Examkin

IP Connectivity

493 soru

Tüm türler493Çoktan seçmeli250Çoklu seçim113Eşleştirme25Sıralama60Boşluk doldurma22Kısa cevap23
Soru 301Soru →

An administrator is troubleshooting OSPFv2 neighbor connectivity between Router A and Router B connected directly over a GigabitEthernet broadcast segment. Both routers are configured in OSPF Area 0.

Router A has the following operational status:
- Loopback0 interface IP: 172.16.1.1/24 (Up/Up)
- Loopback1 interface IP: 192.168.100.1/24 (Up/Up)
- GigabitEthernet0/1 interface IP: 10.1.12.1/24 (Up/Up)
- Ten minutes after the OSPF process initialized, the administrator executed `router-id 1.1.1.1` under `router ospf 1`, but did not restart the OSPF process.
- An inbound IPv4 ACL applied to GigabitEthernet0/1 permits IP unicast traffic from Router B, but drops all IP multicast traffic addressed to 224.0.0.5.

Router B has the following operational status:
- Loopback0 interface IP: 10.2.2.2/32 (Up/Up)
- GigabitEthernet0/1 interface IP: 10.1.12.2/24 (Up/Up)
- Active OSPF Router ID: 10.2.2.2

When executing `show ip ospf neighbor` on Router B, the neighbor state for Router A is listed as `INIT/ -`. However, executing `show ip ospf neighbor` on Router A displays no output.

Which statement accurately explains why Router B is in the INIT state while Router A shows no neighbor, and identifies the Router ID that Router B receives from Router A?

Cevabı ve açıklamayı göster

Cevap: Router B receives outgoing multicast Hellos from Router A containing Router ID 192.168.100.1 and moves Router A into the INIT state; Router A displays no neighbor because its inbound ACL drops Router B's multicast Hello packets.

Cevap

Router B receives outgoing multicast Hellos from Router A containing Router ID 192.168.100.1 and moves Router A into the INIT state; Router A displays no neighbor because its inbound ACL drops Router B's multicast Hello packets.
The correct statement identifies that Router A's active Router ID is 192.168.100.1 (the highest active loopback IP address at startup, because the `router-id` command is non-preemptive until the OSPF process is cleared). Router B receives Router A's multicast Hello packets containing this Router ID and transitions Router A to the INIT state because Router B is not yet listed in Router A's Hello neighbor field. Meanwhile, Router A receives zero Hello packets from Router B because its inbound ACL filters all multicast traffic to 224.0.0.5, causing Router A to remain in the DOWN state with no neighbor table entries.

Adım Adım Çözüm

1
Determine Router A's active OSPF Router ID
Router A's active Router ID is 192.168.100.1.
When OSPF initializes without an explicit command, the router selects the highest IP address among active loopback interfaces. Loopback1 (192.168.100.1) is higher than Loopback0 (172.16.1.1). The `router-id 1.1.1.1` command was entered later but is non-preemptive; it requires `clear ip ospf process` or a reload to take effect.
2
Analyze outbound Hello packet transmission from Router A to Router B
Router B receives Router A's Hello packet containing Router ID 192.168.100.1.
Router A sends multicast Hello packets to 224.0.0.5 out GigabitEthernet0/1. Since Router A hasn't received Hellos from Router B yet, Router B's Router ID is not listed in the neighbor field of Router A's Hello packet.
3
Analyze Router B's state transition upon receiving Router A's Hello
Router B transitions Router A to the INIT state.
When a router receives a valid Hello packet from a neighbor that does not yet list the receiving router's own Router ID, it places that neighbor into the INIT state.
4
Analyze inbound packet processing on Router A
Router A drops Router B's multicast Hello packets (224.0.0.5) and shows no neighbor entry.
Router B responds by sending multicast Hellos to 224.0.0.5 containing Router A's Router ID in its neighbor list. However, Router A's inbound ACL drops all traffic to 224.0.0.5. As a result, Router A never receives Router B's Hellos, remains in the DOWN state, and displays no output for `show ip ospf neighbor`.

Anahtar Kavram

OSPFv2 Router ID election precedence (manual command requiring process reset vs. highest active loopback) combined with unidirectional Hello packet flow causing one-sided INIT neighbor states.
Tahmini Süre:3m 0s
Soru 302Soru →

A network administrator is evaluating an OSPFv2 implementation across a shared Ethernet segment (172.16.1.0/24). Router R1 initialized first on the segment and assumed the Designated Router (DR) role. Routers R2 and R3 joined subsequently. Router R4 was added last, configured with an OSPF interface priority of 200, whereas R1, R2, and R3 retain the default interface priority of 1.

Executing `show ip ospf neighbor` on Router R4 produces the following output:

text
R4# show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 1 FULL/DR 00:00:36 172.16.1.1 GigabitEthernet0/1
2.2.2.2 1 FULL/BDR 00:00:34 172.16.1.2 GigabitEthernet0/1
3.3.3.3 1 FULL/DROTHER 00:00:38 172.16.1.3 GigabitEthernet0/1

Based on this output and OSPF operational behavior, why has Router R4 not assumed the Designated Router role despite having a higher interface priority?

Cevabı ve açıklamayı göster

Cevap: OSPF DR and BDR elections are non-preemptive; once an active DR is elected, a newly connected router will not trigger a election takeover even if configured with a higher priority.

Cevap

OSPF DR and BDR elections are non-preemptive; once an active DR is elected, a newly connected router will not trigger a election takeover even if configured with a higher priority.
OSPF DR and BDR election processes are strictly non-preemptive. Once a router is elected as Designated Router, it retains that position until its OSPF process reboots, its interface goes down, or the process is manually cleared. Bringing up a new router with a higher interface priority (such as 200) does not preempt the active DR.

Adım Adım Çözüm

1
Analyze the OSPF interface state and neighbor table output from Router R4.
Router R1 (Router ID 1.1.1.1) is serving as the active DR, and Router R2 (Router ID 2.2.2.2) is serving as the active BDR.
Both roles were established when R1 and R2 initially formed adjacencies on the 172.16.1.0/24 broadcast segment.
2
Evaluate the non-preemptive election mechanics of OSPFv2.
Even though Router R4 has an interface priority of 200 (which exceeds R1's priority of 1), OSPF does not preempt an existing DR or BDR.
Preemption would cause unnecessary LSA re-flooding and adjacency resets on multiaccess segments.
3
Determine how R4 could become the DR.
R4 will only become DR if the active DR and BDR fail, or if the OSPF routing processes on R1 and R2 are cleared/restarted.
Election procedures run only when the DR or BDR position becomes vacant.

Anahtar Kavram

Non-preemptive nature of OSPF DR/BDR elections on broadcast multiaccess networks
Tahmini Süre:2m 0s
Soru 303Soru →

During the OSPFv2 ExStart neighbor state, routers exchange initial Database Description (DBD) packets to establish a master-slave relationship. Which router attribute is compared to elect the master router?

Cevabı ve açıklamayı göster

Cevap: Router ID; OSPF Router ID; router id; Router-ID; router-id; The Router ID; the router id

Cevap

Router ID (the router with the numerically higher OSPF Router ID is elected as the master).
In the OSPF ExStart neighbor state, routers exchange empty Database Description (DBD) packets to decide which router controls the packet sequence numbers (the master). The router with the higher OSPF Router ID is elected master.

Adım Adım Çözüm

1
Identify the neighbor state and process described in the prompt.
The scenario refers to the ExStart state where routers negotiate master/slave roles using DBD packets.
ExStart is designed to establish sequence numbers and determine control over database exchange.
2
Determine the parameter used to break ties and elect the master router.
The router with the higher OSPF Router ID is selected as the master.
OSPF specifies that the router possessing the highest Router ID acts as master to initiate DBD sequence numbering.

Anahtar Kavram

OSPFv2 Master/Slave Election during ExStart State
Soru 304Soru →

Match each OSPFv2 network type on the left to its correct DR/BDR election requirement and default Hello timer on the right.

Soldaki öğeye tıklayın, sonra eşleşen sağdaki öğeye tıklayın

Öğeler

Broadcast Multiaccess
Point-to-Point
Point-to-Multipoint

Eşleşmeler

Cevabı ve açıklamayı göster

Cevap

Broadcast Multiaccess matches with 'Elects DR/BDR; default Hello timer is 10 seconds'. Point-to-Point matches with 'Does NOT elect DR/BDR; default Hello timer is 10 seconds'. Point-to-Multipoint matches with 'Does NOT elect DR/BDR; default Hello timer is 30 seconds'.
Broadcast Multiaccess networks use a 10-second Hello timer and perform DR/BDR elections to manage multiaccess adjacencies. Point-to-Point networks use a 10-second Hello timer but suppress DR/BDR elections because only two endpoints exist. Point-to-Multipoint networks suppress DR/BDR elections and operate with a 30-second Hello timer.

Adım Adım Çözüm

1
Determine DR/BDR election requirements for each OSPFv2 network type.
DR/BDR elections only occur on multiaccess media (Broadcast and Non-Broadcast Multiaccess). Point-to-Point and Point-to-Multipoint types bypass DR/BDR elections.
DR/BDR selection prevents unnecessary adjacency overhead on multiaccess networks.
2
Recall default OSPFv2 Hello timers for each network type.
Broadcast and Point-to-Point network types default to 10-second Hello timers. Non-Broadcast and Point-to-Multipoint default to 30-second Hello timers.
OSPF timer defaults depend on whether the underlying physical medium is considered high-speed broadcast/point-to-point or slower non-broadcast media.
3
Match the attributes of each network type.
Broadcast Multiaccess -> DR/BDR elected, 10s Hello. Point-to-Point -> No DR/BDR, 10s Hello. Point-to-Multipoint -> No DR/BDR, 30s Hello.
Combines the DR/BDR requirement with the appropriate interface default Hello timer.

Anahtar Kavram

OSPFv2 Network Types, DR/BDR Selection, and Default Timers
Tahmini Süre:1m 30s
Soru 305Soru →

A network administrator intends to configure a floating static route on Router R1 to serve as a backup to a primary route dynamically learned via OSPF (Administrative Distance 110) for destination network 172.16.50.0/24172.16.50.0/24. However, while the primary OSPF link remains healthy and operational, the administrator observes that the newly added static route immediately overrides the OSPF route in the IPv4 routing table. Which command did the administrator incorrectly execute on Router R1?

Cevabı ve açıklamayı göster

Cevap: ip route 172.16.50.0 255.255.255.0 192.168.1.2 90

Cevap

The command 'ip route 172.16.50.0 255.255.255.0 192.168.1.2 90' was incorrectly configured because assigning an Administrative Distance lower than 110 causes the static route to immediately preempt the primary OSPF path.
In Cisco IOS, static routes have a default Administrative Distance (AD) of 1. A floating static route acts as a backup path and must be configured with an AD higher than the primary route's protocol AD. Because OSPF has a default AD of 110, setting the static route's AD to 90 gives it higher priority (lower AD number) than OSPF. Consequently, the router immediately installs the static route into the routing table and ignores the active OSPF route.

Adım Adım Çözüm

1
Analyze the requirement for a floating static route.
A floating static route must have an Administrative Distance (AD) higher than the primary routing protocol so that it remains inactive in the routing table until the primary route fails.
Cisco IOS routing logic selects paths based on the lowest Administrative Distance first.
2
Compare the AD of the primary route (OSPF) against the attempted static route.
OSPF has a default AD of 110. To act as a backup, the static route AD must be greater than 110 (such as 120).
If the static route is configured with an AD lower than 110 (such as 90), the router prefers the static route over the OSPF route.
3
Identify which misconfiguration caused the immediate routing table override.
The command specifying an AD of 90 is preferred over OSPF's AD of 110, causing immediate installation into the routing table.
Lower AD numbers indicate higher trustworthiness in Cisco IOS.

Anahtar Kavram

Floating Static Route Administrative Distance Selection
Soru 306Soru →

A network engineer is configuring OSPFv2 on two directly connected routers. Which TWO parameters must match identically in the OSPF Hello packets exchanged between the routers for a neighbor adjacency to form successfully? (Select TWO.)

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: Area ID; Hello and Dead timer intervals

Cevap

The parameters that must match identically in OSPF Hello packets are the Area ID and the Hello and Dead timer intervals.
For two OSPFv2 routers to form an adjacency, they must agree on key interface configuration parameters transmitted in Hello packets. Both the Area ID and the Hello/Dead timer intervals are mandatory matching fields. If any of these fields differ, the routers will ignore or drop the Hello packets and remain unable to form a neighbor relationship.

Adım Adım Çözüm

1
Analyze OSPF Hello packet fields required for neighbor adjacency formation.
Identify parameters carried in Hello packets that undergo validation upon receipt.
OSPF routers verify specific fields in incoming Hello packets before allowing neighbor state transitions.
2
Evaluate mandatory matching parameters versus non-matching parameters.
Area ID and Hello/Dead timer intervals must match. Router IDs must be unique, and Process IDs are locally significant only.
Matching Area IDs ensure routers agree on network membership, and matching timers maintain synchronized keepalive expectations.

Anahtar Kavram

OSPFv2 Neighbor Adjacency Requirements
Soru 307Soru →

An enterprise router receives its default route via an eBGP session established with ISP-A. A network administrator attempts to configure a secondary floating static backup default route pointing to ISP-B using the following command:

`ip route 0.0.0.0 0.0.0.0 198.51.100.2 15`

Assuming the eBGP session remains active and continues advertising the default route, which outcome will occur on the router?

Cevabı ve açıklamayı göster

Cevap: The static route will immediately enter the routing table and replace the eBGP default route as the primary path.

Cevap

The static route will immediately enter the routing table and replace the eBGP default route as the primary path.
In Cisco IOS, route selection between different protocol sources is determined by Administrative Distance (AD), where lower values are preferred. The default AD for External BGP (eBGP) is 20. Because the engineer configured the static route with an AD of 15, the router considers the static path more trustworthy than the eBGP path (15<2015 < 20). Consequently, the static route immediately takes precedence in the routing table, failing to function as a floating backup.

Adım Adım Çözüm

1
Identify the default administrative distance (AD) of the primary routing source.
External BGP (eBGP) has a default administrative distance of 20.
Cisco IOS assigns specific default AD values to judge route trustworthiness among different routing sources.
2
Compare the configured static route AD against the primary route's AD.
The configured static route AD is 15, which is lower than the eBGP AD of 20 (15<2015 < 20).
Lower administrative distance values indicate higher trustworthiness in Cisco IOS forwarding selection logic.
3
Determine which route is installed into the routing table.
The static route with AD 15 overrides the eBGP route with AD 20 and is actively installed into the routing table.
To create a valid floating static backup, the backup route's AD must be strictly greater than the primary route's AD (e.g., AD > 20).

