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Question 321Question →

A network administrator is troubleshooting neighbor visibility on a Cisco Catalyst switch (SW-1) connected to a non-Cisco switch. The administrator executes the `show lldp entry Core-SW2` command on SW-1 and receives the following CLI output:

text
Local Interface: Gi1/0/24
Chassis id: 0014.f2ca.8800
Port id: Eth1/1
Port Description: Trunk-to-Core1
System Name: Core-SW2

System Description:
Cisco Nexus Operating System (NX-OS) Software, Version 9.3(5)

Time remaining: 92 seconds
System Capabilities: B, R
Enabled Capabilities: B, R

Management Addresses:
IP: 10.1.100.2

Auto Negotiation: supported, enabled
Physical media capabilities:
1000baseT(FD)

Media Attachment Unit type: 30
VLAN Advertised: 10, 20, 99
Port VLAN ID (PVID): 99

Based on this LLDP detailed output, which conclusion correctly interprets the neighbor properties and link configuration?

The local switch interface receiving the LLDP frames is GigabitEthernet1/0/24, while the remote neighbor's egress port is Ethernet1/1 with a native VLAN (PVID) of 99.

The local switch interface connected to the neighbor is Ethernet1/1, and GigabitEthernet1/0/24 represents the remote switch interface.

The Port VLAN ID (PVID) of 99 indicates the native VLAN currently configured on the local switch interface GigabitEthernet1/0/24.

The neighbor device has an active LLDP holdtime set to 92 seconds, which is the default holdtime value for LLDP on Cisco switches.

Show answer & explanation

Answer: The local switch interface receiving the LLDP frames is GigabitEthernet1/0/24, while the remote neighbor's egress port is Ethernet1/1 with a native VLAN (PVID) of 99.

Answer

The local switch interface receiving the LLDP frames is GigabitEthernet1/0/24, while the remote neighbor's egress port is Ethernet1/1 with a native VLAN (PVID) of 99.

In Cisco IOS LLDP detailed entries (`show lldp entry` or `show lldp neighbors detail`), 'Local Interface' indicates the interface on the local device where the frame arrived (Gi1/0/24). The 'Port id' field identifies the remote neighboring device's egress interface (Eth1/1). Furthermore, the 'Port VLAN ID (PVID)' field reflects the native VLAN advertised by the adjacent device for that link.

Step-by-Step Solution

Analyze the Local Interface and Port ID fields in the LLDP output

'Local Interface: Gi1/0/24' represents the local switch's port receiving the LLDP frame. 'Port id: Eth1/1' specifies the interface on the remote neighboring device (Core-SW2).

LLDP output explicitly distinguishes between the local port where traffic is received and the remote port ID advertised by the neighbor.

Examine the Port VLAN ID (PVID) TLV information

'Port VLAN ID (PVID): 99' is the native VLAN ID advertised by the neighbor device (Core-SW2) for its port Eth1/1.

IEEE 802.1AB LLDP includes Organizationally Specific TLVs that advertise port attributes of the remote sender, including its configured native VLAN (PVID).

Evaluate the remaining timer information

'Time remaining: 92 seconds' is the dynamic countdown timer before the cached entry expires, not the configured holdtime constant.

The default LLDP holdtime multiplier (4) with a default message frequency (30s) yields a default holdtime of 120s; 92 seconds is merely the current countdown state.

Key Concept

Interpretation of LLDP Detailed CLI Neighbor Data and IEEE 802.1AB TLVs

Estimated Time:2m 0s

Question 322Question →

A network administrator is evaluating the IPv4 configuration on a core router interface assigned the IP address $172.31.223.254/22$ . Which of the following statements regarding this IPv4 addressing assignment are correct? (Select TWO.)

Select all that apply

The configured interface IP address represents the last usable host IP address within the subnet.

The IP address falls within the RFC 1918 private IPv4 address space.

The subnet provides a maximum capacity of

1,024

usable host IP addresses for connected endpoints.

The IP address is a globally routable public address because the Class B private space ends at

172.30.255.255

Show answer & explanation

Answer: The configured interface IP address represents the last usable host IP address within the subnet.; The IP address falls within the RFC 1918 private IPv4 address space.

Answer

The statements confirming that the configured interface IP address is the last usable host within the subnet and that the IP address belongs to the RFC 1918 private IPv4 space are correct.

The subnet mask 255.255.252.0 (/22) creates subnets in increments of 4 in the third octet. For 172.31.223.254, the network address is 172.31.220.0 and the broadcast address is 172.31.223.255. Therefore, 172.31.223.254 is the last assignable host address in the subnet. Furthermore, RFC 1918 specifies the Class B private range as 172.16.0.0 to 172.31.255.255, so this address is a valid private IPv4 address.

Step-by-Step Solution

Determine host bits and total/usable address capacity for a /22 prefix.

A /22 prefix leaves

32 - 22 = 10

host bits. Total addresses =

2^{10} = 1,024

. Usable host capacity =

2^{10} - 2 = 1,022

host addresses.

Network ID and broadcast ID cannot be assigned to individual endpoints.

Calculate subnet network boundaries for

172.31.223.254/22

The subnet mask is

255.255.252.0

. The third octet block size is

256 - 252 = 4

. Multiplying by 55 yields

55 \times 4 = 220

. The network ID is

172.31.220.0/22

, and the broadcast address is

172.31.223.255

Finding the block size in the interesting octet identifies the network boundary and broadcast address.

