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Tüm alıştırma soruları

1987 soru

Tüm türler1,987Çoktan seçmeli1,020Çoklu seçim452Sayısal18Eşleştirme229Sıralama203Boşluk doldurma22Kısa cevap43
Soru 181Soru →

Two Cisco routers, R10 and R20, are directly connected via their GigabitEthernet0/1 interfaces. OSPFv2 is configured on both routers, but running the command 'show ip ospf neighbor' on R10 reveals no neighbor entries. IP ping between the directly connected interface addresses succeeds. Which interface configuration difference between R10 and R20 will prevent the routers from even forming an OSPF Init state?

Cevabı ve açıklamayı göster

Cevap: Mismatched OSPF Area IDs on the interconnecting interfaces

Cevap

Mismatched OSPF Area IDs on the interconnecting interfaces prevent the routers from establishing an OSPF neighbor relationship.
OSPF routers require several parameters to match in incoming Hello packets before creating a neighbor entry. Because Area ID is part of the Hello header validation, a mismatch causes the router to drop the Hello packet, resulting in no neighbor entry (no Init state).

Adım Adım Çözüm

1
Analyze OSPF Hello packet primary validation requirements.
For two OSPFv2 routers to establish a neighbor relationship, fields in the Hello packet must match across the link: Area ID, Subnet Mask, Hello/Dead Timers, and Authentication credentials.
If any primary parameter such as Area ID or Subnet Mask mismatches, the router ignores the incoming Hello packet entirely.
2
Evaluate the impact of an Area ID mismatch.
When R10 receives a Hello packet with a different Area ID than what is configured on its interface, it discards the packet, preventing any neighbor entry from appearing in 'show ip ospf neighbor'.
Area membership must strictly match for interfaces sharing a common network segment.
3
Contrast with MTU, Process ID, and DR Priority behavior.
Process IDs are local; DR priorities affect election roles only; MTU mismatches allow neighbor discovery up to ExStart state.
Distinguishing between parameters that break Hello discovery versus parameters that stall database synchronization is key to OSPF troubleshooting.

Anahtar Kavram

OSPFv2 Neighbor Adjacency Requirements and Hello Packet Matching
Soru 182Soru →

Which Cisco IOS command configures an IPv4 floating static route to destination network 172.20.0.0/16172.20.0.0/16 through next-hop IP address 10.0.0.210.0.0.2 so that it serves as a backup to a primary route learned via Internal EIGRP (Administrative Distance of 9090)?

Cevabı ve açıklamayı göster

Cevap: ip route 172.20.0.0 255.255.0.0 10.0.0.2 130

Cevap

ip route 172.20.0.0 255.255.0.0 10.0.0.2 130 correctly configures the backup floating static route with an administrative distance higher than the primary EIGRP route.
The command correctly uses the standard subnet mask format for destination network 172.20.0.0/16 and sets an administrative distance of 130. Because 130 is greater than EIGRP's administrative distance of 90, the router keeps this static route inactive in reserve until the primary EIGRP route is lost.

Adım Adım Çözüm

1
Identify the proper Cisco IOS static route command syntax.
Syntax is: ip route <destination-prefix> <subnet-mask> <next-hop-ip> [distance]
Cisco IOS requires a subnet mask (255.255.0.0) rather than a wildcard mask.
2
Determine the required Administrative Distance (AD) for a floating static route.
The AD must be greater than 90 (the AD of Internal EIGRP).
Routes with lower AD values are preferred in the routing table. To act as a backup, the static route must have a higher AD so it is only installed when the primary route goes down.
3
Select the command matching both syntax and AD requirements.
ip route 172.20.0.0 255.255.0.0 10.0.0.2 130
130 is greater than 90 and the syntax uses the valid subnet mask format.

Anahtar Kavram

IPv4 Floating Static Route Configuration and Administrative Distance Selection
Tahmini Süre:45s
Soru 183Soru →

To permit multiple internal private hosts to share the single public IPv4 address assigned to the GigabitEthernet0/0/0 WAN interface, which Cisco IOS command correctly implements Port Address Translation (PAT) for traffic permitted by Access Control List 15?

Cevabı ve açıklamayı göster

Cevap: ip nat inside source list 15 interface GigabitEthernet0/0/0 overload

Cevap

The command 'ip nat inside source list 15 interface GigabitEthernet0/0/0 overload' correctly enables Port Address Translation (PAT).
The command specifying 'ip nat inside source list 15 interface GigabitEthernet0/0/0 overload' correctly binds the access list to the egress interface and appends the 'overload' keyword, which enables Port Address Translation (PAT) so multiple internal devices can share a single public IPv4 address.

Adım Adım Çözüm

1
Identify the requirement for Port Address Translation (PAT)
Multiple internal hosts sharing a single public interface IP requires PAT (overload).
PAT uses unique source port numbers to track connections for multiple internal hosts behind a single IP address.
2
Formulate the Cisco IOS PAT interface command syntax
The correct command structure is 'ip nat inside source list <acl> interface <interface> overload'.
The 'inside source list' parameter references the internal traffic ACL, 'interface' specifies the egress IP source, and 'overload' enables port multiplexing.