Anahtar Kavram

Floating Static Route Administrative Distance Requirements
Tahmini Süre:1m 30s
Soru 308Soru →

An engineer is configuring a fully specified IPv6 static route on a Cisco router to forward traffic destined for 2001:db8:abc:33::/642001:\text{db8}:\text{abc}:33::/64. What local interface keyword completes the command syntax when using the next-hop link-local address fe80::cafe\text{fe80}::\text{cafe} via interface GigabitEthernet0/0/2?

Aşağıdaki boşlukları doldurun

Router(config)# ipv6 route 2001:db8:abc:33::/64 fe80::cafe
Cevabı ve açıklamayı göster

Cevap

GigabitEthernet0/0/2 (or Gi0/0/2)
When configuring an IPv6 static route with a link-local next-hop address, Cisco IOS requires the local exit interface (GigabitEthernet0/0/2) to precede the link-local IPv6 address. Without the exit interface, the router cannot determine which local link reaches the specified link-local address.

Adım Adım Çözüm

1
Identify the mandatory components of a link-local IPv6 static route in Cisco IOS.
When a link-local address (FE80::/10) is specified as the next hop, Cisco IOS requires the local exit interface to be included preceding the next-hop address.
Link-local addresses are non-routable and exist independently on every link, making them ambiguous without specifying the outbound local interface.
2
Complete the command syntax.
The proper command structure is 'ipv6 route <destination-prefix/prefix-length> <exit-interface> <link-local-address>'. Inserting GigabitEthernet0/0/2 into {{blank_1}} correctly specifies the route.
This provides both interface scope and next-hop link-local identification.

Anahtar Kavram

Fully specified IPv6 static routes with link-local next hops
Soru 309Soru →

A network engineer is configuring IPv4 static routes on a Cisco IOS router. Which TWO statements accurately describe the characteristics and syntax of Cisco IPv4 static routing? (Select two.)

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: A floating static route must be configured with an administrative distance higher than the administrative distance of the primary route.; Static routes configured pointing directly to a point-to-point exit interface do not require a recursive lookup to resolve the next-hop IP address.

Cevap

The two correct statements state that a floating static route requires an administrative distance higher than the primary route, and that static routes pointing to a point-to-point exit interface bypass recursive lookup.
Floating static routes rely on having a higher administrative distance than the primary route so they stay out of the routing table until the primary route fails. Additionally, specifying a point-to-point exit interface allows direct frame transmission without a recursive next-hop lookup.

Adım Adım Çözüm

1
Evaluate the administrative distance requirement for floating static routes.
Floating static routes are designed as backup routes. Routers prefer lower administrative distance (AD) values. Therefore, a floating static route must have a higher AD than the primary route to remain inactive until the primary route fails.
Lower AD indicates higher trustworthiness in Cisco IOS forwarding decisions.
2
Analyze how next-hop resolution works with point-to-point exit interfaces.
Specifying a point-to-point exit interface resolves the egress interface immediately without needing a second (recursive) lookup for a next-hop IP address.
Point-to-point links have only one destination on the link, so the router knows directly where to send frames.
3
Verify incorrect distractor statements.
Setting an AD of 10 for a backup to EIGRP (AD 90) makes the static route active immediately, overriding EIGRP instead of floating behind it. Additionally, static route syntax uses subnet masks, not wildcard masks.
Wildcard masks are syntax elements of ACLs/OSPF, not Cisco IOS 'ip route' commands.

Anahtar Kavram

IPv4 Static Route Syntax and Floating Static Route Principles
Soru 310Soru →

A Cisco router is running OSPFv2 with an active Loopback 0 interface (10.10.10.1/32) and a GigabitEthernet0/0 interface (192.168.1.1/24). No explicit router ID command was configured under the OSPF process, so OSPF selected 10.10.10.1 as the Router ID when the process initialized. A network engineer subsequently configures a new Loopback 1 interface with IP address 172.16.100.1/32 and brings it into an operational up/up state. Which statement accurately describes the status of the OSPF Router ID immediately after Loopback 1 is brought up?

Cevabı ve açıklamayı göster

Cevap: The OSPF Router ID remains 10.10.10.1 until the OSPF process is restarted or the router is reloaded.

Cevap

The OSPF Router ID remains 10.10.10.1 until the OSPF process is restarted or the router is reloaded.
OSPF Router ID selection is non-preemptive. Once the OSPF routing process selects a Router ID at startup (10.10.10.1 from the active Loopback 0), it retains that Router ID even if another interface with a higher IP address (such as Loopback 1 at 172.16.100.1) is subsequently configured and brought up. The new Router ID will only take effect if the OSPF process is manually reset (using 'clear ip ospf process') or if the router is rebooted.

Adım Adım Çözüm

1
Determine initial OSPF Router ID election outcome.
OSPF selected 10.10.10.1 because Loopback 0 was the highest IP active loopback interface when the OSPF process initialized.
OSPF follows election precedence: manual 'router-id' command > highest IP among active loopbacks > highest IP among active physical interfaces.
2
Analyze OSPF Router ID election behavior upon configuration changes.
The OSPF process maintains its currently active Router ID and does not preempt it when a new interface with a higher IP address is brought up.
Router ID stability prevents unnecessary SPF recalculations and neighbor adjacency resets. A process restart (e.g., using 'clear ip ospf process') is required to force re-election.

