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Question 261:

Which OSPF network type normally uses a designated router (DR) and backup designated router (BDR) to reduce the number of required adjacencies?

1. Point-to-point
2. Broadcast
3. Loopback
4. Point-to-multipoint

Correct Answer: 2

Explanation:

OSPF broadcast networks, such as Ethernet segments, use a designated router and backup designated router to reduce the number of full adjacencies required. Without a DR, every router on a shared segment would need to form a full adjacency with every other router, creating unnecessary control-plane overhead. The DR represents the shared segment when exchanging link-state information, while the BDR provides redundancy if the DR fails. Point-to-point networks generally do not require DR or BDR elections because only two routers participate in the link. Understanding the network type is therefore important when troubleshooting OSPF adjacency behavior.

Question 262:

What happens when an OSPF router’s dead interval expires without receiving a valid Hello from a neighbor?

1. The router increases the neighbor’s metric
2. The router declares the neighbor down
3. The router changes the neighbor to Full state
4. The router starts a BGP session

Correct Answer: 2

Explanation:

The OSPF dead interval determines how long a router waits for Hello packets from a neighbor before declaring that neighbor unavailable. If no valid Hello is received during the entire dead interval, the neighbor relationship is removed. The router then updates its OSPF topology information and may perform another SPF calculation to determine new paths. This behavior allows OSPF to react to failed links or unreachable neighbors without waiting indefinitely. Matching Hello and dead intervals between neighboring routers is important because incompatible timer values can prevent an OSPF adjacency from forming or cause an otherwise healthy adjacency to repeatedly go down.

Question 263:

Which OSPF packet allows two neighboring routers to describe the contents of their link-state databases during adjacency establishment?

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

Correct Answer: 1

Explanation:

Database Description (DBD) packets are exchanged when OSPF neighbors synchronize their link-state databases. A DBD packet contains summaries of LSAs known by the sending router rather than carrying the complete contents of every LSA. The receiving router compares the information with its own LSDB and determines whether additional LSAs are needed. It can then use Link State Request packets to request missing or newer information. Hello packets are used for neighbor discovery and maintenance, while Link State Acknowledgment packets acknowledge received LSAs. DBD exchanges are therefore an important stage in establishing a fully synchronized OSPF adjacency.

Question 264:

Which BGP attribute is commonly used to communicate a preference for how traffic should enter an autonomous system from a neighboring AS?

1. Local Preference
2. MED
3. Router ID
4. Cluster ID

Correct Answer: 2

Explanation:

The Multi-Exit Discriminator (MED) is a BGP attribute that can be used to influence how a neighboring autonomous system selects among multiple entry points into an autonomous system. A lower MED is generally preferred when the attribute is compared. This allows a network to suggest which connection should be used for inbound traffic when multiple links exist between the same autonomous systems. Local Preference has a different purpose and is primarily used inside an AS to influence outbound path selection. Router ID and Cluster ID are used for BGP identification and route-reflector-related functions rather than directly expressing an entry-point preference.

Question 265:

What is the main purpose of a BGP community attribute?

1. To provide a tag that can be used to apply routing policy
2. To identify the physical interface speed
3. To replace the AS Path
4. To establish the TCP connection

Correct Answer: 1

Explanation:

BGP communities provide a flexible way to tag routes with additional information that can be used in routing policies. An administrator can assign a community to a route and then use policy logic to match that community and perform an action, such as changing local preference, modifying advertisements, or rejecting selected routes. Communities are particularly useful when the same routing treatment needs to be applied to groups of prefixes without matching every prefix individually. Communities do not replace the AS Path, establish the underlying TCP connection, or identify physical interface characteristics. They are primarily policy-oriented BGP attributes.

Question 266:

Which BGP session type is normally established between routers belonging to different autonomous systems?

1. iBGP
2. eBGP
3. OSPF
4. EVPN

Correct Answer: 2

Explanation:

External BGP, or eBGP, is used to exchange routing information between routers in different autonomous systems. It is commonly used between service providers, customers, Internet peers, or separate administrative domains. Internal BGP, or iBGP, is used between BGP routers within the same autonomous system. Both eBGP and iBGP use TCP as their transport protocol, but their operational behavior and design considerations differ. OSPF is an interior gateway protocol, while EVPN is a BGP-based control-plane technology used for services such as Ethernet VPN. Understanding whether a peer relationship is internal or external is fundamental to BGP configuration and troubleshooting.

Question 267:

Which BGP attribute contains the sequence of autonomous systems through which a route has passed?

1. Origin
2. MED
3. AS Path
4. Local Preference

Correct Answer: 3

Explanation:

The AS Path attribute contains the sequence of autonomous system numbers associated with a BGP route advertisement. Each eBGP autonomous system generally adds its own AS number when advertising a route to another AS. Besides being useful for route selection, the AS Path provides an important loop-prevention mechanism. If a router receives a route containing its own AS number in the path, it can reject the route rather than accepting a potentially looping advertisement. Local Preference influences outbound routing within an AS, MED can influence entry-point selection, and Origin indicates how the route was introduced into BGP. AS Path therefore has both selection and loop-prevention significance.

