Service Provider Routing and Switching -
Specialist (JNCIS-SP)
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, 1.You must ensure that your routing platform with redundant REs continues to forward packets, even if
one RE fails.
Which technology would you use to accomplish this task?
A. NSB
B. LAG
C. BFD
D. GRES
Answer: D
Explanation:
For Juniper platforms equipped with dual Routing Engines (REs), the fundamental technology required to
provide high availability during a hardware or software failure of the primary RE is Graceful Routing
Engine Switchover (GRES).
According to Juniper Networks technical documentation, GRES allows the backup RE to stay in a "hot"
standby state. When GRES is enabled, the primary RE synchronizes critical state information with the
backup RE, specifically the chassis state and the interface state. This synchronization includes the Packet
Forwarding Engine (PFE) configuration.
When the primary RE fails, the backup RE takes over immediately. Because the PFE (which resides on
the line cards) was already synchronized and is not restarted during the switchover, the router continues
to forward packets that are already in flight or part of established flows. This prevents a complete network
outage during an RE failover.
Comparison with other options:
NSB (Non-Stop Bridging - Option A): Focuses specifically on maintaining Layer 2 protocol states (like
STP) during a switchover.
LAG (Link Aggregation - Option B): Provides redundancy for physical links, not the control plane or the
RE.
BFD (Bidirectional Forwarding Detection - Option C): Is a protocol used for rapid detection of link or
neighbor failures; it does not protect the RE or maintain forwarding during an internal switchover.
It is important to note that while GRES maintains the forwarding state, it does not by itself maintain the
routing protocol state (adjacencies). To keep OSPF or BGP sessions from dropping during the switchover,
GRES must be paired with Non-Stop Active Routing (NSR). However, as the question focuses on the core
requirement of continuing to forward packets, GRES is the foundational technology.
2.Which two statements regarding GRE and IP-IP tunnels are correct? (Choose two.)
A. These tunnels add additional overhead to the packets that traverse them.
B. These tunnels do not add any overhead to the packets that traverse them.
C. These tunnels offer secure encryption mechanisms.
D. These tunnels do not offer encryption mechanisms.
Answer: A D
Explanation:
In Juniper Networks Junos OS, Generic Routing Encapsulation (GRE) and IP-in-IP (IP-IP) are common
tunneling mechanisms used to transport packets across a network by encapsulating them within another
protocol. Understanding the header structure and the limitations of these protocols is essential for proper
MTU (Maximum Transmission Unit) management and security design.
Overhead (Option A):
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