Network Implementation

424 soru

Tüm türler424 Çoktan seçmeli220 Çoklu seçim80 Sayısal11 Eşleştirme53 Sıralama42 Kısa cevap18

An enterprise network topology features four switches operating standard IEEE 802.1D Spanning Tree Protocol (STP) with the following bridge configurations:
- Switch-A: Priority 32768, MAC 00:00:0C:11:11:11
- Switch-B: Priority 28672, MAC 00:00:0C:33:33:33
- Switch-C: Priority 28672, MAC 00:00:0C:22:22:22
- Switch-D: Priority 32768, MAC 00:00:0C:44:44:44

The switches are connected in a physical ring topology: Switch-A connects to Switch-B, Switch-B connects to Switch-C, Switch-C connects to Switch-D, and Switch-D connects to Switch-A. All inter-switch links are Gigabit Ethernet (STP path cost = 4), except the link between Switch-B and Switch-C, which is 10-Gigabit Ethernet (STP path cost = 2). Which switch will be elected as the Root Bridge, and what role will Switch-D assign to its port on the link connecting directly to Switch-A?

Switch-C is elected as the Root Bridge, and Switch-D assigns the Designated Port role to its interface connected to Switch-A.

Switch-B is elected as the Root Bridge, and Switch-D assigns the Designated Port role to its interface connected to Switch-A.

Switch-C is elected as the Root Bridge, and Switch-D assigns the Alternate/Blocking Port role to its interface connected to Switch-A.

Switch-B is elected as the Root Bridge, and Switch-D assigns the Root Port role to its interface connected to Switch-A.

Cevabı ve açıklamayı göster

Cevap: Switch-C is elected as the Root Bridge, and Switch-D assigns the Designated Port role to its interface connected to Switch-A.

Cevap

Switch-C is elected as the Root Bridge, and Switch-D assigns the Designated Port role to its interface connected to Switch-A.

Switch-C is elected as the Root Bridge because it ties for the lowest priority (28672) with Switch-B and has a lower MAC address (00:00:0C:22:22:22). For port roles, Switch-D's direct link to Switch-C yields a Root Path Cost of 4. Switch-A reaches Switch-C via Switch-B with a Root Path Cost of 6 (4 + 2). On the segment connecting Switch-A and Switch-D, Switch-D advertises a superior path cost to the Root (4 vs. 6), causing Switch-D to assume the Designated Port role on that link.

Adım Adım Çözüm

Determine the Root Bridge election result across all four switches.

Switch-B and Switch-C share the lowest numerical bridge priority value of 28672. Comparing their MAC addresses, Switch-C (00:00:0C:22:22:22) is lower than Switch-B (00:00:0C:33:33:33). Therefore, Switch-C is elected Root Bridge.

STP elects the Root Bridge based first on the lowest Bridge Priority, and breaks ties using the lowest MAC address.

Calculate the Root Path Cost for Switch-D and identify its Root Port.

Switch-D's direct link to Switch-C has a path cost of 4 (Gigabit Ethernet). Switch-D's alternate path (Switch-D -> Switch-A -> Switch-B -> Switch-C) has a cost of 4 + 4 + 2 = 10. Switch-D designates its direct port to Switch-C as its Root Port with a Root Path Cost of 4.

Each non-root bridge selects the interface offering the lowest cumulative path cost back to the Root Bridge.

Calculate the Root Path Cost for Switch-A and evaluate the segment between Switch-A and Switch-D.

Switch-A's best path to Root is via Switch-B (cost 4 to Switch-B + cost 2 to Switch-C = 6). On the link between Switch-A and Switch-D, Switch-D advertises a Root Path Cost of 4, while Switch-A advertises a Root Path Cost of 6. Because 4 < 6, Switch-D's interface on this link becomes the Designated Port.

On any shared segment between two switches, the switch that advertises the lower Root Path Cost wins the Designated Port role for that segment.

Anahtar Kavram

Spanning Tree Protocol Root Bridge election and port role calculation based on lowest priority, MAC tie-breaking, and path cost evaluation.

Soru 202Soru →

A network administrator is provisioning a small subnet for point-to-multipoint router interconnects using a subnet mask of $255.255.255.248$ (/ $29$ ). What is the maximum number of usable host IP addresses that can be assigned to devices within this subnet?

Cevabı ve açıklamayı göster

Cevap: 6

Cevap

The maximum number of usable host IP addresses in a /29 subnet is 6.

A /29 subnet mask leaves 3 bits for host addressing (

32 - 29 = 3

). Calculating total IP addresses gives

2^3 = 8

. Subtracting the reserved network ID and broadcast ID (

8 - 2

) results in 6 usable host addresses.

Adım Adım Çözüm

Determine the number of host bits in the /29 subnet mask

Host bits =

32 - 29 = 3

bits

An IPv4 address consists of 32 bits. Subtracting the CIDR prefix length yields the host portion.

Calculate the total number of IP addresses in the subnet

Total IP addresses =

2^3 = 8

The total number of addresses supported by

n

host bits is given by

2^n

Subtract network and broadcast addresses to find usable host IPs

Usable host IPs =

8 - 2 = 6

The first IP address represents the network ID and the last IP address represents the subnet broadcast ID; neither can be assigned to a host interface.

Anahtar Kavram

Usable Host Calculation for IPv4 Subnetting

Tahmini Süre:45s

Soru 203Soru →

Place the standard 802.1D Spanning Tree Protocol (STP) port state transitions in the correct chronological order from initial switch port activation to full operational traffic handling.

Öğeleri doğru sıraya koymak için sürükleyin

Cevabı ve açıklamayı göster

Cevap

The correct sequence of standard 802.1D STP port states from activation to active traffic forwarding is Blocking State, Listening State, Learning State, and Forwarding State.

Standard 802.1D Spanning Tree Protocol transitions switch ports through four sequential states upon activation: Blocking (prevents loops, reads BPDUs), Listening (elects root bridge and determines port roles), Learning (populates the MAC address table without forwarding data), and Forwarding (fully processes user data frames).

Adım Adım Çözüm

Determine initial state upon switch port initialization

The port starts in the Blocking state, dropping data frames to prevent topology loops while reading BPDU control frames.

STP must enforce loop prevention immediately before allowing active participation.

Identify the topology election phase

The port transitions to the Listening state to process BPDUs and decide root bridge and port role assignments.

Roles must be settled before the switch modifies its MAC address tables.

Identify the MAC address table population phase

The port enters the Learning state, recording source MAC addresses without forwarding user data frames.

Pre-populating the MAC table prevents unnecessary frame flooding when data transmission begins.

Identify the final operational state

The port moves to the Forwarding state to send and receive all network traffic.

Convergence is complete and the link is verified as loop-free.

Anahtar Kavram

Spanning Tree Protocol (802.1D) Port State Transitions

Soru 204Soru →

A layer 3 switch on a multi-site network receives a frame carrying an IP packet addressed to host $10.120.4.138$ . The switch's Routing Information Base (RIB) contains four active candidate route entries matching the destination address:

Prefix	Protocol Source	Administrative Distance	Metric	Next-Hop Interface
$10.120.4.0/23$	Static	1	0	GigabitEthernet0/1
$10.120.4.128/25$	OSPF	110	45	GigabitEthernet0/2
$10.120.4.128/26$	RIPv2	120	2	GigabitEthernet0/3
$10.120.4.136/29$	EIGRP	90	1560	GigabitEthernet0/4

Which next-hop interface will the layer 3 switch select to forward this packet?

GigabitEthernet0/4, because the EIGRP entry provides the longest prefix match for the destination address.

GigabitEthernet0/1, because the static route entry possesses the lowest administrative distance value.

GigabitEthernet0/3, because the RIPv2 path has the lowest numerical metric value.

GigabitEthernet0/2, because OSPF link-state announcements automatically supersede distance-vector protocol entries.

Cevabı ve açıklamayı göster

Cevap: GigabitEthernet0/4, because the EIGRP entry provides the longest prefix match for the destination address.

Cevap

GigabitEthernet0/4 is selected because the

10.120.4.136/29

route provides the longest subnet mask match for destination address

10.120.4.138

When a router or layer 3 switch forwards a packet, it compares the packet's destination IP address against all entries in its routing table. The primary criteria for path selection is Longest Prefix Match (LPM)—the route with the highest number of matching network bits (most specific subnet mask). Here,

10.120.4.136/29

covers

10.120.4.136

through

10.120.4.143

, which includes

10.120.4.138

. Because

/29

is more specific than

/26

/25

, or

/23

, the switch forwards the packet out GigabitEthernet0/4 immediately.

Adım Adım Çözüm

Evaluate subnet coverage for destination address

10.120.4.138

against each candidate route prefix in the RIB.

All four routes cover the host address:

10.120.4.0/23

(

10.120.4.0

–

10.120.5.255

10.120.4.128/25

(

10.120.4.128

–

10.120.4.255

10.120.4.128/26

(

10.120.4.128

–

10.120.4.191

), and

10.120.4.136/29

(

10.120.4.136

–

10.120.4.143

Before comparing protocols, the router must identify all valid matching prefixes.

Determine prefix length specificity for all matching candidate routes.

The prefix masks are

/23

/25

/26

, and

/29

. The

/29

mask has 29 network bits, making it the most specific route.

The fundamental routing logic rule dictates that the longest prefix match (LPM) always wins regardless of administrative distance or protocol metric.

Select the egress interface tied to the longest prefix match.

The route for

10.120.4.136/29

points to next-hop interface GigabitEthernet0/4.

Because

/29

is the longest matching prefix, the router immediately selects GigabitEthernet0/4 without evaluating administrative distance or metric values.

Anahtar Kavram

Longest Prefix Match (LPM) Path Selection Hierarchy

Tahmini Süre:1m 30s

Soru 205Soru →

A network engineer configures an IP helper address on a Layer 3 switch's VLAN interface ( $192.168.10.1/24$ ) to relay client requests to a centralized DHCP server at $10.100.1.50$ . When a workstation on VLAN 10 broadcasts a DHCPDISCOVER message, which set of actions does the DHCP relay agent perform on the packet before sending it to the server?

It populates the giaddr field with

192.168.10.1

, sets the source IP to its outgoing interface address, and unicasts the packet to

10.100.1.50

via UDP port 67.

It encapsulates the DHCP broadcast inside a TCP port 67 session established with

10.100.1.50

to ensure reliable delivery across the routed network.

It changes the destination UDP port from 67 to 68 so that the central DHCP server receives the request on its listening service port.

It floods the unmodified Layer 2 broadcast frame across all active Layer 3 routed ports until it reaches the VLAN where the DHCP server resides.

Cevabı ve açıklamayı göster

Cevap: It populates the giaddr field with $192.168.10.1$ , sets the source IP to its outgoing interface address, and unicasts the packet to $10.100.1.50$ via UDP port 67.

Cevap

The DHCP relay agent populates the giaddr (gateway IP address) field with the local interface address (

192.168.10.1

), converts the client's Layer 2 broadcast into a Layer 3 unicast packet, and forwards it directly to the DHCP server (

10.100.1.50

) using UDP destination port 67.

When a Layer 3 device functions as a DHCP relay agent (via `ip helper-address`), it intercepts client DHCPDISCOVER broadcast packets on the receiving interface. It modifies the packet by inserting its own local interface IP address into the `giaddr` (Gateway IP Address) header field and replaces the broadcast destination address with the specific unicast IP address of the DHCP server. It then forwards the packet across the routed infrastructure using standard UDP port 67.

Adım Adım Çözüm

Analyze incoming broadcast request

The client sends a local broadcast DHCPDISCOVER frame to 255.255.255.255 on UDP port 67.

Clients lacking an IP address must broadcast locally to find a DHCP server.

Process and modify packet header at the relay agent

The Layer 3 switch relay agent intercepts the broadcast, inserts its own interface IP (

192.168.10.1

) into the `giaddr` field, sets its egress IP as the source IP, and sets the destination IP to

10.100.1.50

The `giaddr` field informs the remote DHCP server which subnet scope must be used to select an available IP address.

Unicast packet transport across routed network

The packet is transmitted via standard Layer 3 routing to destination IP

10.100.1.50

on UDP port 67.

Unicast IP packets can be forwarded across routers, whereas Layer 2 broadcasts are blocked at subnet boundaries.

Anahtar Kavram

DHCP Relay Agent and GIADDR Operation

Soru 206Soru →

A network engineer is configuring an IEEE 802.1Q trunk link between two switches, SW-DIST-01 and SW-ACCESS-02. Switch SW-DIST-01 has port GigabitEthernet1/0/1 configured with 'switchport trunk native vlan 99'. Switch SW-ACCESS-02 has port GigabitEthernet0/1 configured as a trunk using the default native VLAN (VLAN 1). Which of the following statements accurately describe the operational impact of this configuration or the steps required to resolve it? (Select TWO.)

Geçerli olan tümünü seçin

Untagged frames transmitted from VLAN 99 on SW-DIST-01 will be improperly received into VLAN 1 on SW-ACCESS-02.

Tagged VLAN traffic, such as VLAN 20 and VLAN 30, will be automatically blocked across the trunk until the native VLAN mismatch is resolved.

Executing 'switchport trunk native vlan 99' on interface GigabitEthernet0/1 of SW-ACCESS-02 will align both ends and eliminate cross-VLAN traffic leakage.

Changing the port mode on SW-DIST-01 to switchport mode access will maintain trunking capabilities while resolving the tag mismatch.

Cevabı ve açıklamayı göster

Cevap: Untagged frames transmitted from VLAN 99 on SW-DIST-01 will be improperly received into VLAN 1 on SW-ACCESS-02.; Executing 'switchport trunk native vlan 99' on interface GigabitEthernet0/1 of SW-ACCESS-02 will align both ends and eliminate cross-VLAN traffic leakage.

Cevap

Untagged frames transmitted from VLAN 99 on SW-DIST-01 will be improperly received into VLAN 1 on SW-ACCESS-02, and executing 'switchport trunk native vlan 99' on interface GigabitEthernet0/1 of SW-ACCESS-02 will align both ends and eliminate cross-VLAN traffic leakage.

On an IEEE 802.1Q trunk, frames belonging to the native VLAN are transmitted without an 802.1Q tag header. When a native VLAN mismatch exists between two switches, untagged traffic sent by one switch is placed into whichever native VLAN is configured on the receiving switch port, causing cross-VLAN frame leakage. Aligning the native VLAN configurations on both trunk ports ensures consistent frame interpretation and resolves the mismatch.

Adım Adım Çözüm

Analyze 802.1Q native VLAN frame encapsulation behavior across trunk endpoints.

802.1Q trunks leave native VLAN frames untagged. When SW-DIST-01 sends untagged VLAN 99 frames, SW-ACCESS-02 receives them on a port expecting VLAN 1 to be untagged, misplacing the frames into VLAN 1.

Trunk links do not insert an 802.1Q tag header for frames belonging to the configured native VLAN.

Determine the effect of a native VLAN mismatch on tagged VLANs traversing the trunk.

Frames with explicit 802.1Q tags (VLAN 20, VLAN 30) are correctly identified and processed by both switches based on their tag headers.

Native VLAN mismatch affects only untagged traffic and control plane protocols; tagged traffic is processed independently based on the 4-byte 802.1Q header.

Identify the proper remediation command.

Configuring matching native VLAN IDs (VLAN 99) on both trunk interfaces aligns ingress and egress frame processing.

Matching native VLAN configurations prevent VLAN leaking and clear STP/CDP native VLAN mismatch warnings.

Anahtar Kavram

802.1Q Trunking Native VLAN Mismatch Consequences and Configuration Alignment

Tahmini Süre:1m 30s

Soru 207Soru →

A network technician is configuring a dedicated point-to-point wireless link between two enterprise buildings using the IPv4 subnet $192.168.10.16/28$ . What is the maximum number of usable host IPv4 addresses available for assignment to physical network interfaces in this subnet?

Cevabı ve açıklamayı göster

Cevap: 14

Cevap

The maximum number of usable host IPv4 addresses in a

/28

subnet is 14.

For a

/28

subnet, there are 4 host bits (

32 - 28 = 4

). Calculating total IP addresses yields

2^4 = 16

. Subtracting 2 reserved addresses (one network address and one broadcast address) leaves 14 usable host IPv4 addresses.

Adım Adım Çözüm

Calculate the number of host bits available from the CIDR prefix

4 host bits (

32 - 28 = 4

)

An IPv4 address contains 32 bits in total, so subtracting the prefix length gives the remaining bits allocated for host addresses.

Calculate the total number of IP addresses in the subnet

16 total IP addresses (

2^4 = 16

)

The number of total IP combinations for

n

host bits is

2^n

Calculate the usable host address count by excluding reserved addresses

14 usable host IPv4 addresses (

16 - 2 = 14

)

The first IP address in the range is reserved as the network address, and the final IP address is reserved as the directed broadcast address.

Anahtar Kavram

Calculating Usable Host Addresses in an IPv4 Subnet

Soru 208Soru →

A network engineer is auditing switchport trunk configurations and frame tagging operations across enterprise switches. Match each IEEE 802.1Q trunking configuration scenario or operational event on the left with its corresponding frame behavior or interface outcome on the right.

Soldaki öğeye tıklayın, sonra eşleşen sağdaki öğeye tıklayın

Cevabı ve açıklamayı göster

Cevap

Each 802.1Q trunking scenario correctly pairs with its respective protocol error behavior, frame tagging rule, or allowed list pruning action as outlined in the solution steps.

Matching each event to its technical description demonstrates core 802.1Q trunking principles: Native VLAN mismatches lead to protocol inconsistencies and improper VLAN leakage; untagged ingress frames map directly to the configured native VLAN without header addition; removing a VLAN from the trunk allowed list prunes traffic for that VLAN in both directions; and non-native egress frames are encapsulated with 4-byte 802.1Q headers containing TPID 0x8100 and the corresponding VLAN ID.

