)# switchport mode fex-fabric
Error: feature-set fex is not enabled
Okay, we have to install (!) and enable the fex feature before we can continue
switch(config)# install feature-set fex
switch(config)# feature-set fex
And try again to configure the fex-fabric mode: