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Tüm alıştırma soruları

1987 soru

Tüm türler1,987Çoktan seçmeli1,020Çoklu seçim452Sayısal18Eşleştirme229Sıralama203Boşluk doldurma22Kısa cevap43
Soru 1301Soru →

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

text
Codes: C - connected, S - static, R - RIP, D - EIGRP, O - OSPF, B - BGP

S 192.168.1.0/24 [1/0] via 10.0.0.3, GigabitEthernet0/0/3
D 192.168.1.128/25 [90/307200] via 10.0.0.2, GigabitEthernet0/0/2
O 192.168.1.128/26 [110/20] via 10.0.0.1, GigabitEthernet0/0/1
B 192.168.1.136/29 [20/0] via 10.0.0.4, GigabitEthernet0/0/4

The router receives a packet destined for host IPv4 address 192.168.1.138. Which next-hop IPv address and exit interface will the router select to forward this packet?

Cevabı ve açıklamayı göster

Cevap: 10.0.0.4 via GigabitEthernet0/0/4, because the /29 prefix provides the longest prefix match for the destination IP address.

Cevap

10.0.0.4 via GigabitEthernet0/0/4, because the /29 prefix provides the longest prefix match for the destination IP address.
When a router receives a packet, it compares the destination IP against all entries in its routing table. The fundamental rule for packet forwarding is Longest Prefix Match (LPM). Among all matching routes for 192.168.1.138, the route 192.168.1.136/29 has the longest subnet mask (/29 vs /26, /25, /24). Therefore, administrative distance and metrics are ignored, and the router selects next-hop 10.0.0.4 via GigabitEthernet0/0/4.

Adım Adım Çözüm

1
Identify all matching routes for destination IP 192.168.1.138 in the routing table.
Routes 192.168.1.0/24, 192.168.1.128/25, 192.168.1.128/26, and 192.168.1.136/29 all encompass 192.168.1.138.
Before comparing routing metrics or administrative distance, candidate matching routes must be identified.
2
Compare the prefix lengths (subnet masks) of all matching routes.
The prefix lengths are /24, /25, /26, and /29. /29 is the longest (most specific) match.
Cisco routers use the Longest Prefix Match (LPM) rule as the primary decision criterion when selecting a route from the routing table to forward a packet.
3
Determine the next-hop IP and exit interface associated with the longest prefix match route.
The route for 192.168.1.136/29 points to next-hop 10.0.0.4 out exit interface GigabitEthernet0/0/4.
The router forwards the packet to the next-hop specified by the winning route.

Anahtar Kavram

Router Forwarding Decision Logic and Longest Prefix Match (LPM)
Soru 1302Soru →

A network administrator is configuring static routing on router R1 to forward traffic toward network 2001:db8:3c4d:10::/64. The administrator intends to use the link-local address fe80::211:22ff:fe33:4455 of the neighboring router connected to local interface GigabitEthernet0/1. Which Cisco IOS command correctly configures this static route?

Cevabı ve açıklamayı göster

Cevap: ipv6 route 2001:db8:3c4d:10::/64 GigabitEthernet0/1 fe80::211:22ff:fe33:4455

Cevap

The command 'ipv6 route 2001:db8:3c4d:10::/64 GigabitEthernet0/1 fe80::211:22ff:fe33:4455' correctly configures the fully specified IPv6 static route.
The statement specifying the local exit interface GigabitEthernet0/1 followed by the next-hop link-local address fe80::211:22ff:fe33:4455 complies exactly with Cisco IOS requirements for fully specified IPv6 static routes.

Adım Adım Çözüm

1
Identify the proper Cisco IOS command prefix for IPv6 routing
The command must start with 'ipv6 route' rather than 'ip route'.
Cisco IOS separates IPv4 and IPv6 static route configurations into distinct global commands.
2
Evaluate the next-hop address scope
The next-hop address 'fe80::211:22ff:fe33:4455' is a link-local IPv6 address (fe80::/10).
Link-local addresses exist on every IPv6-enabled interface, so an egress interface MUST be supplied to resolve ambiguity.
3
Verify Cisco IOS syntax parameter ordering
The syntax requires 'ipv6 route <prefix/length> <exit-interface> <link-local-address>'.
Specifying GigabitEthernet0/1 followed by fe80::211:22ff:fe33:4455 forms a valid fully specified static route.

Anahtar Kavram

Fully Specified IPv6 Static Routes with Link-Local Next-Hops
Soru 1303Soru →

An network administrator reviews routing table entries using the `show ip route` command on a Cisco IOS router. Which two statements correctly describe components of an IPv4 routing table entry?

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: Administrative distance indicates the trustworthiness of the route source, with lower values being preferred.; The metric is a value calculated by a routing protocol to select the best path among multiple routes to the same destination network.

Cevap

The two correct statements are that administrative distance measures the trustworthiness of a routing source (with lower values preferred) and that metric is used by a routing protocol to select the best path to a destination network.
Administrative distance measures the trustworthiness of a routing source (where lower numbers represent greater trust), and metrics are used by individual routing protocols to identify the optimal path among available routes.