Determine the usable host IP address range.

The usable range is

172.31.220.1

through

172.31.223.254

. Thus,

172.31.223.254

is the last assignable host address.

Usable host addresses lie strictly between the network ID and the broadcast ID.

Verify RFC 1918 private address range compliance.

RFC 1918 designates

172.16.0.0/12

(

172.16.0.0 - 172.31.255.255

) as private space.

172.31.223.254

falls directly within this block.

Checking official RFC 1918 prefix allocations determines public versus private status.

Key Concept

IPv4 subnet boundary calculation, usable host calculation (

2^n - 2

), and RFC 1918 private IP address range boundaries.

Question 323Question →

A network technician notices that connecting an end-user host to an access port does not generate a Topology Change Notification (TCN) or cause MAC address table flushing on neighboring switches. Which feature configured on the access interface is responsible for suppressing these STP topology change notifications upon link state changes?

PortFast

BPDU Guard

Root Guard

Loop Guard

Show answer & explanation

Answer: PortFast

Answer

PortFast suppresses Topology Change Notifications (TCNs) when edge interfaces change state, avoiding unnecessary MAC table flushing across the network.

PortFast is intended for switch ports connected to end devices. Besides bypassing the Listening and Learning states to transition immediately to Forwarding, PortFast ensures that link state changes on edge ports do not trigger Spanning Tree Topology Change Notifications (TCNs), thereby protecting the network from unnecessary MAC address table aging and flushing.

Step-by-Step Solution

Identify the STP behavior caused by connecting end-user devices.

Standard 802.1D STP generates a Topology Change Notification (TCN) whenever a link comes up or goes down, causing switches in the broadcast domain to shorten their MAC address table aging timer.

End-user workstations power on and off frequently, which would cause constant MAC table flushing if TCNs were transmitted.

Evaluate the role of PortFast.

PortFast designates a port as an edge port, immediately transitioning it to Forwarding while suppressing TCN generation upon link state changes.

Since end-user workstations do not interconnect switches, link state changes on these ports do not affect the overall Spanning Tree topology.

Key Concept

PortFast TCN Suppression and Edge Port Operation

Question 324Question →

An engineer inspects the IPv6 neighbor discovery table on a Cisco router and observes the dynamically generated link-local address fe80::2e0:a3ff:fe14:5678 assigned to an auto-configured host interface. Based on the standard EUI-64 calculation process, what is the original burned-in MAC address of the host network interface card?

00e0.a314.5678

02e0.a314.5678

00e0.a3ff.5678

04e0.a314.5678

Show answer & explanation

Answer: 00e0.a314.5678

Answer

The original burned-in MAC address of the host network interface card is 00e0.a314.5678.

To reverse the EUI-64 process for the interface ID 02e0:a3ff:fe14:5678, first remove the 16-bit 'FFFE' inserted into the middle, which leaves 02e0.a314.5678. Next, invert the 7th bit (Universal/Local bit) in the first byte. Hexadecimal 02 is binary 00000010; inverting the 7th bit produces binary 00000000 (hexadecimal 00). Therefore, the original MAC address is 00e0.a314.5678.

Step-by-Step Solution

Isolate the 64-bit interface identifier from the link-local IPv6 address

The interface identifier portion of fe80::2e0:a3ff:fe14:5678 is 02e0:a3ff:fe14:5678.

Link-local addresses append a 64-bit interface identifier to the fe80::/64 prefix.

Remove the 16-bit FFFE value inserted into the middle of the EUI-64 interface identifier

Removing 'ff:fe' from 02e0:a3ff:fe14:5678 leaves 02e0:a314:5678.

The EUI-64 process creates a 64-bit interface ID from a 48-bit MAC by inserting FFFE (1111 1111 1111 1110) between the 3rd and 4th bytes of the MAC address.

Invert the 7th bit (Universal/Local bit) of the first octet to restore the original MAC address

First octet 02 (0000 0010 binary) inverted at the 7th bit yields 00 (0000 0000 binary), resulting in MAC 00e0.a314.5678.

EUI-64 generation flips the 7th bit of the first byte (changing 0 for universal to 1 for local); reversing the process requires flipping this bit back.

Key Concept

Reversing standard IPv6 EUI-64 interface identifier generation to recover the original 48-bit MAC address

Estimated Time:1m 30s

Question 325Question →

An enterprise network relies on standard Syslog services over UDP port 514 to collect event logs from remote edge switches. When comparing transport protocol characteristics, which header feature directly accounts for UDP's lower processing overhead compared to TCP?

UDP incorporates sequence numbers in its header to allow receiver packet reordering without transmitting acknowledgments.

UDP utilizes a fixed 8-byte header that omits fields for connection state tracking, flow control, and acknowledgments.

UDP dynamically varies its header size between 8 and 20 bytes depending on network congestion levels.

UDP relies on the underlying IP layer header fields to negotiate sliding window sizes and perform retransmissions.

Show answer & explanation

Answer: UDP utilizes a fixed 8-byte header that omits fields for connection state tracking, flow control, and acknowledgments.

Answer

UDP utilizes a fixed 8-byte header that omits fields for connection state tracking, flow control, and acknowledgments.

