View Full Juniper JN0-637 Exam Dumps and Practice Test Dumps

 

Question 141: Which BGP attribute is used to identify the autonomous systems a route has traversed?

1. MED
2. Local preference
3. Community
4. AS path

Correct Answer: 4. AS path

Explanation:
The BGP AS path attribute records the sequence of autonomous systems that a route advertisement has traversed. Each AS typically adds its own autonomous system number to the path when advertising the route to an external BGP neighbor. The AS path provides loop-prevention information because a router can reject a route if its own AS number is already present. It also participates in BGP path selection, where a shorter AS path is generally preferred after higher-priority attributes have been considered. AS path should not be confused with local preference, MED, or communities, which serve different purposes in BGP routing policy and path selection.

Question 142: Which Junos command displays the currently active routing table?

1. show route
2. show configuration
3. show interfaces terse
4. show chassis hardware

Correct Answer: 1. show route

Explanation:
The Junos show route command displays information from the routing table, including destination prefixes, protocol sources, route preferences, next hops, and route states. It is one of the most commonly used commands for troubleshooting routing behavior. Administrators can also specify a particular prefix or routing instance to narrow the output. show configuration examines configuration statements, while show interfaces terse provides interface status and show chassis hardware displays hardware information. When investigating why traffic is following a particular path, show route provides an important starting point for understanding which routes are available and which route has been selected.

Question 143: What is the main function of an OSPF Area Border Router (ABR)?

1. To connect different OSPF areas
2. To assign MPLS labels
3. To establish BGP sessions between autonomous systems
4. To provide Ethernet link aggregation

Correct Answer: 1. To connect different OSPF areas

Explanation:
An OSPF Area Border Router (ABR) connects one or more non-backbone OSPF areas to the OSPF backbone, Area 0. An ABR maintains link-state information for the areas to which it is connected and can advertise summarized or inter-area reachability information between them. This hierarchical structure helps OSPF scale by limiting the amount of detailed link-state information that must be maintained throughout the entire routing domain. An ABR is different from an AS Boundary Router, which connects OSPF to external routing domains. MPLS labels, BGP sessions, and Ethernet aggregation are handled by other technologies.

Question 144: Which Junos command is useful for checking the status and details of a BGP session with a specific peer?

1. show ospf neighbor
2. show route receive-protocol bgp <peer>
3. show bgp neighbor <peer>
4. show ldp neighbor

Correct Answer: 3. show bgp neighbor <peer>

Explanation:
The Junos show bgp neighbor <peer> command provides detailed information about a specific BGP neighbor. The output can include the peer’s address, autonomous system, session state, message statistics, timers, capabilities, and route-related information. It is particularly useful when a BGP session is not behaving as expected and more detail is required than the summary command provides. show bgp summary is useful for viewing multiple peers at once, while the other commands listed focus on OSPF or LDP. Examining the specific BGP neighbor output can help identify session establishment problems, capability mismatches, or unexpected route behavior.

Question 145: Which MPLS label operation replaces an incoming label with a different outgoing label?

1. Push
2. Pop
3. Swap
4. Encapsulate

Correct Answer: 3. Swap

Explanation:
An MPLS swap operation replaces an incoming MPLS label with another label before forwarding the packet. This is a common operation performed by Label-Switched Routers in the MPLS core. The router uses its label forwarding information to determine the outgoing interface and replacement label. A push operation adds a label, while a pop operation removes a label. Understanding these three basic MPLS operations is important for interpreting MPLS forwarding behavior and troubleshooting label-switched paths. The exact label operation performed depends on the packet’s position in the MPLS forwarding path and the forwarding information programmed into the device.

Question 146: Which BGP attribute is normally used to influence route selection within the local autonomous system for outbound traffic?

1. Local preference
2. MED
3. Origin
4. Community

Correct Answer: 1. Local preference

Explanation:
Local preference is used within an autonomous system to influence which external route should be selected for outbound traffic. A higher local-preference value is generally preferred. Because the attribute is propagated through the autonomous system, administrators can use routing policy to establish a consistent preferred exit path. This differs from MED, which can be used to influence how another autonomous system selects an entry point. Local preference is therefore an important BGP traffic-engineering tool for controlling outbound routing decisions. It is typically evaluated before attributes such as AS path length, origin, and MED in the BGP decision process.

Question 147: Which protocol is commonly used by Junos devices to automatically negotiate an aggregated Ethernet link?

1. LLDP
2. LACP
3. BFD
4. VRRP

Correct Answer: 2. LACP

Explanation:
Link Aggregation Control Protocol (LACP) allows compatible devices to dynamically negotiate and maintain a link aggregation group. Multiple physical Ethernet interfaces can be combined into a single logical aggregated connection, providing redundancy and potentially increased aggregate bandwidth. LACP exchanges control information with the neighboring device to determine which links can participate in the bundle. LLDP is primarily used for neighbor discovery, BFD detects forwarding failures, and VRRP provides first-hop gateway redundancy. LACP is therefore the protocol specifically associated with dynamic link aggregation and is commonly used when configuring aggregated Ethernet interfaces on Junos devices.

