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Soru 1261Soru →

When a Cisco router processes an ingress IPv4 packet destined for a remote network, it executes a deterministic evaluation sequence to determine the forwarding path and transmit the frame. Place the operational steps in the correct chronological order from packet ingress to egress frame encapsulation.

Öğeleri doğru sıraya koymak için sürükleyin

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Cevap

The correct evaluation sequence begins with extracting the destination IPv4 address, followed by performing Longest Prefix Match lookup in the routing table, evaluating protocol metrics for equal prefix ties, resolving the next-hop IP and egress interface, and finally resolving ARP to rewrite Layer 2 headers for frame transmission.
Router forwarding logic follows a mandatory sequence: packet header inspection, route selection via Longest Prefix Match (LPM), tie-breaking via metric for matching prefix length, identification of exit interface/next-hop IP, and Layer 2 frame encapsulation via ARP lookup.

Adım Adım Çözüm

1
Parse packet header
Destination IPv4 address identified
The router must inspect the Layer 3 header to determine where the packet is destined.
2
Perform Longest Prefix Match (LPM)
Candidate route with most specific subnet mask selected
Longest Prefix Match is the absolute primary rule in IP route selection.
3
Evaluate protocol metric
Single best route or equal-cost paths selected
If identical routes exist within a single protocol source, metric breaks the tie.
4
Determine egress parameters
Next-hop IP and outbound interface bound
The router maps the selected routing entry to its configured exit interface and next hop.
5
Encapsulate and transmit frame
Layer 2 MAC rewrite complete and bits transmitted
Address Resolution Protocol (ARP) supplies the next-hop MAC address to build the new data link layer frame.

Anahtar Kavram

Router Forwarding Decision Logic
Soru 1262Soru →

An engineer connects a new host to interface FastEthernet0/12 on a Cisco Catalyst switch. The host immediately sends a unicast Ethernet frame intended for a server whose MAC address is already dynamically learned on interface FastEthernet0/18. Arrange the operational steps in the exact chronological order that the switch executes upon receiving this frame.

Öğeleri doğru sıraya koymak için sürükleyin

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Cevap

The correct operational sequence begins with frame reception on FastEthernet0/12, followed by source MAC address learning, destination MAC lookup in the table, identifying the egress port match on FastEthernet0/18, and finally unicast forwarding out FastEthernet0/18.
Layer 2 switch operation dictates a strict sequence of events upon frame arrival: frame ingress occurs first, followed immediately by source MAC address learning (adding or updating the source MAC and interface association in the MAC address table). Next, the switch performs a table lookup for the destination MAC address, identifies the matching egress interface (FastEthernet0/18), and lastly forwards the unicast frame directly out that specific interface.

Adım Adım Çözüm

1
Identify the ingress port event.
The switch receives the raw frame on FastEthernet0/12.
Frame processing cannot occur until the physical interface receives and buffers the frame.
2
Perform ingress source MAC learning.
The switch associates the frame's source MAC address with interface FastEthernet0/12 in its Layer 2 MAC address table.
Cisco switches always process source MAC learning prior to destination forwarding logic.
3
Perform destination MAC table lookup.
The switch checks its MAC address table for the frame's destination address.
The destination MAC determines whether the frame will be unicast forwarded, flooded, or filtered.
4
Evaluate the table lookup result.
An existing mapping points to interface FastEthernet0/18.
Since the server's MAC was previously learned, the destination lookup succeeds.
5
Execute frame forwarding.
The switch transmits the frame solely out interface FastEthernet0/18.
Known unicast frames are forwarded strictly to the matching egress port, preventing unnecessary broadcast domain traffic.

Anahtar Kavram

L2 Switch Ingress Processing, MAC Address Learning, and Known Unicast Forwarding
Soru 1263Soru →

Four Cisco Catalyst switches (SW1, SW2, SW3, and SW4) are deployed in an enterprise network running Rapid PVST+ for VLAN 10. SW1 is elected as the Root Bridge. SW4 connects to SW2 via interface GigabitEthernet0/1 and to SW3 via interface GigabitEthernet0/2. Both paths yield an identical cumulative root path cost of 4. SW2 has a lower Bridge ID than SW3. In addition, interfaces GigabitEthernet0/3 and GigabitEthernet0/4 on SW4 are both connected to the same unmanaged hub on a single shared collision domain. Which two statements correctly describe the Rapid PVST+ port roles and state operations on SW4 for VLAN 10? (Select two.)

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: GigabitEthernet0/2 is assigned the Alternate port role and operates in the Discarding state.; GigabitEthernet0/4 is assigned the Backup port role and operates in the Discarding state.

Cevap

The correct statements are that GigabitEthernet0/2 is assigned the Alternate port role operating in the Discarding state, and GigabitEthernet0/4 is assigned the Backup port role operating in the Discarding state.
In Rapid PVST+ (802.1w), port roles are defined based on path location and the source of BPDUs. GigabitEthernet0/1 is the Root Port because SW2 has a lower Bridge ID than SW3. GigabitEthernet0/2 receives BPDUs from another switch (SW3) offering a secondary root path, making it an Alternate port operating in the Discarding state. For GigabitEthernet0/3 and GigabitEthernet0/4 connected to the same hub, SW4 receives its own BPDUs; the port with the higher Port ID (GigabitEthernet0/4) becomes a Backup port operating in the Discarding state.