Adım Adım Çözüm

1
Analyze the role of Administrative Distance (AD)
AD defines route trustworthiness from 0 (most trusted) to 255 (unbelievable/untrusted). Lower values are preferred.
AD helps the router choose which routing source to populate into the routing table when multiple sources offer the exact same destination network prefix.
2
Analyze the role of Metric
Metric measures path cost within a single routing protocol (e.g., OSPF cost, RIP hop count).
Routing protocols use metrics to evaluate competing paths to the same destination prefix and choose the best route.
3
Verify forwarding decision order and source codes
Longest prefix match is evaluated first during packet lookup, not AD. Source code 'S' stands for Static, while 'O' stands for OSPF.
This invalidates options suggesting AD precedes prefix length or misidentifying static routes as OSPF.

Anahtar Kavram

Routing Table Components and Metrics
Soru 1304Soru →

A network administrator is inspecting the IPv4 routing table on a Cisco IOS XE router using the `show ip route` command. Match each routing table entry line on the left to its corresponding architectural component description on the right.

Soldaki öğeye tıklayın, sonra eşleşen sağdaki öğeye tıklayın

Öğeler

D EX 10.5.0.0/16 [170/2578560] via 192.168.1.2
O IA 10.2.0.0/24 [110/30] via 172.16.10.1
L 10.1.1.1/32 is directly connected, GigabitEthernet0/0/0
S* 0.0.0.0/0 [1/0] via 192.168.254.1

Eşleşmeler

Cevabı ve açıklamayı göster

Cevap

Each routing entry line matches its unique protocol source code and administrative metric: 'D EX' matches external EIGRP (AD 170); 'O IA' matches OSPF inter-area; 'L 10.1.1.1/32' matches the interface local host route; and 'S* 0.0.0.0/0' matches the candidate default static route.
Each entry correctly aligns with its routing protocol source flag and structural component: 'D EX' designates external EIGRP with AD 170; 'O IA' identifies OSPF inter-area routes; 'L' with a /32 mask represents a local interface host route; and 'S*' indicates a static candidate default route.

Adım Adım Çözüm

1
Examine the prefix source code flags at the beginning of each routing entry.
Identify 'D EX' as EIGRP external, 'O IA' as OSPF inter-area, 'L' as local host route, and 'S*' as static candidate default route.
Source codes in Cisco IOS show ip route output define how the route was learned or populated into the RIB.
2
Analyze the Administrative Distance (AD) and metric values inside the brackets [AD/metric].
Verify [170/2578560][170/2578560] for external EIGRP, [110/30][110/30] for OSPF, and [1/0][1/0] for static route.
Administrative Distance rates the trustworthiness of routing information sources.
3
Match each entry to its exact functional component definition.
All four entries correlate to their distinct protocol and structural roles.
Direct mapping of Cisco IOS routing table output identifiers to architectural standards.

Anahtar Kavram

Cisco IOS Routing Table Components and Protocol Source Codes
Soru 1305Soru →

A Cisco router has the following interface operational statuses and IPv4 configurations:

- GigabitEthernet0/0 (192.168.50.1/24192.168.50.1/24): line protocol up, operational state UP
- GigabitEthernet0/1 (192.168.100.1/24192.168.100.1/24): line protocol up, operational state UP
- Loopback 0 (10.254.1.1/3210.254.1.1/32): administratively down, line protocol down
- Loopback 1 (10.200.1.1/3210.200.1.1/32): line protocol down, operational state DOWN
- Loopback 2 (172.16.20.1/32172.16.20.1/32): line protocol up, operational state UP

The OSPFv2 routing process is initialized using `router ospf 1` without an explicitly configured static Router ID via the `router-id` command. What exact IPv4 address will OSPFv2 elect as the active Router ID for this process?

Cevabı ve açıklamayı göster

Cevap: 172.16.20.1

Cevap

172.16.20.1
OSPFv2 uses a strict three-tier precedence logic to select the Router ID: 1) An explicitly configured 'router-id' command, 2) The highest IPv4 address among active (up/up) loopback interfaces, 3) The highest IPv4 address among active (up/up) physical non-loopback interfaces. Here, no explicit Router ID exists. Loopback 0 and Loopback 1 are both down, making Loopback 2 (172.16.20.1) the sole active loopback interface. Because active loopback interfaces take precedence over physical interfaces (such as GigabitEthernet0/1 with 192.168.100.1), 172.16.20.1 is selected as the Router ID.

Adım Adım Çözüm

1
Check for an explicitly configured router ID using the 'router-id' command.
No explicit router ID is configured under 'router ospf 1'.
Explicit configuration takes highest priority in OSPF Router ID selection.
2
Evaluate all active (up/up) loopback interfaces to find the highest IPv4 address.
Loopback 0 and Loopback 1 are inactive (down). Loopback 2 (172.16.20.1) is active (up/up).
OSPF prefers active loopback interfaces over physical interfaces, but inactive loopbacks cannot participate in election.
3
Compare candidate addresses among active loopbacks.
172.16.20.1 is the only active loopback address.
Since Loopback 2 is the only active loopback interface, its IP address (172.16.20.1) is chosen over the physical interface IP addresses.

Anahtar Kavram

OSPFv2 Router ID Selection Priority Logic
Tahmini Süre:1m 30s
Soru 1306Soru →

A network administrator is configuring a backup route on a Cisco IOS router to reach a remote branch office network with the prefix 2001:db8:fedc:9900::/562001:\text{db8}:\text{fedc}:9900::/56. The primary path is currently provided by OSPFv3 with an administrative distance of 110110. The administrator must configure a floating static route using the next-hop router's link-local address fe80::cafe:1fe80::cafe:1 over the local exit interface GigabitEthernet0/0/1GigabitEthernet0/0/1. Which command correctly configures this backup floating static route on the router?