Anahtar Kavram

Port Address Translation (PAT) Interface Overload Configuration
Soru 184Soru →

A network administrator is provisioning a new VLAN for an enterprise VoIP deployment that requires support for up to 500500 usable IP phones. The network block allocated for this subnetwork starts at 172.25.100.0172.25.100.0. To accommodate the required number of host devices while minimizing unallocated address space, what is the broadcast address of this subnetwork?

Cevabı ve açıklamayı göster

Cevap: 172.25.101.255172.25.101.255

Cevap

The broadcast address of the subnetwork is 172.25.101.255172.25.101.255.
To support 500 usable host devices, 9 host bits are required (29−2=5102^9 - 2 = 510 hosts). This yields a prefix length of /23/23 (32−9=2332 - 9 = 23). Starting at network address 172.25.100.0172.25.100.0, a /23/23 subnet encompasses the range 172.25.100.0172.25.100.0 through 172.25.101.255172.25.101.255, making 172.25.101.255172.25.101.255 the correct broadcast address.

Adım Adım Çözüm

1
Determine the minimum number of host bits required.
n=9n = 9 host bits because 29−2=510≥5002^9 - 2 = 510 \ge 500.
A host bit count of 8 (28−2=2542^8 - 2 = 254) is insufficient for 500 hosts.
2
Calculate the prefix length and subnet mask.
Prefix length is /23/23 (32−9=2332 - 9 = 23), corresponding to subnet mask 255.255.252.0255.255.252.0.
Subtracting 9 host bits from 32 total bits yields a 23-bit network prefix.
3
Determine the subnet boundaries for 172.25.100.0/23172.25.100.0/23.
Network address is 172.25.100.0172.25.100.0, usable host range is 172.25.100.1172.25.100.1 to 172.25.101.254172.25.101.254, and the broadcast address is 172.25.101.255172.25.101.255.
The block size in the third octet for a /23 subnet is 256−252=4256 - 252 = 4 or 21=22^1 = 2, spanning 172.25.100.0172.25.100.0 through 172.25.101.255172.25.101.255.

Anahtar Kavram

Subnet Mask Derivation and Broadcast Address Calculation
Tahmini Süre:1m 30s
Soru 185Soru →

A network engineer needs to configure a floating static route on a Cisco router to serve as a backup path for the destination network 172.28.32.0/21172.28.32.0/21. The primary path to this network is currently learned via OSPF, which operates with an Administrative Distance of 110. Which Cisco IOS command correctly configures the floating static route so that it only enters the routing table if the primary OSPF route fails?

Cevabı ve açıklamayı göster

Cevap: ip route 172.28.32.0 255.255.248.0 10.200.1.2 120

Cevap

ip route 172.28.32.0 255.255.248.0 10.200.1.2 120
The correct command specifies 'ip route 172.28.32.0 255.255.248.0 10.200.1.2 120'. A /21 subnet mask corresponds to 255.255.248.0. Since the primary route is learned via OSPF with an Administrative Distance (AD) of 110, a backup (floating) static route must be configured with an AD greater than 110 (such as 120). This keeps the route out of the routing table until the primary OSPF route is withdrawn.

Adım Adım Çözüm

1
Determine the subnet mask representation for the prefix /21
A /21 network mask consists of 21 contiguous binary 1s: 11111111.11111111.11111000.00000000, which evaluates to 255.255.248.0 in dotted-decimal notation.
Cisco IOS IPv4 static route command syntax requires the netmask parameter in dotted-decimal format.
2
Identify the administrative distance (AD) of the primary dynamic routing protocol
OSPF has a default Administrative Distance of 110.
To create a floating static route, the static route must have an AD strictly greater than the primary route protocol's AD.
3
Select an Administrative Distance value for the floating static route
An AD of 120 is higher than 110, ensuring the route stays inactive in the routing table until OSPF fails.
Lower AD values are preferred by Cisco IOS. Setting the AD to 120 keeps the static route inactive (floating) while OSPF is active.
4
Construct the full Cisco IOS static route command
'ip route 172.28.32.0 255.255.248.0 10.200.1.2 120'
Matches the syntax: 'ip route <prefix> <mask> <next-hop-ip> [distance]'.

Anahtar Kavram

IPv4 Floating Static Route Configuration and Administrative Distance Selection
Soru 186Soru →

A network engineer is reconfiguring interface GigabitEthernet0/5 on a Cisco Catalyst switch. The port was previously configured as an 802.1Q trunk, but it must now be assigned to connect an end-user workstation in VLAN 45. Which two Cisco IOS configuration commands are required on the interface to complete this configuration?