Question 148: What is the primary purpose of a route target in an MPLS Layer 3 VPN?

1. To identify the physical interface of a PE router
2. To create an OSPF adjacency
3. To determine the BGP router ID
4. To control VPN route import and export**

Correct Answer: 4. To control VPN route import and export

Explanation:
Route targets are extended BGP communities used in MPLS Layer 3 VPNs to control which VPN routes are imported into or exported from VRF routing tables. A provider can configure import and export route-target policies so that specific VPNs can exchange routes while remaining isolated from others. Route targets therefore define VPN route membership and connectivity. They should be distinguished from route distinguishers, which make overlapping customer prefixes unique within VPN routing tables. Route targets do not identify physical interfaces or directly establish routing adjacencies. They are an important component of MPLS VPN policy and route distribution.

Question 149: Which OSPF packet type is used to request specific link-state information from a neighboring router?

1. Link State Request
2. Hello
3. Database Description
4. Link State Acknowledgment

Correct Answer: 1. Link State Request

Explanation:
An OSPF Link State Request (LSR) packet is used by a router to request specific link-state information from a neighboring router. During database synchronization, routers compare their link-state information and request any LSAs they are missing or need to update. Link State Update packets then carry the requested LSAs, while Link State Acknowledgment packets confirm their receipt. Hello packets are used primarily for neighbor discovery and maintenance, and Database Description packets summarize the contents of a router’s link-state database during adjacency formation. Understanding these packet types is useful when troubleshooting OSPF adjacency and database synchronization issues.

Question 150: Which Junos command can be used to view routes learned from a specific BGP neighbor?

1. show bgp summary
2. show route receive-protocol bgp <peer>
3. show ospf database
4. show interfaces terse

Correct Answer: 2. show route receive-protocol bgp <peer>

Explanation:
The Junos show route receive-protocol bgp <peer> command displays routes received from a specified BGP neighbor. It is useful when troubleshooting route advertisements because it allows an administrator to determine which prefixes a particular peer is sending to the local router. This can help distinguish between a problem with route advertisement by the neighbor and a problem involving local routing policy or route installation. show bgp summary provides session-level information, while OSPF and interface commands examine different areas of the device. Examining received routes is an important step when investigating missing BGP prefixes.

Question 151: Which Junos configuration statement is used to define a routing policy term’s match conditions?

1. then
2. from
3. apply-groups
4. family

Correct Answer: 2. from

Explanation:
In a Junos routing policy term, the from section specifies the conditions that determine whether the term matches a route. Conditions can include prefixes, protocols, communities, route types, autonomous system information, and other supported attributes. Once a route matches the conditions, the actions defined in the then section can be applied. The distinction between from and then is fundamental to Junos policy configuration: from identifies what should match, while then specifies what should happen to matching routes. Carefully structuring these sections allows administrators to create precise import and export routing policies.

Question 152: Which IS-IS level is primarily responsible for routing within an individual IS-IS area?

1. Level 1
2. Level 2
3. Level 3
4. Level 0

Correct Answer: 1. Level 1

Explanation:
IS-IS Level 1 routing is responsible for routing within an individual IS-IS area. Level 1 routers maintain information about destinations inside their local area and can use Level 2 routers to reach destinations outside that area. Level 2 routing provides the backbone function between areas. Routers can also operate as Level 1-2 routers, participating in both levels and connecting local-area routing with the broader IS-IS domain. Understanding the distinction between Level 1 and Level 2 is important when designing or troubleshooting hierarchical IS-IS networks, particularly when determining how routes should move between local areas.

Question 153: Which Junos command can be used to examine the forwarding table rather than the routing table?

1. show route
2. show configuration
3. show route forwarding-table
4. show bgp summary

Correct Answer: 3. show route forwarding-table

Explanation:
The Junos show route forwarding-table command displays information from the forwarding table used by the forwarding plane. This differs from the routing table, which contains routing information learned from protocols and other sources. The forwarding table contains information that the Packet Forwarding Engine uses to actually forward packets. Examining it can be useful when troubleshooting situations where the routing table appears correct but forwarding behavior is unexpected. show route primarily examines routing information, while configuration and BGP commands provide other types of information. Understanding the distinction between routing and forwarding tables is important for Junos troubleshooting.

Question 154: What is the purpose of a BGP route reflector cluster ID?

