[Arista EOS]BGP neighbor default-originate [ always ]

Tech Keypoint Summary

1. Previsouly, BGP advertise default route unconditionally, which means regardless default route present on local router or not, BGP always advertise the default routes to peer.

2. The old behavior cause some problem, if two BGP speaker configured neighbor default-originate each other and that will cause loop happen because this unconditional behavior, even worse, in certain scenario, the default-route can not be withdrawl after command “neighbor default-originate” removed, there is a bug changed the old behavior.

3. The new behavior is if there is a default route in BRIB is the winner regardless where is learnt from, then BGP will not advertise default route to peer. If the default route in BRIB is not winner, then BGP will still advertise default route.

4. The bug changed the previous behavior which cause some customer escalation as they still want the old behavior, so a new feature introduced a new option “always”, with “always” configured, BGP will advertise default route regardless default route winner present in BRIB or not.

Introduction

This updates: BGP neighbor default-originate.
With the fix for bug, the behavior of default-originate changed to advertise the BRIB winner (if available) instead of a fabricated default route. This change causes some escalations for customers who expect the old behavior. Because of that, we decided to implement a new CLI knob to support the old behavior for backward compatibility.

CLI

The following CLI knob will be introduced to support the old behavior:

[ no | default ] neighbor ( ip-address | peer-group-name ) default-originate [ route-map map-name ] [ always ]

always: Enforce the advertisement of a fabricated default route, irrespective of availability of other default routes.

Configuration