Adım Adım Çözüm

Analyze Native VLAN Mismatch Behavior

Configuring conflicting native VLAN IDs (VLAN 99 vs VLAN 1) causes untagged traffic to cross broadcast domains, triggering CDP and PVST+ mismatch alerts and potential STP port inconsistency states.

Both endpoints of an 802.1Q trunk must share an identical native VLAN ID to prevent cross-VLAN frame leakage.

Determine Ingress Untagged Frame Association

Untagged frames arriving on an 802.1Q trunk configured with native VLAN 20 are internally classified under VLAN 20.

IEEE 802.1Q specifies that unencapsulated ingress frames are assigned to the port's configured native VLAN.

Evaluate CLI Allowed VLAN List Removal Command

Running 'switchport trunk allowed vlan remove 50' prunes VLAN 50 from the active trunk pass-through list.

Allowed VLAN lists restrict which VLAN broadcast domain traffic is permitted to traverse a trunk interface.

Examine Egress Tagging for Non-Native VLANs

Frames belonging to VLAN 10 sent over a trunk with native VLAN 20 must be tagged with a 4-byte 802.1Q header containing TPID 0x8100 and VLAN ID 10.

All traffic not belonging to the native VLAN requires explicit 802.1Q tagging to maintain VLAN identity across network switches.

Anahtar Kavram

802.1Q Trunk Tagging, Native VLAN Processing, and Allowed List Pruning

Soru 209Soru →

An enterprise network topology consists of four switches (Switch-1, Switch-2, Switch-3, and Switch-4) running 802.1D Spanning Tree Protocol (STP) using default revised 802.1D-1998 / 802.1w path cost values (10 Gbps = 2, 1 Gbps = 4, 100 Mbps = 19). The switches are configured with the following parameters:

* Switch-1: Priority 4096, MAC address 0011.2233.4455
* Switch-2: Priority 8192, MAC address 0011.2233.4422
* Switch-3: Priority 32768, MAC address 0011.2233.4411
* Switch-4: Priority 32768, MAC address 0011.2233.4433

The physical interconnections and link speeds between the switches are:
* Switch-1 to Switch-2: 10 Gbps
* Switch-1 to Switch-3: 1 Gbps
* Switch-2 to Switch-4: 10 Gbps
* Switch-3 to Switch-4: 1 Gbps
* Switch-2 to Switch-3: 100 Mbps

Which THREE of the following statements accurately describe the converged STP topology, root path costs, and port roles? (Select THREE)

Geçerli olan tümünü seçin

Switch-4 selects its connection to Switch-2 as its Root Port because it yields a lower Root Path Cost of 4 compared to a cost of 8 via Switch-3.

Switch-3 is elected as the Root Bridge because it possesses the lowest MAC address (0011.2233.4411) among all switches in the topology.

On the link segment connecting Switch-3 and Switch-4, Switch-3 hosts the Designated Port while Switch-4 blocks its port because Switch-3 has a lower MAC address.

Switch-4 selects its port connected to Switch-3 as its Root Port because Switch-3 has a lower Bridge ID than Switch-2.

Switch-3 places its port connected to Switch-2 into an Alternate/Blocking state because Switch-2 advertises a lower Root Path Cost (cost of 2) on that segment.

Cevabı ve açıklamayı göster

Cevap: Switch-4 selects its connection to Switch-2 as its Root Port because it yields a lower Root Path Cost of 4 compared to a cost of 8 via Switch-3.; On the link segment connecting Switch-3 and Switch-4, Switch-3 hosts the Designated Port while Switch-4 blocks its port because Switch-3 has a lower MAC address.; Switch-3 places its port connected to Switch-2 into an Alternate/Blocking state because Switch-2 advertises a lower Root Path Cost (cost of 2) on that segment.

Cevap

The three correct statements are: Switch-4 selects its connection to Switch-2 as its Root Port due to a lower Root Path Cost of 4; Switch-3 hosts the Designated Port on the segment to Switch-4 based on a lower MAC address tie-breaker; and Switch-3 blocks its port connected to Switch-2 because Switch-2 has a lower Root Path Cost on that segment.

The Root Bridge is Switch-1 (lowest priority of 4096). Switch-4 reaches Switch-1 with a path cost of 4 via Switch-2 (10G + 10G) versus a path cost of 8 via Switch-3 (1G + 1G), making the port connected to Switch-2 its Root Port. On the segment between Switch-3 and Switch-4, both switches have an equal root path cost of 4; Switch-3 wins the Designated Port role because its MAC address is lower than Switch-4's MAC address. On the segment between Switch-2 and Switch-3, Switch-2 advertises a lower root path cost (2) than Switch-3 (4), making Switch-2's port Designated and causing Switch-3 to block its port on that link.

Adım Adım Çözüm

Determine the Root Bridge

Switch-1 is elected Root Bridge

Bridge ID consists of Priority + MAC address. Switch-1 has the lowest numerical priority (4096).

Calculate Root Path Costs for each switch

Switch-2 cost = 2 (10G direct link); Switch-3 cost = 4 (1G direct link); Switch-4 cost via Switch-2 = 2 + 2 = 4, via Switch-3 = 4 + 4 = 8

Path cost accumulates cost of egress interfaces toward the Root Bridge.

Identify Root Ports for Switch-2, Switch-3, and Switch-4

Switch-2 Root Port -> Switch-1; Switch-3 Root Port -> Switch-1; Switch-4 Root Port -> Switch-2

Each non-root switch chooses the single interface with the lowest total path cost to the Root Bridge.

Determine Designated and Blocking Ports on remaining segments

Segment Switch-2 <-> Switch-3: Switch-2 is Designated (cost 2 < 4), Switch-3 blocks. Segment Switch-3 <-> Switch-4: Path costs tied (4 = 4), Switch-3 has lower MAC (0011.2233.4411 < 0011.2233.4433), so Switch-3 is Designated and Switch-4 blocks.

Segment with lowest advertising root path cost wins Designated status; tie-breakers use lower Bridge ID (Priority then MAC).

