@node Filtering
@comment  node-name,  next,  previous,  up
@chapter Filtering

Frr provides many very flexible filtering features.  Filtering is used
for both input and output of the routing information.  Once filtering is
defined, it can be applied in any direction.

@menu
* IP Access List::              
* IP Prefix List::              
@end menu

@node IP Access List
@comment  node-name,  next,  previous,  up
@section IP Access List

@deffn {Command} {access-list @var{name} permit @var{ipv4-network}} {}
@deffnx {Command} {access-list @var{name} deny @var{ipv4-network}} {}
@end deffn

Basic filtering is done by @code{access-list} as shown in the
following example.

@example
access-list filter deny 10.0.0.0/9
access-list filter permit 10.0.0.0/8
@end example

@node IP Prefix List
@comment  node-name,  next,  previous,  up
@section IP Prefix List

@command{ip prefix-list} provides the most powerful prefix based
filtering mechanism.  In addition to @command{access-list} functionality,
@command{ip prefix-list} has prefix length range specification and
sequential number specification.  You can add or delete prefix based
filters to arbitrary points of prefix-list using sequential number specification.

If no ip prefix-list is specified, it acts as permit.  If @command{ip prefix-list} 
is defined, and no match is found, default deny is applied.

@c @deffn {Command} {ip prefix-list @var{name} [seq @var{number}] permit|deny [le @var{prefixlen}] [ge @var{prefixlen}]} {}
@deffn {Command} {ip prefix-list @var{name} (permit|deny) @var{prefix} [le @var{len}] [ge @var{len}]} {}
@deffnx {Command} {ip prefix-list @var{name} seq @var{number} (permit|deny) @var{prefix} [le @var{len}] [ge @var{len}]} {}

You can create @command{ip prefix-list} using above commands.

@table @asis

@item @asis{seq}
seq @var{number} can be set either automatically or manually.  In the
case that sequential numbers are set manually, the user may pick any
number less than 4294967295.  In the case that sequential number are set
automatically, the sequential number will increase by a unit of five (5)
per list.  If a list with no specified sequential number is created
after a list with a specified sequential number, the list will
automatically pick the next multiple of five (5) as the list number.
For example, if a list with number 2 already exists and a new list with
no specified number is created, the next list will be numbered 5.  If
lists 2 and 7 already exist and a new list with no specified number is
created, the new list will be numbered 10.

@item @asis{le}
@command{le} command specifies prefix length.  The prefix list will be 
applied if the prefix length is less than or equal to the le prefix length.

@item @asis{ge}
@command{ge} command specifies prefix length.  The prefix list will be 
applied if the prefix length is greater than or equal to the ge prefix length.

@end table

@end deffn

Less than or equal to prefix numbers and greater than or equal to
prefix numbers can be used together.  The order of the le and ge
commands does not matter.

If a prefix list with a different sequential number but with the exact
same rules as a previous list is created, an error will result.
However, in the case that the sequential number and the rules are
exactly similar, no error will result.

If a list with the same sequential number as a previous list is created,
the new list will overwrite the old list.

Matching of IP Prefix is performed from the smaller sequential number to the
larger.  The matching will stop once any rule has been applied.

In the case of no le or ge command, the prefix length must match exactly the
length specified in the prefix list.

@deffn {Command} {no ip prefix-list @var{name}} {}
@end deffn

@menu
* ip prefix-list description::  
* ip prefix-list sequential number control::  
* Showing ip prefix-list::      
* Clear counter of ip prefix-list::  
@end menu

@node ip prefix-list description
@subsection ip prefix-list description

@deffn {Command} {ip prefix-list @var{name} description @var{desc}} {}
Descriptions may be added to prefix lists.  This command adds a
description to the prefix list.
@end deffn

@deffn {Command} {no ip prefix-list @var{name} description [@var{desc}]} {}
Deletes the description from a prefix list.  It is possible to use the
command without the full description.
@end deffn

@node  ip prefix-list sequential number control
@subsection ip prefix-list sequential number control

@deffn {Command} {ip prefix-list sequence-number} {}
With this command, the IP prefix list sequential number is displayed.
This is the default behavior.
@end deffn

@deffn {Command} {no ip prefix-list sequence-number} {}
With this command, the IP prefix list sequential number is not
displayed.
@end deffn

@node  Showing ip prefix-list
@subsection Showing ip prefix-list

@deffn {Command} {show ip prefix-list} {}
Display all IP prefix lists.
@end deffn

@deffn {Command} {show ip prefix-list @var{name}} {}
Show IP prefix list can be used with a prefix list name.
@end deffn

@deffn {Command} {show ip prefix-list @var{name} seq @var{num}} {}
Show IP prefix list can be used with a prefix list name and sequential
number.
@end deffn

@deffn {Command} {show ip prefix-list @var{name} @var{a.b.c.d/m}} {}
If the command longer is used, all prefix lists with prefix lengths equal to
or longer than the specified length will be displayed.
If the command first match is used, the first prefix length match will be
displayed.
@end deffn

@deffn {Command} {show ip prefix-list @var{name} @var{a.b.c.d/m} longer} {}
@end deffn

@deffn {Command} {show ip prefix-list @var{name} @var{a.b.c.d/m} first-match} {}
@end deffn

@deffn {Command} {show ip prefix-list summary} {}
@end deffn
@deffn {Command} {show ip prefix-list summary @var{name}} {}
@end deffn

@deffn {Command} {show ip prefix-list detail} {}
@end deffn
@deffn {Command} {show ip prefix-list detail @var{name}} {}
@end deffn

@node  Clear counter of ip prefix-list
@subsection Clear counter of ip prefix-list

@deffn {Command} {clear ip prefix-list} {}
Clears the counters of all IP prefix lists.  Clear IP Prefix List can be
used with a specified name and prefix.
@end deffn

@deffn {Command} {clear ip prefix-list @var{name}} {}
@end deffn

@deffn {Command} {clear ip prefix-list @var{name} @var{a.b.c.d/m}} {}
@end deffn

