This article explains why all BGP sessions may flap when configuration changes are made under the protocols bgp hierarchy on a Junos device acting as an AS boundary router, even when the changes are applied to a different BGP group. In particular, when VPN address families such as family inet-vpn unicast are configured, modifications related to VPN table advertisement can trigger BGP session resets. As a result, BGP sessions across the device may momentarily flap during such configuration updates.
protocols bgp
family
inet-vpn unicast
We have two groups configured for BGP protocol on a Junos Device.
For e.g: Group A and Group B.
Group A and Group B is having similar type of configuration and neighbor type as same. If we are making group A neighbor type as external from internal, this will make the device to act as ASBR device and under groups VPN families are enabled, it will trigger a BGP session reset for the Group B as well although it is configured in different group.
Syslog entries showing BGP Notification with Cease/Other Configuration Change:
Code 6 (Cease) Subcode 6 (Other Configuration Change) Reason: Configuration change - VPN table advertise
The flaps seems to be expected behavior, please check the below details:
We can see the following logs when BGP peer flapped:
bgp_adv_main_update:14105: NOTIFICATION sent to 100.x.x.x (Internal AS 32xxxx): code 6 (Cease) subcode 6 (Other Configuration Change), Reason: Configuration change - VPN table advertise
We can see the following code in Notification Message:
Code 6 (Cease) subcode 6 (Other Configuration Change), Reason: Configuration change - VPN table advertise
If a BGP speaker decides to administratively reset the peering with a neighbor due to a configuration change other than the ones described above, then the speaker SHOULD send a NOTIFICATION message with the Error Code Cease and the Error Subcode "Other Configuration Change".
Reference:https://datatracker.ietf.org/doc/html/rfc4486
When a router or switch is configured as AS boundary router (an external BGP peer) and a VPN family (for example, the family inet-vpn unicast statement) is configured, a flap of the EBGP session causes flaps of all other BGP sessions that are configured with the family inet-vpn unicast statement.
The reason for the flapping behavior is related to BGP operation in Junos OS when originating VPN routes.
Please refer to the below document for more details and how this issue can be avoided:
https://www.juniper.net/documentation/en_US/junos12.3/topics/topic-map/bgp-sessions.html