Adım Adım Çözüm

1
Determine Root Port on SW4
GigabitEthernet0/1 selected as Root Port
Both SW2 and SW3 offer an equal root path cost of 4. The tie-breaker evaluates the neighbor Bridge ID. Because SW2 has a lower Bridge ID than SW3, the path through SW2 (GigabitEthernet0/1) is chosen as the Root Port.
2
Determine role for non-root path to another switch (GigabitEthernet0/2)
GigabitEthernet0/2 becomes an Alternate Port in Discarding state
An interface that receives BPDUs offering an alternate path to the Root Bridge from a neighboring switch acts as an Alternate port. In Rapid PVST+, Alternate ports are placed in the Discarding state.
3
Determine roles for interfaces connected to the shared hub (GigabitEthernet0/3 and GigabitEthernet0/4)
GigabitEthernet0/3 becomes Designated; GigabitEthernet0/4 becomes Backup in Discarding state
When multiple interfaces on the same switch connect to the same collision domain/hub, the switch receives its own BPDUs. The interface with the lower Port ID (GigabitEthernet0/3) becomes Designated, while the higher Port ID (GigabitEthernet0/4) takes the Backup port role in the Discarding state.

Anahtar Kavram

Rapid PVST+ Port Roles (Root, Designated, Alternate, Backup) and States (Discarding, Learning, Forwarding)
Soru 1264Soru →

Refer to the following partial output from the show ip route command on a Cisco router:

text
Gateway of last resort is 10.1.1.1 to network 0.0.0.0

D 10.50.0.0/16 [90/307200] via 10.2.2.2, GigabitEthernet0/1
O 10.50.10.0/24 [110/20] via 10.3.3.3, GigabitEthernet0/2
S 10.50.10.64/26 [1/0] via 10.4.4.4, GigabitEthernet0/3
S* 0.0.0.0/0 [1/0] via 10.1.1.1, GigabitEthernet0/0

The router receives an IPv4 packet destined for host 10.50.10.75. Which next-hop IP address will the router choose to forward this packet?

Cevabı ve açıklamayı göster

Cevap: 10.4.4.4

Cevap

The router will select the next-hop IP address 10.4.4.4 associated with the longest prefix match route 10.50.10.64/26.
When a router performs a routing lookup for a packet destination IP, it checks for matching entries in the IP routing table and selects the route with the most specific match (the longest subnet mask). In this case, 10.50.10.75 matches 10.50.0.0/16, 10.50.10.0/24, and 10.50.10.64/26. The /26 prefix is the longest match, so the packet is forwarded via its next hop, 10.4.4.4.

Adım Adım Çözüm

1
Identify all routes in the routing table that match the destination IP address 10.50.10.75.
The IP address 10.50.10.75 matches three specific routes: 10.50.0.0/16, 10.50.10.0/24, and 10.50.10.64/26 (range: 10.50.10.64 to 10.50.10.127), plus the default route 0.0.0.0/0.
Routing lookup matches the destination address against all configured prefixes.
2
Compare the prefix lengths of all matching routes to determine the Longest Prefix Match (LPM).
Prefix lengths are /16, /24, /26, and /0. The longest prefix match is /26 (10.50.10.64/26).
Routers always prioritize the most specific matching route (longest subnet mask / prefix length) regardless of administrative distance or metric.
3
Determine the next-hop IP address associated with the longest matching prefix.
The route 10.50.10.64/26 points to the next hop 10.4.4.4.
The next-hop address specified by the LPM entry is used for packet forwarding.

Anahtar Kavram

Longest Prefix Match (LPM) Rule
Soru 1265Soru →

A network technician is configuring an IPv6 static route on a Cisco router. The destination network is 2001:db8:c0ff:50::/642001:\text{db8}:\text{c0ff}:50::/64. The next-hop router's link-local IPv6 address is fe80::a5\text{fe80}::a5, and traffic must exit via the local interface GigabitEthernet0/0/0. What is the exact, complete Cisco IOS command required to configure this fully specified static route with a custom administrative distance of 130?

Aşağıdaki boşlukları doldurun

Enter the complete Cisco IOS command:
Cevabı ve açıklamayı göster

Cevap

ipv6 route 2001:db8:c0ff:50::/64 GigabitEthernet0/0/0 fe80::a5 130
Configuring an IPv6 static route with a link-local next-hop address requires a fully specified route format: 'ipv6 route <destination-prefix/prefix-length> <exit-interface> <link-local-next-hop> [administrative-distance]'. In this scenario, combining the target prefix '2001:db8:c0ff:50::/64', local exit interface 'GigabitEthernet0/0/0', link-local next-hop 'fe80::a5', and administrative distance '130' results in 'ipv6 route 2001:db8:c0ff:50::/64 GigabitEthernet0/0/0 fe80::a5 130'.