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: switchport mode access; switchport access vlan 45

Cevap

The commands required under interface configuration mode are 'switchport mode access' to define the operational mode as access, and 'switchport access vlan 45' to statically assign the port to VLAN 45.
To transition an interface from a trunk link to a dedicated workstation access port in VLAN 45, the engineer must explicitly set the interface mode using 'switchport mode access' and associate the port with the target VLAN using 'switchport access vlan 45'.

Adım Adım Çözüm

1
Set interface mode to access
Interface is explicitly configured as an access port
Executing 'switchport mode access' disables dynamic negotiation for trunking and forces access mode operation.
2
Assign the access VLAN ID
Untagged traffic on this interface is assigned to VLAN 45
Executing 'switchport access vlan 45' associates incoming untagged frames on the port with VLAN 45.

Anahtar Kavram

Configuring Cisco IOS L2 switchports as access ports and assigning static VLAN membership.
Tahmini Süre:1m 30s
Soru 187Soru →

A network administrator is setting up Port Address Translation (PAT) on a Cisco IOS router using a public address pool named `PAT_POOL` and Access Control List `5`. Which two commands are required to correctly establish PAT and configure the LAN interface to participate in address translation? (Select two.)

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: ip nat inside source list 5 pool PAT_POOL overload; ip nat inside

Cevap

The two required commands are 'ip nat inside source list 5 pool PAT_POOL overload' entered in global configuration mode and 'ip nat inside' entered under the LAN interface configuration mode.
Configuring Port Address Translation (PAT) with an IP pool requires appending the 'overload' parameter to the global 'ip nat inside source list' command. Additionally, the internal interface connected to the local network must be identified with the interface-level command 'ip nat inside'.

Adım Adım Çözüm

1
Identify the global configuration command for pool-based PAT
Determine that 'ip nat inside source list 5 pool PAT_POOL overload' is required to map inside local hosts matching ACL 5 to the PAT_POOL while enabling port overloading.
The 'overload' keyword allows multiple private internal IP addresses to share public IP addresses in the pool by tracking unique TCP/UDP port numbers.
2
Identify the interface configuration command for internal boundary identification
Select 'ip nat inside' on the LAN interface.
Cisco IOS routers require explicit designation of NAT boundaries to determine where packet translation takes place.

Anahtar Kavram

Inside Source Port Address Translation (PAT) configuration requiring the overload keyword and inside interface designation.
Soru 188Soru →

A Cisco router is configured to run OSPFv2 without an explicitly configured manual router ID. The router has the following active interface IP addresses:

- Loopback0: 10.10.1.1/3210.10.1.1/32
- Loopback1: 10.20.1.1/3210.20.1.1/32
- GigabitEthernet0/0: 192.168.1.254/24192.168.1.254/24
- GigabitEthernet0/1: 172.16.50.1/24172.16.50.1/24

Which IP address will OSPFv2 select as the router ID?

Cevabı ve açıklamayı göster

Cevap: 10.20.1.110.20.1.1

Cevap

The OSPFv2 router ID selected by the router is 10.20.1.110.20.1.1.
In OSPFv2, when a router ID is not manually specified with the 'router-id' command, the router selects the highest IPv4 address among all active loopback interfaces. Comparing Loopback0 (10.10.1.110.10.1.1) and Loopback1 (10.20.1.110.20.1.1), 10.20.1.110.20.1.1 is the highest loopback IP address and is selected as the OSPF Router ID.

Adım Adım Çözüm

1
Check for an explicitly configured manual OSPF Router ID
No manual 'router-id' command is present.
Manual configuration takes highest precedence in OSPF Router ID election.
2
Evaluate active loopback interfaces
Two active loopbacks exist: Loopback0 (10.10.1.110.10.1.1) and Loopback1 (10.20.1.110.20.1.1).
If no manual router ID is specified, OSPF evaluates active loopback interfaces next.
3
Select the highest IP address among active loopback interfaces
Compare 10.20.1.110.20.1.1 and 10.10.1.110.10.1.1; 10.20.1.110.20.1.1 is numerically higher.
OSPF selects the highest active loopback IP address over lower loopbacks and over any physical interfaces.

Anahtar Kavram

OSPFv2 Router ID Election Precedence
Soru 189Soru →

A network administrator configures a Cisco IOS router to synchronize its internal clock with an enterprise NTP server operating at Stratum 2. Arrange the operational steps in chronological order from initial packet transmission to the point where the router can act as a valid time source for downstream clients.

Öğeleri doğru sıraya koymak için sürükleyin

Cevabı ve açıklamayı göster

Cevap

The correct sequence of operations is: 1) The router sends an NTP client mode query (UDP port 123) to the server. 2) The router receives an NTP server mode response with Stratum 2 metadata. 3) The router computes round-trip delay, dispersion, and clock offset algorithms. 4) The router synchronizes its system clock and increments its operational stratum to Stratum 3. 5) The router begins answering incoming NTP queries from downstream clients.
NTP synchronization follows a strict sequential process: outbound UDP 123 request initiation, receipt of server time payload and stratum attributes, statistical filtering of offset and round-trip delay, local clock adjustment accompanied by stratum incrementing (N+1N+1), and finally responding to downstream client requests as a synchronized master time source.