Anahtar Kavram

Spanning Tree Protocol Convergence Mechanics and Path Cost Calculation

Soru 210Soru →

A network engineer is configuring a newly provisioned server rack in a data center using the assigned IPv4 subnet block $10.50.16.0/27$ . What is the maximum number of usable host IPv4 addresses that can be assigned to active devices within this subnet block?

Cevabı ve açıklamayı göster

Cevap: 30

Cevap

The maximum number of usable host IPv4 addresses in a /27 subnet is 30.

A CIDR prefix of /27 leaves 5 host bits (

32 - 27 = 5

). Raising 2 to the power of 5 gives 32 total addresses. Subtracting the network address and broadcast address (

32 - 2

) results in 30 usable host IP addresses.

Adım Adım Çözüm

Determine the number of available host bits.

Host bits =

32 - 27 = 5

bits.

An IPv4 address has 32 bits total. Subtracting the prefix length yields the bits remaining for host addressing.

Calculate the total size of the address block.

Total IP addresses =

2^5 = 32

addresses.

Five host bits allow

2^5

distinct binary combinations.

Subtract reserved addresses to find the usable host count.

Usable host addresses =

32 - 2 = 30

addresses.

The network address (all host bits 0) and the directed broadcast address (all host bits 1) cannot be assigned to network hosts.

Anahtar Kavram

Usable Host Calculation in Subnetting

Soru 211Soru →

A network engineer is configuring a newly provisioned Layer 3 switch interface to relay DHCP traffic from a client subnet ( $10.100.20.0/24$ ) to a centralized DHCP server located at $10.200.10.5$ . Although the command `ip helper-address 10.200.10.5` has been applied to the client-facing VLAN interface, workstations on the subnet fail to obtain IP addresses. Packet captures on the centralized DHCP server indicate that relayed unicast packets arrive, but the server discards them because the Gateway IP Address ( $giaddr$ ) field in the DHCP header is set to $0.0.0.0$ . Which of the following configuration issues is the primary cause of this behavior?

The client-facing VLAN interface on the Layer 3 switch lacks an assigned IPv4 address, preventing the relay agent from identifying the client subnet scope.

The IP helper address was configured on the egress interface connecting toward the centralized DHCP server rather than the client gateway interface.

The switch modified the destination UDP port from port 67 to port 68 when converting the broadcast frame into a unicast packet.

The Layer 3 switch failed to flood the broadcast frame across all ports member to the management VLAN prior to encapsulation.

Cevabı ve açıklamayı göster

Cevap: The client-facing VLAN interface on the Layer 3 switch lacks an assigned IPv4 address, preventing the relay agent from identifying the client subnet scope.

Cevap

The client-facing VLAN interface on the Layer 3 switch lacks an assigned IPv4 address, preventing the relay agent from identifying the client subnet scope.

DHCP Relay agents require a valid Layer 3 IPv4 address on the client-facing interface where the broadcast is received. This interface IP address is written into the

giaddr

field of the DHCP header before forwarding the packet via unicast to the DHCP server. If the interface lacks an IP address, the relay agent sets

giaddr

0.0.0.0

, causing the DHCP server to discard the request because it cannot determine which address pool/scope to allocate from.

Adım Adım Çözüm

Analyze the role of the Gateway IP Address (

giaddr

) field in DHCP relay operation.

The

giaddr

field tells the DHCP server which subnet/pool the client belongs to when the request originates from a different broadcast domain.

Without a valid

giaddr

, the server cannot perform scope matching for cross-subnet clients.

Determine how the relay agent populates the

giaddr

field.

The relay agent inserts the IP address of its own interface receiving the client's original broadcast message.

This IP address represents the default gateway of the client subnet.

Evaluate the symptom (

giaddr = 0.0.0.0

If the receiving interface does not have an IP address configured, the relay agent cannot insert a valid gateway address into the header.

An unconfigured or unassigned interface IP address leaves

giaddr

initialized as

0.0.0.0

, causing the server to reject scope matching.

Anahtar Kavram

DHCP Relay Agent Subnet Selection via GIADDR Field

Tahmini Süre:2m 0s

Soru 212Soru →

An enterprise edge router participating in an OSPF dynamic routing domain learns three distinct paths to reach the remote subnet $10.10.0.0/16$ :

- Path 1: Learned as an Inter-area route (O IA) via Router West with a calculated total metric of $45$ .
- Path 2: Learned as an External Type 1 route (O E1) via Router East with a calculated total metric of $15$ .
- Path 3: Learned as an External Type 2 route (O E2) via Router North with a fixed external metric of $5$ .

Assuming all links are operational and default administrative distances apply, which route will the router install into its active routing table for traffic destined to $10.10.15.1$ ?

The Inter-area route (O IA) via Router West, because OSPF prioritizes Inter-area routes over External routes regardless of metric cost.

The External Type 2 route (O E2) via Router North, because it presents the absolute lowest metric value of 5.

The External Type 1 route (O E1) via Router East, because Type 1 routes include internal path cost to achieve a lower cumulative cost than Inter-area routes.

Equal-cost multi-path (ECMP) traffic splitting across all three routes because they originate from the same dynamic routing protocol instance.

Cevabı ve açıklamayı göster

Cevap: The Inter-area route (O IA) via Router West, because OSPF prioritizes Inter-area routes over External routes regardless of metric cost.

Cevap

The Inter-area route (O IA) via Router West is selected and installed into the routing table because OSPF path-type precedence (Intra-area > Inter-area > External Type 1 > External Type 2) takes precedence over metric calculations.

In OSPF path selection, routes are evaluated according to a strict order of preference: Intra-area (O) > Inter-area (O IA) > External Type 1 (O E1) > External Type 2 (O E2). Because an Inter-area (O IA) route exists, OSPF selects it immediately over any External routes (E1 or E2), regardless of whether the external routes have lower metric costs.

Adım Adım Çözüm

Analyze the prefix lengths of all candidate routes.

All three routes cover the identical prefix length of

10.10.0.0/16

, so Longest Prefix Match (LPM) does not eliminate any path.

Prefix length comparison always occurs first in IP routing selection.

Evaluate administrative distance across protocol sources.

All routes originate from the same OSPF process (Administrative Distance

110

Administrative Distance is only compared across different routing sources.

