Examkin

IP Connectivity

493 soru

Tüm türler493Çoktan seçmeli250Çoklu seçim113Eşleştirme25Sıralama60Boşluk doldurma22Kısa cevap23
Soru 221Soru →

A network administrator needs to manually configure an IPv6 static route on router R2 to forward traffic toward subnet 2001:db8:cafe:20::/642001:\text{db8}:cafe:20::/64. The next-hop router R1 uses a link-local IPv6 address of fe80::1\text{fe80}::1 on the shared point-to-point link attached to R2's local interface GigabitEthernet0/1. Which Cisco IOS command correctly configures this route?

Cevabı ve açıklamayı göster

Cevap: ipv6 route 2001:db8:cafe:20::/64 GigabitEthernet0/1 fe80::1

Cevap

The command 'ipv6 route 2001:db8:cafe:20::/64 GigabitEthernet0/1 fe80::1' correctly configures the fully specified IPv6 static route.
In IPv6 static routing, when a link-local address (fe80::/10 range) is referenced as the next-hop address, the router requires a fully specified route. The syntax must explicitly state the local outbound interface followed by the link-local IPv6 address.

Adım Adım Çözüm

1
Identify the target IPv6 prefix, exit interface, and next-hop address type.
Destination is 2001:db8:cafe:20::/642001:\text{db8}:cafe:20::/64, local exit interface is GigabitEthernet0/1, and next-hop is link-local address fe80::1\text{fe80}::1.
IPv6 link-local addresses are non-routable beyond the local link and can exist on multiple interface links on the same router.
2
Apply Cisco IOS IPv6 fully specified static route syntax rules.
The correct command format is 'ipv6 route <ipv6-prefix/prefix-length> <exit-interface> <link-local-next-hop>'.
Without the local exit interface parameter specified first, the router cannot resolve which link the link-local neighbor resides on.

Anahtar Kavram

IPv6 Fully Specified Static Routing with Link-Local Next-Hop
Tahmini Süre:1m 30s
Soru 222Soru →

Router HQ-RTR has been actively running OSPFv2 process 10 with several interfaces active. When the OSPF process was originally started, the active interfaces were Loopback0 (172.16.1.1/32), GigabitEthernet0/0 (192.168.1.1/24), and GigabitEthernet0/1 (10.10.10.1/24), with no explicitly configured router ID.

Later, a network engineer configures Loopback1 with IP address 10.255.255.255/32 and executes the command `router-id 1.1.1.1` under OSPF process 10. However, the engineer does not reload the router or restart the OSPF process.

When HQ-RTR sends Hello packets to a newly connected OSPF neighbor on GigabitEthernet0/0, which IP address is used as HQ-RTR's OSPF Router ID?

Cevabı ve açıklamayı göster

Cevap: 172.16.1.1, because OSPF Router ID changes are non-preemptive and require restarting the OSPF process to take effect

Cevap

172.16.1.1, because OSPF Router ID changes are non-preemptive and require restarting the OSPF process to take effect
The correct answer explains that OSPF Router ID election is non-preemptive. When OSPF process 10 was first initialized, Loopback0 (172.16.1.1) was chosen as the Router ID because it had the highest IP address among active loopback interfaces. Subsequent changes—such as adding a higher loopback address or entering the `router-id` command—will take effect only after restarting the OSPF process using `clear ip ospf process` or reloading the router.

Adım Adım Çözüm

1
Determine initial OSPF Router ID selection
Loopback0 (172.16.1.1) was selected as the Router ID when OSPF process 10 initially started, as it was the highest IP address on an active loopback interface.
OSPF Router ID selection order is: 1) manual `router-id` command, 2) highest IP on an active loopback interface, 3) highest IP on an active physical interface.
2
Evaluate the impact of subsequent configuration changes without process restart
Configuring Loopback1 (10.255.255.255) and setting `router-id 1.1.1.1` updates the configured state in running-config, but does NOT dynamically update the active operational Router ID.
OSPF Router ID election is non-preemptive. Changes take effect only after the router reboots or the administrator executes `clear ip ospf process`.
3
Identify the active Router ID used in outgoing Hello packets
The active Router ID remains 172.16.1.1.
Because no process restart occurred, HQ-RTR continues to identify itself using 172.16.1.1 in OSPF Hello packets.