UDP is designed for low-overhead, best-effort transport. Its header contains only 4 fields totaling 8 bytes: Source Port (2 bytes), Destination Port (2 bytes), Length (2 bytes), and Checksum (2 bytes). By leaving reliability, sequencing, and flow control to application layers or accepting packet loss, UDP avoids the 20-byte minimum header and state maintenance required by TCP.

Step-by-Step Solution

Analyze transport layer header structures

TCP headers require a minimum of 20 bytes to support sequence numbers, acknowledgment numbers, window sizes, flags, and control mechanisms. UDP headers consist of only 8 bytes (4 fields: Source Port, Destination Port, Length, and Checksum).

Lower header size directly reduces data overhead per packet.

Evaluate protocol feature set differences

UDP is connectionless and stateless. It does not establish sessions, manage flow control (windowing), perform segment sequencing, or require ACKs.

Omitting operational state management reduces router/host CPU and memory processing overhead.

Key Concept

TCP vs UDP Header Overhead and Protocol Mechanics

Question 326Question →

A network administrator is verifying IPv6 autoconfiguration on a Cisco router interface. The interface has a burned-in MAC address of `7069.5a12.3456` and is configured with the command `ipv6 address 2001:db8:abc:10::/64 eui-64`. Based on standard EUI-64 interface identifier construction and IPv6 address formats, which TWO statements regarding the resulting IPv6 configuration on this interface are correct?

Select all that apply

The derived 64-bit EUI-64 interface identifier for this interface is `7269:5aff:fe12:3456`.

The dynamically generated link-local IPv6 address for this interface begins with the `fe80::/10` prefix combined with the modified interface identifier.

The EUI-64 calculation inserts the 16-bit hexadecimal sequence `ffff` into the midpoint of the 48-bit MAC address.

The 7th bit (universal/local bit) of the MAC address is left un-inverted, yielding an interface identifier beginning with `7069`.

Executing the command with the `eui-64` keyword automatically creates a link-local address within the unique local address scope (`fc00::/7`).

Show answer & explanation

Answer: The derived 64-bit EUI-64 interface identifier for this interface is `7269:5aff:fe12:3456`.; The dynamically generated link-local IPv6 address for this interface begins with the `fe80::/10` prefix combined with the modified interface identifier.

Answer

The two correct statements are: (1) The derived 64-bit EUI-64 interface identifier for this interface is `7269:5aff:fe12:3456`, and (2) The dynamically generated link-local IPv6 address for this interface begins with the `fe80::/10` prefix combined with the modified interface identifier.

Generating an IPv6 EUI-64 interface identifier from a 48-bit MAC address requires two transformations: toggling the 7th bit of the first byte (changing 0x70 to 0x72) and inserting FFFE into the midpoint, forming the 64-bit identifier `7269:5aff:fe12:3456`. Additionally, IPv6 automatically configures a link-local address on the interface using the designated prefix `fe80::/10` combined with this EUI-64 identifier.

Step-by-Step Solution

Split the 48-bit MAC address into two 24-bit halves

Left half: `70-69-5A`, Right half: `12-34-56`

EUI-64 generation requires inserting a 16-bit delimiter into the middle of the MAC address.

Invert the 7th bit (Universal/Local bit) of the first byte

First byte `0x70` in binary is `0111 0000`. Inverting the 7th bit (2nd least significant bit of first byte) yields `0111 0010` in binary, which is `0x72`. The first half becomes `7269.5a`.

Inverting the U/L bit indicates that the address has been modified for global uniqueness scoping in IPv6 EUI-64.

Insert `FFFE` at the midpoint between the two halves

`7269:5A` + `FFFE` + `:123456` = `7269:5aff:fe12:3456`

This expands the 48-bit MAC address into a 64-bit interface identifier.

Verify the link-local prefix and global unicast address formation

Link-local address = `fe80::7269:5aff:fe12:3456`, Global unicast address = `2001:db8:abc:10:7269:5aff:fe12:3456`

Link-local addresses always use the `fe80::/10` prefix block (specifically formatted as `fe80::/64`).

Key Concept

IPv6 EUI-64 Interface Identifier Derivation and Link-Local Address Scoping

Estimated Time:2m 0s

Question 327Question →

A network engineer inspects packet captures from a server connection and notes a transport layer header size of 20 bytes featuring Sequence Number and Window Size fields. Which statement correctly identifies the transport protocol in use and its operational trade-off relative to UDP?

The packet uses TCP, which provides reliable connection-oriented delivery and flow control but incurs higher header overhead and processing delay than UDP.

The packet uses UDP, which provides reliable delivery by adjusting the Window Size field dynamically to prevent network congestion.

The packet uses TCP, which operates statelessly with a fixed 8-byte header to minimize transmission latency across WAN links.

The packet uses UDP, which uses a 20-byte header to perform sequence tracking while maintaining lightweight, connectionless operations.

Show answer & explanation

Answer: The packet uses TCP, which provides reliable connection-oriented delivery and flow control but incurs higher header overhead and processing delay than UDP.

Answer

The packet uses TCP, which provides reliable connection-oriented delivery and flow control but incurs higher header overhead and processing delay than UDP.

The presence of a 20-byte header along with Sequence Number and Window Size fields indicates the Transmission Control Protocol (TCP). TCP is connection-oriented and stateful, providing retransmission, sequencing, and flow control. The trade-off for these features is higher header overhead (20 bytes minimum compared to UDP's fixed 8 bytes) and additional latency required for state tracking.

