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Question 221

Which IPv4 subnet mask corresponds to a /30 prefix?

1. 255.255.255.0
2. 255.255.255.252
3. 255.255.255.248
4. 255.255.255.240

Correct Answer: 2

Explanation

A /30 IPv4 prefix uses 30 bits for the network portion and leaves 2 bits for host addressing. The corresponding subnet mask is 255.255.255.252. A /30 subnet contains four total IPv4 addresses, although traditional point-to-point subnetting generally provides two usable host addresses because the network and broadcast addresses are reserved. /30 networks have historically been common for point-to-point links because they provide a small, efficient address block.

Question 222

How many bits are contained in an IPv6 address?

1. 64
2. 96
3. 128
4. 256

Correct Answer: 3

Explanation

An IPv6 address contains 128 bits. This is significantly larger than the 32-bit address space used by IPv4. IPv6 addresses are normally written as eight groups of hexadecimal digits separated by colons. The larger address space provides a very large number of possible addresses and supports modern network scalability. IPv6 also introduces mechanisms such as Neighbor Discovery Protocol and multicast addressing. Understanding the 128-bit structure is fundamental when configuring and troubleshooting IPv6 networks on Junos devices.

Question 223

Which IPv6 prefix is reserved for multicast addresses?

1. FF00::/8
2. FE80::/10
3. FC00::/7
4. 2000::/3

Correct Answer: 1

Explanation

IPv6 multicast addresses use the FF00::/8 prefix. Multicast allows packets to be delivered to a group of receivers rather than a single destination. IPv6 uses multicast extensively for network operations, including Neighbor Discovery and various routing functions. This differs from unicast addressing, which identifies a particular interface, and link-local addressing, which uses the FE80::/10 range. Recognizing the major IPv6 address ranges helps administrators understand the purpose of addresses seen in interface and routing information.

Question 224

Which IPv6 prefix is commonly associated with unique local addresses?

1. 2000::/3
2. FF00::/8
3. FC00::/7
4. FE80::/10

Correct Answer: 3

Explanation

The FC00::/7 range is reserved for IPv6 Unique Local Addresses, commonly abbreviated as ULA. These addresses are intended for private addressing within organizations and are not globally routable on the public Internet. Unique local addressing provides an IPv6 equivalent for many private-network use cases. The range includes addresses beginning with FC or FD. Administrators should distinguish ULA addresses from globally routable unicast addresses and from link-local addresses, which use the FE80::/10 range.

Question 225

Which command displays IPv6 neighbor information on a Junos device?

1. show ipv6 neighbors
2. show ndp
3. show neighbor ipv6
4. show system ndp-table

Correct Answer: 2

Explanation

The show ndp command displays IPv6 Neighbor Discovery information on a Junos device. NDP performs functions that are comparable in some ways to ARP in IPv4, including discovering neighboring nodes and resolving IPv6 addresses to link-layer addresses. Reviewing the NDP table can help troubleshoot IPv6 connectivity problems. Administrators can compare neighbor information with interface status and IPv6 addressing to determine whether local IPv6 communication is operating correctly.

Question 226

Which transport protocol provides reliable, connection-oriented communication?

1. UDP
2. ICMP
3. TCP
4. ARP

Correct Answer: 3

Explanation

TCP, or Transmission Control Protocol, provides reliable, connection-oriented communication. It uses mechanisms such as sequencing, acknowledgments, retransmission, and flow control to provide dependable delivery of data. Applications that require reliable transport commonly use TCP. UDP, in contrast, is connectionless and does not provide the same built-in reliability mechanisms. Understanding the differences between TCP and UDP is important when troubleshooting application connectivity, firewall behavior, and network traffic.

Question 227

Which transport protocol is connectionless and does not provide built-in retransmission?

1. TCP
2. UDP
3. SSH
4. HTTP

Correct Answer: 2

Explanation

UDP, or User Datagram Protocol, is a connectionless transport protocol. It does not provide TCP-style acknowledgments, sequencing, or automatic retransmission. This lightweight design can reduce protocol overhead and is useful for applications where speed or simplicity is important. Applications using UDP may implement their own reliability mechanisms when required. Network administrators should understand UDP behavior when troubleshooting traffic because UDP sessions do not behave like TCP connections and may be handled differently by security policies and monitoring tools.

Question 228

Which protocol is commonly used by the ping utility to test IP reachability?

1. ICMP
2. FTP
3. SSH
4. SNMP

Correct Answer: 1

Explanation

Ping commonly uses ICMP, or Internet Control Message Protocol, to test IP connectivity. An ICMP Echo Request is sent to the destination, and an Echo Reply may be returned if the destination and intermediate security policies allow it. Ping can help determine whether a destination is reachable and can provide basic response-time information. A failed ping does not always prove that the destination is unavailable because firewalls or security policies may block ICMP traffic while allowing other types of traffic.

Question 229

Which command can be used to test IP connectivity to a remote destination from a Junos device?

1. test connection
2. ping
3. verify reachability
4. check-ip

Correct Answer: 2

Explanation

The ping command is used to test IP connectivity from a Junos device to a specified destination. It sends ICMP Echo Requests and reports responses when they are received. Administrators can use ping to verify basic reachability between network devices and hosts. The command can also be useful for identifying packet loss or increased response times. When troubleshooting, ping should be combined with routing and interface checks because successful ICMP communication alone does not confirm that every application or service is functioning.

Question 230

Which command is used to trace the path packets take toward a destination?

1. route-path
2. traceroute
3. trace-route-table
4. path-check

Correct Answer: 2

Explanation

The traceroute command helps identify the Layer 3 path packets take toward a destination. It can display intermediate routers between the source and destination and provide response-time information for those hops. This makes traceroute useful for locating routing or connectivity problems beyond the local network. A hop that does not respond does not necessarily mean that traffic stops there because some routers filter or rate-limit diagnostic responses. Administrators should interpret traceroute results together with routing and interface information.