Anahtar Kavram

OSPFv2 Router ID Precedence and Non-Preemptive Election Logic
Soru 223Soru →

A network administrator needs to configure a backup floating static default route on router Edge-R1 to reach an upstream provider. The primary default route is currently learned via OSPFv3 with an administrative distance of 110110. The next-hop provider router interface has a global unicast address of 2001:db8:200:1::1/642001:\text{db8}:200:1::1/64 and a link-local address of fe80::250:56ff:fe9a:1234\text{fe80}::250:56\text{ff}:\text{fe9a}:1234 connected directly to interface GigabitEthernet0/0/0 on Edge-R1. Which command correctly configures the floating static default route using the provider's link-local address with an administrative distance of 130130?

Cevabı ve açıklamayı göster

Cevap: ipv6 route ::/0 GigabitEthernet0/0/0 fe80::250:56ff:fe9a:1234 130

Cevap

The correct command is 'ipv6 route ::/0 GigabitEthernet0/0/0 fe80::250:56ff:fe9a:1234 130'.
The option specifying 'ipv6 route ::/0 GigabitEthernet0/0/0 fe80::250:56ff:fe9a:1234 130' is correct because '::/0' represents the default route, the exit interface GigabitEthernet0/0/0 is explicitly declared alongside the link-local next hop, and the administrative distance of 130 makes it a floating static backup route relative to OSPFv3 (110).

Adım Adım Çözüm

1
Identify the IPv6 network prefix representation for a default route.
The default route in IPv6 is represented by the prefix '::/0'.
Default routes match all destination IPv6 addresses not specifically listed in the routing table.
2
Determine the syntax requirements for specifying a link-local address as a next-hop.
When a link-local address (fe80::/10) is specified as the next hop, the local exit interface (GigabitEthernet0/0/0) must precede the next-hop address.
Link-local addresses are only unique on the local link, requiring explicit egress interface designation.
3
Set the administrative distance for floating static route functionality.
Set the administrative distance to 130, which is higher than OSPFv3's administrative distance of 110.
A floating static route remains inactive in the routing table until the primary dynamic routing path fails.

Anahtar Kavram

IPv6 Static Route Syntax with Link-Local Next-Hop and Floating Administrative Distance
Soru 224Soru →

A network administrator needs to configure a backup static route to destination network 192.168.50.0/24 via next-hop IP address 10.1.1.2. The primary route to this network is learned dynamically through OSPF, which has a default administrative distance of 110. Which command correctly configures a floating static route that remains inactive in the routing table until the primary OSPF route fails?

Cevabı ve açıklamayı göster

Cevap: ip route 192.168.50.0 255.255.255.0 10.1.1.2 120

Cevap

The command 'ip route 192.168.50.0 255.255.255.0 10.1.1.2 120' correctly configures the floating static route.
A floating static route acts as a backup path and must be configured with an administrative distance higher than the primary route's protocol. Because OSPF has a default administrative distance of 110, setting the static route's administrative distance to 120 ensures it stays out of the routing table until the primary OSPF path fails.

Adım Adım Çözüm

1
Determine the administrative distance of the primary routing protocol
OSPF has a default administrative distance of 110.
A floating static route must have a higher administrative distance than the primary route to remain inactive while the primary route is operational.
2
Select an administrative distance value for the static route higher than 110
The value 120 is greater than 110.
Specifying 120 at the end of the 'ip route' command creates a floating static route that only enters the routing table if the OSPF route (110) disappears.

Anahtar Kavram

Floating Static Routes and Administrative Distance
Soru 225Soru →

Which TWO parameters in OSPFv2 Hello packets must match between two neighboring Cisco routers for them to successfully form an OSPF neighbor adjacency? (Select TWO.)