Adım Adım Çözüm

1
Identify the base global configuration command and destination prefix.
The static route command begins with 'ipv6 route' followed by the target IPv6 network prefix and prefix length '2001:db8:c0ff:50::/64'.
Cisco IOS requires the keyword 'ipv6 route' followed immediately by the destination network identifier.
2
Identify the requirement for specifying the local exit interface.
Place 'GigabitEthernet0/0/0' after the destination prefix.
Because link-local addresses (fe80::/10) are scope-local and ambiguous across multiple router interfaces, Cisco IOS requires specifying the exit interface whenever a link-local address is used as a next hop.
3
Append the link-local next-hop address and administrative distance.
Add the link-local next-hop IPv6 address 'fe80::a5' followed by the administrative distance integer '130'.
Completes the syntax for a fully specified IPv6 static route while applying the requested custom administrative distance.

Anahtar Kavram

Fully Specified IPv6 Static Route Configuration
Tahmini Süre:1m 30s
Soru 1266Soru →

A network administrator is connecting two Cisco Catalyst switches using two physical Gigabit Ethernet links. On Switch-1, the physical interfaces are assigned using the command `channel-group 12 mode active`. On Switch-2, the corresponding physical interfaces are assigned using `channel-group 21 mode passive`. All physical interface speed, duplex, and VLAN settings match on both ends. What is the operational status of this EtherChannel bundle?

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Cevap: The EtherChannel bundle forms successfully because channel group numbers are locally significant, and active-to-passive LACP modes successfully negotiate.

Cevap

The EtherChannel bundle forms successfully because channel group numbers are locally significant, and active-to-passive LACP modes successfully negotiate.
The channel group number specified in the `channel-group <number> mode <mode>` command is strictly locally significant to the local Cisco switch. It identifies which logical Port-channel interface (e.g., Port-channel 12 vs Port-channel 21) member ports belong to locally. Furthermore, LACP negotiation succeeds when one switch is in `active` mode (initiating LACP packets) and the peer switch is in `passive` mode (responding to LACP packets).

Adım Adım Çözüm

1
Evaluate channel group number significance across switch boundaries.
Channel group numbers (e.g., 12 on Switch-1 and 21 on Switch-2) define the local Port-channel interface ID on each individual switch and are not exchanged in LACP Data Units (LACPDUs).
Channel group numbers are strictly locally significant.
2
Evaluate LACP negotiation modes between Switch-1 and Switch-2.
Switch-1 is set to 'active' (actively initiates LACP negotiation) and Switch-2 is set to 'passive' (listens and responds to incoming LACP packets).
An active-to-passive combination satisfies LACP negotiation requirements.
3
Determine final EtherChannel bundle state.
Because physical parameters match and LACP negotiation succeeds, the Port-channel forms and transitions to an operational bundled state.
No configuration parameters block EtherChannel formation.

Anahtar Kavram

LACP Mode Negotiation and Channel Group Local Significance
Soru 1267Soru →

A network administrator needs to configure an IPv6 default static route on a Cisco IOS router pointing to the exit interface GigabitEthernet0/0. Complete the command by specifying the IPv6 default route prefix notation.

Aşağıdaki boşlukları doldurun

ipv6 route GigabitEthernet0/0
Cevabı ve açıklamayı göster

Cevap

The correct prefix notation to complete the IPv6 static default route command is ::/0.
The IPv6 default route prefix is designated as ::/0, which matches all destination networks regardless of prefix length.

Adım Adım Çözüm

1
Identify the IPv6 address representation for a default route.
In IPv6 addressing, all zeros with a prefix length of zero bits is represented using compressed format as ::/0.
The prefix ::/0 matches any IPv6 destination network when no more specific match exists in the routing table.

Anahtar Kavram

IPv6 Default Static Route Syntax
Soru 1268Soru →

Refer to the following partial IPv4 routing table output from a Cisco router:

text
Gateway of last resort is 10.10.10.1 to network 0.0.0.0

D 10.150.24.0/26 [90/307200] via 10.1.1.2, 00:15:10, GigabitEthernet0/0
O 10.150.24.0/24 [110/20] via 10.2.2.2, 01:20:45, GigabitEthernet0/1
S 10.150.24.32/28 [1/0] via 10.3.3.2, 02:04:12, GigabitEthernet0/2
S* 0.0.0.0/0 [1/0] via 10.10.10.1, 12:00:00, GigabitEthernet0/3

The router receives an IPv4 packet destined for host 10.150.24.4010.150.24.40. Which two statements accurately describe how the router makes its forwarding decision for this packet?

Geçerli olan tümünü seçin

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Cevap: The packet is forwarded out interface GigabitEthernet0/2 because 10.150.24.32/28 has the longest prefix match for the destination address.; The router compares subnet mask lengths prior to evaluating Administrative Distance values across candidate routes.

Cevap

The router forwards the packet out interface GigabitEthernet0/2 because 10.150.24.32/28 represents the longest matching prefix for host 10.150.24.40, and prefix length evaluation strictly precedes Administrative Distance comparison.
When a router receives a packet, it searches its routing table for all matching prefixes and selects the route with the longest prefix length (most specific mask). The destination address 10.150.24.40 matches 10.150.24.32/28 (/28), 10.150.24.0/26 (/26), 10.150.24.0/24 (/24), and 0.0.0.0/0 (/0). Since /28 is the longest mask, the route via GigabitEthernet0/2 is chosen. The router checks prefix length before Administrative Distance or metric values.