Anahtar Kavram

OSPFv2 Router ID Non-Preemptive Election Logic
Soru 311Soru →

A Cisco router starts an OSPFv2 process without an explicitly configured router ID using the 'router-id' command. The router has the following active interfaces:

- Loopback 0: 10.1.1.1/32
- Loopback 1: 10.2.2.2/32
- GigabitEthernet 0/0: 172.16.10.1/24
- GigabitEthernet 0/1: 192.168.1.1/24

Which IPv4 address will OSPFv2 select as the router ID?

Cevabı ve açıklamayı göster

Cevap: 10.2.2.2

Cevap

10.2.2.2
When no manual router ID is specified via the 'router-id' command, OSPFv2 selects the highest IPv4 address of any active loopback interface. Between Loopback 0 (10.1.1.1) and Loopback 1 (10.2.2.2), 10.2.2.2 is the higher IP address and is selected as the Router ID.

Adım Adım Çözüm

1
Check for an explicitly configured router ID
No explicit 'router-id' command has been configured.
Explicit configuration takes top priority in OSPF router ID selection.
2
Evaluate active loopback interfaces
Two active loopbacks exist: 10.1.1.1 and 10.2.2.2.
Loopback interfaces take precedence over physical interfaces.
3
Select the highest IPv4 address among active loopback interfaces
10.2.2.2 is higher than 10.1.1.1, making 10.2.2.2 the chosen OSPF Router ID.
When multiple loopbacks are present, OSPF breaks the tie using the highest IPv4 address.

Anahtar Kavram

OSPFv2 Router ID Selection Priority
Soru 312Soru →

An enterprise router R1 learns the path to a remote branch subnet 10.150.0.0/1610.150.0.0/16 via Internal EIGRP, which has a default administrative distance of 9090. A network engineer intends to configure a secondary floating static route via next-hop IP 192.168.99.2192.168.99.2 to serve strictly as a backup path when EIGRP fails. However, the engineer enters the following command on R1:

`ip route 10.150.0.0 255.255.0.0 192.168.99.2 85`

Which two statements correctly describe the operational impact of this configuration? (Select two.)

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: The newly configured static route will immediately enter the Routing Information Base (RIB) and displace the EIGRP route as the active path.; To function correctly as a floating static backup route, the static route's administrative distance must be configured with a value greater than 90.

Cevap

The static route will immediately enter the routing table and displace the EIGRP route because its assigned administrative distance (85) is lower than Internal EIGRP (90). To act as a backup floating static route, its administrative distance must be set to a value greater than 90.
Cisco routers select routes from different routing sources based on Administrative Distance (AD), where lower AD values indicate higher preference. Internal EIGRP has a default AD of 90. Because the static route command explicitly defines an AD of 85, the static route is considered more trustworthy than EIGRP and is immediately placed into the routing table. To function properly as a floating static route, the static route must have an AD set higher than the primary route's AD (greater than 90) so it remains inactive until the primary EIGRP route vanishes.

Adım Adım Çözüm

1
Identify the administrative distance of the primary route protocol.
Internal EIGRP has a default Administrative Distance (AD) of 90.
Administrative Distance defines the trustworthiness of a routing information source in Cisco IOS.
2
Analyze the configured static route's administrative distance parameter.
The command `ip route 10.150.0.0 255.255.0.0 192.168.99.2 85` explicitly assigns an AD of 85 to the static route.
The trailing numeric argument in the `ip route` syntax overrides the default static route AD of 1.
3
Compare administrative distances to determine routing table (RIB) selection.
Since 85<9085 < 90, the static route wins route selection over Internal EIGRP and is immediately installed into the RIB as the active route.
Lower AD values are strictly preferred over higher AD values.
4
Determine the necessary administrative distance for floating static functionality.
To float (remain inactive until the EIGRP path fails), the static route must be configured with an AD value strictly greater than 90 (e.g., 95, 130).
Floating static routes rely on a higher AD so they are suppressed while the lower-AD primary route is present in the routing table.

Anahtar Kavram

Floating Static Route Administrative Distance Selection
Soru 313Soru →

Four OSPFv2 routers are connected to a shared Layer 2 Ethernet switch on the 192.168.10.0/24 broadcast multiaccess network in Area 0. The interface configurations and boot order are as follows:

1. First, Router R3 (Priority 1, Router ID 10.3.3.3) and Router R4 (Priority 2, Router ID 10.1.1.1) booted up and established an adjacency. R4 was elected as the Designated Router (DR) and R3 was elected as the Backup Designated Router (BDR).
2. Later, Router R1 (Priority 0, Router ID 10.10.10.10) and Router R2 (Priority 2, Router ID 10.2.2.2) joined the segment and established adjacencies with all routers.

If Router R4 suddenly suffers a power outage and drops offline, which routers will assume the roles of Designated Router (DR) and Backup Designated Router (BDR) on this network segment?