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: OSPF Area ID; Hello and Dead timer intervals

Cevap

The OSPF Area ID and the Hello/Dead timer intervals must match between neighboring routers to establish an OSPF adjacency.
For two routers to establish an OSPFv2 neighbor adjacency, key configuration parameters exchanged in Hello packets must match. Specifically, the Area ID and the Hello/Dead timer intervals must be identical on both sides of the link.

Adım Adım Çözüm

1
Identify OSPF neighbor adjacency requirements
Neighboring routers exchange Hello packets containing configuration parameters.
For an OSPF adjacency to reach FULL state, specific fields in the Hello packet must match on both routers.
2
Evaluate the parameters
Area ID and Hello/Dead timer intervals are mandatory matching parameters.
Router IDs must be unique per router, and Process IDs are only locally significant.

Anahtar Kavram

OSPFv2 Hello Packet Adjacency Requirements
Soru 226Soru →

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

text
Gateway of last resort is 192.168.1.1 to network 0.0.0.0

S* 0.0.0.0/0 [1/0] via 192.168.1.1
10.0.0.0/8 is variably subnetted, 4 subnets, 3 masks
O 10.150.0.0/16 [110/20] via 172.16.1.1, 00:10:22, GigabitEthernet0/0/1
D 10.150.45.128/25 [90/307200] via 172.16.2.1, 00:05:12, GigabitEthernet0/0/2
S 10.150.45.136/29 [1/0] via 172.16.3.1
O 10.150.45.136/30 [110/50] via 172.16.4.1, 00:01:45, GigabitEthernet0/0/3

The router receives an IPv4 packet destined for 10.150.45.13810.150.45.138. Which next-hop IP address will the router select to forward this packet?

Cevabı ve açıklamayı göster

Cevap: 172.16.4.1

Cevap

The router forwards the packet to next-hop IP address 172.16.4.1.
When a router receives a packet, it compares the destination IP address against all entries in its routing table. The rule of Longest Prefix Match (LPM) dictates that the route with the most specific (longest) subnet mask is selected. The target IP address 10.150.45.138 matches multiple routes, but 10.150.45.136/30 has the longest prefix mask (/30 vs /29, /25, /16, /0). The next-hop IP for 10.150.45.136/30 is 172.16.4.1.

Adım Adım Çözüm

1
Identify all candidate routes matching the destination IP address 10.150.45.138.
Matching routes in table: 0.0.0.0/0, 10.150.0.0/16, 10.150.45.128/25, 10.150.45.136/29, and 10.150.45.136/30.
The IP address 10.150.45.138 falls within the address range of all listed subnets.
2
Compare the prefix lengths (subnet masks) of all matching routes to determine the Longest Prefix Match (LPM).
Prefix lengths are /0, /16, /25, /29, and /30. The /30 prefix is the longest and most specific match.
Cisco IP forwarding logic evaluates subnet mask length first before checking Administrative Distance or metric.
3
Determine the next-hop IP address associated with the winning /30 route.
Route 10.150.45.136/30 points to next-hop IP 172.16.4.1.
The router selects the next-hop tied directly to the route entry with the longest prefix match.

Anahtar Kavram

Router Forwarding Decision Logic (Longest Prefix Match Rule)
Tahmini Süre:1m 30s
Soru 227Soru →

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

text
Gateway of last resort is 10.10.10.1 to network 0.0.0.0

D 192.168.16.0/20 [90/307200] via 10.1.1.2, GigabitEthernet0/0
O 192.168.24.0/22 [110/20] via 10.2.2.2, GigabitEthernet0/1
S 192.168.24.0/24 [1/0] via 10.3.3.2, GigabitEthernet0/2
S* 0.0.0.0/0 [1/0] via 10.10.10.1, GigabitEthernet0/3

Which TWO statements correctly describe how the router makes forwarding decisions based on this routing table?