Cevabı ve açıklamayı göster

Cevap: ipv6 route 2001:db8:fedc:9900::/56 GigabitEthernet0/0/1 fe80::cafe:1 120

Cevap

The command 'ipv6 route 2001:db8:fedc:9900::/56 GigabitEthernet0/0/1 fe80::cafe:1 120' correctly configures the backup floating static route.
The correct command syntax for an IPv6 static route using a link-local next-hop requires specifying both the local exit interface and the link-local address of the neighbor. Furthermore, setting the administrative distance to 120120 ensures it is higher than the primary OSPFv3 route's administrative distance of 110110, making it a true floating static route.

Adım Adım Çözüm

1
Determine the required administrative distance for the backup route.
Since OSPFv3 has an administrative distance of 110110, the backup route must have an administrative distance greater than 110110 (such as 120120) to remain floating (inactive until the primary route fails).
Floating static routes rely on a higher administrative distance than the primary routing protocol.
2
Identify the next-hop address requirements for IPv6 static routing.
When using a link-local IPv6 address (fe80::/10fe80::/10) as the next-hop, Cisco IOS mandates a fully specified static route that includes the local exit interface (GigabitEthernet0/0/1GigabitEthernet0/0/1).
Link-local addresses are non-routable and only unique to the specific local link/interface.
3
Construct the exact Cisco IOS syntax.
'ipv6 route 2001:db8:fedc:9900::/56 GigabitEthernet0/0/1 fe80::cafe:1 120'
Syntax follows 'ipv6 route <prefix/mask> <exit-interface> <next-hop-address> [administrative-distance]'.

Anahtar Kavram

Fully Specified IPv6 Floating Static Route Configuration
Soru 1307Soru →

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

text
Gateway of last resort is not set

10.0.0.0/8 is subnetted, 4 subnets
C 10.10.20.0/20 is directly connected, GigabitEthernet0/0
S 10.10.20.0/24 [1/0] via 172.16.1.1
O 10.10.20.128/25 [110/20] via 172.16.2.1
D 10.10.20.144/28 [90/307200] via 172.16.3.1

The router receives an IPv4 packet destined for host 10.10.20.150. Which two statements regarding the router forwarding decision are correct?

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: The router forwards the packet using next-hop IP 172.16.3.1 because the /28 route provides the longest prefix match for the destination address.; Longest prefix match logic is evaluated before comparing administrative distance values across routing protocols.

Cevap

The router forwards the packet to next-hop 172.16.3.1 based on the longest prefix match rule, and prefix length evaluation strictly precedes administrative distance comparisons.
The router applies Longest Prefix Match (LPM) logic first when forwarding traffic. Among the matching entries in the routing table for 10.10.20.150, the subnet 10.10.20.144/28 has 28 matching bits, making it more specific than /25, /24, or /20. Therefore, the router forwards the packet to next-hop 172.16.3.1. Additionally, prefix length comparison occurs before comparing administrative distance or metric parameters.

Adım Adım Çözüm

1
Determine which routes match the destination host IP 10.10.20.150.
The destination matches 10.10.20.0/20, 10.10.20.0/24, 10.10.20.128/25, and 10.10.20.144/28.
All four entries contain the IP address 10.10.20.150 within their subnet boundaries.
2
Compare prefix lengths among all matching routes to find the most specific match.
The /28 prefix (10.10.20.144/28) has 28 matching network bits, which is longer than /25, /24, or /20.
The longest prefix match rule requires routers to choose the route with the highest number of matching leading subnet bits.
3
Select the forwarding path according to the longest prefix match route.
The route via 172.16.3.1 is selected, regardless of the lower administrative distance of the static route.
Administrative Distance (AD) is only used to select between identical routes from different sources, not between routes of different prefix lengths.

Anahtar Kavram

Router Forwarding Decision Logic (Longest Prefix Match precedence)
Soru 1308Soru →

An administrator is verifying IPv6 stateless address autoconfiguration (SLAAC) on an Ethernet interface with a burned-in MAC address of 0011.2233.4455. Which TWO statements accurately describe the standard EUI-64 interface identifier generation process for this interface? (Select two.)

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: The hexadecimal value fffe is inserted into the middle of the 48-bit MAC address between the third and fourth bytes.; The resulting 64-bit interface identifier derived from the MAC address is 0211:22ff:fe33:4455.

Cevap

The correct statements are that the hexadecimal value fffe is inserted into the middle of the MAC address between the third and fourth bytes, and the resulting derived 64-bit interface identifier is 0211:22ff:fe33:4455.
Generating an IPv6 EUI-64 interface identifier from a 48-bit MAC address requires two key steps: inserting the 16-bit hex value fffe into the middle of the MAC address between the 3rd and 4th bytes, and inverting the 7th bit (Universal/Local bit) of the first byte. For MAC 0011.2233.4455, the first byte 0x00 (0000 0000) becomes 0x02 (0000 0010), and inserting fffe produces 0211:22ff:fe33:4455.