Apply OSPF route preference rules based on path type hierarchy.

OSPF path type order is: 1. Intra-area (O), 2. Inter-area (O IA), 3. External Type 1 (O E1), 4. External Type 2 (O E2).

OSPF path type precedence is evaluated before comparing metric costs.

Determine the winning path for installation into the Routing Information Base (RIB).

The Inter-area route (O IA) via Router West beats External Type 1 (O E1) and External Type 2 (O E2) paths, even though its metric cost (

45

) is higher.

Inter-area routes outrank any external route types in OSPF.

Anahtar Kavram

OSPF Route Selection Hierarchy (Path Type Precedence)

Soru 213Soru →

An enterprise network engineer configures a DHCP relay service on a Layer 3 router interface servicing a remote VoIP VLAN ( $172.16.30.0/24$ ). When an IP phone boots up and sends a broadcast DHCPDISCOVER frame, the router encapsulates this message into a unicast IPv4 packet targeted directly at the centralized DHCP server ( $10.10.5.50$ ). Which field in the DHCP message header does the relay agent populate with its own interface IP address ( $172.16.30.1$ ) so that the DHCP server selects the appropriate address pool?

giaddr (Gateway IP Address)

ciaddr (Client IP Address)

yiaddr (Your IP Address)

chaddr (Client Hardware Address)

Cevabı ve açıklamayı göster

Cevap: giaddr (Gateway IP Address)

Cevap

The giaddr (Gateway IP Address) field is populated by the DHCP relay agent with its own interface IP address to tell the server which IP scope to allocate from.

When a DHCP relay agent intercepts a broadcast DHCPDISCOVER request, it modifies the packet by inserting the IP address of the local receiving interface into the giaddr (Gateway IP Address) field. It then forwards the packet via unicast to the remote DHCP server. Upon receipt, the DHCP server evaluates the giaddr value to match it against configured scopes, ensuring the client receives an IP address valid for its local IP subnet.

Adım Adım Çözüm

Analyze the client DHCP request process across subnets

The client issues a layer 2/3 broadcast message (DHCPDISCOVER) because it does not yet possess an IP address or know the server location.

Routers drop layer 2 broadcast frames by default, requiring a relay agent (IP helper) to bridge communication across subnets.

Examine the role of the DHCP Relay Agent

The relay agent intercepts the local broadcast, sets the giaddr field to the router interface's IP address (

172.16.30.1

), and unicasts the packet to the DHCP server.

The centralized server uses the giaddr field to determine which address pool (

172.16.30.0/24

) matches the client's physical network segment.

Anahtar Kavram

DHCP Relay Agent and giaddr Header Field Processing

Soru 214Soru →

A network engineer is configuring an 802.1Q trunk link between `SW-CORE-01` and `SW-ACCESS-05`. Interface `GigabitEthernet 0/1` on `SW-CORE-01` is configured with `switchport trunk native vlan 50`. Interface `GigabitEthernet 0/1` on `SW-ACCESS-05` retains the default configuration of `switchport trunk native vlan 1`. Both switches have VLANs 10, 20, and 50 allowed on the trunk link.

When an untagged frame originating from an access port assigned to VLAN 50 on `SW-CORE-01` is forwarded across the trunk link, how will `SW-ACCESS-05` handle this frame upon arrival?

It will accept the untagged frame and forward it within VLAN 1 because VLAN 1 is configured as its local native VLAN.

It will drop the frame immediately because the frame's VLAN ID does not match the local native VLAN configuration.

It will inspect the 802.1Q header tag, strip it, and place the frame directly into VLAN 50.

It will automatically perform Layer 2 routing to forward the frame from VLAN 50 to VLAN 1 without requiring a router.

Cevabı ve açıklamayı göster

Cevap: It will accept the untagged frame and forward it within VLAN 1 because VLAN 1 is configured as its local native VLAN.

Cevap

SW-ACCESS-05 will accept the untagged frame and process it as part of VLAN 1 because untagged frames arriving on an 802.1Q trunk are automatically assigned to the receiving interface's configured native VLAN.

The correct response highlights that untagged frames arriving on an 802.1Q trunk interface are mapped directly to the local interface's native VLAN. SW-CORE-01 transmits VLAN 50 frames untagged because VLAN 50 is its native VLAN. SW-ACCESS-05 receives the untagged frame and associates it with VLAN 1, which is its own native VLAN setting.

Adım Adım Çözüm

Analyze frame egress behavior at SW-CORE-01

Since VLAN 50 is configured as the native VLAN on SW-CORE-01's trunk port, traffic originating from VLAN 50 is transmitted across the 802.1Q trunk link without an 802.1Q VLAN tag.

By standard 802.1Q behavior, frames belonging to the native VLAN are sent untagged across trunk links.

Analyze frame ingress behavior at SW-ACCESS-05

SW-ACCESS-05 receives an untagged frame on its trunk port where `native vlan 1` is configured.

When a switch receives an untagged frame on an 802.1Q trunk port, it maps that frame to its own configured native VLAN.

Determine the resulting network outcome

The frame sent from VLAN 50 on SW-CORE-01 leaks into VLAN 1 on SW-ACCESS-05.

A native VLAN mismatch across a trunk link causes traffic from one VLAN to bleed into a different VLAN on the remote switch.

Anahtar Kavram

802.1Q Native VLAN Tagging & Mismatch Behavior

Tahmini Süre:1m 30s

Soru 215Soru →

A network router interface configured with an IP helper address receives an incoming DHCPDISCOVER broadcast packet from a local host. Which of the following actions does the router perform as part of its DHCP relay operation? (Select TWO.)

Geçerli olan tümünü seçin

Replaces the client broadcast destination IP address with a unicast IP address directed to the specified DHCP server.

Populates the gateway IP address (

giaddr

) field in the DHCP payload with its own receiving interface IP address.

Encapsulates the DHCP request into a TCP stream on port 67 to establish a reliable connection with the DHCP server.

Floods the broadcast packet out of all router interfaces to locate an available DHCP server across connected VLANs.

