4A0-100 Questions and Answers

AVirtual Local Area Network (VLAN)is a logical separation of devices atLayer 2, even ifthose devices are connected to the same physical switch. Each VLAN forms itsown broadcast domain, and traffic cannot cross from one VLAN to anotherwithout Layer 3 routing.

Option Ais incorrect – devices on the same switch but in different VLANs still cannot communicate directly.

Option Bis incorrect – VLANs explicitlycreate separate broadcast domains.

Option Dis technically incorrect – communication is possible with the right setup.

Option Cis correct – to enable communication between different VLANs, arouteror aLayer 3 switchwith inter-VLAN routing capability is required.

This process is calledinter-VLAN routing, and it's a fundamental task in enterprise networks using VLANs.

BGP (Border Gateway Protocol)uses amulti-step decision processto select the best route among multiple paths. It doesnot use SPF or simple metrics like hop count.

Key BGP selection criteria include:

Local preference

AS path length

Origin type

MED (Multi-Exit Discriminator)

eBGP over iBGP

IGP metric to next hop

Option C is correct– BGP evaluatesmultiple attributesfor route selection.

A Virtual Private Network (VPN) is designed to provide secure and private communication over a shared or public infrastructure. Key characteristics of VPNs include:​

Traffic Isolation:Each customer's traffic is kept separate from others, ensuring privacy and security.​

Shared Infrastructure:Service providers can support multiple VPNs over the same physical infrastructure, optimizing resource utilization.​

Customization:VPNs can be tailored to meet the specific requirements of individual customers, including security policies, routing, and quality of service.​

However,customer data is not alteredas it traverses a VPN. Instead, VPNs employ encryption and tunneling protocols to protect data integrity and confidentiality during transmission. The primary goal is to ensure that data remains unchanged and secure from end to end.​

A/31 subnetin IPv4 provides exactlytwo IP addresses(e.g., 192.168.1.0/31 → usable: 192.168.1.0 and 192.168.1.1). Traditionally, these would represent anetwork address and a broadcast address, butRFC 3021redefines /31 subnets forpoint-to-point links, such as router-to-router connections.

In a /31 subnet:

Broadcast address is not used.

Both IPs are treated as usable host addresses.

It'sideal for point-to-point links, saving address space.

This is widely supported andstandardized in Nokia IP and routing platforms.

TheDHCP client/server exchangefollows a specific four-step sequence known asDORA:

Discover– Client broadcasts to find available DHCP servers.

Offer– DHCP server responds with an IP address offer.

Request– Client requests the offered IP.

Acknowledgement– Server confirms the lease.

This ensuresdynamic IP configurationand is used in enterprise and home networks.

AVPRN (Virtual Private Routed Network)provides aLayer 3 VPN serviceover a service provider’s network.

Each customer site connects to aPE router.

Sites are connected via arouted networkusingseparate routing instances.

Customer routers seerouted connectivity, as if connected to their own private WAN.

Option C is correct– VPRN providesrouted connectivitybetween sites.

In Nokia SR OS, event logging allows the router to report system events, alarms, and operational changes to external systems or users. The valid logging destinations include:

SNMP– Used to send traps or informs to SNMP managers.

Syslog– Sends logs to centralized syslog servers, a standard for log management.

NETCONF– Can be used for event notification in model-driven management setups, although it is more frequently used for configuration and state management.

However,BOF (Boot Options File)isnota valid logging destination. TheBOFis used to store critical system boot configurations, such as:

Which image to boot from

Network interface settings

Auto-boot parameters

BOF plays no role in the logging infrastructure.