Cevabı ve açıklamayı göster

Cevap: Router R3 becomes the DR, and Router R2 becomes the BDR.

Cevap

Router R3 becomes the Designated Router (DR), and Router R2 becomes the Backup Designated Router (BDR).
When the active Designated Router (R4) fails, OSPF non-preemption rules mandate that the existing Backup Designated Router (R3) is automatically promoted to DR. An election is then held solely for the newly vacated BDR position. Between the remaining routers, R1 is ineligible due to its OSPF priority of 0, leaving R2 (Priority 2) as the sole eligible router to become BDR.

Adım Adım Çözüm

1
Evaluate initial state prior to failure.
R4 is DR (Priority 2) and R3 is BDR (Priority 1). When R1 (Priority 0) and R2 (Priority 2) join later, no preemption occurs. R4 remains DR and R3 remains BDR.
OSPF DR and BDR roles are non-preemptive once elected on a broadcast multiaccess segment.
2
Determine DR replacement when R4 fails.
R3 (the active BDR) immediately transitions to DR.
When an active DR fails, the existing BDR is automatically promoted to DR without triggering a brand new DR election from scratch.
3
Evaluate candidates for the vacant BDR role among remaining active routers (R1 and R2).
R1 is disqualified because its priority is 0 (`ip ospf priority 0`). R2 has priority 2 (> 0) and is eligible.
Routers with an OSPF priority of 0 are permanently excluded from DR/BDR elections and remain in DROTHER state.
4
Conclude final roles.
R3 is DR and R2 is elected as the new BDR.
R2 is the only remaining eligible router with a priority greater than 0.

Anahtar Kavram

OSPF DR/BDR election rules: Non-preemption, BDR promotion, and Priority 0 exclusion.
Tahmini Süre:2m 0s
Soru 314Soru →

An administrator connects a router interface to a broadcast multiaccess Ethernet network running OSPFv2. The administrator executes the command `ip ospf priority 0` under the interface configuration mode. How will this router participate in the OSPF Designated Router (DR) and Backup Designated Router (BDR) election on this segment?

Cevabı ve açıklamayı göster

Cevap: It becomes completely ineligible to serve as a DR or BDR.

Cevap

The router becomes completely ineligible to serve as a DR or BDR on the network segment.
Configuring `ip ospf priority 0` explicitly disables a router's eligibility to participate in Designated Router (DR) and Backup Designated Router (BDR) elections on multiaccess network types. The router will always remain in the DROTHER state for that interface segment.

Adım Adım Çözüm

1
Evaluate the interface priority value
The command `ip ospf priority 0` sets the OSPF priority for the interface to 0.
In OSPFv2, interface priority determines DR/BDR election participation (default priority is 1).
2
Apply OSPF DR/BDR election rules for priority 0
A priority of 0 prevents the interface from ever becoming a DR or BDR.
Routers with a priority of 0 remain in the DROTHER state on multiaccess networks.

Anahtar Kavram

OSPF Interface Priority 0 Ineligibility
Soru 315Soru →

A Cisco router receives an IPv4 unicast packet on an ingress interface and prepares to forward it toward its final destination. Place the sequential steps of the router's packet forwarding decision process in the correct chronological order from first to last.

Öğeleri doğru sıraya koymak için sürükleyin

Cevabı ve açıklamayı göster

Cevap

The correct sequence starts with decapsulating the incoming Layer 2 frame, searching the routing table for candidate prefix matches, selecting the best match using Longest Prefix Match (LPM), determining the egress interface and next-hop IP, resolving the Layer 2 address of the next-hop device via ARP, and finally decrementing the TTL and encapsulating the packet into a new frame for transmission.
The router processes ingress packets sequentially: it first strips the Layer 2 frame to read the destination IP, searches the routing table, applies the Longest Prefix Match rule to pick the most specific network prefix, determines the next-hop IP and egress interface, resolves the next-hop Layer 2 MAC address, and finishes by decrementing TTL, updating the checksum, encapsulating the packet, and transmitting the frame.

Adım Adım Çözüm

1
Frame Ingress & Decapsulation
The router strips the Layer 2 frame header/trailer to inspect the Layer 3 destination IPv4 address.
Routing decisions occur at Layer 3, requiring packet header extraction.
2
Routing Table Candidate Lookup
Identifies all routes in the IPv4 routing table that contain the destination IP address.
All matching network entries must be collected before evaluating prefix specificity.
3
Longest Prefix Match Selection
The route with the longest subnet mask (most matching network bits) is selected as the forwarding path.
Longest Prefix Match is the primary criterion for route lookup selection during packet forwarding.
4
Egress Interface & Next-Hop Identification
Extracted destination next-hop IPv4 address and outgoing physical/logical interface.
The selected route specifies where to send the packet next.
5
Layer 2 Next-Hop Address Resolution
ARP table lookup retrieves the MAC address associated with the next-hop IP.
Data-link layer framing requires a destination hardware address on Ethernet media.
6
Header Modification, Encapsulation, and Egress Transmission
TTL is decremented, checksum recalculated, new Layer 2 header attached, and frame sent out egress port.
Prevents routing loops via TTL expiration and prepares frame for transit across the next physical link segment.