Cevabı ve açıklamayı göster

Cevap: Replaces the client broadcast destination IP address with a unicast IP address directed to the specified DHCP server.; Populates the gateway IP address ( $giaddr$ ) field in the DHCP payload with its own receiving interface IP address.

Cevap

When a router acts as a DHCP relay agent, it converts the client's local broadcast packet into a unicast packet directed toward the centralized DHCP server and populates the gateway IP address (

giaddr

) field with the receiving interface's IP address.

A DHCP relay agent processes local client broadcast messages by converting the destination IP address to the unicast IP of the remote DHCP server and writing the receiving interface's IP address into the gateway IP address (

giaddr

) field of the DHCP payload so the server knows which subnet scope to select.

Adım Adım Çözüm

Identify the primary role of a DHCP relay agent upon receiving a broadcast request.

The router intercepts the broadcast DHCPDISCOVER packet on the client subnet interface.

DHCP clients initially send broadcast requests because they do not know the network configuration or server address.

Determine how the router modifies the IP header for relaying.

The destination address changes from a broadcast address to the configured unicast address of the DHCP server.

Routers do not forward broadcast packets across network boundaries; unicast routing delivers the request across Layer 3 subnets.

Determine how the DHCP server identifies the correct scope.

The router inserts its own receiving interface IP address into the

giaddr

header field.

The DHCP server requires the

giaddr

information to select an IP address from the pool corresponding to the client's subnet.

Anahtar Kavram

DHCP Relay Unicast Forwarding and Gateway IP Address (

giaddr

) Insertion

Soru 216Soru →

An enterprise network has deployed a centralized DHCP server on VLAN 100 ( $10.100.0.10/24$ ). Client workstations on VLAN 15 ( $172.16.15.0/24$ ) and VLAN 25 ( $172.16.25.0/24$ ) connect to a Layer 3 switch serving as their default gateway but fail to receive dynamic IP leases, resulting in APIPA address assignments. Which of the following configuration steps and operational mechanics must be implemented on the Layer 3 switch to resolve this issue? (Select TWO.)

Geçerli olan tümünü seçin

Configure the `ip helper-address 10.100.0.10` command directly under the Switched Virtual Interfaces (SVIs) for VLAN 15 and VLAN 25.

The switch converts incoming client DHCP broadcasts into unicast UDP packets destined for port 67 of the central server address.

Configure the `ip helper-address 10.100.0.10` command once in global configuration mode to apply across all defined switch subnets.

Configure inter-VLAN Access Control Lists (ACLs) to permit TCP destination port 67 traffic from the client SVIs to the DHCP server.

Cevabı ve açıklamayı göster

Cevap: Configure the `ip helper-address 10.100.0.10` command directly under the Switched Virtual Interfaces (SVIs) for VLAN 15 and VLAN 25.; The switch converts incoming client DHCP broadcasts into unicast UDP packets destined for port 67 of the central server address.

Cevap

The Layer 3 switch must be configured with `ip helper-address 10.100.0.10` on the SVIs for VLAN 15 and VLAN 25, and the switch operates by relaying broadcast DHCP client packets as unicast UDP destination port 67 traffic to the central server.

DHCP clients broadcast initial DHCPDISCOVER packets within their local VLAN. Because Layer 3 devices drop broadcasts, a DHCP Relay Agent (`ip helper-address`) must be configured on each client-facing Layer 3 interface (SVI). Upon receiving the broadcast, the relay agent converts the request into a unicast UDP packet (using UDP port 67 for both source and destination or forwarding to UDP 67) and sends it directly to the unicast IP address of the remote DHCP server.

Adım Adım Çözüm

Identify the boundary requiring DHCP Relay Agent functionality.

Client broadcast packets for DHCP Discovery (UDP port 67) cannot cross Layer 3 VLAN boundaries natively.

Routers and Layer 3 switches drop broadcast traffic by default.

Determine interface-level configuration requirements.

Apply `ip helper-address` to the client-facing interface SVIs (VLAN 15 and VLAN 25).

The relay agent requires interface context to populate the `giaddr` header field with the interface's IP address, allowing the central server to select the correct IP address pool.

Verify protocol and transport-layer characteristics of relayed traffic.

Broadcast UDP packets received on port 67 are unicast to the target server on UDP port 67.

DHCP relay services convert local Layer 2/3 broadcasts into routable Layer 3 unicast UDP packets.

Anahtar Kavram

DHCP Relay Agent Architecture and UDP Forwarding Mechanics

Tahmini Süre:2m 0s

Soru 217Soru →

A network administrator is configuring static IP address assignments for high-availability database servers within an enterprise subnet designated as $172.20.48.0/28$ . Which of the following IP addresses are valid usable host IP addresses that can be assigned to these servers? (Select TWO)

Geçerli olan tümünü seçin

172.20.48.1

172.20.48.14

172.20.48.0

172.20.48.15

172.20.48.16

Cevabı ve açıklamayı göster

Cevap: 172.20.48.1; 172.20.48.14

Cevap

The valid usable host IP addresses within the 172.20.48.0/28 subnet are 172.20.48.1 and 172.20.48.14.

For the network block 172.20.48.0/28, a prefix length of /28 provides 16 total IP addresses (

2^{32-28} = 16

). The reserved network address is 172.20.48.0 and the reserved broadcast address is 172.20.48.15. The range of assignable host addresses is 172.20.48.1 through 172.20.48.14 inclusive. Therefore, 172.20.48.1 and 172.20.48.14 are valid usable host addresses.

Adım Adım Çözüm

Determine the block size for a /28 subnet prefix.

A /28 prefix leaves

32 - 28 = 4

host bits. The total number of IP addresses per subnet is

2^4 = 16

Calculating the total size of the subnet identifies the boundary conditions.

Identify the network ID and broadcast address for the subnet block.

The network address is 172.20.48.0. The broadcast address is

172.20.48.0 + 16 - 1 = 172.20.48.15

The network address is the first address in the block and the broadcast address is the last.

Determine the range of usable host IP addresses.

The usable host IP range spans from

172.20.48.1

(network ID + 1) to

172.20.48.14

(broadcast ID - 1).

Network and broadcast addresses are reserved and cannot be configured on individual host interfaces.