Adım Adım Çözüm

1
Determine which routes match the destination IP address 10.150.24.40.
Matching routes are 10.150.24.0/24, 10.150.24.0/26, 10.150.24.32/28, and default route 0.0.0.0/0.
The destination address 10.150.24.40 falls into the address ranges of all four listed routes.
2
Apply the Longest Prefix Match (LPM) rule across all matching routes.
10.150.24.32/28 has a 28-bit mask length, which is the most specific match compared to /26, /24, and /0.
Routers always prefer the route with the highest number of matching leading network bits (longest prefix).
3
Determine the egress interface and next-hop for the winning route 10.150.24.32/28.
The packet will be forwarded to next-hop 10.3.3.2 via interface GigabitEthernet0/2.
The routing table explicitly points the static route 10.150.24.32/28 out interface GigabitEthernet0/2.

Anahtar Kavram

Router Forwarding Decision Logic and Longest Prefix Match precedence
Soru 1269Soru →

A network engineer is configuring interface IP addresses for a cluster of management servers assigned to the 10.100.80.0/2310.100.80.0/23 IPv4 subnet. Which two IPv4 addresses are valid, assignable host addresses within this subnet? (Select two.)

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: 10.100.80.25510.100.80.255; 10.100.81.25410.100.81.254

Cevap

The addresses 10.100.80.25510.100.80.255 and 10.100.81.25410.100.81.254 are valid, assignable host addresses in the 10.100.80.0/2310.100.80.0/23 subnet.
For the network block 10.100.80.0/2310.100.80.0/23, the 9 host bits span from 10.100.80.010.100.80.0 to 10.100.81.25510.100.81.255. The network address is 10.100.80.010.100.80.0 (all host bits 0), and the broadcast address is 10.100.81.25510.100.81.255 (all host bits 1). The valid usable host IP range is 10.100.80.110.100.80.1 to 10.100.81.25410.100.81.254. Therefore, both 10.100.80.25510.100.80.255 and 10.100.81.25410.100.81.254 fall within the valid host range.

Adım Adım Çözüm

1
Determine the subnet mask and block size for a /23 prefix
A /23 prefix uses a subnet mask of 255.255.254.0255.255.254.0, providing 9 host bits (29=5122^9 = 512 total IP addresses) and a block size of 2 in the third octet.
Calculating block size allows identification of the subnet boundaries.
2
Calculate the network and broadcast addresses for 10.100.80.0/2310.100.80.0/23
Network address is 10.100.80.010.100.80.0. The broadcast address is the last address before the next subnet (10.100.82.010.100.82.0), which is 10.100.81.25510.100.81.255.
Host addresses cannot be assigned the network ID or broadcast ID.
3
Identify the usable host address range
The assignable host range extends from 10.100.80.110.100.80.1 through 10.100.81.25410.100.81.254.
Usable host range includes all IPs between the network ID and broadcast ID.
4
Evaluate the given options against the usable host range
10.100.80.25510.100.80.255 and 10.100.81.25410.100.81.254 both fall strictly within the assignable range [10.100.80.1,10.100.81.254][10.100.80.1, 10.100.81.254].
Addresses within this inclusive range are valid host assignments.

Anahtar Kavram

IPv4 Subnet Boundaries and Host Address Ranges for Non-Byte-Aligned Prefixes
Soru 1270Soru →

A network administrator is reviewing the network configuration of a server assigned the IPv4 address 172.28.143.100172.28.143.100 with a subnet mask of 255.255.252.0255.255.252.0 (/22). Which IPv4 address is the broadcast address for this subnet?

Cevabı ve açıklamayı göster

Cevap: 172.28.143.255172.28.143.255

Cevap

The broadcast address for the subnet containing host 172.28.143.100/22172.28.143.100/22 is 172.28.143.255172.28.143.255.
For a /22 subnet mask (255.255.252.0255.255.252.0), the third octet increments in steps of 4 (256−252=4256 - 252 = 4). For the IP address 172.28.143.100172.28.143.100, the containing network boundary starts at 172.28.140.0/22172.28.140.0/22 and ends at 172.28.143.255172.28.143.255. The last address in the subnet range (172.28.143.255172.28.143.255) is reserved as the directed broadcast address.

Adım Adım Çözüm

1
Determine the block size in the third octet from the subnet mask
A mask of 255.255.252.0255.255.252.0 (/22) leaves 256−252=4256 - 252 = 4 as the block size in the third octet.
The third octet is the interesting octet where subnetting occurs for a /22 prefix.
2
Find the network address boundary for the host IP address 172.28.143.100
Multiples of 4 in the third octet are 0, 4, 8, ..., 136, 140, 144. Since 143 falls between 140 and 144, the network address is 172.28.140.0172.28.140.0.
The subnet boundary begins at the nearest lower multiple of the block size (140).
3
Calculate the broadcast address of the subnet
The next subnet begins at 172.28.144.0172.28.144.0, so subtracting 1 IP address gives the broadcast address 172.28.143.255172.28.143.255.
The broadcast address is always one address below the network ID of the next consecutive subnet.

Anahtar Kavram

IPv4 Subnet Boundaries and Broadcast Address Calculation
Soru 1271Soru →

A network architect is assigned the IPv4 address block 10.116.0.0/1810.116.0.0/18 to provision subnets for remote office sites. Each site requires a dedicated subnet that can support at least 120120 usable host IP addresses. What is the maximum number of subnets of this size that can be created from the allocated block?