Step-by-Step Solution

Analyze the header characteristics in the packet capture.

Identified a 20-byte transport header with Sequence Number and Window Size fields.

These fields and the 20-byte minimum size specifically belong to the TCP header; UDP headers are fixed at 8 bytes.

Evaluate protocol operational mechanics and trade-offs.

TCP provides stateful, reliable connection management and windowing-based flow control at the cost of higher overhead.

The extra header fields (20 bytes vs UDP's 8 bytes) and acknowledgment mechanisms guarantee in-order delivery but introduce latency and bandwidth overhead.

Key Concept

TCP vs UDP Header Overhead and Reliability Mechanics

Question 328Question →

A network administrator needs to configure a fully specified IPv6 static route on a Cisco router to reach the remote network $2001:\text{DB8}:\text{ACAD}:1::/64$ using the neighbor router's link-local address $\text{FE80}::2$ reachable via the local $\text{GigabitEthernet0/1}$ interface. Which command correctly configures this route?

ipv6 route 2001:DB8:ACAD:1::/64 GigabitEthernet0/1 FE80::2

ipv6 route 2001:DB8:ACAD:1::/64 FE80::2

ipv6 route 2001:DB8:ACAD:1::/64 GigabitEthernet0/1 FE80::2 110

ipv6 route 2001:DB8:ACAD:1::/64 GigabitEthernet0/1 FE80::FFFE:2

Show answer & explanation

Answer: ipv6 route 2001:DB8:ACAD:1::/64 GigabitEthernet0/1 FE80::2

Answer

The command 'ipv6 route 2001:DB8:ACAD:1::/64 GigabitEthernet0/1 FE80::2' correctly configures the fully specified IPv6 static route.

When configuring an IPv6 static route using a link-local address as the next-hop, Cisco IOS mandates a fully specified route that includes both the local exit interface and the link-local address of the adjacent router.

Step-by-Step Solution

Identify the mandatory components of an IPv6 static route command with a link-local next hop.

The general syntax requires specifying both the local exit interface and the link-local next-hop address: 'ipv6 route <prefix/mask> <exit-interface> <link-local-address>'.

Because IPv6 link-local addresses (FE80::/10) are only unique on a single local link, Cisco IOS cannot determine which outbound interface to use unless the interface is explicitly defined.

Evaluate the specified parameters.

Destination prefix = 2001:DB8:ACAD:1::/64, Exit interface = GigabitEthernet0/1, Next-hop = FE80::2.

Combining these exact parameters in order produces a valid fully specified static route configuration.

Key Concept

Fully specified IPv6 static routes requiring both an exit interface and link-local next-hop address.

Question 329Question →

A network administrator is configuring Port Address Translation (PAT) on an enterprise Cisco IOS router. The internal subnets matched by Access Control List 15 require multiple internal IP addresses to share a dynamic pool of public IPv4 addresses named $GUEST_NAT_POOL$ . Which Cisco IOS global configuration command correctly enables PAT using this dynamic address pool?

ip nat inside source list 15 pool GUEST_NAT_POOL overload

ip nat inside source list 15 pool GUEST_NAT_POOL

ip nat outside source list 15 pool GUEST_NAT_POOL overload

ip nat inside source static list 15 pool GUEST_NAT_POOL overload

Show answer & explanation

Answer: ip nat inside source list 15 pool GUEST_NAT_POOL overload

Answer

The correct command to configure dynamic PAT using an IP address pool is 'ip nat inside source list 15 pool GUEST_NAT_POOL overload'.

The correct command syntax for dynamic NAT with PAT using an IP address pool is 'ip nat inside source list <acl-number> pool <pool-name> overload'. The 'overload' keyword enables Layer 4 source port tracking so multiple internal IP addresses can share the IP addresses in the pool simultaneously.

Step-by-Step Solution

Identify the source direction and dynamic NAT type

Inside source traffic matching an ACL requires 'ip nat inside source list <ACL>'.

Internal private hosts initiating outbound connections must undergo inside source NAT.

Specify the target public address pool

Append 'pool GUEST_NAT_POOL' to map matching ACL traffic to the designated pool.

The scenario requires using a pre-defined named pool of public IP addresses instead of a single interface.

Enable port multiplexing (PAT)

Append the 'overload' keyword at the end of the command.

Without 'overload', Cisco IOS configures standard dynamic NAT (1-to-1 translation), whereas PAT (many-to-one/many-to-few using layer 4 ports) explicitly requires 'overload'.

Key Concept

Port Address Translation (PAT) pool configuration using the overload keyword

Question 330Question →

An engineer configures a next-hop IPv4 static route on a Cisco router using the command `ip route 10.1.2.0 255.255.255.0 192.168.12.2`. Place the processing steps in the correct sequential order from first to last that the router performs when forwarding an incoming packet destined for $10.1.2.45$ .

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence for packet forwarding with a next-hop static route is: First, match the packet destination IP

10.1.2.45

to the static route entry pointing to next-hop

192.168.12.2

. Second, perform a recursive lookup in the routing table for

192.168.12.2

to find the outgoing interface. Third, look up the MAC address of

192.168.12.2

in the ARP table. Fourth, encapsulate the packet into a Layer 2 frame and transmit it out the egress interface.