Evaluate the candidate options against the valid host range.

172.20.48.1 and 172.20.48.14 both fall within the usable range [172.20.48.1 - 172.20.48.14].

Only IP addresses strictly between the network ID and broadcast ID can be statically assigned to host devices.

Anahtar Kavram

IPv4 Host Range Determination

Soru 218Soru →

A network administrator is deploying a multi-VLAN network on a Layer 3 switch. Workstations on VLAN 50 ( $10.50.0.0/24$ ) are failing to acquire IP addresses from a centralized DHCP server ( $192.168.10.10$ ). During troubleshooting, the administrator notices that the `ip helper-address 192.168.10.10` command was mistakenly configured on the physical trunk uplink interface connecting to the core router instead of the client subnet interface. Which configuration change must be implemented to allow VLAN 50 workstations to obtain DHCP leases?

Apply the `ip helper-address 192.168.10.10` command directly under the VLAN 50 Switch Virtual Interface (SVI).

Reconfigure the DHCP relay agent to forward client requests using TCP port 67 instead of UDP port 67.

Relocate the `ip helper-address` configuration statement to the network adapter properties of the central DHCP server.

Enable global broadcast routing on all physical access switchports assigned to VLAN 50.

Cevabı ve açıklamayı göster

Cevap: Apply the `ip helper-address 192.168.10.10` command directly under the VLAN 50 Switch Virtual Interface (SVI).

Cevap

Configure the `ip helper-address 192.168.10.10` command directly under the VLAN 50 Switch Virtual Interface (SVI).

DHCP clients issue Layer 2 broadcast requests (`255.255.255.255`) that are constrained to their local VLAN. To relay these requests across subnets to a remote DHCP server, the DHCP relay service (`ip helper-address`) must be configured on the Layer 3 interface serving as the local default gateway for that VLAN—specifically the VLAN 50 Switch Virtual Interface (SVI). Once configured on the SVI, the switch intercepts the local broadcast, sets the Gateway IP Address (`giaddr`) field to the SVI IP address, and forwards the request as a unicast packet to

192.168.10.10

Adım Adım Çözüm

Identify the ingress interface for client broadcast traffic

Workstations on VLAN 50 send initial DHCPDISCOVER messages as Layer 2 broadcasts targeting their local default gateway interface (the VLAN 50 SVI).

DHCP broadcast messages are contained within their local broadcast domain (VLAN) and will not reach physical trunk uplinks without local SVI relay processing.

Evaluate relay agent placement rules

The `ip helper-address` statement must reside on the interface listening for client broadcasts.

Placing the helper address on an outbound trunk interface bypasses the client broadcast domain, preventing the router/switch from intercepting client requests.

Apply the correct configuration location

Configuring `ip helper-address 192.168.10.10` under `interface Vlan50` enables the relay agent to capture broadcast requests, populate the `giaddr` field with

10.50.0.1

, and unicast the request to the central server.

This allows the remote DHCP server to select an available pool address matching the

10.50.0.0/24

subnet.

Anahtar Kavram

DHCP Relay Agent Placement on Switch Virtual Interfaces (SVIs)

Soru 219Soru →

A network administrator needs to publish an internal web server to the internet. The server is assigned a fixed private IPv4 address, and the organization requires a permanent, dedicated one-to-one mapping to a single public IPv4 address. Which NAT translation method should the network administrator implement?

Static NAT

Port Address Translation (PAT)

Frame Translation NAT

Dynamic NAT

Cevabı ve açıklamayı göster

Cevap: Static NAT

Cevap

Static NAT is the correct solution because it provides a permanent, dedicated one-to-one mapping between a private IP address and a public IP address.

Static NAT configures a fixed, persistent 1-to-1 translation between an inside local private IP address and an inside global public IP address. This static mapping ensures that external users can consistently access the internal web server.

Adım Adım Çözüm

Analyze the technical requirements of the scenario

The internal web server requires external internet access using a single dedicated public IP address that never changes.

Publicly accessible services such as web servers require consistent IP addressing so domain name records and external clients can reliably reach them.

Match the requirement to the appropriate Network Address Translation type

Static NAT provides a permanent 1:1 translation between an inside local private IP address and an inside global public IP address.

Unlike dynamic methods, Static NAT ensures that incoming traffic sent to the public IP is always routed to the designated internal web server.

Anahtar Kavram

Static NAT 1-to-1 Mapping

Soru 220Soru →

A system administrator is designing an isolated VLAN for a database cluster. The cluster requires $27$ usable IPv4 addresses for database nodes, $1$ address for the default gateway, and $2$ addresses for virtual IP load balancers. Which of the following represents the smallest CIDR prefix mask that provides sufficient usable IPv4 addresses for all required devices?

/28

/27

/26

/25

Cevabı ve açıklamayı göster

Cevap: $/27$

Cevap

The smallest CIDR prefix mask that satisfies the requirement is

/27

The scenario requires

30

usable IP addresses (

27 + 1 + 2 = 30

). A

/27

subnet has

5

host bits (

32 - 27 = 5

), providing

2^5 = 32

total IP addresses. Subtracting

2

for the network address and broadcast address leaves exactly

30

usable host addresses (

32 - 2 = 30

), making

/27

the smallest prefix mask that satisfies the requirement.

Adım Adım Çözüm

Calculate total usable IPv4 addresses required.

27 \text{ nodes} + 1 \text{ gateway} + 2 \text{ load balancers} = 30 \text{ usable host IP addresses}

All active host interfaces on the network segment require individual usable IP addresses.

Determine the required host bits (

h

) using the formula for usable hosts.

2^h - 2 \ge 30 \implies 2^h \ge 32 \implies h = 5

host bits.

Two IP addresses in every standard subnet are reserved for the network ID and broadcast address.

Calculate the CIDR prefix length.

32 - 5 = 27

, resulting in a

/27

subnet mask.

An IPv4 address consists of 32 bits; subtracting 5 host bits leaves 27 prefix bits for the network.

Anahtar Kavram

Calculating required subnet size and usable host counts using CIDR notation

Tahmini Süre:1m 30s

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