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: A packet with destination IP 192.168.24.45 is routed via GigabitEthernet0/2 because 192.168.24.0/24 represents the longest prefix match.; Longest prefix match is evaluated first during packet forwarding lookup, independent of administrative distance values across different prefix lengths.

Cevap

The router routes traffic destined for 192.168.24.45 out interface GigabitEthernet0/2 using the longest prefix match (/24), and longest prefix match logic is evaluated prior to administrative distance during the forwarding lookup.
When a router receives a packet, it compares the packet's destination IP address against all network entries in its routing table. The rule of Longest Prefix Match (LPM) specifies that the route with the most specific (longest) subnet mask is chosen for forwarding, regardless of protocol or administrative distance. Furthermore, administrative distance is utilized when populating the routing table between equal prefix matches, not during the packet packet forwarding lookup process.

Adım Adım Çözüm

1
Evaluate all candidate matching routes for destination address 192.168.24.45.
The destination falls within 192.168.16.0/20 (range 192.168.16.0–192.168.31.255), 192.168.24.0/22 (range 192.168.24.0–192.168.27.255), 192.168.24.0/24 (range 192.168.24.0–192.168.24.255), and 0.0.0.0/0.
Routing decision logic compares the destination binary pattern against all active routes in the RIB.
2
Determine the winning route based on the Longest Prefix Match (LPM) rule.
192.168.24.0/24 has 24 matching bits, which is the maximum matching prefix length among all candidate entries.
The router always selects the route entry with the highest number of matching leading bits.
3
Analyze the relationship between Administrative Distance (AD) and Longest Prefix Match.
Administrative distance is used during routing table selection when installing paths from different routing sources with exact matching prefixes. For packet forwarding lookups, LPM is evaluated first.
Administrative distance does not override a longer subnet mask during packet forwarding decisions.

Anahtar Kavram

Router Forwarding Decision Logic (Longest Prefix Match precedence over Administrative Distance)
Soru 228Soru →

An enterprise Cisco IOS-XE router displays the following IPv4 routing table entries:

text
Gateway of last resort is not set

172.16.0.0/16 is variably subnetted, 4 subnets, 3 masks
O 172.16.10.0/24 [110/65] via 10.0.0.1, 01:15:22, GigabitEthernet0/1
D 172.16.10.0/25 [90/307200] via 10.0.0.2, 00:45:10, GigabitEthernet0/2
S 172.16.0.0/16 [1/0] via 10.0.0.3
C 172.16.10.128/25 is directly connected, GigabitEthernet0/3

Which two statements correctly describe how the router processes traffic based on these routing table components?

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: A packet destined to 172.16.10.50 is forwarded out interface GigabitEthernet0/2 because the /25 EIGRP route represents the longest prefix match.; A packet destined to 172.16.10.200 is forwarded out interface GigabitEthernet0/3 because the connected subnet 172.16.10.128/25 is the longest prefix match.

Cevap

Packets destined to 172.16.10.50 are egressed via GigabitEthernet0/2 due to the /25 EIGRP route being the longest prefix match, and packets destined to 172.16.10.200 are egressed via GigabitEthernet0/3 because the connected /25 route provides the longest prefix match for that address range.
Router forwarding decision logic evaluates routes using the Longest Prefix Match (LPM) rule. For 172.16.10.50, the EIGRP subnet 172.16.10.0/25 (/25 mask length) is longer than the OSPF /24 and static /16 routes. For 172.16.10.200, the directly connected subnet 172.16.10.128/25 (/25 mask length) is longer than the OSPF /24 and static /16 routes. Thus, both statements reflecting LPM selections out GigabitEthernet0/2 and GigabitEthernet0/3 are correct.