Cevabı ve açıklamayı göster

Cevap: 128

Cevap

The maximum number of subnets that can be created is 128.
To support at least 120 usable host IP addresses per subnet, 7 host bits are required because 27−2=1262^7 - 2 = 126 usable hosts (26−2=622^6 - 2 = 62 is insufficient). This results in a /25/25 prefix (32−7=2532 - 7 = 25). Borrowing bits from /18/18 to /25/25 gives 25−18=725 - 18 = 7 subnet bits. The total number of subnets created is 27=1282^7 = 128.

Adım Adım Çözüm

1
Calculate the required host bits (hh) for at least 120120 usable host IP addresses.
7 host bits are required (27−2=126≥1202^7 - 2 = 126 \ge 120).
6 host bits provide only 26−2=622^6 - 2 = 62 usable hosts, which is insufficient. 7 host bits provide 126 usable hosts.
2
Determine the prefix length needed for 7 host bits.
The subnet prefix length is /25/25 (32−7=2532 - 7 = 25).
An IPv4 address consists of 32 bits, so subtracting 7 host bits leaves 25 network/subnet bits.
3
Determine the number of subnet bits borrowed from the allocated block.
7 bits are borrowed (25−18=725 - 18 = 7).
The original allocation is /18/18 and the new subnets are /25/25.
4
Compute the total number of valid subnets.
The total number of subnets is 27=1282^7 = 128.
Borrowing 7 bits allows 272^7 distinct subnet combinations.

Anahtar Kavram

Subnet Sizing and Subnet Count Calculation
Tahmini Süre:1m 30s
Soru 1272Soru →

An administrator reviews the following IPv4 routing table snippet on a Cisco router:

text
Gateway of last resort is 172.20.10.1 to network 0.0.0.0

B 10.100.0.0/16 [200/0] via 172.20.10.2, 04:12:30
O IA 10.100.16.0/20 [110/35] via 192.168.20.2, 01:05:18, GigabitEthernet0/1
D 10.100.20.0/22 [90/156160] via 192.168.30.2, 00:18:42, GigabitEthernet0/2
C 192.168.20.0/24 is directly connected, GigabitEthernet0/1
L 192.168.20.1/32 is directly connected, GigabitEthernet0/1

A packet arrives at the router addressed to 10.100.21.5010.100.21.50. Which TWO statements correctly describe how the routing table components are evaluated to forward this packet? (Select TWO.)

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: The router selects the route for 10.100.20.0/22 because it provides the longest prefix match (/22) for the destination IP address.; The routing entry for 10.100.20.0/22 indicates an administrative distance of 90 and a metric of 156160.

Cevap

The router selects the route for 10.100.20.0/22 based on the longest prefix match rule, and the routing entry defines an administrative distance of 90 with a metric of 156160.
When evaluating incoming packets for forwarding, Cisco routers determine all matching routes and choose the route with the longest subnet mask (most specific prefix). The address 10.100.21.50 matches three entries, but 10.100.20.0/22 has the longest prefix length (/22). Furthermore, Cisco routing tables present protocol metadata in the bracketed structure [Administrative Distance / Metric], which identifies an administrative distance of 90 and a metric value of 156160 for the EIGRP route.

Adım Adım Çözüm

1
Determine which routing table entries match the destination IP address 10.100.21.50.
The destination address matches 10.100.0.0/16, 10.100.16.0/20, and 10.100.20.0/22.
10.100.21.50 falls within the host ranges of all three subnets.
2
Apply the Longest Prefix Match (LPM) forwarding rule.
Select 10.100.20.0/22 because /22 has the longest subnet mask length.
Cisco routers always prefer the route with the most specific prefix length first before evaluating administrative distance or metric.
3
Parse the bracketed components [90/156160] for the selected route.
Administrative Distance is 90 and Metric is 156160.
Cisco output displays bracketed metrics formatted as [Administrative Distance / Metric].

Anahtar Kavram

Routing Table Component Interpretation and Longest Prefix Match Selection
Soru 1273Soru →

A Cisco Catalyst switch with an empty MAC address table receives an ingress Ethernet frame on interface GigabitEthernet1/0/24 assigned to VLAN 50. The frame contains a source MAC address of 001B.D455.A1B2 and a destination MAC address of 001B.D488.F9E0. Which processing action does the switch perform upon receiving this frame?

Cevabı ve açıklamayı göster

Cevap: It records source MAC address 001B.D455.A1B2 associated with interface GigabitEthernet1/0/24 in VLAN 50 in its MAC address table and floods the frame out all active interfaces in VLAN 50 except GigabitEthernet1/0/24.

Cevap

The switch records the source MAC address 001B.D455.A1B2 associated with interface GigabitEthernet1/0/24 in VLAN 50 in its MAC address table and floods the frame out all active interfaces in VLAN 50 except GigabitEthernet1/0/24.
When a switch receives a frame, it always performs MAC learning by binding the source MAC address to the ingress port and VLAN. If the destination MAC address is not found in the MAC address table for that VLAN, the switch performs an unknown unicast flood, transmitting the frame out all operational ports within the VLAN except the port on which the frame arrived.

