R0 is a Juniper Networks MX router with dual Routing Engines. You must load new software
on R0 while ensuring no control plane disruption and minimal data loss. Which three
features meet the requirement? (Choose three.)
A.
BFD
B.
unified ISSU
C.
graceful Routing-Engine switchover (GRES)
D.
graceful restart
E.
NSR
B, C, E
Unified ISSU
A unified in-service software upgrade (unified ISSU) enables you to upgrade between
two different Junos OS Releases with no disruption on the control plane and with minimal
disruption of traffic. Unified ISSU is only supported by dual Routing Engine platforms. In
addition, graceful Routing Engine switchover (GRES) and nonstop active routing (NSR)
must be enabled.
With a unified ISSU, you can eliminate network downtime, reduce operating costs, and
deliver higher services levels.
B,D,E
Graceful Routing Engine switchover (GRES) enables a routing platform with redundant Routing Engines to continue forwarding packets, even if one Routing Engine fails. Graceful Routing Engine switchover preserves interface and kernel information. Traffic is not interrupted. However, graceful Routing Engine switchover does not preserve the control plane. Neighboring routers detect that the router has experienced a restart and react to the event in a manner prescribed by individual routing protocol specifications.
No. B,C,E are correct. (D) is wrong – DUAL RE eliminates need of restart routing process.
“Unified ISSU takes advantage of the redundancy provided by dual Routing Engines and works in conjunction with the graceful Routing Engine switchover feature and the nonstop active routing feature.”
https://www.juniper.net/documentation/en_US/junos/topics/concept/issu-oveview.html