Adım Adım Çözüm

1
Initiate communication
Router sends an outbound NTP client packet over UDP port 123 to the NTP server address.
Synchronization starts when the client polls the server for time information.
2
Receive server response
Server replies with timestamp, stratum level (Stratum 2), and reference clock identification.
The server must supply its current time and stratum attributes back to the client.
3
Process NTP statistical filtering
Router calculates offset and network delay while filtering out jitter and invalid timestamps.
Packet delay and clock drift must be calculated before modifying the local system time.
4
Update local system time and stratum
Local clock synchronizes, and local stratum becomes Stratum 3 (2+12 + 1).
A synchronized NTP device always assumes a stratum number one unit higher than its synchronization source.
5
Serve downstream clients
Router processes and responds to NTP requests from local hosts.
Downstream devices can only receive valid, synchronized time after the router completes synchronization and establishes a valid stratum (< 16).

Anahtar Kavram

NTP Client-Server Initialization Sequence and Stratum Calculation
Soru 190Soru →

A network engineer is configuring Port Address Translation (PAT) on a Cisco IOS router using an IP NAT pool named `INTERNET_POOL` for internal endpoints matched by access list `10`. Which global configuration command correctly enables PAT using this address pool?

Cevabı ve açıklamayı göster

Cevap: ip nat inside source list 10 pool INTERNET_POOL overload

Cevap

The command 'ip nat inside source list 10 pool INTERNET_POOL overload' correctly enables Port Address Translation using the specified pool.
The correct command uses 'ip nat inside source list 10 pool INTERNET_POOL overload'. The 'inside source' parameter specifies translation for outbound traffic originating inside the network, 'list 10' identifies hosts permitted by ACL 10, 'pool INTERNET_POOL' designates the global address pool, and 'overload' enables port-level multiplexing (PAT) so multiple internal endpoints can share pool addresses simultaneously.

Adım Adım Çözüm

1
Identify the direction of translation.
Internal hosts initiating outbound connections require 'inside source' translation.
Inside source NAT translates private local IP addresses to public global addresses.
2
Identify the method of matching source addresses and defining the public addresses.
Access list 10 filters inside local hosts, and the named pool 'INTERNET_POOL' defines the public IPv4 addresses.
The 'list 10 pool INTERNET_POOL' syntax binds the ACL host match condition to the pool range.
3
Determine the keyword required for Port Address Translation (PAT).
Adding the 'overload' keyword enables multiplexing multiple internal hosts onto pool addresses using unique TCP/UDP port numbers.
Without 'overload', Cisco IOS restricts dynamic NAT to a strict 1-to-1 IP address mapping.

Anahtar Kavram

Port Address Translation (PAT) configuration using dynamic address pools in Cisco IOS
Tahmini Süre:1m 0s
Soru 191Soru →

An administrator executes the command `show ip ospf neighbor` on a router and observes that a connected neighbor remains continuously in the INIT state. Which condition is the most likely cause of this issue?

Cevabı ve açıklamayı göster

Cevap: One router is rejecting incoming Hello packets because of an OSPF Area ID mismatch.

Cevap

One router is rejecting incoming Hello packets because of an OSPF Area ID mismatch.
The correct answer identifies that an Area ID mismatch causes incoming Hello packets to be discarded. In OSPF, a router enters the INIT state when it receives a valid Hello packet from a neighbor. However, if the neighbor drops incoming Hellos from the local router due to an Area ID mismatch, the neighbor will never add the local router's Router ID to its Hello packet neighbor field. Consequently, the local router remains stuck in the INIT state.

Adım Adım Çözüm

1
Analyze OSPF neighbor state definitions.
The INIT state indicates that a router has received a Hello packet from a neighbor, but the receiving router's own Router ID was not present in that Hello packet.
For OSPF neighbors to transition from INIT to 2-WAY, bidirectional communication must be established by seeing one's own Router ID in the received Hello packet's neighbor list.
2
Evaluate the impact of an Area ID mismatch on Hello packet processing.
When Area IDs mismatch, incoming Hello packets are dropped on receipt before the neighbor list is processed.
Because Hellos are discarded due to parameter mismatch (such as Area ID, Hello/Dead timers, or subnet mask), bidirectional communication fails to establish, keeping the relationship stuck in INIT.

Anahtar Kavram

OSPFv2 Neighbor Adjacencies and Router ID
Tahmini Süre:1m 0s
Soru 192Soru →

A network administrator is selecting an IPv4 subnetwork block for a new internal department segment that requires support for up to 6060 usable host interfaces. The network design policy requires using an RFC 1918 private IPv4 address block and selecting the most efficient prefix length to avoid wasting addresses. Which subnetwork address and CIDR prefix satisfies all requirements?

