Config Templates: Accessing IPAM Information from Device context

[bradley-rose]

I'm trying to create a config template for some switches. Part of the core of the switch configuration is the default gateway:

ip default-gateway {{ default-gateway-for-subnet }}

From within the Config Template context, it looks like I only have access to the device object. Is there any way I can access any IPAM objects like prefixes? Typically I use the first address in the subnet for the default gateway, so I'm wanting to do something like this:

ip default-gateway {% for prefix in ipam.prefixes.filter({{ device.primary_ip4.address }}) %} {%- if prefix.split("/")[1] == {{ device.primary_ip4.address }}.split("/")[1] %} {{ prefix.split("/")[0].split(".")[0] + "." + prefix.split("/")[0].split(".")[1] + "." + prefix.split("/")[0].split(".")[2] + "." + (prefix.split("/")[0].split(".")[3] + 1) }} {%- endif %} {%- endfor %}

The logic:

• For each prefix identified via querying the device's primary IP address:
  • If the prefix's subnet mask matches the subnet mask of the primary IP address of the device, we've got a match.
  • Split the prefix into four pieces (one for each octet).
  • Write the first three octets (w.x.y.), and for the fourth, increment it by a value of 1. This would give me the first address in the subnet.

I'm not sure how to translate this into proper Jinja2 templating for the Config Template. If there's a much simpler way to do this, please, I'm all ears.

[adparis99]

As of NetBox 3.6, you can access models directly from a configuration template. In your example, the for loop should start off like so:
for prefix in ipam.Prefix.objects.filter({some filter here})...

For what it's worth, in my organization we define default gateways in a Config Context associated with a particular site and then reference that config context object in the template. I suppose that's slightly more manual, but it has served us well.

[bradley-rose]

Thanks for the reply! I hadn't realized this was such a recent feature.

• Is that the exact syntax that you provided, or do I still have to wrap it in Jinja2 syntax?
• Is there documentation to support which models are available?

[adparis99]

No problem. To answer your questions,

1. Yes, it should be wrapped up in in Jinja2 syntax. So as an example, {% for prefix in ipam.Prefix.objects.all() %} do stuff {% endfor %}
2. Expose more objects in the configuration rendering feature #12814 is where the request was originally made. It seems like all models are available for reference, but I can't confirm that because it wasn't said explicitly in that thread. Assuming all are there, if you need a list of the models, see this link for documentation on the NetBox Shell.

[brandan-schmitz]

@bradley-rose Did you ever figure this out? I have a similar situation where I am trying to set an ip default-gateway using a custom field I have attached to the Prefix. However I cannot seem to figure out how to find the prefix based on the primary IP of the device.

[bradley-rose]

@brandan-schmitz Unfortunately, I did not. I ended up giving up entirely on the feature as it felt like, in its current state, it was over-complicating the job. It's a really great idea in theory, but in execution it's not excellent. I think you'd be better off performing configuration and orchestration management with a more purpose-built tool like Ansible, and leaving Netbox to do the thing that it does best: IPAM and DCIM.

What I did recently find out was the value of having a centralized, team-oriented Git tool like Gitlab, Github, or otherwise. This immediately removes a lot of the scary pieces to centralized configuration management for those less inclined to change their ways. Even if it's used for housing legacy text-file-based configurations, they're version controlled. If you can centralize your configuration here, and then replace variables with calls to Netbox, I think you're definitely headed somewhere.

[wz4]

Here is a solution that I came up with. It requires the following.

1. Primary IP with valid prefix assigned to the device
2. Custom field for default gateway on the prefix. This needs to be an IP address object.

The configuration template will determine the default gateway based on it's primary IP.

jinja2 sample

{%- set primary_ip = device.primary_ip|string -%}
{%- set prefix = ipam.Prefix.objects.filter(status="active", prefix__net_contains=primary_ip.split('/')[0]).first() -%}
{%- set gw_id = prefix.custom_field_data.gateway -%}
{%- set gateway = ipam.IPAddress.objects.get(id=gw_id).address |string %}

ip route default-gateway {{ gateway.split('/')[0] }}