Anahtar Kavram

Router IPv4 Forwarding Decision Pipeline
Soru 316Soru →

An administrator is configuring a backup floating static route on a Cisco router for destination network 10.50.0.0/1610.50.0.0/16. The primary path to this network is currently learned via EIGRP with an administrative distance of 90. Which `ip route` command correctly implements a backup static route via next-hop IP 192.168.100.2192.168.100.2 that takes effect only if the primary EIGRP route fails?

Cevabı ve açıklamayı göster

Cevap: ip route 10.50.0.0 255.255.0.0 192.168.100.2 95

Cevap

The command 'ip route 10.50.0.0 255.255.0.0 192.168.100.2 95' correctly configures a floating static route by specifying a higher Administrative Distance (95) than EIGRP (90).
The correct option uses valid Cisco IOS static route syntax with a standard subnet mask (255.255.0.0) and assigns an administrative distance of 95. Because 95 is higher than the primary EIGRP path AD of 90, the route remains inactive in the routing table until the primary EIGRP path becomes unavailable.

Adım Adım Çözüm

1
Identify the Administrative Distance (AD) of the primary dynamic routing protocol
EIGRP internal routes have a default Administrative Distance of 90.
Floating static routes must have an AD higher than the primary route's AD to remain inactive until the primary route fails.
2
Verify standard Cisco IOS IPv4 static routing CLI syntax
The correct format is 'ip route <destination-network> <subnet-mask> <next-hop-ip> [administrative-distance]'.
IPv4 static routes require dotted-decimal subnet masks rather than wildcard masks.
3
Select the command with a valid subnet mask and an AD greater than 90
An AD of 95 ensures the static route is floating and only populated in the routing table when the EIGRP route is withdrawn.
An AD of 95 is strictly greater than 90 and less than the default static route AD of 1 or backup limits.

Anahtar Kavram

Floating Static Route Administrative Distance Selection
Soru 317Soru →

Two Cisco routers are directly connected via an Ethernet link and configured to run OSPFv2 in Area 0. Router A is configured with an OSPF Hello interval of 10 seconds, while Router B is configured with an OSPF Hello interval of 15 seconds. Which outcome will occur when the OSPF process runs between these two routers?

Cevabı ve açıklamayı göster

Cevap: The routers will fail to form a neighbor relationship because OSPF Hello intervals must match exactly.

Cevap

The routers will fail to form a neighbor relationship because OSPF Hello intervals must match exactly.
For two routers to establish an OSPFv2 neighbor adjacency, several parameters contained in OSPF Hello packets must match exactly. These include the Area ID, Subnet Mask, Hello/Dead intervals, Authentication parameters, and Stub Area flags. Because Router A is configured with a 10-second Hello timer and Router B with a 15-second Hello timer, the routers reject each other's Hello packets and fail to form an adjacency.

Adım Adım Çözüm

1
Identify the OSPF neighbor requirement being tested
OSPF neighbor adjacencies require key parameters inside Hello packets to match between directly connected interfaces.
OSPF routers exchange Hello packets to discover neighbors and verify compatibility before forming adjacencies.
2
Evaluate the configured parameters
Router A has a 10-second Hello interval, whereas Router B has a 15-second Hello interval.
Hello/Dead intervals are mandatory matching parameters in OSPFv2.
3
Determine the operational outcome
Because the Hello intervals differ, each router will drop the incoming Hello packets from the other router, preventing adjacency formation.
Timer mismatch blocks the transition from Init to 2-Way/Full state.

Anahtar Kavram

OSPFv2 Neighbor Adjacency Requirements (Hello/Dead Timers)
Soru 318Soru →

An administrator observes the following command output on Router R2 regarding a broadcast multiaccess Ethernet segment:

text
R2# show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 1 FULL/DR 00:00:35 10.1.1.1 GigabitEthernet0/0
3.3.3.3 1 FULL/BDR 00:00:32 10.1.1.3 GigabitEthernet0/0
10.10.10.10 0 FULL/DROTHER 00:00:38 10.1.1.10 GigabitEthernet0/0

The administrator executes `clear ip ospf process` simultaneously across all routers on this segment to trigger a new election. Assuming all routers re-establish OSPF neighbor relationships at the same time, which router will be elected as the new Designated Router (DR) and why?

Cevabı ve açıklamayı göster

Cevap: Router 3.3.3.3 will be elected as DR because Router 10.10.10.10 is ineligible due to a priority of 0, and Router 3.3.3.3 has the highest Router ID among the eligible routers.

Cevap

Router 3.3.3.3 will be elected as DR because Router 10.10.10.10 is ineligible due to a priority of 0, and Router 3.3.3.3 has the highest Router ID among the eligible routers.
On multiaccess broadcast networks, OSPF DR/BDR elections evaluate interface priority first. A router configured with priority 0 is completely ineligible to become a DR or BDR. Among the remaining eligible routers (1.1.1.1, 2.2.2.2, and 3.3.3.3), all have equal priority (1), so the highest Router ID breaks the tie. Router 3.3.3.3 has the highest Router ID among eligible routers and is elected DR.

