# 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.

## IP Access List

access-list NAME [seq (1-4294967295)] <permit|deny> <A.B.C.D/M [exact-match]|any>
  seq

    seq 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.

  Basic filtering is done by access-list as shown in the following example.

      access-list filter deny 10.0.0.0/9
      access-list filter permit 10.0.0.0/8
      access-list filter seq 13 permit 10.0.0.0/7

access-list NAME [seq (1-4294967295)] <deny|permit> ip <A.B.C.D A.B.C.D|host A.B.C.D|any> <A.B.C.D A.B.C.D|host A.B.C.D|any>

  The extended access-list syntax enables filtering on both source and destination IP addresses (or source and group, if used for multicast boundaries). The source address is first in order in the command.

  If providing a mask, note that the access-lists use wildcard masks (inverse matching logic of subnet masks). If specifying `host`, only the single address given will be matched.

  A basic example is as follows:

      access-list filter seq 5 permit ip host 10.0.20.2 232.1.1.0 0.0.0.128
      access-list filter seq 10 deny ip 10.0.20.0 0.0.0.255 232.1.1.0 0.0.0.255
      access-list filter seq 15 permit ip any any

  Note

  If an access-list is specified but no match is found, the default verdict is deny.

show <ip|ipv6> access-list [json]

  Display all IPv4 or IPv6 access lists.

  If the `json` option is specified, output is displayed in JSON format.

show <ip|ipv6> access-list WORD [json]

  Display the specified IPv4 or IPv6 access list.

  If the `json` option is specified, output is displayed in JSON format.

## IP Prefix List

ip prefix-list provides the most powerful prefix based filtering mechanism. In addition to access-list functionality, 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 ip prefix-list is defined, and no match is found, default deny is applied.

ip prefix-list NAME (permit|deny) PREFIX [le LEN] [ge LEN]

ip prefix-list NAME seq NUMBER (permit|deny) PREFIX [le LEN] [ge LEN]

  You can create ip prefix-list using above commands.

  seq

    seq 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.

  le

    Specifies prefix length. The prefix list will be applied if the prefix length is less than or equal to the le prefix length.

  ge

    Specifies prefix length. The prefix list will be applied if the prefix length is greater than or equal to the ge prefix length.

  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.

### ip prefix-list description

ip prefix-list NAME description DESC

  Descriptions may be added to prefix lists. This command adds a description to the prefix list.

### Showing ip prefix-list

show ip prefix-list [json]

  Display all IP prefix lists.

  If the `json` option is specified, output is displayed in JSON format.

show ip prefix-list NAME [json]

  Show IP prefix list can be used with a prefix list name.

  If the `json` option is specified, output is displayed in JSON format.

show ip prefix-list NAME seq NUM [json]

  Show IP prefix list can be used with a prefix list name and sequential number.

  If the `json` option is specified, output is displayed in JSON format.

show ip prefix-list NAME 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.

show ip prefix-list NAME A.B.C.D/M longer

show ip prefix-list NAME A.B.C.D/M first-match

show ip prefix-list summary [json]

show ip prefix-list summary NAME [json]

show ip prefix-list detail [json]

show ip prefix-list detail NAME [json]

debug prefix-list NAME match <A.B.C.D/M|X:X::X:X/M> [address-mode]

  Execute the prefix list matching code for the specified list and prefix. Shows which entry matched, if any. (`address-mode` is used for PIM RP lookups and skips prefix length checks.)

  The return value from this command is success only if the prefix-list result is to permit the prefix, so the command can be used in scripting.

### Clear counter of ip prefix-list

clear ip prefix-list [NAME [A.B.C.D/M]]

  Clears the counters of all IP prefix lists. Clear IP Prefix List can be used with a specified NAME or NAME and prefix.