Author: Arturo

Jinja2 filters for IP addresses, the easy way

Why

On networking and network automation, we need to extract info about IP addresses as a combination of two values:

• a host address
• a subnet mask

For 10.10.10.5/24, the host address is 10.10.10.5 and the subnet mask is 255.255.255.0, and its prefix length is 24.

There is additional information we can infer from this single item, as its network address, broadcast address.

Useful data for network engineers are wildcards or hostmasks, network size, class, type, and so on.

Jinja2 provides several integrated filters to work with, however it can be complicated to use complex data types.

Ansible provides a way to work this on its ansible.utils.ipaddr collection.

However, probably you won’t need the entire Ansible package just to be able to use it.

This package intends to provide a set of filters and handler to the Python 3 netaddr module, on a way that is hopefully easy and lightweight to use.

What

Included filters are the following:

ip_address(addr)

Returns an IP address for a combination of IP address and subnet mask

ip_address('10.10.10.5/24')
> 10.10.10.5
{{ '10.10.10.5/24 | ip_address }}
> 10.10.10.5

ip_prefixlen(addr)

Returns a prefix length for a combination of IP address and subnet mask

ip_prefixlen('10.10.10.5/24')
> 24
{{ '10.10.10.5/24 | ip_prefixlen }}
> 24

ip_netmask(addr)

Returns a subnet mask for a combination of IP address and subnet mask

ip_netmask('10.10.10.5/24')
> 255.255.255.0
{{ '10.10.10.5/24 | ip_netmask }}
> 255.255.255.0

ip_hostmask(addr)

Returns a wilcard or hostmask for a combination of IP address and subnet mask

ip_hostmask('10.10.10.5/24')
> 0.0.0.255
{{ '10.10.10.5/24 | ip_hostmask }}
> 0.0.0.255

ip_wildcard(addr)

Alias for ip_hostmask(addr)

ip_wildcard('10.10.10.5/24')
> 0.0.0.255
{{ '10.10.10.5/24 | ip_wildcard }}
> 0.0.0.255

ip_network(addr)

Returns a network address for a combination of IP address and subnet mask

ip_network('10.10.10.5/24')
> 10.10.10.0
{{ '10.10.10.5/24 | ip_network_hosts_size }}
> 10.10.10.0

ip_broadcast(addr)

Returns a broadcast address for a combination of IP address and subnet mask

ip_broadcast('10.10.10.5/24')
> 10.10.10.255
{{ '10.10.10.5/24 | ip_broadcast }}
> 10.10.10.255

ip_network_hosts_size(addr)

Returns the size of the subnet for a combination of IP address and subnet mask

ip_network_hosts_size('10.10.10.5/24')
> 255
{{ '10.10.10.5/24 | ip_network_hosts_size }}
> 255

ip_network_first(addr)

Returns the first usable address in network address for a combination of IP address and subnet mask

ip_network('10.10.10.5/24')
> 10.10.10.1
{{ '10.10.10.5/24 | ip_network_hosts_size }}
> 10.10.10.1

ip_network_last(addr)

Returns the last usable address in network address for a combination of IP address and subnet mask

ip_network('10.10.10.5/24')
> 10.10.10.254
{{ '10.10.10.5/24 | ip_network_hosts_size }}
> 10.10.10.254

How

Simply install with pip.

$ pip install j2ipaddr

To insert the filters on your Jinja2 processor, simply use the following syntax. The filter name can be changed by adjusting the dict key name.

import jinja2
import j2ipaddr.filters
jinja2.filters.FILTERS['ip_prefixlen'] = filters.ip_prefixlen

Or, probably an easier way, use the following one-liner to load all the filters into your Jinja2 filters

import jinja2
import j2ipaddr.filters
jinja2.filters.FILTERS = {**jinja2.filters.FILTERS, **filters.load_all()}

On your templates, you can do this as an example:

Variables

host:
  interfaces:
    Te1/0/1:
      ipv4_addresses:
        - 10.10.10.5/24

Template

router ospf 10
  network {{host.interfaces.Te1/0/1.ipv4_addresses[0] | ip_network }} {{host.interfaces.Te1/0/1.ipv4_addresses[0] | ip_wildcard  }} area 0.0.0.0

The output would looks like this:

router ospf 10
  network 10.0.0.0 0.0.0.255 area 0.0.0.0

Where

You can find this project on

• https://github.com/baldoarturo/j2ipaddr
• https://pypi.org/project/j2ipaddr/