IPRoute – work with interfaces, addresses and routes¶
Create IPRoute and get network objects¶
IPRoute objects provide kernel RTNL API, just as Linux iproute2 utility does. The differences are that IPRoute provides a subset – so your contributions are more than welcome, – and IPRoute returns parsed netlink packets, only adding a few extra fields.
Netlink protocol and packets structure: https://docs.pyroute2.org/netlink.html
More about netlink packets structure and API see below in this lab.
Let’s start with a simple exercise: create an IPRoute object and get IP addresses. Most of pyroute2 classes, that provide some netlink API, create a netlink socket and allocate some other resources. Because of the netlink protocol, there may be not more than 1024 netlink sockets opened at the same time per process ID, and it may be important to close objects if they’re not in use.
IPRoute methods always return iterables, as a response from the kernel always is a series of [1..x] messages.
To continue, run the exercise by pressing the execute button.
Create an IPRoute object and list addresses.
- create exactly on IPRoute() object
- run get_addr() at least once
- run close() exactly once
Access messages data¶
All the messages returned by IPRoute methods provide standard nlmsg/nla API. Every message is a recursive dict-like structure, with fields accessible via __getitem__(), and an optional NLA list accessible via msg[‘attrs’], as you can see in the exercise above. If a message or NLA has value field defined, this field is being returned by getvalue() method, otherwise getvalue() returns the message or NLA itself. This makes simple type NLA retrieval a bit more convenient.
These are methods to get fields and NLA values:
__getitem__(‘field’) – return a field of this name
.get(‘field’), get(‘NLA_TYPE’), .get((‘NLA_TYPE’, …, ‘field’)) – the universal get method, see below
.getvalue() – return the value field, if defined, otherwise the object itself
.get_attr(‘NLA_TYPE’) – get one NLA by the type; if there atr several NLA of the same type, get the first one in the list
.get_attrs(‘NLA_NAME’) – get a list of NLA of this type
Some notes on get() method:
returns a field or NLA value
case insensitive for NLA types
if NLA has prefix defined, it allows type notation both with and without the prefix, thus get(‘IFLA_IFNAME’) == get(‘IFNAME’) == get(‘ifname’)
the method first looks up for an NLA, and only then for a field of this name; if a message has both, like as ndmsg has a field ifindex and NLA type NDA_IFINDEX, then you can use __getitem__() and getattr()
Access netlink message attributes.
- get_links() returns an iterator over link objects
- msg.get('index') returns index field just like msg['index'] does
- msg.get('ifname') returns IFLA_IFNAME value as a string
- msg.get('af_spec') returns IFLA_AF_SPEC as a dict
- msg.get(('af_spec', 'af_inet', 'forwarding')) as an int