FFHO – SDN Clinic

Semantic Tags in NetBox

Although NetBox has a pretty nice data model and a lot of things found in common environments can be modeled pretty well, it sometimes reaches its limits. In such situations you’re faced with multiple options to go forward

Introduce (a number of) custom field(s) to extend the data model
Write a plugin to extend the data model (and logic)
Introduce a (set of) tag(s) to allow users to place bumper stickers on things
File a feature request to add some generic missing feature

In this post we’ll look into options for using Tags to denote characteristics of devices, VMs, interfaces, prefixes, IPs, etc.

Simple labels

Sometimes it’s enough to just label a device, an interfaces, etc. with a static bit of information. Examples would be

Enable backup on this device (e.g. tag backup)
Enable DHCP on this interface (e.g. tag DHCP)
Mark an interface as planned or offline (e.g. tags planned or offline)
Denote an interface is of type Wireguard (e.g. tag Wireguard)
etc.

For those cases you can create a tag, e.g. planned, and apply it to any interface which is configured in NetBox, should be configured on the device but isn’t connected yet, so that effectively you can push down (parts of) the interface configuration to the device but inhibit alarms for it being offline or IGP adjacencies being down. The same is true for device which need to be backed up, etc.

One way of thinking of these example is as a boolean switch, which is set to true if the tag is applied. This is easy for cases where the “false” value is the default, so only the outliers – meaning “true” values – need to be represented explicitly.

Semantic labels

But what to do when there is a need for a tri-state value, e.g. true, false, unset, with unset being the default?

One example would be a part of an SDN controller which figures out if uRPF should be enabled on a given interface or not. This usually can be done programmatically, but in some situations an explicit override may be required. That’s where – what I would call them – Semantic Labels come in!

This means, that we also put the value we want to assign a given label into the tag. In this case, we create two labels called urpf=on as well as urpf=off (or urpf=enable and urpf=disable as you fancy) and apply these to any interface requiring an explicit override. If no tag is present the code decides about the fate of uRPF.

Why not use custom fields?!

At this point you may be wondering “Why bother? Just create a custom field, you can provide the allowed options and get input validation for free!

The reason is that if you go down this path, you can create a fairly long list of custom fields in the UI (and API) which are likely not set for the majority of you interfaces (in this example). This creates clutter within the UI and is likely to confuse users, especially if you end up with a number of custom fields.

My rule of thumb is, that I only create a custom field if it’s relevant for all or a least the majority of entities of a given kind. For example, if you wanted to store the data center tier of all the DC (read: Sites) you are present in, it might make sense to store this information as a custom fields on the Site model, with a predefined list of values (1 – 4).

More examples

In the example above we could also have created two labels, e.g. uRPF enable and uRPF disable and let our automation handle the differentiation – which actually is how the FFHO SDN is built as of today.

For other bits of information, with more possible values, the benefits of the key=value approach can shine, for example if you want to

explicitly set the OSPF cost of an interface (e.g. ospf_cost=100)
store the maximum capacity of VRFs of a box (e.g. capacity=62 for a box with a Mellanox Spectrum 1 ASIC with a default + mgmt VRF in place)

Although I now prefer the key=value approach as it’s easy to recognize and parse, you can obviously place values in labels by following any common format you define. For the Freifunk Hochstift Backbone I introduced labels of the format batman_connect_<instance_name> (e.g. batman_connect_pad-cty) enable B.A.T.M.A.N. adv. overlay for a given instance on a tagged interface.

The next level – prefix lists

Oliver – takt – Geiselhardt-Herms took this to the next level in a previous role and created tags with a hierarchical naming structure for prefixes, following the format prefix-list=key1:key2:key3…

The idea is that any prefix with a prefix-list tag with value key1:key2:key3 is added into the prefix lists name

key1:key2:key3
key1:key2
key1

An example structure could be

<VRF>:<purpose>:<label>, e.g. INTERNET:CUSTOMER:<customer name here>
<purpose>:<region>:<device>, e.g. CUSTOMERS:DE:core01.fra01
etc.

This obviously can be extended to more levels if it were to be required.

Hardware platforms of a Freifunk network

This post is part of the series Building your own Software Defined Network with Linux and Open Source Tools and covers the hardware platforms used within the backbone network infrastructure.

In the early days into the project we didn’t have much funds but thankfully received quite some donations in terms of old hardware as well as money. As we were young and didn’t know what we know today, we went down quite some different roads, made lots of experiences along the way, eventually reaching the setup we have today. This posts lists most the platforms we used within the last years, basically only leaving out early wireless platforms and sponsored server machines.

As most Freifunk communities rely heavily on products from the portfolio of Ubiquiti Networks, quite some devices will be covered. In the following I will just call them ubnt.

Continue reading Hardware platforms of a Freifunk network

Custom Links in Netbox – Shortcut to device WebUI/IPMI

Netbox allows to create Custom Links to a number of models for a while now. I’ve been reminded of that feature quite recently and follow the idea to have a direct link on the device page which leads to the management interface of that device.

In the Freifunk Hochstift environment we have a number of wireless backbone links which happen to have issues now and then and require some love in that case. As we use lots of Ubnt gear that love has to be applied via the Web interface of the device which is reachable via the management IP, which is configured as the primary IP of the device in Netbox.