Adım Adım Çözüm

1
Inspect the ingress frame's source MAC address
The switch reads source MAC address 001B.D455.A1B2 on port GigabitEthernet1/0/24 in VLAN 50.
Layer 2 switches continuously learn source MAC addresses and bind them to their ingress interface and VLAN ID.
2
Update the switch MAC address table
An entry mapping 001B.D455.A1B2 to GigabitEthernet1/0/24 in VLAN 50 is dynamically created with an aging timer.
Populating the table allows future unicast traffic destined for 001B.D455.A1B2 to be forwarded directly out GigabitEthernet1/0/24.
3
Lookup the destination MAC address 001B.D488.F9E0 in the MAC address table
The MAC address table lookup results in a miss (unknown unicast).
The initial state of the MAC address table was completely empty.
4
Execute unknown unicast forwarding logic
The frame is replicated and sent out all active ports assigned to VLAN 50, excluding GigabitEthernet1/0/24.
Flooding ensures the unknown host receives the frame without causing split-horizon interface loops.

Anahtar Kavram

Layer 2 MAC Address Table Learning and Unknown Unicast Flooding Logic
Soru 1274Soru →

A Cisco switch running Rapid PVST+ receives BPDUs across multiple candidate paths leading toward the Root Bridge. Place the tie-breaking criteria evaluated by the switch to elect its Root Port in the correct sequential order from first (1st) to last (4th).

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Cevap

The correct sequence for Rapid PVST+ Root Port election is: 1) Lowest cumulative Root Path Cost, 2) Lowest sender Bridge ID, 3) Lowest sender Port ID, and 4) Lowest local (receiver) Port ID.
Rapid PVST+ follows a strict four-step decision tree to select a single Root Port on a non-root switch: 1) Lowest cumulative Root Path Cost, 2) Lowest sender Bridge ID (BID), 3) Lowest sender Port ID, and 4) Lowest local (receiver) Port ID.

Adım Adım Çözüm

1
Evaluate incoming BPDU path cost values
Identify the link offering the lowest cumulative Root Path Cost to the Root Bridge
Rapid PVST+ prioritizes overall network topology bandwidth and cost over local port attributes.
2
Evaluate upstream switch Bridge IDs if path costs are equal
Select the neighbor switch that has the lowest BID value (Priority + System ID Extension + MAC Address)
When path costs match, preference is given to paths traversing higher-priority upstream bridges.
3
Evaluate sender Port IDs if BIDs are equal
Select the interface connected to the upstream neighbor port with the lowest Port ID
Multiple parallel links to the same upstream neighbor share identical Root Path Costs and sender BIDs.
4
Evaluate local receiver Port IDs if sender Port IDs are identical
Select the local receiving interface with the lowest Port ID
Serves as the final deterministic tie-breaker when connecting through an unmanaged hub or shared medium.

Anahtar Kavram

Rapid PVST+ Root Port Selection Tie-Breaker Order
Tahmini Süre:1m 15s
Soru 1275Soru →

During a network maintenance audit on a Cisco Catalyst switch running legacy IEEE 802.1D Spanning Tree Protocol (STP), an engineer observes an access port bringing up a new link without Cisco PortFast configured. Place the standard 802.1D STP port states in chronological sequence, starting from the moment physical link protocol comes UP until full Layer 2 data frame transmission begins.

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Cevap

The correct chronological sequence of 802.1D STP port states from link initialization to full frame transmission is Blocking state, Listening state, Learning state, and Forwarding state.
Under standard IEEE 802.1D STP operation without PortFast, an access interface experiences a total convergence delay of 30 seconds across standard state transitions. The interface moves sequentially through Blocking (loop detection), Listening (path calculation/BPDU processing for 15 seconds), Learning (MAC address table population for 15 seconds), and finally Forwarding (active user frame transmission).

Adım Adım Çözüm

1
Identify the initial state immediately after physical link protocol initialization.
The port initializes in the Blocking state.
Under IEEE 802.1D, non-PortFast ports enter Blocking to evaluate potential Layer 2 topology loops by listening for BPDUs.
2
Determine the state transition following loop evaluation.
The port transitions to the Listening state.
In Listening state, the interface actively sends and receives BPDUs to elect Root Bridges and establish port roles without populating MAC tables or forwarding user traffic.
3
Identify the state transition after the first Forward Delay timer (15 seconds) expires.
The port enters the Learning state.
In Learning state, the switch begins learning source MAC addresses from received frames to populate its MAC table, but still drops user data frames.
4
Determine the final state transition after the second Forward Delay timer (15 seconds) expires.
The port reaches the Forwarding state.
With convergence established and MAC tables populated, the interface transitions to Forwarding to send and receive Layer 2 user data traffic.

Anahtar Kavram

802.1D Spanning Tree Protocol Port State Transition Sequence
Soru 1276Soru →

A network administrator needs to manually configure a backup floating static route on a Cisco IOS router. Arrange the following syntax elements in the correct sequential order from left to right to construct a valid Cisco IOS floating static route command.