Adım Adım Çözüm

1
Analyze matching prefix routes for destination address 172.16.10.50.
Destination 172.16.10.50 matches 172.16.0.0/16 (static), 172.16.10.0/24 (OSPF), and 172.16.10.0/25 (EIGRP range 172.16.10.0 - 172.16.10.127).
Routing decisions prioritize prefix mask length over Administrative Distance or metric.
2
Determine the forwarding interface for 172.16.10.50.
The /25 route (172.16.10.0/25) has the longest mask length. Traffic is routed via 10.0.0.2 out GigabitEthernet0/2.
Longest Prefix Match (LPM) rule dictates selecting the longest subnet mask among all matching routes.
3
Analyze matching prefix routes for destination address 172.16.10.200.
Destination 172.16.10.200 matches 172.16.0.0/16 (static), 172.16.10.0/24 (OSPF), and 172.16.10.128/25 (Connected range 172.16.10.128 - 172.16.10.255). It does NOT match 172.16.10.0/25.
Address 172.16.10.200 falls strictly into the upper half of the /24 network block.
4
Determine the forwarding interface for 172.16.10.200.
The connected route 172.16.10.128/25 has the longest prefix match (/25 vs /24 vs /16). Traffic egresses directly out GigabitEthernet0/3.
LPM resolution selects /25 over /24 and /16.

Anahtar Kavram

Longest Prefix Match (LPM) Rule in Cisco IPv4 Forwarding
Soru 229Soru →

A network engineer must configure path redundancy on a Cisco IOS router for reaching the remote IPv6 prefix 2001:db8:4000:50::/642001:\text{db8}:4000:50::/64. The primary path must forward packets through interface GigabitEthernet0/0/1 using the next-hop router's link-local IPv6 address fe80::2\text{fe80}::2. The secondary backup path must forward packets toward the global unicast next-hop IPv6 address 2001:db8:1000:20::22001:\text{db8}:1000:20::2 only if the primary path fails. Which TWO Cisco IOS commands are required to satisfy these requirements?

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: ipv6 route 2001:db8:4000:50::/64 GigabitEthernet0/0/1 fe80::2; ipv6 route 2001:db8:4000:50::/64 2001:db8:1000:20::2 130

Cevap

The correct configuration requires both the command specifying the local exit interface alongside the link-local next-hop address ('ipv6 route 2001:db8:4000:50::/64 GigabitEthernet0/0/1 fe80::2') and the command defining a higher administrative distance for the backup route ('ipv6 route 2001:db8:4000:50::/64 2001:db8:1000:20::2 130').
The combination of using a fully-specified route syntax for link-local next-hops ('GigabitEthernet0/0/1 fe80::2') and appending an elevated Administrative Distance of 130 for the global unicast backup path ensures that link-local scoping syntax rules are respected and that the backup route remains floating until primary path failure.

Adım Adım Çözüm

1
Analyze link-local IPv6 static routing requirements.
Link-local addresses (fe80::/10) are only unique per link. Cisco IOS cannot determine which interface to send traffic through if only a link-local next-hop address is provided. Therefore, the exit interface MUST be specified when using a link-local next-hop.
Ensures proper outgoing interface binding for link-scoped IPv6 destinations.
2
Analyze floating static route AD requirements.
To configure a floating static route as a secondary backup path, an Administrative Distance (AD) higher than default static routes (AD 1) must be explicitly appended to the command (e.g., AD 130).
Prevents the secondary route from populating the IPv6 routing table while the primary route is active.

Anahtar Kavram

IPv6 Static Route Syntax & Floating Static Administrative Distance
Soru 230Soru →

A Cisco IOS router (R1) is configured with three routes for the destination prefix 192.168.10.0/24192.168.10.0/24: a primary static route (`ip route 192.168.10.0 255.255.255.0 10.0.12.2`), an active OSPFv2 dynamic route (Administrative Distance 110 via 10.0.14.210.0.14.2), and a backup floating static route (`ip route 192.168.10.0 255.255.255.0 10.0.13.2 120`). Place the control plane and data plane events in the correct chronological sequence starting immediately after the physical interface connected to 10.0.12.210.0.12.2 fails.