Question 268:

Which BGP attribute indicates how a route was originally introduced into BGP?

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

Correct Answer: 1

Explanation:

The BGP Origin attribute indicates the origin type of a route and provides information about how the route was introduced into BGP. The common origin codes are IGP, EGP, and Incomplete. When comparing otherwise eligible BGP routes, a more preferred origin type can influence route selection. The Origin attribute is different from the AS Path, which records autonomous systems through which the route has traveled. Local Preference is used to influence outbound routing within an AS, while MED can influence inbound path selection by a neighboring AS. Understanding the individual BGP attributes is essential for diagnosing why a particular route becomes the preferred path.

Question 269:

Which Junos command can be used to inspect detailed information about a particular BGP neighbor?

1. show bgp neighbor
2. show ospf database
3. show arp
4. show interfaces terse

Correct Answer: 1

Explanation:

The show bgp neighbor command provides detailed information about configured BGP neighbors and their sessions. Depending on the Junos output, administrators can examine session state, negotiated capabilities, message statistics, timers, route information, and other details useful for troubleshooting. This command is particularly helpful after show bgp summary identifies a peer with an unexpected state. show bgp summary provides a more concise overview, while show ospf database, show arp, and show interfaces terse focus on different areas of the network. Detailed BGP neighbor information can help identify session establishment problems, policy behavior, and route-exchange issues.

Question 270:

Which Junos policy action explicitly prevents a route from being accepted or advertised when the policy term matches it?

1. next-hop
2. community
3. reject
4. metric

Correct Answer: 3

Explanation:

The reject policy action prevents a matching route from being accepted or advertised, depending on whether the policy is being applied as an import or export policy. This provides administrators with direct control over routing information. For example, an import policy can reject unwanted routes received from a BGP peer, while an export policy can prevent selected routes from being advertised to another neighbor. Other policy actions can modify attributes such as the next hop, community, or metric rather than simply denying the route. Routing policy is therefore a powerful mechanism for controlling and manipulating route advertisements in Junos OS.

Question 271:

Which Junos configuration statement is used to apply a routing policy to routes received from a BGP neighbor?

1. export
2. import
3. scheduler
4. rewrite-rule

Correct Answer: 2

Explanation:

In Junos BGP configuration, an import policy controls routes received from a BGP neighbor. The policy can match prefixes or attributes and then accept, reject, or modify routes before they are installed or otherwise processed according to the routing configuration. An export policy serves the opposite direction by controlling routes advertised to a neighbor. Scheduler and rewrite-rule configuration belongs to Class of Service rather than BGP routing policy. Correctly applying import and export policies is important because a route may be successfully received at the BGP protocol level but still be rejected or modified by policy before becoming usable in the routing table.

Question 272:

Which Junos routing-policy action can modify the BGP local preference of a matching route?

1. local-preference
2. router-id
3. dead-interval
4. vni

Correct Answer: 1

Explanation:

A Junos routing policy can modify the local preference attribute of matching BGP routes. This is commonly used to influence outbound path selection within an autonomous system. For example, routes received from a preferred upstream or external connection can be assigned a higher local preference than routes from a backup connection. Because local preference is propagated within the AS through BGP, it can help multiple routers make consistent decisions. Router ID and dead interval are associated with routing-protocol identification and OSPF timing, while VNI belongs to VXLAN. Routing policy therefore provides a flexible mechanism for dynamically applying local-preference values to selected routes.

Question 273:

What is the primary function of an IRB interface in an Ethernet switching environment?

1. Provide Layer 3 routing for a VLAN
2. Provide PoE power
3. Establish an eBGP session
4. Perform VXLAN encapsulation

Correct Answer: 1

Explanation:

An Integrated Routing and Bridging (IRB) interface provides Layer 3 connectivity for a VLAN or Layer 2 switching domain. Hosts within a VLAN can use the IRB interface as their default gateway, allowing traffic to be routed between different VLANs or toward external networks. IRB interfaces are also commonly used in EVPN environments to provide routing between Layer 2 segments and Layer 3 networks. PoE is responsible for delivering electrical power, eBGP provides inter-AS routing, and VXLAN encapsulation is performed by VTEPs. Understanding IRB interfaces is important when troubleshooting communication between hosts located in different VLANs or EVPN segments.

Question 274:

In an EVPN-VXLAN deployment, what is the role of an IRB interface when routing traffic between different VLANs?

1. It provides Layer 3 gateway functionality
2. It performs BGP route reflection
3. It assigns ESI values
4. It creates OSPF adjacencies

Correct Answer: 1

Explanation:

An IRB interface can serve as the Layer 3 gateway for a VLAN in an EVPN-VXLAN environment. This allows traffic from one VLAN or bridge domain to be routed toward another VLAN or Layer 3 destination. In a distributed gateway design, multiple VTEPs can provide gateway functionality for hosts while the EVPN control plane distributes necessary reachability information. The IRB interface therefore connects Layer 2 switching behavior with Layer 3 routing functionality. BGP route reflection, ESI assignment, and OSPF adjacency formation are separate control-plane functions and are not the primary purpose of an IRB interface.

