PBR — FRR 7.5.1/frr-7.5.1 documentation

# PBR

PBR is Policy Based Routing. This implementation supports a very simple interface to allow admins to influence routing on their router. At this time you can only match on destination and source prefixes for an incoming interface. At this point in time, this implementation will only work on Linux.

## Starting PBR

Default configuration file for pbrd is `pbrd.conf`. The typical location of `pbrd.conf` is /etc/frr/pbrd.conf.

If the user is using integrated config, then `pbrd.conf` need not be present and the `frr.conf` is read instead.

PBR supports all the common FRR daemon start options which are documented elsewhere.

## Nexthop Groups

Nexthop groups are a way to encapsulate ECMP information together. It's a listing of ECMP nexthops used to forward packets for when a pbr-map is matched.

`nexthop-group NAME`

  Create a nexthop-group with an associated NAME. This will put you into a sub-mode where you can specify individual nexthops. To exit this mode type exit or end as per normal conventions for leaving a sub-mode.

`nexthop [A.B.C.D|X:X::X:XX] [interface] [nexthop-vrf NAME] [label LABELS]`

  Create a v4 or v6 nexthop. All normal rules for creating nexthops that you are used to are allowed here. The syntax was intentionally kept the same as creating nexthops as you would for static routes.

`[no] pbr table range (10000-4294966272) (10000-4294966272)`

  Set or unset the range used to assign numeric table ID's to new nexthop-group tables. Existing tables will not be modified to fit in this range, so it is recommended to configure this before adding nexthop groups.

  See also

  PBR Details

### Showing Nexthop Group Information

`show pbr nexthop-groups [NAME] [json]`

  Display information on a PBR nexthop-group. If `NAME` is omitted, all nexthop groups are shown. Setting `json` will provide the same information in an array of objects which obey the schema below:

  Key | Description | Type
  --- | --- | ---
  id | Unique ID | Integer
  name | Name of this group | String
  valid | Is this group well-formed? | Boolean
  installed | ... and is it installed? | Boolean
  nexthops | Nexthops within this group | Array

  Each element within `nexthops` describes a single target within this group, and its structure is described by the JSON below:

  Key | Description | Type
  --- | --- | ---
  nexthop | Name of this nexthop | String
  valid | Is this nexthop well-formed? | Boolean

## PBR Maps

PBR maps are a way to group policies that we would like to apply to individual interfaces. These policies when applied are matched against incoming packets. If matched the nexthop-group or nexthop is used to forward the packets to the end destination.

`pbr-map NAME seq (1-700)`

  Create a pbr-map with NAME and sequence number specified. This command puts you into a new submode for pbr-map specification. To exit this mode type exit or end as per normal conventions for leaving a sub-mode.

`match src-ip PREFIX`

  When a incoming packet matches the source prefix specified, take the packet and forward according to the nexthops specified. This command accepts both v4 and v6 prefixes. This command is used in conjunction of the `match dst-ip PREFIX` command for matching.

`match dst-ip PREFIX`

  When a incoming packet matches the destination prefix specified, take the packet and forward according to the nexthops specified. This command accepts both v4 and v6 prefixes. This command is used in conjunction of the `match src-ip PREFIX` command for matching.

`match mark (1-4294967295)`

  Select the mark to match. This is a linux only command and if attempted on another platform it will be denied. This mark translates to the underlying ip rule .... fwmark XXXX command.

`match dscp (DSCP|0-63)`

  Match packets according to the specified differentiated services code point (DSCP) in the IP header; if this value matches then forward the packet according to the nexthop(s) specified. The passed DSCP value may also be a standard name for a differentiated service code point like cs0 or af11.

  You may only specify one dscp per route map sequence; to match on multiple dscp values you will need to create several sequences, one for each value.

`match ecn (0-3)`

  Match packets according to the specified explicit congestion notification (ECN) field in the IP header; if this value matches then forward the packet according to the nexthop(s) specified.

`set nexthop-group NAME`

  Use the nexthop-group NAME as the place to forward packets when the match commands have matched a packet.

`set nexthop [A.B.C.D|X:X::X:XX] [interface] [nexthop-vrf NAME]`

  Use this individual nexthop as the place to forward packets when the match commands have matched a packet.

`set vrf unchanged|NAME`

  If unchanged is set, the rule will use the vrf table the interface is in as its lookup. If NAME is specified, the rule will use that vrf table as its lookup.

  Not supported with NETNS VRF backend.

`show pbr map [NAME] [detail|json]`

  Display pbr maps either all or by `NAME`. If `detail` is set, it will give information about the rules unique ID used internally and some extra debugging information about install state for the nexthop/nexthop group. Setting `json` will provide the same information in an array of objects which obey the schema below:

  Key | Description | Type
  --- | --- | ---
  name | Map name | String
  valid | Is the map well-formed? | Boolean
  policies | Rules to match packets against | Array

  Each element of the `policies` array is composed of a handful of objects representing the policies associated with this map. Each policy is described as below (not all fields are required):

  Key | Description | Type
  --- | --- | ---
  id | Unique ID | Integer
  sequenceNumber | Order of this policy within the map | Integer
  ruleNumber | Rule number to install into | Integer
  vrfUnchanged | Use interface's VRF | Boolean
  installed | Is this policy installed? | Boolean
  installedReason | Why (or why not?) | String
  matchSrc | Match packets with this source address | String
  matchDst | ... or with this destination address | String
  matchMark | ... or with this marker | Integer
  vrfName | Associated VRF (if relevant) | String
  nexthopGroup | This policy's nexthop group (if relevant) | Object

  Finally, the `nexthopGroup` object above cotains information we know about the configured nexthop for this policy:

  Key | Description | Type
  --- | --- | ---
  tableId | Nexthop table ID | Integer
  name | Name of the nexthop group | String
  installed | Is this nexthop group installed? | Boolean
  installedInternally | Do we think this group is installed? | Integer

## PBR Policy

After you have specified a PBR map, in order for it to be turned on, you must apply the PBR map to an interface. This policy application to an interface causes the policy to be installed into the kernel.

`pbr-policy NAME`

  This command is available under interface sub-mode. This turns on the PBR map NAME and allows it to work properly.

Note

This will not dynamically create PBR maps on sub-interfaces (i.e. vlans) even if one is on the master. Each must have the PBR map explicitly added to the interface.

`show pbr interface [NAME] [json]`

  Enumerates all interfaces which `pbrd` is keeping track of. Passing `json` will return an array of interfaces; each returned interface will adhere to the JSON schema below:

  Key | Description | Type
  --- | --- | ---
  name | Interface name | String
  index | Device Index | Integer
  policy | PBR map for this interface | String
  valid | Is the map well-formed? | Boolean

## PBR Details

Under the covers a PBR map is translated into two separate constructs in the Linux kernel.

The PBR map specified creates a ip rule ... that is inserted into the Linux kernel that points to a table to use for forwarding once the rule matches.

The creation of a nexthop or nexthop-group is translated to a default route in a table with the nexthops specified as the nexthops for the default route.