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.bandwidth link attribute sets the BGP Link Bandwidth extended community. It can be an integer (in Mbps), in which case the Link Bandwidth community is attached to inbound EBGP updates[1], a dictionary with in and out integer values if you want to set the Link Bandwidth community in both directions (or just on the outbound updates), or auto keyword if you want to copy interface bandwidth into incoming EBGP updates[2].

  • 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[3])

  • 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

bandwidth

❌

✅

locpref

✅

✅

med

❌

✅

prepend

❌

✅

weight

❌

✅

Platform Support

The plugin implements BGP policy attributes on these devices:

Operating system

Local
preference

MED

Weight

AS-path
prepending

Link
bandwidth

Arista EOS

✅

✅

✅

✅

✅

Aruba AOS-CX

✅

✅

✅

✅

❌

Cisco IOSv

✅

✅

✅

✅

✅❗

Cisco IOS-XE

✅

✅

✅

✅

✅❗

Cumulus Linux

✅

✅

✅

✅

✅

FRR

✅

✅

✅

✅

✅

Nokia SR Linux

✅

✅

❌

❌

❌

Nokia SR OS

✅

✅

❌

❌

✅

VyOS

✅

✅

❌

✅

❌

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