When a static route specifies only a next-hop IPv4 address (recursive static route), the router must first identify the static route via longest-prefix match. Next, it performs a recursive RIB lookup on the next-hop IP address to determine the exit interface. After identifying the exit interface, it performs an ARP table lookup to find the next-hop MAC address, and finally encapsulates and transmits the frame.

Step-by-Step Solution

Evaluate incoming packet destination IP against routing table entries.

The destination address

10.1.2.45

matches static route

10.1.2.0/24

with next-hop

192.168.12.2

Routing decisions begin with a longest-prefix match lookup in the RIB.

Perform recursive routing lookup for next-hop IP address

192.168.12.2

The router identifies the directly connected network prefix and egress interface used to reach

192.168.12.2

Static routes configured solely with a next-hop IP require a recursive lookup to identify the exit interface.

Resolve Layer 2 destination hardware address via ARP cache lookup for

192.168.12.2

The target next-hop MAC address is retrieved for frame header construction.

Ethernet interfaces require the next-hop MAC address to format the data-link layer encapsulation.

Encapsulate IPv4 packet into Layer 2 Ethernet frame and send out the egress interface.

The packet is transmitted on the physical wire.

All forwarding requirements (interface and Layer 2 rewrite info) are complete.

Key Concept

IPv4 Static Route Recursive Lookup & Forwarding Process

Estimated Time:1m 30s

Question 331Question →

What prefix and prefix length parameter completes the Cisco IOS command to configure a default IPv6 static route pointing to next-hop address $2001:

\text{db8}:1::2$?

Fill in the blanks below

Router(config)# ipv6 route 2001:db8:1::2

Show answer & explanation

Answer

The correct notation to represent a default route in IPv6 static routing is ::/0.

In IPv6 static routing, ::/0 is the prefix notation for a default route, serving the same function as 0.0.0.0/0 in IPv4.

Step-by-Step Solution

Identify the network prefix used to match all possible IPv6 destinations.

The default IPv6 route prefix is written as ::/0.

In IPv6 addressing, :: represents all zeros, and /0 indicates a prefix length of zero bits, matching any destination address.

Substitute the default prefix into the Cisco IOS IPv6 static routing command syntax.

The completed command is 'ipv6 route ::/0 2001:db8:1::2'.

The standard command syntax requires 'ipv6 route <destination-prefix/prefix-length> <next-hop-address>'.

Key Concept

IPv6 Default Static Route Configuration

Estimated Time:45s

Question 332Question →

A network engineer is configuring Rapid PVST+ on a Cisco Catalyst switch to force it to become the Root Bridge for VLAN 40. The engineer attempts to configure a custom bridge priority value using the Cisco IOS CLI command line syntax. Which command entry contains a valid bridge priority value that Cisco IOS will accept, and what total bridge priority value will the switch advertise in its outbound Spanning Tree Protocol BPDUs for VLAN 40?

The command 'spanning-tree vlan 40 priority 4096' will be accepted, and the advertised total bridge priority will be 4136.

The command 'spanning-tree vlan 40 priority 4000' will be accepted, and the advertised total bridge priority will be 4040.

The command 'spanning-tree vlan 40 priority 4096' will be accepted, and the advertised total bridge priority will be 4096.

The command 'spanning-tree vlan 40 priority 4136' will be accepted, and the advertised total bridge priority will be 4136.

Show answer & explanation

Answer: The command 'spanning-tree vlan 40 priority 4096' will be accepted, and the advertised total bridge priority will be 4136.

Answer

The command 'spanning-tree vlan 40 priority 4096' will be accepted, and the advertised total bridge priority will be 4136.

In Cisco Rapid PVST+, the 16-bit priority portion of the 8-byte Bridge ID (BID) is divided into a 4-bit Bridge Priority and a 12-bit System ID Extension. Because only 4 bits are allocated to user configuration (

2^4 = 16

levels), priority values in CLI commands must increase in steps of 4096 (

4096 \times 1 = 4096

). When the command 'spanning-tree vlan 40 priority 4096' is executed, Cisco IOS validates

4096

as a valid base priority. During BPDU generation for VLAN 40, the switch adds the VLAN ID (

40

) as the System ID Extension, resulting in a total priority value of

4096 + 40 = 4136

Step-by-Step Solution

Verify CLI input validation rules for Rapid PVST+ bridge priority

Cisco IOS requires configurable bridge priority values to be explicit multiples of 4096 (

0, 4096, 8192, 12288, \dots, 61440

The 16-bit Priority field in the Bridge ID (BID) uses the 4 most significant bits for configurable priority and the remaining 12 bits for the System ID Extension (VLAN ID).

Calculate the total advertised Bridge Priority field value

Base Priority (

4096

) + System ID Extension (

40

) = Total Priority (

4136

Rapid PVST+ dynamically inserts the 12-bit VLAN ID into the System ID Extension field for per-VLAN spanning tree identification.

Key Concept

Rapid PVST+ Bridge ID Structure and System ID Extension Calculation

Question 333Question →

An administrator connects a switch access port to a user workstation without enabling Cisco PortFast. Place the standard IEEE 802.1D Spanning Tree Protocol (STP) port states in the chronological sequence that the interface transitions through from initial physical link up to active user data forwarding.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct chronological sequence of IEEE 802.1D STP port state transitions is: Blocking state, Listening state, Learning state, and Forwarding state.