Öğeleri doğru sıraya koymak için sürükleyin

Cevabı ve açıklamayı göster

Cevap

The correct sequence of events is: Interface link failure → Primary static route RIB withdrawal → AD evaluation selecting OSPF over floating static → FIB table update → Forwarding of packets via the OSPF path.
When an active egress interface fails, Cisco IOS immediately removes the connected static route from the Routing Information Base (RIB). The router then re-evaluates all available candidate routes for the exact destination prefix (192.168.10.0/24192.168.10.0/24). Because the prefix lengths are identical, the router compares Administrative Distance (AD). OSPF (AD 110) is preferred over the floating static route (AD 120). Once the RIB settles on the OSPF path, the control plane programs the Forwarding Information Base (FIB), and data plane traffic resumes forwarding out the OSPF next-hop.

Adım Adım Çözüm

1
Identify link status change
Interface going down invalidates directly associated static route next-hops.
Cisco IOS requires an active interface to keep static routes active in the RIB.
2
Withdraw primary static route from RIB
Primary static route with Administrative Distance 1 is purged.
Unreachable next-hop interfaces trigger route removal.
3
Compare Administrative Distance of remaining matching prefixes
OSPF route (AD 110) is selected instead of the floating static route (AD 120).
When prefix lengths match exactly (192.168.10.0/24192.168.10.0/24), the route with the lowest Administrative Distance is installed.
4
Update Cisco Express Forwarding (CEF) FIB hardware tables
FIB updates pointer for 192.168.10.0/24192.168.10.0/24 to point to 10.0.14.210.0.14.2.
RIB modifications must sync to the FIB for hardware-accelerated forwarding.
5
Process data plane traffic
Packets targeting 192.168.10.50192.168.10.50 switch path to 10.0.14.210.0.14.2.
Subsequent ingress traffic matches the newly installed FIB lookup entry.

Anahtar Kavram

IPv4 Static Route RIB Lifecycle, Floating Static Administrative Distance Calibration, and CEF FIB Convergence
Soru 231Soru →

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

text
Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 4 subnets, 4 masks
O 10.88.164.32/28 [110/50] via 192.168.12.2, 00:14:22, GigabitEthernet0/0/1
D 10.88.164.0/25 [90/307200] via 192.168.23.3, 01:45:10, GigabitEthernet0/0/2
S 10.88.160.0/20 [1/0] via 192.168.34.4, 12:00:05, GigabitEthernet0/0/3
R 10.88.164.32/29 [120/2] via 192.168.45.5, 00:00:18, GigabitEthernet0/0/4

A packet with destination IP address 10.88.164.3710.88.164.37 arrives at the router. Which two statements correctly describe how the router processes and forwards this packet?

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: The router forwards the packet via next-hop 192.168.45.5 out interface GigabitEthernet0/0/4.; Longest prefix match is evaluated prior to administrative distance and routing protocol metric.

Cevap

The router forwards the packet via next-hop 192.168.45.5 out GigabitEthernet0/0/4, because longest prefix match is evaluated before administrative distance and metric.
When a router receives an IP packet, it searches its routing table for routes that enclose the destination IP address. If multiple routes match, the router strictly selects the route with the longest prefix mask (most specific network mask). Here, 10.88.164.32/29 matches 10.88.164.37 with 29 bits of match, which is longer than /28, /25, or /20. Therefore, the router forwards the packet to 192.168.45.5 via GigabitEthernet0/0/4. Administrative distance and metrics are never considered across different prefix lengths.