Question 231

Which routing protocol uses a shortest-path-first algorithm based on link-state information?

1. BGP
2. OSPF
3. DHCP
4. ARP

Correct Answer: 2

Explanation

OSPF uses a link-state approach and calculates shortest paths using the Shortest Path First algorithm. OSPF routers exchange link-state information to build a topology database and then calculate appropriate routes. This differs from BGP, which uses path attributes and policy-based route selection. OSPF is commonly deployed as an interior gateway protocol within an autonomous system. Administrators can inspect OSPF neighbors, interfaces, and link-state information when troubleshooting routing behavior.

Question 232

What is the purpose of the OSPF link-state database?

1. Store Ethernet MAC addresses
2. Store DNS records
3. Represent topology information learned by OSPF
4. Store user passwords

Correct Answer: 3

Explanation

The OSPF link-state database stores information about the network topology learned through OSPF link-state advertisements. Each OSPF router uses this information to build a view of the topology within its area. The router then runs the shortest-path algorithm against that information to calculate routes. A consistent link-state database is important for proper OSPF operation. When troubleshooting OSPF, administrators can inspect the database to understand what topology information the router has learned and compare it with the expected network design.

Question 233

Which BGP attribute is generally preferred when selecting an outbound path within an autonomous system?

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

Correct Answer: 1

Explanation

Local preference is a BGP attribute used to influence outbound path selection within an autonomous system. When comparing otherwise applicable routes, a higher local-preference value is generally preferred. This allows network administrators to establish preferred exit points for external traffic. Local preference is propagated within the autonomous system, making it useful for coordinating outbound routing decisions across multiple routers. It is different from MED, which is primarily used to provide path-selection information to a neighboring autonomous system.

Question 234

Which BGP attribute can be used to help prevent routing loops between autonomous systems?

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

Correct Answer: 3

Explanation

The AS path attribute records autonomous system numbers associated with a BGP route advertisement. It helps BGP routers detect potential routing loops. If a router receives a route advertisement containing its own autonomous system number in the AS path, it can reject the route. The AS path is also useful for applying routing policies based on the path a route has taken. Administrators can inspect AS-path information when troubleshooting BGP route selection and external routing behavior.

Question 235

Which Junos command displays detailed information about a specific route?

1. show route detail
2. show route extensive
3. show route <destination> detail
4. show routing detail

Correct Answer: 3

Explanation

The show route command can be combined with a destination prefix and the detail option to examine information about a specific route. Detailed route information can include the protocol that installed the route, next-hop information, preference, and other attributes. This is useful when multiple possible routes exist and an administrator needs to understand why a particular route was selected. Reviewing a specific route is often more effective than examining the entire routing table when troubleshooting a single destination.

Question 236

What does route preference help determine in Junos?

1. Which route to prefer when multiple routes are available
2. Which interface receives DHCP
3. Which user can log in
4. Which VLAN receives broadcasts

Correct Answer: 1

Explanation

Route preference is used by Junos as part of the process of selecting between routes to the same destination learned from different sources. The routing table may contain information from connected, static, OSPF, BGP, or other routing sources. Route preference helps determine which route source should be preferred when appropriate. It should not be confused with BGP local preference, which is a specific BGP attribute used within an autonomous system. Administrators can inspect route information to understand route-selection decisions.

Question 237

Which Junos feature allows multiple independent routing tables on the same device?

1. Routing instances
2. Interface groups
3. Firewall filters
4. Chassis clusters

Correct Answer: 1

Explanation

Routing instances allow a Junos device to maintain separate routing tables and routing contexts. This can be useful when networks need logical separation on the same physical device. Different routing instances can support different interfaces, routes, and routing protocols according to the configuration. They are commonly used in service-provider environments and other designs requiring traffic or routing separation. Administrators should understand that routing instances provide logical isolation rather than requiring separate physical routers for every routing domain.

Question 238

Which configuration hierarchy is used to configure routing instances?

1. routing-instances
2. routing-options instances
3. protocols instances
4. system routing-instances

Correct Answer: 1

Explanation

The routing-instances hierarchy is used to configure routing instances in Junos. Administrators can define separate routing contexts and associate appropriate interfaces, routing options, and protocols with them. Routing instances are useful for separating routing information on a single physical device. The exact configuration depends on the routing-instance type and the intended network design. Careful planning is required because interfaces and routes associated with one instance may not be directly available to another instance without appropriate configuration.

Question 239

Which Junos feature can filter packets based on criteria such as source or destination addresses?

1. Firewall filters
2. Routing instances
3. NTP
4. Interface descriptions

Correct Answer: 1

Explanation

Junos firewall filters can examine packet characteristics and apply configured actions. Depending on the filter configuration, criteria can include source addresses, destination addresses, protocols, ports, and other packet properties. Firewall filters can be used for traffic control, classification, counting, and other packet-processing purposes. They are different from routing policies, which primarily control route import, export, and selection behavior. Administrators should carefully evaluate filter terms and actions because an incorrect filter can unintentionally affect network traffic.

Question 240

Which action can a Junos firewall filter term use to discard a matching packet?

1. accept
2. reject
3. discard
4. forward

Correct Answer: 3

Explanation

The discard action causes a matching packet to be silently dropped by the firewall filter. A filter can contain match conditions and actions that determine what happens when traffic meets those conditions. Discard differs from reject because reject can provide a response to the sender depending on the protocol and configuration, while discard simply drops the packet. Firewall filters should be designed carefully because incorrect terms or ordering can block legitimate traffic. Administrators should review filter counters and configuration when troubleshooting packet filtering behavior.