j2ipaddr

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. IPv4 and IPv6 are supported. Every filter returns a str, except ip_prefixlen and ip_network_hosts_size which return an int. Surrounding whitespace in the input is ignored.

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

Returns an int.

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 wildcard 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 }}
> 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

Returns None when there is no broadcast address: IPv6, /31 and /32. Jinja2 renders None as the text "None", so guard it with {% if %} or | default('') if those can show up.

ip_network_hosts_size(addr)

Returns the number of usable hosts for a combination of IP address and subnet mask

ip_network_hosts_size('10.10.10.5/24')
> 254

{{ '10.10.10.5/24' | ip_network_hosts_size }}
> 254

Returns an int. The network and broadcast addresses are not counted. /31 gives 2 (RFC 3021) and /32 gives 1.

ip_network_first(addr)

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

ip_network_first('10.10.10.5/24')
> 10.10.10.1

{{ '10.10.10.5/24' | ip_network_first }}
> 10.10.10.1

For /31 and /32 there is nothing to skip, so it returns the first address of the network.

ip_network_last(addr)

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

ip_network_last('10.10.10.5/24')
> 10.10.10.254

{{ '10.10.10.5/24' | ip_network_last }}
> 10.10.10.254

For /31 and /32 there is nothing to skip, so it returns the last address of the network.

Invalid input

An input that is not a valid IP address or network (including None or an undefined variable) raises netaddr.AddrFormatError with a message that shows the offending value:

invalid IP address or network: '10.0.0.300/24' (expected something like '10.10.10.5/24')

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
from j2ipaddr import 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
from j2ipaddr import filters
jinja2.filters.FILTERS.update(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 10.10.10.0 0.0.0.255 area 0.0.0.0