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Cevap

The correct sequence to construct the command is: ip route 172.16.1.0 255.255.255.0 10.1.1.2 130.
The correct order follows the standard Cisco IOS static route syntax: 'ip route <destination-prefix> <subnet-mask> {ip-address | exit-interface} [distance]'. The command starts with 'ip route', followed by the target destination network (172.16.1.0), the subnet mask (255.255.255.0), the next-hop address (10.1.1.2), and finally the optional Administrative Distance value (130).

Adım Adım Çözüm

1
Begin with the global configuration command keyword.
Specifies 'ip route' at the beginning of the command string.
Cisco IOS requires the 'ip route' command keyword to define a static routing entry.
2
Append the destination network address followed by its subnet mask.
Adds '172.16.1.0 255.255.255.0'.
The router needs the target IP subnet prefix and corresponding subnet mask to evaluate match length in the routing table.
3
Specify the next-hop IP address or local exit interface.
Adds '10.1.1.2'.
Defines the forwarding destination or gateway to reach the target network.
4
Append the optional Administrative Distance value at the end.
Adds '130'.
Assigning an Administrative Distance higher than the primary route (e.g., OSPF AD 110) creates a floating static route that remains inactive until the primary route drops.

Anahtar Kavram

Cisco IOS IPv4 static route CLI syntax structure and floating static route parameter placement.
Soru 1277Soru →

An enterprise network uses Rapid PVST+ for spanning tree management across four Catalyst switches (SW-A, SW-B, SW-C, and SW-D) servicing VLAN 25. The bridge priorities for VLAN 25 are configured as follows:
- SW-A: priority 4096
- SW-B: priority 8192
- SW-C: priority 16384
- SW-D: priority 32768

SW-C has two direct 1 Gbps links (STP cost 4) connected to SW-B: interface Gi0/1 connects to SW-B interface Gi0/1, and interface Gi0/2 connects to SW-B interface Gi0/2. SW-C also has a direct 10 Gbps link (STP cost 2) on interface Gi0/3 connected directly to SW-A. SW-B connects directly to SW-A via a 1 Gbps link on interface Gi0/24.

If all switch MAC addresses follow standard numbering based on their switch letter (e.g., SW-A has the lowest MAC address) and default port priorities (128) are used throughout, which port role and state will interface Gi0/1 on SW-C adopt for VLAN 25?

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Cevap: Alternate port in the Discarding state

Cevap

Interface Gi0/1 on SW-C assumes the Alternate port role in the Discarding state.
In Rapid PVST+, SW-A is elected Root Bridge because it has the lowest Bridge ID (4096+25=41214096 + 25 = 4121). SW-C compares its path costs to SW-A: interface Gi0/3 has a 10 Gbps link (STP cost 2), giving a total cost of 2 to reach the Root Bridge. Interfaces Gi0/1 and Gi0/2 connect to SW-B (cost 4 to SW-B + cost 4 from SW-B to SW-A = total cost 8). Therefore, Gi0/3 is elected as SW-C's Root Port. On the links between SW-B and SW-C, SW-B is the Designated bridge because it advertises a lower Root Path Cost (4) than SW-C's path cost via SW-B. As a result, SW-C places its non-root interfaces connected to SW-B (Gi0/1 and Gi0/2) into the Alternate port role in the Discarding state.

Adım Adım Çözüm

1
Determine the Root Bridge for VLAN 25.
SW-A has the lowest Bridge ID (4096+25=41214096 + 25 = 4121) and is elected as the Root Bridge.
STP elects the switch with the lowest Bridge ID (Priority + System ID Extension + MAC Address) as Root Bridge.
2
Calculate cumulative path costs from SW-C to Root Bridge (SW-A) to elect the Root Port.
Path via Gi0/3 (10 Gbps) has a cost of 22. Path via Gi0/1 or Gi0/2 through SW-B has a cost of 4 (SW-C to SW-B)+4 (SW-B to SW-A)=84 \text{ (SW-C to SW-B)} + 4 \text{ (SW-B to SW-A)} = 8. SW-C selects Gi0/3 as its Root Port in the Forwarding state.
The non-root bridge selects the interface with the lowest cumulative cost to the Root Bridge as its Root Port.
3
Determine Designated Bridge selection between SW-B and SW-C for the links on Gi0/1 and Gi0/2.
SW-B's Root Path Cost is 44 and Bridge ID is 82178217, whereas SW-C's Root Path Cost on those links would be higher. Additionally, SW-B has a superior Bridge ID (8217<164098217 < 16409). SW-B becomes the Designated switch for both links.
On each segment, the switch advertising the lowest Root Path Cost (or lowest Bridge ID as a tie-breaker) becomes the Designated Bridge.
4
Assign the port role and state to interface Gi0/1 on SW-C.
Because SW-C receives superior BPDUs on Gi0/1 from SW-B and the port is not its Root Port, Gi0/1 is designated as an Alternate port and placed in the Discarding state.
In Rapid PVST+, non-root ports that receive superior BPDUs from another switch are designated as Alternate ports and held in the Discarding state to prevent loops.

Anahtar Kavram

Rapid PVST+ Port Role and State Elections in Multi-Switch Topologies
Soru 1278Soru →

A Cisco router receives an IPv4 packet destined for a remote host and evaluates its routing table containing multiple routes from different sources. Place the steps of the router's forwarding decision logic in the correct order from first to last.