Up to now this meant searching for the device in Netbox and copy the IP address of the device in the browsers URL bar and hit return. This can be achieved much nicer with a custom link which directly points to https://primary_ip and is accessible via a button on the device page.

This can be achieved by creating a Custom Link in Netbox (Customization -> Custom Link) for the appropriate Content Type, Link text + URL. As the intention is to add a Custom Link to wireless backbone devices, the appropriate Content Type is DCIM > device. Button class allows to configure the color of the button.

Using a little Jinja2 in the Link text it’s possible to only show this link on WBBL devices and certain switches: If the expression(s) given there renders as empty text the link will not be shown. My first instinct was to check for the device role and manufacturer:

{% if obj.device_role.slug == 'wbbl' or
      obj.device_type.manufacturer.slug == 'netonix'
%}
WebUI
{% endif %}

But checking for the platforms makes more sense as that’s the primary indicator for the devices which are managed via a web interface and they may be used in different roles (we have wireless local links too for example):

{% if obj.platform.name in [ 'AirOS', 'Netonix' ] %}
WebUI
{% endif %}

As shown above the device or “thing” referenced by the Content Type is represented via the obj object and it’s attributes are directly accessible. A look into the API representation or the Django model(s) of the device (or “thing” for that matter) may help to figure out the correct name.

What I did not find in the docs nor API nor model is that how you can access the IP part of an IP address, which in Netbox always carries the netmask. While searching I stumbled across an issue and learned that the following is possible:

https://{{ obj.primary_ip4.address.ip }}

Netbox also allows to group custom links within a drop down. All links sharing the same Group name will show up in a drop down named like the group.

With those pieces it’s easily possible to create custom links for special devices which point to the primary IP and provide the OPS team with a few clicks solution in case of trouble. Thanks to Tim for the hint 🙂

Deploying a Freifunk Hochstift backbone POP with Netbox Scripts

Some weeks ago Network to Code held the first (virtual) Netbox Day (YouTube playlist, Slides repo on github). John Anderson gave a great NetBox Extensibility Overview and introduced me to Netbox Scripts (Video, Slide deck, Slide 28) which allow to add custom Python code to add own procedures to netbox. I was hooked. About three to four hours of fiddling, digging through the docs, and some hundred lines of Python later I had put together a procedure to provision a complete Freifunk Hochstift Backbone POP within Netbox according to our design. I’m going to share my proof of concept code here and walk you through the key parts of the script.

Netbox scripts provide a great and really simple interface to codify procedures and design principles which apply to your infrastructure and fire up complex network setups within netbox by just entering a set of config parameters in a form like the following and a click of one button.

Continue reading Deploying a Freifunk Hochstift backbone POP with Netbox Scripts

OpenVPN and VRFs

Using VRFs on Linux enables a whole new set of network setups.

As described in the previous post about VRFs on Linux, VRFs allow to isolate different interfaces at layer 3. In the Freifunk Hochstift network we chose to consider the main or default VRF as the internal network and move any internet facing interfaces into an external VRF. Following this concept allows, to safely contain traffic within the internal network and only at designated border routers leak eligible traffic into the internet.

In an distributed environment like the Freifunk Hochstift network, it is inevitable to connect different islands using VPN tunnels over the Internet. This could be done by the means of GRE tunnels as shown in the previous article about the border routers, or by means of encrypted VPNs like OpenVPN, IPsec or Wireguard. As the old infrastructure quite heavily relied on OpenVPN tunnels, and they worked quite well, the new setup should keep this building block in place.

Topology of a Freifunk network

This post is part of the series Building your own Software Defined Network with Linux and Open Source Tools and covers the re-designed topology of the distributed infrastructure.

From a birds eye perspective, the Freifunk Hochstift infrastructure mainly consists of three building blocks:

Distributed servers hosted in data centers in Paderborn as remotely in Germany providing infrastructure services
Wireless backbones within the city centers of Paderborn, Warburg, etc.
Freifunk nodes at homes, shops, enterprises, or elsewhere

This post will focus on the distributed servers as well as the wireless backbones and will only cover the around 1.000 client nodes from the perspective of connecting them to the backbone (“gateways“).

With all the things mentions in Specifics and history of a Freifunk network in mind I got back to the drawing board and thought about a new design.

Continue reading Topology of a Freifunk network

Specifics and history of a Freifunk network

This post is part of the series Building your own Software Defined Network with Linux and Open Source Tools and covers the specifics of a Freifunk network as well as the history for the Freifunk Hochstift network which led to the latest re-design.

From a birds eye perspective, the Freifunk Hochstift infrastructure mainly consists of three building blocks:

Distributed servers hosted in data centers in Paderborn as remotely in Germany providing infrastructure services
Wireless backbones within the city centers of Paderborn, Warburg, etc.
Freifunk nodes at homes, shops, enterprises, or elsewhere

Continue reading Specifics and history of a Freifunk network

Building your own Software Defined Network with Linux and Open Source Tools

Nearly two years ago, I started thinking about a next generation design for the Freifunk Hochstift backbone infrastructure, motivated by the limits and design choices made before (we were young and didn’t know better.. or didn’t listen..).

This post is the starting point of a series of posts about building a software defined wireless ISP network with Linux, a fistful of Open Source tools and low cost hardware.

Continue reading Building your own Software Defined Network with Linux and Open Source Tools