1. To identify the physical chassis
2. To determine the MPLS label value
3. To identify a group of route reflectors and help prevent reflection loops
4. To assign a BGP community

Correct Answer: 4. To identify a group of route reflectors and help prevent reflection loops

Explanation:
A BGP route reflector cluster ID identifies a route-reflector cluster and contributes to loop prevention when routes are reflected within an iBGP environment. When a route reflector reflects a route, cluster information can be carried with the route so that another route reflector can recognize that the route has already passed through the same cluster. This helps prevent routing loops in networks containing multiple route reflectors. The cluster ID is therefore associated with BGP route reflection rather than MPLS labels, physical chassis identification, or community assignment. Proper route-reflector design is important for scalable and stable iBGP deployments.

Question 155: Which IPv6 feature allows a host to automatically learn a network prefix and default router information?

1. Router Advertisement
2. ARP
3. DHCPv4
4. BGP Update

Correct Answer: 1. Router Advertisement

Explanation:
IPv6 Router Advertisement (RA) messages are part of Neighbor Discovery Protocol and allow hosts to learn information such as network prefixes, default-router information, and other configuration parameters. Routers periodically send Router Advertisements, and hosts can also solicit them using Router Solicitation messages. This mechanism supports IPv6 stateless address autoconfiguration and helps hosts determine how to reach destinations outside their local network. IPv6 does not use ARP for these functions, and DHCPv4 is an IPv4 mechanism. BGP Update messages are exchanged between BGP speakers and are unrelated to host-level IPv6 configuration.

Question 156: Which Junos feature allows an administrator to schedule an automatic rollback of a committed configuration if the change is not confirmed?

1. commit confirmed
2. commit synchronize
3. commit at
4. commit check

Correct Answer: 1. commit confirmed

Explanation:
Junos commit confirmed provides a safety mechanism for configuration changes by requiring the administrator to confirm the commit within a specified period. If confirmation does not occur, Junos automatically reverts to the previously committed configuration. This is particularly valuable when administrators make changes remotely, because an incorrect configuration could otherwise interrupt management access. The feature reduces the risk associated with changes to interfaces, routing, firewall policies, or other critical services. commit check validates configuration syntax and semantics but does not activate a configuration, while commit synchronize has a different role on systems with redundant Routing Engines.

Question 157: Which technology can provide first-hop gateway redundancy for hosts on an Ethernet network?

1. LACP
2. VRRP
3. LLDP
4. LDP

Correct Answer: 2. VRRP

Explanation:
Virtual Router Redundancy Protocol (VRRP) provides first-hop gateway redundancy by allowing multiple routers to share a virtual gateway identity. Hosts use the virtual IP address as their default gateway rather than depending on the physical address of a single router. One router normally forwards traffic while another can assume the forwarding role if the active device fails. This improves gateway availability without requiring hosts to change their gateway configuration during a failure. LACP is used for link aggregation, LLDP for Layer 2 neighbor discovery, and LDP for MPLS label distribution. VRRP therefore directly addresses redundant default-gateway functionality.

Question 158: Which BGP attribute can be used to influence the preferred entry point into an autonomous system?

1. Local preference
2. MED
3. Origin
4. Router ID

Correct Answer: 2. MED

Explanation:
The Multi-Exit Discriminator (MED) is a BGP attribute that can be used to suggest which entry point another autonomous system should use when multiple connections exist between the same autonomous systems. In the relevant BGP comparison, a lower MED is generally preferred. MED is therefore commonly associated with influencing inbound traffic toward an autonomous system. Local preference serves a different purpose by influencing outbound path selection within an AS. MED is an optional policy tool and its comparison can depend on configuration and the BGP implementation. Understanding its role helps distinguish inbound traffic engineering from outbound traffic engineering.

Question 159: Which Junos command can be used to display detailed information about an interface, including statistics and operational details?

1. show interfaces <interface>
2. show route summary
3. show bgp summary
4. show system users

Correct Answer: 1. show interfaces <interface>

Explanation:
The Junos show interfaces <interface> command provides detailed operational information about a specified interface. Depending on the interface and platform, the output can include administrative and operational state, traffic statistics, errors, encapsulation information, protocol state, and other interface details. This makes the command useful for troubleshooting physical or logical connectivity problems. The show interfaces terse command provides a more concise summary when only basic interface states are needed. Routing, BGP, and system-user commands examine different areas of the device. Detailed interface output is particularly useful when investigating packet loss, link failures, or interface errors.

Question 160: Which protocol is commonly used to securely manage a Junos device through a command-line interface?

1. Telnet
2. FTP
3. SSH
4. HTTP

Correct Answer: 3. SSH

Explanation:
Secure Shell (SSH) is commonly used to securely access and manage Junos devices through a command-line interface. SSH encrypts the management session, helping protect credentials and configuration information from interception while the administrator is connected to the device. Telnet does not provide the same level of encryption and is generally unsuitable for secure management. FTP is primarily a file-transfer protocol, while HTTP is an application protocol commonly associated with web services. Using secure management protocols is an important operational and security practice when administering network infrastructure remotely.