Adım Adım Çözüm

1
Evaluate OSPF interface priority values for election eligibility.
Router 10.10.10.10 has priority 0 and is disqualified from DR/BDR candidacy.
Setting the OSPF interface priority to 0 (`ip ospf priority 0`) makes a router completely ineligible to become DR or BDR.
2
Compare priority values of remaining candidate routers.
Router 1.1.1.1 (Pri 1), Router 2.2.2.2 (Pri 1), and Router 3.3.3.3 (Pri 1) are tied.
All remaining eligible routers share the default interface priority of 1.
3
Apply the tie-breaker criterion (highest OSPF Router ID).
Router 3.3.3.3 wins the DR role.
When eligible candidates have equal non-zero priority, the router with the numerically highest Router ID (3.3.3.3 > 2.2.2.2 > 1.1.1.1) is selected as DR.

Anahtar Kavram

OSPFv2 DR/BDR Election Criteria and Priority 0 Ineligibility
Soru 319Soru →

A network engineer configures an OSPFv2 process on a router interface connected to a broadcast multiaccess Ethernet network. The engineer issues the command `ip ospf priority 0` on the interface. How does this specific priority configuration affect the router's role in the OSPF DR/BDR election process?

Cevabı ve açıklamayı göster

Cevap: The interface is strictly prohibited from participating in the election and remains in the DROTHER state.

Cevap

Setting an OSPF interface priority to 0 disqualifies the router from participating in elections, forcing its state to DROTHER.
In OSPFv2, interface priority ranges from 0 to 255. A priority of 0 specifically signifies that the router is disqualified from becoming either the Designated Router (DR) or the Backup Designated Router (BDR) on a multiaccess network segment. As a result, the interface transitions to and stays in the DROTHER state.

Adım Adım Çözüm

1
Evaluate the effect of the interface subcommand `ip ospf priority <0-255>` on multiaccess networks.
The default priority on multiaccess interfaces is 1.
Higher priority values are preferred during DR/BDR elections.
2
Determine the special significance of priority value 0.
A priority of 0 explicitly makes the interface ineligible to become DR or BDR.
This is a design mechanism used to prevent hub or low-capacity routers from accepting DR/BDR responsibilities.

Anahtar Kavram

OSPF Interface Priority 0 Selection Ineligibility
Tahmini Süre:45s
Soru 320Soru →

A network administrator evaluates an OSPFv2-enabled router interface on a multiaccess Ethernet network and issues the following Cisco IOS command:

text
Router1# show ip ospf interface GigabitEthernet0/1
GigabitEthernet0/1 is up, line protocol is up
Internet Address 192.168.10.1/24, Area 0
Process ID 1, Router ID 10.1.1.1, Network Type BROADCAST, Cost: 1
Trans Delay is 1 sec, State DROTHER, Priority 0
Designated Router (ID) 10.4.4.4, Interface address 192.168.10.4
Backup Designated Router (ID) 10.3.3.3, Interface address 192.168.10.3
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

Which two statements accurately describe the operational status and election behavior of this router on the segment? (Choose two.)

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: The router is completely ineligible to be elected as Designated Router (DR) or Backup Designated Router (BDR) because its interface priority is set to 0.; If the active Designated Router (10.4.4.4) fails, the Backup Designated Router (10.3.3.3) will be promoted to Designated Router while this router remains a DROTHER.

Cevap

The correct statements are that the router is completely ineligible for DR/BDR election due to an interface priority of 0, and that if the active DR fails, the active BDR will be promoted to DR while this router remains a DROTHER.
In OSPFv2 broadcast multiaccess networks, setting an interface priority to 0 makes the router completely ineligible for Designated Router (DR) or Backup Designated Router (BDR) roles, forcing it into the DROTHER state. Furthermore, when an active DR fails, the existing BDR is promoted to DR. Because this router's priority is 0, it cannot participate in the election for the replacement BDR and remains a DROTHER.

Adım Adım Çözüm

1
Analyze interface priority settings from the command output.
The interface priority is configured as Priority 0.
In OSPFv2, an interface priority of 0 signifies that the router is ineligible to participate in DR or BDR elections.
2
Determine the router's current state and election behavior.
The state is DROTHER, and it will remain in this state even if the active DR fails.
Upon DR failure, the current BDR (10.3.3.3) takes over as DR. A new BDR election occurs among eligible routers (priority > 0). Since this router has priority 0, it cannot become the new BDR.
3
Evaluate preemption and alternative network types.
OSPF DR/BDR elections are non-preemptive, and Point-to-Point links suppress DR/BDR elections entirely.
Modifying priorities does not trigger preemption on broadcast links, and changing to Point-to-Point eliminates DR/BDR roles entirely.

Anahtar Kavram

OSPFv2 DR/BDR Election Rules and Priority 0 Ineligibility
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