Adım Adım Çözüm

1
Split the MAC address into two 24-bit halves and insert fffe into the midpoint.
Splitting 0011.2233.4455 into 0011.22 and 33.4455 and inserting fffe yields 0011:22ff:fe33:4455.
IEEE EUI-64 expansion converts a 48-bit MAC address into a 64-bit interface identifier by inserting the 16-bit pattern fffe in the middle.
2
Invert the 7th bit (Universal/Local bit) of the first byte.
First byte 0x00 binary is 0000 0000. Inverting the 7th bit gives 0000 0010, which is 0x02.
IPv6 modifies the 7th bit of the OUI to represent universal scope when derived via EUI-64.
3
Combine the inverted first byte with the rest of the expanded interface identifier.
The final 64-bit interface identifier is 0211:22ff:fe33:4455.
Replacing 00 with 02 in the initial 16-bit block forms the complete, valid EUI-64 host portion.

Anahtar Kavram

EUI-64 Interface Identifier Derivation
Soru 1309Soru →

Two directly connected Cisco routers are configured to run OSPFv2 on their connecting GigabitEthernet interfaces. Interface GigabitEthernet0/0 on Router A is placed in OSPF Area 0, while interface GigabitEthernet0/0 on Router B is placed in OSPF Area 1. Which statement correctly describes the result of this configuration?

Cevabı ve açıklamayı göster

Cevap: The routers will fail to form an OSPF neighbor adjacency.

Cevap

The routers will fail to form an OSPF neighbor adjacency.
For two OSPFv2 routers to establish a neighbor adjacency, key fields in their Hello packets must match. These mandatory matching parameters include the Area ID, Subnet Mask, Hello and Dead intervals, and Authentication fields. Because Router A is configured in Area 0 and Router B is configured in Area 1 on the connecting segment, the routers will discard each other's Hello packets and fail to form an adjacency.

Adım Adım Çözüm

1
Identify the OSPF neighbor requirements for directly connected interfaces.
Neighbor adjacencies require identical Hello/Dead timers, Area ID, Subnet Mask, and MTU settings in Hello packets.
OSPF validation rules state that any mismatch in essential Hello packet fields will cause the router to drop incoming Hello packets.
2
Compare the configured OSPF Area IDs of Router A and Router B.
Router A is in Area 0 and Router B is in Area 1.
Because the Area IDs differ, Hello packet validation fails upon receipt.
3
Determine the resulting neighbor state.
No neighbor adjacency is formed and the routers remain in the Down state.
Without matching parameters, OSPF neighbor relationship negotiation cannot proceed.

Anahtar Kavram

OSPFv2 Neighbor Adjacency Requirements
Tahmini Süre:45s
Soru 1310Soru →

A network administrator configures Port Address Translation (PAT) on a Cisco IOS router to allow hosts on the 192.168.10.0/24192.168.10.0/24 internal subnet to access external servers using a dynamic NAT pool. After applying the configuration, only the first host to send traffic successfully establishes an outbound connection. All subsequent internal hosts fail to reach external destinations.

The router configuration is as follows:
text
ip nat pool EDGE_POOL 198.51.100.10 198.51.100.10 netmask 255.255.255.252
access-list 105 permit ip 192.168.10.0 0.0.0.255 any
ip nat inside source list 105 pool EDGE_POOL
!
interface GigabitEthernet0/0
ip address 192.168.10.1 255.255.255.0
ip nat inside
!
interface GigabitEthernet0/1
ip address 198.51.100.9 255.255.255.252
ip nat outside

Which modification to the router configuration will resolve the connectivity failure for all remaining internal hosts?

Cevabı ve açıklamayı göster

Cevap: Append the overload keyword to the ip nat inside source list 105 pool EDGE_POOL command.

Cevap

Appending the overload keyword to the ip nat inside source statement enables Port Address Translation (PAT), allowing multiple inside local addresses to share the single IP address configured in the pool.
The correct response identifies that the 'overload' keyword is missing from the NAT translation statement. When configuring dynamic NAT with a pool containing a single IP address, omitting 'overload' causes the router to perform standard dynamic 1-to-1 NAT rather than PAT. The first internal host consumes the single IP address in the pool (198.51.100.10198.51.100.10). All subsequent hosts fail to obtain a translation entry because the pool is exhausted. Appending 'overload' enables port multiplexing, allowing up to ~65,000 simultaneous connections to share the single pool address.

Adım Adım Çözüm

1
Analyze the existing dynamic NAT pool configuration.
The command 'ip nat pool EDGE_POOL 198.51.100.10 198.51.100.10 netmask 255.255.255.252' defines a pool containing exactly one usable public IP address (198.51.100.10198.51.100.10).
Understanding pool size identifies how many simultaneous dynamic 1-to-1 translations can occur.
2
Evaluate the translation command 'ip nat inside source list 105 pool EDGE_POOL'.
Without the 'overload' keyword, Cisco IOS performs dynamic 1-to-1 NAT instead of Port Address Translation (PAT).
Dynamic 1-to-1 NAT allocates one public IP per active internal host. Once the single IP address in EDGE_POOL is allocated to the first host, the pool is exhausted and subsequent host requests are dropped.
3
Determine the required command modification to allow port multiplexing.
Appending 'overload' to the command ('ip nat inside source list 105 pool EDGE_POOL overload') enables PAT, multiplexing multiple internal hosts across different source port numbers on the single public IP 198.51.100.10198.51.100.10.
PAT allows thousands of concurrent translations on a single IP address by leveraging transport-layer port tracking.