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Cevap

The correct sequence of router forwarding decision logic from first to last is: 1) Select the route with the longest prefix match; 2) Compare Administrative Distance if prefix lengths are identical; 3) Compare metric values if AD and prefix lengths are identical; 4) Forward the packet using the selected route's exit interface and next hop.
When a Cisco router makes a forwarding decision, it follows a strict hierarchical evaluation sequence. First, it identifies all routes in the routing table that match the destination IPv4 address and selects the route with the longest prefix match (most specific subnet mask). Second, if there are multiple matching routes with identical prefix lengths, it evaluates Administrative Distance (AD) to pick the route from the most trustworthy routing protocol. Third, if multiple routes share identical prefix lengths and AD values, it compares the metric (path cost) to choose the lowest metric route. Finally, once the single best route is determined, the router forwards the packet out the associated exit interface.

Adım Adım Çözüm

1
Evaluate Longest Prefix Match (LPM)
The router identifies all routes matching the destination IP address and prioritizes the route with the longest prefix length (most specific subnet mask).
LPM always takes absolute precedence over Administrative Distance and Metric.
2
Compare Administrative Distance (AD)
If multiple routes have the exact same prefix length, the router selects the route from the routing source with the lowest AD.
Administrative Distance measures the believability and trustworthiness of the routing source.
3
Compare Metric
If AD and prefix length are identical (e.g., multiple routes learned via the same dynamic routing protocol), the route with the lowest metric is selected.
Metric measures path cost within a single routing protocol.
4
Forward the Packet
The router encapsulates the packet and sends it via the selected route's exit interface and next-hop IP address.
Once the best route determination is complete, the data plane handles packet transmission.

Anahtar Kavram

Router Forwarding Decision Logic Precedence (Longest Prefix Match > Administrative Distance > Metric)
Soru 1279Soru →

A network infrastructure team must select a topology for a new data center hosting microservices workloads that generate intensive East-West traffic between virtualized servers. The design requires consistent deterministic latency, equal-cost multi-pathing (ECMP) across all available links, and exactly two Layer 3 forwarding hops between any two leaf nodes. Which network topology architecture best satisfies these technical requirements?

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Cevap: Spine-Leaf (Clos) architecture

Cevap

Spine-Leaf (Clos) architecture
The correct answer describes a Spine-Leaf (Clos) architecture. In a two-tier Spine-Leaf topology, leaf switches connect to end systems and to every spine switch, ensuring that any leaf switch can communicate with any other leaf switch via a single spine switch (two network hops). By running Layer 3 routing between spine and leaf nodes, all inter-spine links remain active and carry traffic simultaneously using Equal-Cost Multi-Pathing (ECMP), providing deterministic low latency ideal for East-West data center workloads.

Adım Adım Çözüm

1
Analyze the workload traffic pattern and performance requirements.
Microservices require heavy East-West (server-to-server) communication demanding predictable, low latency and high bandwidth.
Traditional hierarchical networks route traffic north-south through core/distribution layers, causing sub-optimal pathing and latency variance.
2
Evaluate topological hop counts and path redundancy features.
A Spine-Leaf fabric guarantees that any leaf switch is connected directly to every spine switch, resulting in exactly two network hops between any pair of leaf switches.
This full mesh between leaf and spine switches enables routing protocols to utilize all paths simultaneously using Equal-Cost Multi-Pathing (ECMP).

Anahtar Kavram

Spine-Leaf (Clos) Topology Characteristics
Tahmini Süre:1m 15s
Soru 1280Soru →

In a Cisco IOS IPv4 routing table displayed via the `show ip route` command, prefix source codes identify how routes were populated. Match each routing table source code on the left with its corresponding route origin and default administrative distance on the right.

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Öğeler

Source Code C
Source Code S
Source Code O
Source Code D

Eşleşmeler

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Cevap

Source Code C matches Directly connected network (Default AD: 0); Source Code S matches Statically configured route (Default AD: 1); Source Code O matches OSPF dynamic routing protocol (Default AD: 110); Source Code D matches EIGRP dynamic routing protocol (Default AD: 90).
Each routing table code corresponds strictly to a routing source and its trust rating (administrative distance). Code C represents connected interfaces (AD 0), code S represents static routes (AD 1), code O represents OSPF routes (AD 110), and code D represents internal EIGRP routes (AD 90).

Adım Adım Çözüm

1
Identify the meaning of source code C in Cisco IOS routing output.
Code C stands for Connected networks, assigned an Administrative Distance of 0.
Directly connected interfaces are the most trusted route source.
2
Identify the meaning of source code S in Cisco IOS routing output.
Code S stands for Static routes, assigned a default Administrative Distance of 1.
Static routes are manually created by network administrators.
3
Identify the meaning of source code O in Cisco IOS routing output.
Code O stands for Open Shortest Path First (OSPF), assigned a default Administrative Distance of 110.
Cisco IOS assigns OSPF an AD of 110.
4
Identify the meaning of source code D in Cisco IOS routing output.
Code D stands for EIGRP (derived from the Diffusing Update Algorithm - DUAL), assigned a default internal Administrative Distance of 90.
Letter D is used for EIGRP because E uses Exterior Gateway Protocol in older routing tables.

Anahtar Kavram

Routing Table Source Codes and Administrative Distance
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