Description

This article explains why the OSPF and ISIS route is refreshed when a preference setting is changed.

Symptoms

With route refresh, there can be traffic loss during a route refresh if there is active traffic to those route destinations. The duration of traffic loss is based on the route scale.

[MASTER][edit]
root@router# run show route table inet.0    

inet.0: 10 destinations, 10 routes (10 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

0.0.0.0/0          *[Static/5] 2d 07:07:07
                    >  to 10.75.253.251 via fxp0.0
8.8.8.8/32         *[OSPF/10] 00:00:30, metric 1
                    >  to 100.0.0.2 via ge-2/0/6.0

[MASTER][edit]
root@router# set protocols ospf preference 90 

[MASTER][edit]
root@router# commit 
re1: 
configuration check succeeds
re0: 
commit complete
re1: 
commit complete

[MASTER][edit]
root@router# run show route table inet.0 

inet.0: 10 destinations, 10 routes (10 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

0.0.0.0/0          *[Static/5] 2d 07:07:41
                    >  to 10.75.253.251 via fxp0.0
8.8.8.8/32         *[OSPF/90] 00:00:06, metric 1  <-- route is refreshed 
                    >  to 100.0.0.2 via ge-2/0/6.0

The same behavior also happens on the ISIS.

Solution

This behavior is working as designed. This type of change may need to be done during a maintenance window to minimize traffic loss.

Modification History

2022-11-04: Article reviewed for accuracy. Article is valid and relevant