Anahtar Kavram

Port Address Translation (PAT / NAT Overload) using dynamic IP pools
Tahmini Süre:2m 0s
Soru 1311Soru →

A network engineer is allocated the IPv4 address block 172.16.64.0/21172.16.64.0/21 to provision point-to-point WAN links between branch offices. Each link is configured with a /30/30 subnet mask to conserve address space. What is the maximum number of /30/30 subnets that can be created from this /21/21 block?

Cevabı ve açıklamayı göster

Cevap: 512

Cevap

The maximum number of /30/30 subnets that can be created is 512.
To calculate the total number of subnets created, subtract the starting prefix length from the target prefix length: 30−21=930 - 21 = 9 borrowed subnet bits. Applying the formula 2n2^n yields 29=5122^9 = 512 subnets.

Adım Adım Çözüm

1
Calculate the number of borrowed subnet bits.
9 subnet bits borrowed (30−21=930 - 21 = 9).
Subnetting a /21/21 network block into /30/30 subnets requires extending the prefix by 9 bits.
2
Calculate the total number of available subnets.
512 subnets (29=5122^9 = 512).
Each borrowed bit doubles the number of created subnets, yielding 29=5122^9 = 512 total subnets.

Anahtar Kavram

Calculating the total number of subnets created by borrowing host bits from an IPv4 CIDR prefix.
Soru 1312Soru →

An enterprise router displays the following output from the `show ip route` command:

text
Gateway of last resort is not set

172.20.0.0/16 is subnetted, 4 subnets
S 172.20.0.0/16 [1/0] via 10.10.10.1
O 172.20.8.0/21 [110/65] via 10.10.20.1, 00:08:12, GigabitEthernet0/0/1
D 172.20.12.0/23 [90/2578560] via 10.10.30.1, 00:22:45, GigabitEthernet0/0/2
O 172.20.13.0/25 [110/110] via 10.10.40.1, 00:03:50, GigabitEthernet0/0/3

The router receives a packet with a destination IPv4 address of 172.20.13.45172.20.13.45. Based on the routing table components and forwarding logic, which next-hop IP address and outbound interface will the router select to forward this packet?

Cevabı ve açıklamayı göster

Cevap: 10.10.40.1 via GigabitEthernet0/0/3

Cevap

Next-hop 10.10.40.1 via GigabitEthernet0/0/3
When a router receives an IP packet, it evaluates all matching prefix entries in its routing table and selects the entry with the longest prefix length (most specific mask). The destination address 172.20.13.45 falls within the range of 172.20.13.0/25 (172.20.13.0 to 172.20.13.127), which has a /25 prefix length. Because /25 is longer and more specific than /23, /21, or /16, the router forwards the packet to next-hop 10.10.40.1 out interface GigabitEthernet0/0/3 regardless of Administrative Distance.

Adım Adım Çözüm

1
Identify all candidate routes that match the destination IP address 172.20.13.45
Candidate routes are 172.20.0.0/16, 172.20.8.0/21 (range 172.20.8.0 - 172.20.15.255), 172.20.12.0/23 (range 172.20.12.0 - 172.20.13.255), and 172.20.13.0/25 (range 172.20.13.0 - 172.20.13.127). All 4 entries encompass the destination address.
Before comparing route metrics or administrative distances, the router determines which routing table prefixes physically include the destination IP.
2
Apply the Longest Prefix Match (LPM) rule across all candidate matching entries
Prefix lengths are /16, /21, /23, and /25. The longest and most specific prefix mask is /25 (172.20.13.0/25).
The router forwarding decision logic always prioritizes the most specific prefix (highest prefix length value) over Administrative Distance or metric.
3
Determine the next-hop IP and exit interface associated with the winning route prefix
The route for 172.20.13.0/25 specifies next-hop 10.10.40.1 via interface GigabitEthernet0/0/3.
Packet forwarding parameters are derived directly from the winning prefix entry in the Routing Information Base.

Anahtar Kavram

Longest Prefix Match (LPM) resolution in Cisco routing tables
Soru 1313Soru →

A Cisco router receives an IPv4 packet on an ingress interface destined for a remote destination host. In what exact sequence does the router execute its internal forwarding decision and frame processing logic from packet arrival to egress transmission?

Öğeleri doğru sıraya koymak için sürükleyin

Cevabı ve açıklamayı göster

Cevap

The correct sequential order of the Cisco router forwarding decision logic is: First, de-encapsulate the frame, verify IP header integrity, and extract the destination IPv4 address. Second, search the IPv4 routing table for all matching prefix entries. Third, select the single best route entry strictly using Longest Prefix Match (LPM). Fourth, identify the egress exit interface and next-hop IPv4 address from the selected route. Fifth, resolve the next-hop Layer 2 MAC address, decrement TTL, rewrite the Layer 2 header, and transmit the frame.
The correct operational sequence begins when an IPv4 packet arrives at a router interface. The router first strips the ingress Layer 2 header, validates the IP checksum/TTL, and extracts the destination IP address. Next, it queries the IPv4 routing table for all matching subnets. It applies Longest Prefix Match (LPM) precedence to choose the candidate route with the longest subnet mask. After selecting the winning route, it extracts the next-hop IP address and outbound interface. Finally, it uses ARP to find the next-hop MAC address, decrements the TTL by 1, encapsulates the packet in a new Layer 2 header, and transmits it out the exit interface.