Cevabı ve açıklamayı göster

Cevap: 10.40.16.0/2610.40.16.0/26

Cevap

The subnetwork 10.40.16.0/2610.40.16.0/26 meets all design requirements by using an RFC 1918 private IPv4 address and providing 6262 usable host IP addresses, which is the most efficient subnet size for 6060 hosts.
The subnetwork 10.40.16.0/2610.40.16.0/26 utilizes an address within the RFC 1918 Class A private block (10.0.0.0/810.0.0.0/8). A /26/26 prefix leaves 66 host bits (32−26=632 - 26 = 6), providing 26−2=622^6 - 2 = 62 usable host IP addresses. This accommodates the required 6060 host interfaces with the minimum possible address waste.

Adım Adım Çözüm

1
Determine the required number of host bits (hh) for 6060 usable hosts
Using the formula 2h−2≥602^h - 2 \ge 60, we test h=5→30h = 5 \rightarrow 30 usable hosts (too small) and h=6→62h = 6 \rightarrow 62 usable hosts (sufficient). Thus, 66 host bits are needed.
Two addresses in every IPv4 subnet are reserved for the network ID and the directed broadcast address.
2
Calculate the CIDR prefix length
Prefix length =32−6=/26= 32 - 6 = /26.
An IPv4 address consists of 32 total bits.
3
Verify RFC 1918 private IPv4 address range compliance
10.40.16.010.40.16.0 is inside the 10.0.0.0/810.0.0.0/8 private address block (10.0.0.010.0.0.0 to 10.255.255.25510.255.255.255).
RFC 1918 defines private address spaces: 10.0.0.0/810.0.0.0/8, 172.16.0.0/12172.16.0.0/12, and 192.168.0.0/16192.168.0.0/16.

Anahtar Kavram

IPv4 Subnet Sizing and RFC 1918 Private Addressing
Soru 193Soru →

An enterprise router learns the remote network 10.50.0.0/1610.50.0.0/16 via OSPF, which has a default administrative distance of 110. A network administrator must configure a floating static backup route to reach destination 10.50.0.0/1610.50.0.0/16 using next-hop IP address 192.168.12.2192.168.12.2. The backup route must only enter the routing table if the primary OSPF path fails. Which Cisco IOS command correctly configures this floating static route?

Cevabı ve açıklamayı göster

Cevap: ip route 10.50.0.0 255.255.0.0 192.168.12.2 120

Cevap

The command 'ip route 10.50.0.0 255.255.0.0 192.168.12.2 120' correctly configures the floating static route.
A floating static route acts as a backup path and must remain dormant in the routing table until the primary path fails. Since the primary path is installed by OSPF with an Administrative Distance of 110, the backup static route must be assigned an Administrative Distance higher than 110 (e.g., 120). The command 'ip route 10.50.0.0 255.255.0.0 192.168.12.2 120' fulfills this requirement.

Adım Adım Çözüm

1
Identify the primary routing protocol and its Administrative Distance (AD).
The primary route to 10.50.0.0/1610.50.0.0/16 is learned via OSPF, which has an AD of 110.
Floating static routes rely on AD comparison to remain inactive until primary routes fail.
2
Determine the required AD for the backup floating static route.
The floating static route must have an AD greater than 110 (such as 120).
Lower AD values are preferred by the router forwarding logic; a higher AD ensures the route stays out of the routing table while OSPF is active.
3
Construct the Cisco IOS static route command syntax.
'ip route 10.50.0.0 255.255.0.0 192.168.12.2 120'
Syntax requires destination prefix, subnet mask, next-hop IP, and the explicit administrative distance metric at the end.

Anahtar Kavram

Floating Static Route Administrative Distance Selection
Tahmini Süre:1m 30s
Soru 194Soru →

A network administrator needs to create VLAN 60 on a Cisco Catalyst switch, assign it the name PRINTERS, and configure interface GigabitEthernet0/14 as a static access port assigned to this VLAN. Place the Cisco IOS configuration commands in the correct sequential order starting from global configuration mode.

Öğeleri doğru sıraya koymak için sürükleyin

Cevabı ve açıklamayı göster

Cevap

The correct sequence begins by entering VLAN subconfiguration mode with 'vlan 60', setting the VLAN name with 'name PRINTERS', moving to the target interface subconfiguration mode using 'interface gigabitethernet0/14', setting the port operational mode to access with 'switchport mode access', and assigning the interface to the VLAN using 'switchport access vlan 60'.
The correct command order follows Cisco IOS context mode hierarchy: first entering VLAN subconfig mode with 'vlan 60' to create the VLAN, then configuring its name using 'name PRINTERS', next navigating to interface subconfig mode with 'interface gigabitethernet0/14', explicitly defining access mode using 'switchport mode access', and finally binding the port to the VLAN using 'switchport access vlan 60'.