In classic IEEE 802.1D Spanning Tree Protocol (STP), an edge port not configured with PortFast undergoes a strict 30-second convergence timer sequence: Blocking (initial loop prevention) -> Listening (15s, BPDU exchange and role selection) -> Learning (15s, MAC table population without data forwarding) -> Forwarding (active data packet processing).

Step-by-Step Solution

Identify initial link state

Port enters Blocking state

Standard 802.1D STP defaults unconfigured edge ports to Blocking to safely prevent loops during initial topology evaluation.

Transition to neighbor discovery and role determination

Port enters Listening state for 15 seconds (Forward Delay)

BPDUs are transmitted and processed to elect root bridges and designate root/designated port roles.

Prepare Layer 2 forwarding tables

Port enters Learning state for 15 seconds (Forward Delay)

MAC addresses are learned from incoming frames to populate the CAM table, mitigating flooding when forwarding begins.

Complete convergence to operational status

Port enters Forwarding state

With topology determined and MAC table initialized, user frames are actively forwarded.

Key Concept

IEEE 802.1D STP Port State Transitions

Estimated Time:1m 15s

Question 334Question →

An administrator needs to enable Link Aggregation (LAG) on a Cisco Wireless LAN Controller (WLC) connected to an upstream switch stack. Place the configuration and operational steps in the correct chronological sequence from start to finish.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence begins with saving the WLC configuration, enabling LAG in the controller settings, saving and rebooting the WLC to apply the change, and finally configuring the connected switch ports as a static EtherChannel (mode on).

The sequence follows the standard Cisco procedure for turning on controller-wide Link Aggregation (LAG). First, current configuration state is saved. Second, LAG is enabled in the WLC settings menu. Third, the WLC configuration is saved and the controller is rebooted to apply the change. Fourth, the corresponding switch ports are configured into a static EtherChannel using 'channel-group mode on' to complete the physical and logical aggregation.

Step-by-Step Solution

Save the existing WLC configuration

Establishes a baseline configuration state before initiating a system reboot

It is essential to safeguard existing controller configuration prior to changing structural hardware modes.

Enable LAG in WLC settings

Places the WLC into a pending LAG state

The controller feature knob for LAG must be explicitly enabled before hardware interface aggregation takes effect.

Save and reboot the WLC

The controller reboots with LAG operational across all physical distribution system ports

Enabling LAG on a Cisco WLC requires a reboot to reconfigure internal interface mappings.

Configure static EtherChannel on the upstream switch

The switch ports bundle into a single logical link matching the WLC LAG mode

Cisco WLC LAG requires static frame grouping ('mode on') on the switch side since WLCs do not support LACP or PAgP negotiation.

Key Concept

WLC Link Aggregation (LAG) configuration workflow and switch port requirements

Question 335Question →

Match each IPv6 prefix or address block on the left with its correct architectural scope and function on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

2000::/3 matches Global Unicast Address range reserved for publicly routable Internet communication; fe80::/10 matches Link-Local unicast prefix mandatory for single-segment neighbor communication; fc00::/7 matches Unique Local Address prefix used for private internal site routing; ff02::2 matches All-routers link-local multicast address targeting all routers on the segment.

Each IPv6 address prefix maps precisely to its RFC-defined scope: 2000::/3 is Global Unicast, fe80::/10 is Link-Local, fc00::/7 is Unique Local, and ff02::2 is the all-routers multicast group address.

Step-by-Step Solution

Identify the primary block for Global Unicast Addresses (GUA)

2000::/3 encompasses all addresses from 2000:: through 3fff:ffff:ffff:ffff:ffff:ffff:ffff:ffff, which are globally routable.

IANA allocates GUA prefix blocks starting within the 2000::/3 range.

Identify the designated Link-Local unicast prefix scope

fe80::/10 defines the range fe80:: through febf:ffff:ffff:ffff:ffff:ffff:ffff:ffff used for intra-link communication.

IPv6 devices use link-local addresses for neighbor discovery and router solicitations.

Identify the private/internal IPv6 address range

fc00::/7 covers the block fc00:: through fdff:ffff:ffff:ffff:ffff:ffff:ffff:ffff for Unique Local Addresses.

ULAs provide non-globally routable addressing within private organizational boundaries.

Identify specific well-known IPv6 multicast group addresses

ff02::2 is the link-local scope multicast address received by all active routers on a network segment.

Multicast prefix ff00::/8 uses the scope indicator 2 (link-local) and group ID 2 (all routers).

Key Concept

IPv6 Address Scopes and Reserved Prefixes

Question 336Question →

When a Cisco router receives an IP packet, it evaluates several parameters to determine the best route to place into the routing decision process. Place the path selection criteria in the correct sequential order, from the primary (first evaluated) factor to the final tie-breaker factor.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct order of router decision criteria is: 1) Longest Prefix Match, 2) Administrative Distance, 3) Metric, 4) Equal-Cost Multi-Path.

Router forwarding decision logic evaluates parameters in a strict hierarchical order. First, Longest Prefix Match identifies the most specific network prefix for the destination IP address. If multiple routes exist with the exact same prefix length from different protocols, Administrative Distance breaks the tie by choosing the lower value. If multiple candidate routes come from the same routing protocol with identical prefix lengths, the Metric is used as the next tie-breaker. Finally, if prefix length, Administrative Distance, and metric are all identical, Equal-Cost Multi-Path load balancing is performed.