Adım Adım Çözüm

1
Frame De-encapsulation and Header Validation
Layer 2 frame header is stripped, and the destination IPv4 address is extracted from the IPv4 header.
The router must inspect the Layer 3 destination header to determine where the packet needs to be routed.
2
Routing Table Candidate Search
A set of candidate subnet routes that cover the destination IPv4 address is identified.
All active routes in the Routing Information Base (RIB) or Forwarding Information Base (FIB) are scanned for binary subnet matching.
3
Longest Prefix Match (LPM) Evaluation
The route with the highest number of matching network bits (longest prefix mask) is selected.
Longest Prefix Match is the absolute primary criteria for route selection in IP routing, overriding Administrative Distance and routing metrics.
4
Forwarding Path Extraction
The destination next-hop IPv4 address and outgoing physical/logical exit interface are determined.
The router needs the exact forwarding instructions specified inside the winning routing table entry.
5
Layer 2 Encapsulation and Egress Transmission
The packet TTL is decremented, ARP cache provides the next-hop MAC address, a new Layer 2 frame is encapsulated, and the frame is transmitted.
The router must rewrite the Layer 2 header for the next-hop broadcast domain before transmitting the packet on the wire.

Anahtar Kavram

Router Forwarding Decision Logic and Longest Prefix Match
Soru 1314Soru →

A network administrator is creating a new WLAN on a Cisco Wireless LAN Controller (WLC) using the web GUI. The WLAN must support 802.1X authentication using a centralized RADIUS server and allow the RADIUS server to dynamically assign VLANs to clients upon successful authentication. Which TWO configuration settings must be enabled on the WLC GUI for this WLAN? (Select TWO.)

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: Under the Security > Layer 2 tab, select WPA2/WPA3 parameters and set Key Management to 802.1X.; Under the Advanced tab, check the Allow AAA Override checkbox.

Cevap

To configure 802.1X enterprise authentication with dynamic VLAN assignment via RADIUS, the administrator must configure 802.1X under the Security > Layer 2 tab and enable 'Allow AAA Override' under the Advanced tab.
To support RADIUS-based 802.1X authentication, 802.1X Key Management must be selected under the Security > Layer 2 tab. To allow the RADIUS server to dynamically assign clients to specific VLANs based on user credentials, the 'Allow AAA Override' setting must be explicitly enabled under the Advanced tab.

Adım Adım Çözüm

1
Configure Layer 2 Security for 802.1X Enterprise Authentication.
Navigating to Security > Layer 2 allows selecting WPA2/WPA3 and setting Authentication Key Management (AKM) to 802.1X.
802.1X integrates the WLC with a RADIUS server for EAP-based client authentication.
2
Enable AAA Override for Dynamic VLAN Assignment.
Navigating to the Advanced tab and selecting 'Allow AAA Override' permits the WLC to override the default WLAN interface.
Without AAA Override, VLAN assignment attributes sent by RADIUS are ignored by the controller.

Anahtar Kavram

WLC GUI WLAN Security and AAA Override Configuration
Soru 1315Soru →

A network administrator is deploying Link Layer Discovery Protocol (LLDP) across a multi-vendor switch infrastructure. Which two statements correctly describe the default operational characteristics and CLI configuration of LLDP on Cisco Catalyst switches compared to CDP? (Select TWO.)

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: LLDP is globally disabled by default on Cisco Catalyst switches and requires the global configuration command `lldp run` to be enabled.; LLDP allows granular, independent control of message transmission and reception on specific interfaces using `lldp transmit` and `lldp receive` interface commands.

Cevap

LLDP is globally disabled by default on Cisco Catalyst switches requiring `lldp run`, and LLDP provides independent control over transmit and receive states per interface using `lldp transmit` and `lldp receive`.
The correct choices accurately state that LLDP is disabled globally by default on Cisco Catalyst switches (requiring `lldp run` in global configuration mode) and that LLDP supports independent interface-level transmit and receive controls (`lldp transmit` / `lldp receive`).

Adım Adım Çözüm

1
Analyze global protocol state defaults
Cisco Catalyst switches ship with CDP globally enabled by default (`cdp run`), whereas LLDP is globally disabled by default and requires `lldp run` to start discovery processes.
CDP is Cisco proprietary and enabled by default, while IEEE 802.1AB LLDP must be explicitly activated globally on Cisco Catalyst platforms.
2
Evaluate interface-level control capabilities
LLDP allows separate commands for sending (`lldp transmit`) and listening (`lldp receive`), providing granular directional control that CDP (`cdp enable`) does not offer.
LLDP's standard specification allows interfaces to act as receive-only, transmit-only, or bidirectional discovery nodes.
3
Verify protocol default timers
CDP uses a 60-second advertisement interval and a 180-second holdtime. LLDP on Cisco devices uses a 30-second advertisement interval and a 120-second holdtime.
Confusing LLDP default timers with CDP default timers is a common misconception when analyzing discovery protocol operational states.