Adım Adım Çözüm

1
Enter VLAN configuration mode from global configuration mode
Prompt changes to Switch(config-vlan)#
VLAN 60 must be initialized in the switch VLAN database before naming or assigning interface membership.
2
Assign an administrative name to VLAN 60
VLAN 60 is assigned the name PRINTERS
The 'name' command is specific to VLAN subconfiguration mode and provides administrative identification for the broadcast domain.
3
Navigate to the specific interface configuration mode
Prompt changes to Switch(config-if)#
Interface parameters must be configured within interface subconfiguration mode.
4
Configure the interface mode as static access
Interface GigabitEthernet0/14 is defined as an access port
Executing 'switchport mode access' explicitly defines the port as non-trunking and disables dynamic trunk negotiation via DTP.
5
Assign the interface to VLAN 60
Interface GigabitEthernet0/14 becomes an active member of VLAN 60
The 'switchport access vlan 60' command associates untagged ingress/egress frames on GigabitEthernet0/14 with VLAN 60.

Anahtar Kavram

Cisco IOS command syntax and hierarchy for VLAN creation, naming, and access port assignment
Soru 195Soru →

An administrator needs to configure Port Address Translation (PAT) on a Cisco IOS router so that all internal hosts on the subnet 172.16.50.0/24172.16.50.0/24 can access the Internet using the IPv4 address assigned to the WAN interface GigabitEthernet0/1. Interface GigabitEthernet0/0 connects to the internal LAN. Which configuration set correctly accomplishes this requirement?

Cevabı ve açıklamayı göster

Cevap: interface GigabitEthernet0/0
ip nat inside
!
interface GigabitEthernet0/1
ip nat outside
!
access-list 15 permit 172.16.50.0 0.0.0.255
ip nat inside source list 15 interface GigabitEthernet0/1 overload

Cevap

The command sequence configuring GigabitEthernet0/0 as ip nat inside, GigabitEthernet0/1 as ip nat outside, ACL 15 matching 172.16.50.0 0.0.0.255, and 'ip nat inside source list 15 interface GigabitEthernet0/1 overload' correctly enables PAT.
The correct command set properly sets GigabitEthernet0/0 as the inside interface and GigabitEthernet0/1 as the outside interface, specifies standard ACL 15 to match the 172.16.50.0/24 subnet, and uses the 'overload' keyword with the egress interface to enable Port Address Translation (PAT).

Adım Adım Çözüm

1
Identify and designate the NAT interfaces
GigabitEthernet0/0 is configured with 'ip nat inside' (internal LAN) and GigabitEthernet0/1 is configured with 'ip nat outside' (WAN interface).
Cisco IOS NAT requires specifying directionality on interfaces to know where translation occurs.
2
Define an Access Control List (ACL) matching internal private IPs
Access-list 15 matches subnet 172.16.50.0 with wildcard mask 0.0.0.255.
The ACL identifies which internal source IP addresses are eligible for address translation.
3
Configure PAT using interface overloading
Execute 'ip nat inside source list 15 interface GigabitEthernet0/1 overload'.
The 'overload' keyword enables Port Address Translation (PAT), allowing multiple internal hosts to share the single IP address assigned to the egress interface by tracking layer 4 port numbers.

Anahtar Kavram

Port Address Translation (PAT) Configuration using Interface Overload
Tahmini Süre:1m 15s
Soru 196Soru →

A core router receives a packet destined for IP address 172.16.42.95. The router's IPv4 routing table contains four candidate paths to reach this destination:

text O 172.16.40.0/21 [110/65] via 10.1.1.1, 00:14:22, GigabitEthernet0/0/0 D 172.16.42.0/24 [90/307200] via 10.2.2.2, 01:05:10, GigabitEthernet0/0/1 S 172.16.42.64/26 [1/0] via 10.3.3.3 O 172.16.42.80/28 [110/30] via 10.4.4.4, 00:02:45, GigabitEthernet0/0/2

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

Cevabı ve açıklamayı göster

Cevap: 10.4.4.4

Cevap

The router will forward the packet to next-hop IP address 10.4.4.4 via GigabitEthernet0/0/2 because it has the longest prefix match (/28) containing the destination address 172.16.42.95.
When a router makes a forwarding decision, it evaluates all routing table entries that match the destination IP address and selects the entry with the longest prefix mask (the most specific route). For destination 172.16.42.95, the route 172.16.42.80/28 has a 28-bit mask, which is more specific than /26, /24, or /21. Therefore, the router forwards the packet to next-hop 10.4.4.4.

