BGP Routing Policies Plugin

The bgp.policy plugin implements simple BGP routing policies :

  • Per-neighbor weights, local preference and MED

  • Default local preference

Supported BGP Attributes

The plugin adds the following BGP attributes:

  • bgp.locpref is an integer attribute that sets default local preference when applied to a node, or sets local preference on BGP updates received from an EBGP neighbor.

  • bgp.med is an integer attribute that sets MED attribute on BGP updates sent to an EBGP neighbor.

  • bgp.prepend is a dictionary that configures outbound AS-path prepending. It can contain a count attribute (number of times the node AS is prepended) or a path attribute (the prepended AS-path as a string[1])

  • bgp.weight is an integer attribute that sets per-neighbor weight.

BGP policy attributes can be specified on a node or an interface (node-to-link attachment). The following table describes where you could apply individual attributes:

BGP policy

Node

Interface

locpref

✅

✅

med

❌

✅

prepend

❌

✅

weight

❌

✅

Platform Support

The plugin implements BGP policy attributes on these devices:

Operating system

Local
preference

MED

Weight

AS-path
prepending

Arista EOS

✅

✅

✅

✅

Aruba AOS-CX

✅

✅

✅

✅

Cisco IOSv

✅

✅

✅

✅

Cisco IOS-XE

✅

✅

✅

✅

Cumulus Linux

✅

✅

✅

✅

FRR

✅

✅

✅

✅

Nokia SR Linux

✅

✅

✅

❌

Notes:

  • Arista EOS does not support node-level default local preference. Node-level bgp.locpref attribute (if specified) is thus applied to all interfaces that do not have an explicit bgp.locpref attribute.

Applying Policy Attributes

The plugin device-specific configuration templates try to apply as many BGP policy attributes as possible directly to EBGP neighbor sessions. For example, bgp.weight is usually applied directly to a neighbor, as illustrated by the following FRR configuration:

router bgp 65000
 neighbor 10.1.0.2 remote-as 65100
 neighbor 10.1.0.2 description r1
 !
 address-family ipv4 unicast
  neighbor 10.1.0.2 activate
  neighbor 10.1.0.2 weight 10

Most other policy attributes have to be applied through a route-map. The plugin device-specific configuration templates create per-neighbor maps using names unique to each EBGP session, and apply those route maps to EBGP neighbors:

router bgp 65000
 bgp default local-preference 37
 neighbor 10.1.0.2 remote-as 65100
 neighbor 10.1.0.2 description r1
 neighbor 10.1.0.6 remote-as 65100
 neighbor 10.1.0.6 description r1
 !
 address-family ipv4 unicast
  neighbor 10.1.0.2 route-map bp-r1-1-in in
  neighbor 10.1.0.2 route-map bp-r1-1-out out
  neighbor 10.1.0.6 activate
  neighbor 10.1.0.6 route-map bp-r1-2-out out
!
route-map bp-r1-1-in permit 10
 set local-preference 20
!
route-map bp-r1-1-out permit 10
 set metric 101
!
route-map bp-r1-2-out permit 10
 set metric 200

Sample Topologies

The following topology illustrates a simple primary/backup scenario in which a CE-router uses weights and MED to select primary/backup uplinks.

---
defaults.device: frr

module: [ bgp ]
plugin: [ bgp.policy ]

nodes:
  ce:
    bgp.as: 65000
  pe:
    bgp.as: 65100

links:
- ce:
    bgp.weight: 100
    bgp.med: 50
  pe:
  name: Primary uplink
- ce:
    bgp.weight: 50
    bgp.med: 100
  pe:
  name: Backup uplink

The next topology illustrates AS-path prepending functionality. On the backup link, the CE-router prepends its own AS three times, on the primary link it prepends another AS.

---
defaults.device: frr

module: [ bgp ]
plugin: [ bgp.policy ]

nodes:
  ce:
    bgp.as: 65000
  pe:
    bgp.as: 65100

links:
- ce:
    bgp.prepend.path: "65123"
  pe:
  name: Primary uplink
- ce:
    bgp.prepend.count: 3
  pe:
  name: Backup uplink