Step-by-Step Solution

Determine primary routing lookup criteria

Longest Prefix Match is checked first.

Prefix specificity always takes precedence over AD and metric.

Evaluate tie-breaker between different routing protocols for the exact same prefix length

Administrative Distance is compared.

Lower AD indicates a more trustworthy routing source.

Evaluate tie-breaker within the same routing protocol

Metric is compared.

Lower metric indicates a lower internal routing protocol cost.

Handle identical tie-breaker results

Equal-Cost Multi-Path load balancing is applied.

When all parameters match identically, the router balances traffic across the equal routes.

Key Concept

Router Forwarding Decision Logic Sequence

Question 337Question →

A Cisco router receives an IP packet destined for $10.20.12.150$ . Refer to the following routing table output:

text
Codes: C - connected, S - static, D - EIGRP, O - OSPF

Gateway of last resort is 10.1.1.1 to network 0.0.0.0

D 10.20.0.0/14 [90/2172416] via 192.168.1.2, GigabitEthernet0/1
O 10.20.12.0/22 [110/20] via 192.168.1.6, GigabitEthernet0/2
S 10.20.12.0/24 [1/0] via 192.168.1.10, GigabitEthernet0/3
O 10.20.12.128/25 [110/30] via 192.168.1.14, GigabitEthernet0/4
S* 0.0.0.0/0 [1/0] via 10.1.1.1, GigabitEthernet0/0

Which next-hop IP address will the router select to forward this packet?

192.168.1.14

192.168.1.10

192.168.1.6

10.1.1.1

Show answer & explanation

Answer: 192.168.1.14

Answer

The router forwards the packet to next-hop IP 192.168.1.14 because the route 10.20.12.128/25 has the longest prefix match for destination 10.20.12.150.

When forwarding IP packets, a Cisco router always prioritizes the route with the Longest Prefix Match (most specific subnet mask). The destination address 10.20.12.150 falls within the range 10.20.12.128 to 10.20.12.255 defined by 10.20.12.128/25. Because /25 is more specific than /24, /22, /14, or /0, the router uses this route, which forwards to next-hop 192.168.1.14.

Step-by-Step Solution

Identify all candidate routes that encompass the destination IP address 10.20.12.150.

Candidate routes are 10.20.0.0/14, 10.20.12.0/22, 10.20.12.0/24, 10.20.12.128/25, and 0.0.0.0/0.

The router evaluates destination IP bit alignment against subnet masks of all known routes.

Compare the prefix lengths of all matching candidate routes.

Prefix lengths are /14, /22, /24, /25, and /0. The route 10.20.12.128/25 has the longest prefix mask (/25).

Routers use the Longest Prefix Match (LPM) logic first before considering Administrative Distance or Metric.

Select the next-hop IP associated with the longest prefix match route.

The route 10.20.12.128/25 points to next-hop 192.168.1.14.

Longest prefix match determines the exact routing entry used for forwarding.

Key Concept

Longest Prefix Match (LPM) precedence in IP forwarding decision logic.

Question 338Question →

A network engineer is configuring Virtual Router Redundancy Protocol (VRRP) on a router interface that has been assigned the physical IPv4 address $10.1.1.1/24$ . The engineer enters the command `vrrp 1 ip 10.1.1.1`. Which statement correctly describes the operational result of configuring the physical interface IP address as the VRRP virtual IP address?

VRRP accepts the configuration, allowing the router to become the IP address owner with a priority automatically set to 255.

VRRP rejects the command because virtual IP addresses must be outside the physical IP subnet range.

VRRP requires the virtual IP address to be a unique, unassigned IP address in the subnet, identical to standard HSRP behavior.

VRRP accepts the configuration but forces the router into a backup role with a default priority of 100.

Show answer & explanation

Answer: VRRP accepts the configuration, allowing the router to become the IP address owner with a priority automatically set to 255.

Answer

VRRP accepts the configuration, allowing the router to become the IP address owner with a priority automatically set to 255.

In VRRP, an engineer can assign the physical interface IP address as the virtual IP address. When this is done, the router becomes the IP address owner and its priority is automatically assigned as 255, making it the active Master router for that VRRP group.

Step-by-Step Solution

Identify the protocol and command syntax specified in the scenario.

The scenario uses VRRP (`vrrp 1 ip 10.1.1.1`) where the virtual IP address matches the primary physical interface IP address (

10.1.1.1

Understanding protocol-specific rules regarding virtual IP address assignment is essential.

Evaluate VRRP operational rules for IP address ownership.

RFC 5798 / VRRP standards state that if a router's physical interface IP address is configured as the VRRP virtual IP address, that router becomes the IP address owner.

VRRP permits virtual IP reuse, unlike HSRP which enforces separate virtual IP addresses.

Determine the resulting priority value for the IP address owner.

The IP address owner in VRRP automatically receives the highest possible priority value of 255.

This guarantees that the owner router will always become the Master router when functional.