Adım Adım Çözüm

1
Determine which prefixes in the routing table actually match the destination IP address 172.16.42.95.
172.16.40.0/21 covers 172.16.40.0 to 172.16.47.255 (Match). 172.16.42.0/24 covers 172.16.42.0 to 172.16.42.255 (Match). 172.16.42.64/26 covers 172.16.42.64 to 172.16.42.127 (Match). 172.16.42.80/28 covers 172.16.42.80 to 172.16.42.95 (Match).
Before comparing metrics or administrative distances, the router identifies all valid matching routes.
2
Compare the prefix lengths (subnet masks) of all matching routes to apply the Longest Prefix Match rule.
Prefix lengths are /21, /24, /26, and /28. The /28 prefix length is the longest (most specific).
The Cisco IOS forwarding decision always uses the longest prefix match first, regardless of routing source or administrative distance.
3
Identify the next-hop IP address associated with the longest matching route (172.16.42.80/28).
The next-hop address associated with 172.16.42.80/28 is 10.4.4.4.
The router forwards the packet out the exit interface towards 10.4.4.4.

Anahtar Kavram

Longest Prefix Match Rule in Routing Table Lookups
Soru 197Soru →

A network engineer configures a Cisco switch running Rapid PVST+ to serve as the root bridge for VLAN 12. The engineer executes the global configuration command `spanning-tree vlan 12 priority 12288`. What total Bridge Priority value will be carried in the BPDUs transmitted by this switch for VLAN 12?

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Cevap: 12288

Cevap

12300
In Rapid PVST+, Cisco switches use the 802.1t System ID Extension, which split the 16-bit Bridge Priority field into a 4-bit Base Priority field (increments of 4096) and a 12-bit System ID Extension field carrying the VLAN ID. When `spanning-tree vlan 12 priority 12288` is configured, the total priority field transmitted in BPDUs is the sum of the base priority (1228812288) and the VLAN ID (1212), resulting in 1230012300.

Adım Adım Çözüm

1
Identify the configured base bridge priority value.
The base priority is configured as 12288 (a valid multiple of 4096).
STP base priority values must be specified in increments of 4096.
2
Identify the System ID Extension (VLAN ID).
The System ID Extension is 12 for VLAN 12.
Rapid PVST+ uses the 12-bit System ID Extension field in the Bridge Identifier to encode the VLAN number.
3
Calculate the total Bridge Priority transmitted in BPDUs.
Total Priority = 12288 + 12 = 12300.
The total priority contained within BPDUs is the sum of the configured base priority and the System ID Extension.

Anahtar Kavram

Rapid PVST+ System ID Extension and Total Bridge Identifier Priority Calculation
Soru 198Soru →

An enterprise network has a shared Ethernet segment running OSPFv2 in Area 0. Router R1 (Router ID 10.1.1.1, priority 1) is currently serving as the Designated Router (DR), and Router R2 (Router ID 10.2.2.2, priority 1) is serving as the Backup Designated Router (BDR). A network engineer adds Router R5 (Router ID 10.5.5.5, priority 255) to the segment. Shortly after R5 stabilizes as a DROTHER, R1's interface experiences a temporary link failure and goes down for five minutes before recovering. Which router functions as the DR on the segment immediately after R1 recovers and reaches the FULL neighbor state?

Cevabı ve açıklamayı göster

Cevap: Router R2 functions as the DR because it was promoted from BDR when R1 failed, and OSPF DR elections are non-preemptive.

Cevap

Router R2 remains the Designated Router (DR) because OSPF DR/BDR elections are non-preemptive. Upon R1's failure, R2 was promoted to DR and R5 became BDR; when R1 recovers, existing roles are maintained.
OSPF DR and BDR roles are non-preemptive. When R5 joined initially, R1 and R2 retained their roles despite R5 having a higher priority. When R1 failed, BDR R2 was promoted to DR, and R5 was elected as the new BDR. When R1 recovers, it finds an active DR (R2) and an active BDR (R5) already present on the segment, so R1 becomes a DROTHER.

Adım Adım Çözüm

1
Analyze initial state and addition of R5
R1 is DR, R2 is BDR. Adding R5 with priority 255 does not trigger a re-election for DR/BDR because active roles are non-preemptive. R5 becomes a DROTHER.
OSPF avoids network instability by preventing newly connected routers from preempting active DR and BDR roles.
2
Evaluate state changes during R1 failure
When R1 fails, BDR R2 is immediately promoted to DR. An election is held to fill the vacant BDR role, which R5 wins due to having the highest priority (255).
The BDR automatically steps up to DR when the DR fails, and remaining eligible routers elect a new BDR.
3
Determine final state after R1 link recovery
R1 re-establishes adjacency, sees active DR (R2) and active BDR (R5), and assumes the DROTHER role.
Recovered or newly booted routers do not preempt existing operational DR/BDR routers on multiaccess networks.

Anahtar Kavram

Non-preemptive nature of OSPF DR/BDR elections and promotion mechanics on broadcast multiaccess networks
Soru 199Soru →

A network engineer is troubleshooting various network interface issues on Cisco switches and routers. Match each interface status or error counter symptom on the left with its most likely physical or data-link layer root cause on the right.