Anahtar Kavram

CDP vs LLDP Operational Differences and CLI Configuration
Soru 1316Soru →

A network engineer views the following line in a Cisco router's IPv4 routing table:

`O 10.50.4.0/24 [110/65] via 172.16.1.2, 00:18:32, GigabitEthernet0/1`

What component of the routing table entry is represented by the value `110` inside the brackets?

Cevabı ve açıklamayı göster

Cevap: Administrative distance

Cevap

The value 110 represents the administrative distance of the routing protocol.
In Cisco routing table entries, bracketed notation follows the format `[Administrative Distance / Metric]`. The value `110` is the default Administrative Distance for OSPF routes, measuring the trustworthiness of the route source.

Adım Adım Çözüm

1
Analyze the bracketed values in the routing table entry: `[110/65]`.
Identify that Cisco IOS routing entries format protocol trust and path cost as `[Administrative Distance / Metric]`.
Understanding standard Cisco CLI routing table component syntax.
2
Evaluate the first position inside the bracket.
The first number `110` corresponds to Administrative Distance, which is the default trustworthiness value for OSPF routes.
Distinguish Administrative Distance from the route metric.

Anahtar Kavram

Interpretation of Routing Table Bracketed Syntax [AD/Metric]
Soru 1317Soru →

A network administrator is configuring static routing on router HQ to forward traffic bound for remote subnet 2001:db8:feed:10::/642001:\text{db8}:\text{feed}:10::/64. The outbound connection uses a point-to-point serial-like Ethernet link where the remote router interface uses the link-local address fe80::21a:2bff:fe3c:4d5e\text{fe80}::21a:2bff:\text{fe3c}:4d5e on interface GigabitEthernet0/0/1. The primary path must use an administrative distance of 11, but if configured using a link-local next-hop address without an outbound interface specified, Cisco IOS will reject the command. Which command correctly establishes a fully-specified IPv6 static route for this destination using the link-local next hop?

Cevabı ve açıklamayı göster

Cevap: ipv6 route 2001:db8:feed:10::/64 GigabitEthernet0/0/1 fe80::21a:2bff:fe3c:4d5e

Cevap

The correct command is 'ipv6 route 2001:db8:feed:10::/64 GigabitEthernet0/0/1 fe80::21a:2bff:fe3c:4d5e', which specifies both the exit interface and the link-local address for a fully-specified IPv6 static route.
When configuring an IPv6 static route with a link-local address as the next hop, Cisco IOS requires a fully-specified static route syntax: 'ipv6 route <destination-prefix/prefix-length> <exit-interface> <link-local-next-hop>'. Since link-local addresses (FE80::/10) are only unique on the local link, specifying GigabitEthernet0/0/1 clarifies which link to transmit packets across.

Adım Adım Çözüm

1
Identify the destination prefix and prefix length.
The target prefix is 2001:db8:feed:10::/642001:\text{db8}:\text{feed}:10::/64.
The prefix must be explicitly identified at the start of the Cisco IOS IPv6 static route command syntax.
2
Determine the next-hop mechanism requirements for link-local addresses.
When a link-local address (fe80::…\text{fe80}::\dots) is used as a next hop, Cisco IOS requires specifying the local exit interface alongside the link-local address.
Link-local addresses are scope-limited to a single link, so the router needs the exit interface identifier to know which link to send the packet on.
3
Construct the exact syntax for a fully-specified route.
The syntax is 'ipv6 route <prefix/length> <exit-interface> <link-local-address>'.
This syntax creates a valid fully-specified IPv6 static route with the default administrative distance of 1.

Anahtar Kavram

IPv6 Fully-Specified Static Routing with Link-Local Next-Hop
Soru 1318Soru →

A Cisco router is configured to run OSPFv2 without an explicitly set `router-id` under the OSPF process. The current interface IP address configurations and states are as follows:

- Loopback0: 10.10.10.10/3210.10.10.10/32 (Administratively Down)
- Loopback1: 172.16.1.1/24172.16.1.1/24 (Up / Up)
- Loopback2: 192.168.100.1/24192.168.100.1/24 (Up / Up)
- GigabitEthernet0/0: 10.200.200.1/3010.200.200.1/30 (Up / Up)

What IP address will OSPF select as the router ID when the OSPF process initializes?

Cevabı ve açıklamayı göster

Cevap: 192.168.100.1

Cevap

192.168.100.1
OSPFv2 uses a strict order of preference to establish its Router ID: 1) Explicitly configured `router-id` command, 2) Highest IP address among active (Up/Up) loopback interfaces, 3) Highest IP address among active physical interfaces. In this scenario, no manual router ID exists. Loopback0 is down so it is excluded. Loopback1 (172.16.1.1172.16.1.1) and Loopback2 (192.168.100.1192.168.100.1) are both active loopback interfaces. OSPF selects 192.168.100.1192.168.100.1 because it is the highest active loopback IP address.

Adım Adım Çözüm

1
Check for an explicitly configured OSPF router ID
No manual OSPF router ID command is configured.
Explicit configuration takes precedence over all automatic election rules.
2
Evaluate all active (Up/Up) loopback interfaces
Loopback1 (172.16.1.1172.16.1.1) and Loopback2 (192.168.100.1192.168.100.1) are active. Loopback0 (10.10.10.1010.10.10.10) is administratively down and ignored.
OSPF election logic prioritizes active loopback interfaces over physical interfaces.
3
Compare IP addresses of active loopbacks to select the highest value
Between 172.16.1.1172.16.1.1 and 192.168.100.1192.168.100.1, 192.168.100.1192.168.100.1 is numerically higher.
OSPF selects the highest IP address among operational loopback interfaces.

