============
Prefix-Lists
============

.. sidebar:: Contents

  .. contents::
      :depth: 3
      :local:


This chapter covers some aspects related to :osdx:cfg:`protocols ip prefix-list *` and
:osdx:cfg:`protocols ipv6 prefix-list *`, which is one of the tools that allow to filter
routing prefixes within route-maps.

There are certain aspects that are worth mentioning before explaining
the prefix-list configuration:

 * The **rule** id defines the execution order for prefix validation, being the
   most prioritary the 1.
 * The **match** condition is required to proceed with the final verdict.
   There could be specific matches, requiring the route coincide exactly
   with the defined prefix, or on the contrary, using netmask size based
   matches.
 * The **action** available for prefix-lists is either ``accept`` or
   ``deny``. After the **match** condition, the first one confirms that a certain
   prefix is accepted and the other results in a denegation. The default action
   is ``deny``, meaning that a prefix reaching the latest rule configured without
   any match will result in a denegation.


Configuration
=============

This is the syntax to create a :osdx:cfg:`protocols ip prefix-list *` or
:osdx:cfg:`protocols ipv6 prefix-list *`:

.. code-block:: none

  set protocols <ip/ipv6> prefix-list <pl_name> rule <rule_id> [ ... ]

A :osdx:cfg:`protocols ip prefix-list *` or :osdx:cfg:`protocols ipv6 prefix-list *` could
be assigned to any route-map as a match criteria inside it. For doing so, the following
command will be used:

.. code-block:: none

  set protocols route-map <rmap_name> rule <rule_id> match ip address prefix-list <pl_name>


Examples
========

Discarding the default route
----------------------------

Let's suppose we want to set up a :osdx:cfg:`protocols route-map *` where a match with the
default route is necessary.

We want the following features:

  * Default-route will be denied by the route-map.
  * Any other prefix will be accepted.

On OSDx that can achieved by configuring the following commands:

.. code-block:: none

  set protocols ip prefix-list DEF_ROUTE rule 1 prefix 0.0.0.0/0

Finally, to use this prefix-list in a route-map you have to use these commands:

.. code-block:: none

  set protocols route-map DENY_DEF_ROUTE rule 1 action deny
  set protocols route-map DENY_DEF_ROUTE rule 1 match ip address prefix-list DEF_ROUTE
  set protocols route-map DENY_DEF_ROUTE rule 2 action permit

Accepting only a subnet
-----------------------

Let's suppose we want to set up a :osdx:cfg:`protocols route-map *` where a match with a
defined subnet is necessary.

We want the following features:

  * Only a subnet from a certain prefix will be accepted by the route-map.
  * Other prefixes will be denied.

On OSDx that can achieved by configuring the following commands:

.. code-block:: none

  set protocols ip prefix-list SUBNET rule 1 ge 16
  set protocols ip prefix-list SUBNET rule 1 prefix 10.0.0.0/8

Finally, to use this prefix-list in a route-map you have to use these commands:

.. code-block:: none

  set protocols route-map DENY_DEF_ROUTE rule 1 action permit
  set protocols route-map DENY_DEF_ROUTE rule 1 match ip address prefix-list SUBNET


Monitoring
==========

The related operational commands :osdx:op:`protocols ip prefix-list * show` and
:osdx:op:`protocols ipv6 prefix-list * show` can be used to display statistics related
to ``prefix-list`` filters.

*Example:*

.. code-block:: none

  admin@osdx$ protocols ip prefix-list test show
  ZEBRA: ip prefix-list test: 1 entries
     seq 1 permit 0.0.0.0/0
  admin@osdx$

..
  depth=4 to show prefix-list rule options

.. osdx:cmdtree:: cfg
  :maxdepth: 4

  protocols ip prefix-list
  protocols ipv6 prefix-list