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Öğeler

Interface status is down, line protocol is down
Interface status is up, line protocol is down
Interface status is up, line protocol is up, with rapidly incrementing late collisions
Interface status is up, line protocol is up, with rapidly incrementing giants and jabber errors

Eşleşmeler

Cevabı ve açıklamayı göster

Cevap

The interface symptoms match as follows: 'down/down' corresponds to a Layer 1 physical fault; 'up/down' corresponds to a Layer 2 framing or keepalive failure; incrementing late collisions corresponds to a half-duplex/full-duplex mismatch; and incrementing giants/jabbers corresponds to oversized frames or a defective NIC.
Each status pattern and counter maps directly to standard Cisco IOS interface troubleshooting logic: Layer 1 physical link failures cause 'down/down'; Layer 2 framing/keepalive failures cause 'up/down'; half-duplex operating against full-duplex causes late collisions; and frames exceeding 1518 bytes with invalid FCS register as giants/jabber errors.

Adım Adım Çözüm

1
Analyze interface states by differentiating Layer 1 (Line Status) from Layer 2 (Line Protocol).
Line status indicates physical carrier detection, whereas line protocol indicates data link layer framing and keepalive state.
A physical failure results in 'down/down', whereas a framing or encapsulation mismatch maintains physical link ('up') but drops data link signaling ('down').
2
Diagnose the cause of late collision error counters on Ethernet interfaces.
Late collisions indicate that collision detection occurred after transmitting 512 bits (64 bytes).
Because half-duplex expects collisions only during the slot time (first 64 bytes), late collisions uniquely signal that the remote peer is operating in full-duplex mode and ignoring CSMA/CD rules.
3
Evaluate framing error statistics such as giants and jabbers.
Giants represent frames larger than the standard Ethernet MTU (1518 bytes) with bad CRC, while jabbers represent invalid continuous signals.
These symptoms point directly to MTU misconfigurations or damaged Network Interface Cards (NICs) transmitting invalid frame sizes.

Anahtar Kavram

Interface Line Status Combinations and Error Counter Root Causes
Soru 200Soru →

A network architect is establishing standard address allocations and boundary checks for an enterprise network redesign. Match each IPv4 address block or prefix range on the left with its corresponding RFC 1918 classification, CIDR specifications, or Internet routing characteristics on the right.

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Öğeler

10.0.0.0/810.0.0.0/8
172.16.0.0/12172.16.0.0/12
192.168.0.0/16192.168.0.0/16
172.32.0.0/11172.32.0.0/11

Eşleşmeler

Cevabı ve açıklamayı göster

Cevap

10.0.0.0/8 matches the single Class A private block (10.0.0.0 to 10.255.255.255); 172.16.0.0/12 matches the 16 contiguous Class B private subnets (172.16.0.0 to 172.31.255.255); 192.168.0.0/16 matches the 256 contiguous Class C private subnets (192.168.0.0 to 192.168.255.255); 172.32.0.0/11 matches the globally routable public address space.
Each item matches its corresponding RFC 1918 definition or boundary specification correctly: 10.0.0.0/8 is the single Class A private block, 172.16.0.0/12 spans 16 contiguous Class B private /16 networks (172.16.0.0 - 172.31.255.255), 192.168.0.0/16 spans 256 Class C /24 networks (192.168.0.0 - 192.168.255.255), and 172.32.0.0/11 consists of public addresses immediately above the 172.31.255.255 RFC 1918 upper bound.

Adım Adım Çözüm

1
Identify the Class A RFC 1918 block
10.0.0.0/810.0.0.0/8 encompasses the host range 10.0.0.010.0.0.0 to 10.255.255.25510.255.255.255 (16,777,21616,777,216 addresses).
RFC 1918 reserves one /8/8 prefix in the 10.0.0.0 network space for private internal use.
2
Analyze the Class B RFC 1918 block and boundary limits
172.16.0.0/12172.16.0.0/12 encompasses 16 contiguous /16/16 blocks (172.16.0.0172.16.0.0 through 172.31.255.255172.31.255.255).
The prefix length /12/12 spans from 172.16.0.0172.16.0.0 up to 172.31.255.255172.31.255.255. Addresses starting with 172.32.0.0172.32.0.0 are public.
3
Identify the Class C RFC 1918 block
192.168.0.0/16192.168.0.0/16 encompasses 256 contiguous /24/24 subnets (192.168.0.0192.168.0.0 through 192.168.255.255192.168.255.255).
RFC 1918 defines a single /16/16 prefix block within the 192.168.0.0 space for Class C private addressing.
4
Distinguish public ranges from RFC 1918 private ranges
172.32.0.0/11172.32.0.0/11 starts at 172.32.0.0172.32.0.0, which is beyond the 172.31.255.255172.31.255.255 boundary and is therefore public.
Any IP address in the range 172.32.0.0172.32.0.0 to 172.63.255.255172.63.255.255 is public and routable on the global Internet.

Anahtar Kavram

RFC 1918 Private IPv4 Address Space Ranges and Public Boundaries
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