Key Concept

VRRP IP Address Ownership and Priority Assignment

Question 339Question →

A Cisco router receives an IPv4 packet destined for host 10.200.15.42. The router inspects its routing table and finds the following entry routes:

text
O 10.200.15.0/24 [110/20] via 172.16.1.1, GigabitEthernet0/0/1
S 10.200.0.0/16 [1/0] via 172.16.2.1, GigabitEthernet0/0/2
D 10.200.15.32/28 [90/307200] via 172.16.3.1, GigabitEthernet0/0/3
B 10.200.15.40/30 [200/0] via 172.16.4.1, GigabitEthernet0/0/4

Which next-hop IP address and outgoing interface will the router select to forward the packet?

172.16.4.1 via GigabitEthernet0/0/4 because the 10.200.15.40/30 route has the longest prefix match.

172.16.2.1 via GigabitEthernet0/0/2 because the static route has the lowest administrative distance.

172.16.3.1 via GigabitEthernet0/0/3 because EIGRP has a lower administrative distance than BGP.

172.16.1.1 via GigabitEthernet0/0/1 because the /24 route encompasses the entire subnet.

Show answer & explanation

Answer: 172.16.4.1 via GigabitEthernet0/0/4 because the 10.200.15.40/30 route has the longest prefix match.

Answer

The router forwards the packet to next-hop 172.16.4.1 via interface GigabitEthernet0/0/4 because the 10.200.15.40/30 prefix offers the longest prefix match.

When a router receives an IP packet, it compares the destination IP address (10.200.15.42) against all entries in its routing table. The matching entries cover the following ranges:
- 10.200.0.0/16 (/16)
- 10.200.15.0/24 (/24)
- 10.200.15.32/28 (/28: 10.200.15.32 to 10.200.15.47)
- 10.200.15.40/30 (/30: 10.200.15.40 to 10.200.15.43)

Because 10.200.15.42 falls within the /30 range, and /30 is the most specific prefix (longest prefix match), the router selects the entry pointing to 172.16.4.1 via GigabitEthernet0/0/4. Administrative Distance is not evaluated across different prefix lengths.

Step-by-Step Solution

Identify all candidate routes in the routing table that encompass the destination IPv4 address 10.200.15.42.

Candidate routes are 10.200.0.0/16, 10.200.15.0/24, 10.200.15.32/28 (range 10.200.15.32–10.200.15.47), and 10.200.15.40/30 (range 10.200.15.40–10.200.15.43). All four entries match the destination address.

Before comparing routing metrics or administrative distance, the router identifies every route that includes the target IP address within its range.

Apply the Longest Prefix Match (LPM) rule to choose among matching entries.

Prefix lengths are /16, /24, /28, and /30. The /30 route has the longest mask length (30 set subnet bits).

Cisco IOS packet forwarding decision logic prioritizes prefix specificity above all other metrics, including Administrative Distance and routing protocol metrics.

Determine the next-hop IP and outgoing interface from the winning route entry.

The entry 10.200.15.40/30 points to next-hop 172.16.4.1 via GigabitEthernet0/0/4.

The router uses the next-hop parameters specified by the chosen LPM entry to perform Layer 2 frame encapsulation and egress transmission.

Key Concept

Longest Prefix Match (LPM) Rule

Estimated Time:1m 15s

Question 340Question →

A network administrator is configuring edge ports on a Cisco Catalyst switch connected to user workstations. Which two statements describe the operational benefits and behaviors when Cisco PortFast is enabled on an access interface? (Select TWO.)

Select all that apply

The interface bypasses the Listening and Learning STP states, transitioning directly to Forwarding upon link connection.

Link state changes on the PortFast-enabled port do not cause the switch to generate Topology Change Notifications (TCNs).

PortFast should be enabled on switch-to-switch trunk links to eliminate convergence delays between infrastructure switches.

PortFast automatically reduces the switch's system priority in increments of 4096 to optimize STP root bridge selection.

Show answer & explanation

Answer: The interface bypasses the Listening and Learning STP states, transitioning directly to Forwarding upon link connection.; Link state changes on the PortFast-enabled port do not cause the switch to generate Topology Change Notifications (TCNs).

Answer

The correct benefits are that the interface bypasses the Listening and Learning STP states to transition directly to Forwarding, and link state changes on the port do not cause the switch to generate Topology Change Notifications (TCNs).

PortFast provides two primary operational advantages on end-user access ports: first, it bypasses the Listening (15s) and Learning (15s) states to move immediately into Forwarding state when a link comes online. Second, it suppresses Topology Change Notification (TCN) messages when the port changes status, preventing unnecessary MAC table aging throughout the campus network.

Step-by-Step Solution

Identify the main objective of configuring Cisco PortFast on switch ports.

PortFast is intended strictly for access ports connected to end-user devices such as PCs, printers, or IP phones.

End-user devices do not run Spanning Tree Protocol or form Layer 2 redundant loops under normal topology conditions.

Analyze state transition behavior for PortFast-enabled ports.

Upon link activation, the port skips the 15-second Listening and 15-second Learning timer delays and immediately enters Forwarding.

Eliminating this 30-second delay ensures client hosts do not experience address assignment timeouts during initial network startup.

Evaluate the impact of PortFast on STP topology updates across the network.

Port transitions on PortFast interfaces are prevented from triggering Topology Change Notifications (TCNs) sent toward the Root Bridge.

Suppressing TCNs avoids unnecessary flushing of MAC address tables across the entire switching domain when host ports connect or disconnect.

Key Concept

STP PortFast Benefits and Operational Trait

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