Anahtar Kavram

OSPFv2 Router ID Selection Precedence
Tahmini Süre:1m 0s
Soru 1319Soru →

A network administrator executes the `show ipv6 interface gigabitethernet0/0/0` command on a Cisco IOS router. The interface has a burned-in MAC address of `3c4a.9211.2233` and is configured to generate its link-local address dynamically using the IEEE EUI-64 process. Which IPv6 link-local address will be assigned to this interface?

Cevabı ve açıklamayı göster

Cevap: fe80::3e4a:92ff:fe11:2233

Cevap

fe80::3e4a:92ff:fe11:2233
IPv6 link-local addresses use the FE80::/10 prefix. When generating a 64-bit interface identifier using EUI-64 from a 48-bit MAC address (3c4a.9211.2233), FFFE is inserted between the 3rd and 4th bytes (after 92), and the 7th bit (Universal/Local bit) of the first byte (0x3C = 0011 1100) is inverted to 1 (0x3E = 0011 1110). Combining FE80:: with 3e4a:92ff:fe11:2233 produces fe80::3e4a:92ff:fe11:2233.

Adım Adım Çözüm

1
Identify the IPv6 address scope prefix required for interface link-local configuration.
Link-local addresses always begin with the prefix fe80::/10.
IPv6 interfaces automatically assign a link-local address in the fe80::/10 range when IPv6 is enabled.
2
Insert the 16-bit hex value FFFE into the middle of the 48-bit MAC address (3c4a.9211.2233).
Splitting 3c4a.92 and 11.2233 yields 3c4a:92ff:fe11:2233.
EUI-64 expands a 48-bit MAC address into a 64-bit interface identifier by inserting FFFE (1111 1111 1111 1110) in the middle.
3
Invert the 7th bit (Universal/Local bit) of the first byte of the MAC address.
First byte 0x3C in binary is 0011 1100. Inverting the 7th bit (from left) gives 0011 1110, which is 0x3E in hexadecimal.
IEEE EUI-64 rules dictate that the 7th bit of the first byte must be inverted (0 for globally unique/burned-in MACs becomes 1 to indicate local scope in the EUI-64 format).
4
Combine the link-local prefix with the resulting 64-bit EUI-64 interface identifier.
fe80::3e4a:92ff:fe11:2233
Concatenating the prefix fe80:: and the interface identifier 3e4a:92ff:fe11:2233 forms the final IPv6 link-local address.

Anahtar Kavram

EUI-64 Interface Identifier Derivation and Link-Local Address Formation
Soru 1320Soru →

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

text
Gateway of last resort is not set

172.16.0.0/16 is variably subnetted, 4 subnets, 4 masks
O 172.16.10.0/24 [110/20] via 192.168.1.1, 00:05:12, GigabitEthernet0/0
D 172.16.10.0/25 [90/307200] via 192.168.1.2, 00:12:44, GigabitEthernet0/1
S 172.16.10.128/26 [1/0] via 192.168.1.3, 01:15:00, GigabitEthernet0/2
C 172.16.10.128/30 is directly connected, GigabitEthernet0/3

The router receives a packet destined for IP address 172.16.10.130. Which interface or next-hop IP address will the router select to forward this packet?

Cevabı ve açıklamayı göster

Cevap: GigabitEthernet0/3

Cevap

The router will forward the packet out interface GigabitEthernet0/3 because the directly connected route 172.16.10.128/30 provides the longest prefix match for destination 172.16.10.130.
The destination host 172.16.10.130 matches three entries in the routing table: 172.16.10.0/24, 172.16.10.128/26, and 172.16.10.128/30. According to Cisco router forwarding logic, the router evaluates Longest Prefix Match (LPM) first. Because /30 has 30 matching network bits, it is the most specific route and will be used to forward the packet out GigabitEthernet0/3.

Adım Adım Çözüm

1
Evaluate all routes in the routing table against the destination IP address 172.16.10.130 to identify matching subnets.
Matching subnets are 172.16.10.0/24, 172.16.10.128/26, and 172.16.10.128/30. The subnet 172.16.10.0/25 covers addresses .0 through .127 and is not a match.
Routing lookup requires identifying all candidate routes that encompass the target destination host address.
2
Compare the prefix lengths of all matching candidate routes.
Prefix lengths are /24, /26, and /30. The longest prefix length is /30.
Cisco routers use the Longest Prefix Match (LPM) rule as the primary criteria for forwarding decisions before considering Administrative Distance.
3
Select the route corresponding to the longest prefix match.
The route 172.16.10.128/30 is selected, which directs traffic to the directly connected interface GigabitEthernet0/3.
The most specific route (/30) always wins the forwarding decision regardless of administrative distance or metric.

Anahtar Kavram

Longest Prefix Match (LPM) is the fundamental rule routers use to select a route from the routing table when forwarding a packet. The router selects the route with the highest number of matching network bits (longest prefix length), regardless of administrative distance.
Tahmini Süre:1m 30s
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