Description

This article describes the effect of enabling or disabling graceful-restart on existing BGP sessions under global and configured routing-instance.

Symptoms

After configuring set routing-options graceful-restart disable, BGP sessions flapped. However, the BGP session under routing-instance remains stable.
The following configuration was done under global instance on the router: 

set routing-options graceful-restart enable
or 
set routing-options graceful-restart
or 
set routing-options graceful-restart disable
or 
delete/deactivate set routing-options graceful-restart


This re-establishes the BGP session to advertise the graceful-restart capability. The BGP sessions under configured routing-instnace (L3VPN) will not be affected due to the above configuration change.


lab@MX> show bgp summary  

Groups: 2 Peers: 2 Down peers: 0
Table          Tot Paths  Act Paths Suppressed    History Damp State    Pending
inet.0               
                       0          0          0          0          0          0
inet.2               
                       0          0          0          0          0          0
bgp.l3vpn.0          
                      10         10          0          0          0          0
bgp.l3vpn.2          
                       0          0          0          0          0          0
bgp.mvpn.0           
                     738        738          0          0          0          0
Peer                     AS      InPkt     OutPkt    OutQ   Flaps Last Up/Dwn State|#Active/Received/Accepted/Damped...
1.2.1.4            45543        771        589       0       1       28:35 Establ
  inet.0: 0/0/0/0
  inet.2: 0/0/0/0
  bgp.l3vpn.0: 10/10/10/0
  bgp.l3vpn.2: 0/0/0/0
  bgp.mvpn.0: 738/738/738/0
  L3VPN-IPTV.inet.0: 3/10/10/0
  L3VPN-IPTV.mvpn.0: 498/498/498/0
30.30.30.201            100          4          6       0       0          41 Establ
  L3VPN-IPTV.inet.0: 0/0/0/0

lab@MX# set routing-options graceful-restart disable 
 
[edit]
lab@MX# commit and-quit 
commit complete
Exiting configuration mode
 
lab@MX> show bgp summary    
Groups: 2 Peers: 2 Down peers: 1
Table          Tot Paths  Act Paths Suppressed    History Damp State    Pending
inet.0               
                       0          0          0          0          0          0
inet.2               
                       0          0          0          0          0          0
bgp.l3vpn.0          
                       0          0          0          0          0          0
bgp.l3vpn.2          
                       0          0          0          0          0          0
bgp.mvpn.0           
                       0          0          0          0          0          0
Peer                     AS      InPkt     OutPkt    OutQ   Flaps Last Up/Dwn State|#Active/Received/Accepted/Damped...
27.2.192.4            45543          0          0       0       0           4 Active
30.30.30.201            100          5          8       0       0        1:08 Establ  <<< This session which is under routing-instance L3VPN-IPTV did not flap
  L3VPN-IPTV.inet.0: 0/0/0/0

Solution

Graceful-restart is configured on a per instance basis. If BGP is configured under default global instance, such as under [routing-options], it will take effect only for this main instance. If the graceful-restart is applied to the specific routing-instance under [routing-instance <instance-name> routing-options], then it will take effect on that specific instance. Hence, any changes done related to graceful-restart under one routing-instance will not affect BGP sessions in other routing-instances.

This is the expected behavior in Junos.

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