Question 275:

Which EVPN route type is specifically associated with Ethernet Segment information?

1. Route Type 2
2. Route Type 3
3. Route Type 4
4. Route Type 5

Correct Answer: 3

Explanation:

EVPN Route Type 4 is the Ethernet Segment route. It is used to distribute information about an Ethernet segment and plays an important role in EVPN multihoming operations. PE devices connected to the same Ethernet segment use EVPN control-plane information to identify the shared segment and participate in procedures such as designated-forwarder election. Route Type 2 is used for MAC/IP Advertisement, Route Type 3 for Inclusive Multicast Ethernet Tag, and Route Type 5 for IP Prefix information. Knowing these route types is important when troubleshooting EVPN multihoming and determining whether the expected control-plane information is being exchanged.

Question 276:

What is the main benefit of EVPN multihoming for a customer or downstream Ethernet segment?

1. Redundant connectivity through multiple PE devices
2. Elimination of all routing protocols
3. Automatic replacement of IP addressing
4. Removal of the VXLAN underlay

Correct Answer: 1

Explanation:

EVPN multihoming allows a downstream Ethernet segment to connect redundantly to multiple provider-edge or VTEP devices. This provides resiliency because traffic can continue through another PE if one path or device fails. EVPN also includes mechanisms such as Ethernet Segment identification, designated-forwarder election, and split-horizon behavior to coordinate forwarding and prevent loops or unnecessary duplication. Multihoming does not eliminate routing protocols, replace IP addressing, or remove the need for an IP underlay in VXLAN deployments. Instead, it enhances Layer 2 service resiliency while using EVPN control-plane mechanisms to coordinate the multiple connected devices.

Question 277:

Which authentication method allows a switch to authenticate an endpoint using its MAC address rather than requiring an 802.1X supplicant?

1. MAC-based authentication
2. OSPF authentication
3. BGP authentication
4. EVPN authentication

Correct Answer: 1

Explanation:

MAC-based authentication allows a switch to identify an endpoint using its MAC address when traditional 802.1X authentication is not practical or supported. The switch can send authentication information to a RADIUS server, which can determine whether the device should be granted access. This method is useful for devices such as printers, IP phones, cameras, and other endpoints that may not support an 802.1X supplicant. It can also be combined with other access-control mechanisms depending on the deployment. OSPF and BGP authentication protect routing sessions, while EVPN is a network virtualization technology rather than an endpoint authentication method.

Question 278:

What is a common reason to use 802.1X authentication on an enterprise switch port?

1. To control network access based on authenticated users or devices
2. To calculate OSPF SPF paths
3. To select a BGP route reflector
4. To assign VXLAN VNIs

Correct Answer: 1

Explanation:

802.1X provides port-based network access control by requiring an endpoint to authenticate before receiving normal network access. The switch acts as an authenticator, while the endpoint acts as a supplicant. Authentication information is commonly exchanged with a RADIUS server. Depending on the authentication result and configured policies, the endpoint can receive access to an appropriate VLAN or other network resources. This provides stronger access control than simply allowing any device connected to an active Ethernet port. OSPF SPF calculations, BGP route-reflector selection, and VXLAN VNI assignment are unrelated functions and do not provide endpoint authentication.

Question 279:

Which protocol is commonly used as the authentication backend for 802.1X deployments?

1. LLDP-MED
2. RADIUS
3. VXLAN
4. OSPF

Correct Answer: 2

Explanation:

RADIUS is commonly used as the centralized authentication backend for 802.1X network access control. When an endpoint attempts to authenticate, the access switch can communicate with the RADIUS server to validate credentials and obtain authorization information. This centralized approach makes it easier for administrators to apply consistent authentication policies across many switches. LLDP-MED can provide information to compatible IP phones, VXLAN provides network overlay functionality, and OSPF handles interior routing. RADIUS therefore has a different role focused on authentication, authorization, and accounting. Understanding the relationship between the switch, supplicant, and RADIUS server is important when troubleshooting 802.1X.

Question 280:

Which Junos command can be used to compare the candidate configuration with the currently committed configuration?

1. show configuration
2. show | compare
3. show route
4. show system uptime

Correct Answer: 2

Explanation:

The show | compare command is used in Junos configuration mode to display differences between the candidate configuration and the currently committed configuration. This is useful before committing changes because it allows an administrator to review exactly what has been added, removed, or modified. Reviewing configuration differences can help prevent accidental changes from being committed to production devices. The show configuration command displays configuration information but does not provide the same focused comparison. show route displays routing information, while show system uptime provides system runtime details. Therefore, show | compare is an important command for safe configuration management.