Adım Adım Çözüm

1
Determine subnet ranges for all matching candidate routes in the routing table for destination IP 10.88.164.37.
Candidate 1: 10.88.164.32/28 (10.88.164.32–10.88.164.47, prefix /28). Candidate 2: 10.88.164.0/25 (10.88.164.0–10.88.164.127, prefix /25). Candidate 3: 10.88.160.0/20 (10.88.160.0–10.88.175.255, prefix /20). Candidate 4: 10.88.164.32/29 (10.88.164.32–10.88.164.39, prefix /29). All 4 routes match destination 10.88.164.37.
A route is a candidate match if the target IP falls anywhere within its subnet block.
2
Apply the Longest Prefix Match (LPM) rule by comparing the subnet mask prefix lengths.
The prefix lengths are /20, /25, /28, and /29. The /29 route (10.88.164.32/29) has the highest number of matching network bits.
In Cisco IOS forwarding logic, the router always selects the route with the longest prefix match regardless of administrative distance or metric.
3
Identify the egress path associated with the winning route.
The 10.88.164.32/29 route points to next-hop IP 192.168.45.5 out interface GigabitEthernet0/0/4.
The packet is forwarded according to the forwarding table details bound to the longest matching route.

Anahtar Kavram

Router Forwarding Decision Logic & Longest Prefix Match (LPM)
Tahmini Süre:2m 0s
Soru 232Soru →

Two Cisco routers are directly connected via their GigabitEthernet 0/0 interfaces in OSPFv2 Area 0. Router R1 maintains the default interface timers. An administrator executes the command `ip ospf hello-interval 15` on interface GigabitEthernet 0/0 of Router R2, but makes no other configuration changes on either router. What is the impact of this configuration on the OSPF neighbor relationship?

Cevabı ve açıklamayı göster

Cevap: The routers fail to form an OSPF neighbor relationship because OSPF Hello and Dead intervals must match between directly connected neighbors.

Cevap

The routers fail to form an OSPF neighbor relationship because OSPF Hello and Dead intervals must match between directly connected neighbors.
For two routers to form an OSPFv2 neighbor relationship on a link, specific parameters in their Hello packets must match. These include the Area ID, Subnet Mask, Hello Interval, Dead Interval, Authentication settings, and Stub flag. Modifying the Hello interval on Router R2 to 15 seconds causes a mismatch with Router R1's default 10-second Hello interval, leading both routers to reject incoming Hello packets.

Adım Adım Çözüm

1
Identify the mandatory parameters required for OSPFv2 neighbor adjacency.
OSPF Hello packets contain field values that must match between neighbors: Area ID, Subnet Mask, Hello Interval, Dead Interval, Authentication Password/Digest, and Stub Area Flag.
If any mandatory parameter mismatches, the received Hello packet is dropped and neighbor discovery fails.
2
Analyze the effect of modifying the Hello interval on Router R2.
Router R2 sends Hello packets containing a Hello interval of 15 seconds and a Dead interval of 60 seconds (default 4×Hello4 \times \text{Hello}). Router R1 sends Hello packets with a Hello interval of 10 seconds and a Dead interval of 40 seconds.
Changing the Hello interval on one router creates a mismatch with the default Hello interval on the neighboring router.
3
Determine the resulting neighbor state.
Because the Hello and Dead intervals in the incoming Hello packets do not match the local interface settings, both routers drop each other's Hello packets, preventing an adjacency from forming.
Directly connected OSPF neighbors must have identical Hello and Dead timer values on the connecting interface segment.

Anahtar Kavram

OSPFv2 Hello and Dead Timer Matching Requirements
Tahmini Süre:1m 0s
Soru 233Soru →

Two Cisco routers, R1 and R2, are directly connected via their GigabitEthernet0/0 interfaces in OSPFv2 Area 0. Interface GigabitEthernet0/0 on R1 is configured with a maximum transmission unit (MTU) of 1500 bytes, whereas GigabitEthernet0/0 on R2 is configured with an MTU of 1400 bytes. Neither router has the ip ospf mtu-ignore command configured.

In which specific OSPF neighbor state will the adjacency between R1 and R2 become stuck?

Cevabı ve açıklamayı göster

Cevap: ExStart; EXSTART; ExStart state; EXSTART state

Cevap

ExStart
When OSPF neighbor parameters in Hello packets match, routers establish two-way communication and progress to the ExStart state to begin Database Description (DBD) packet negotiation. Because interface MTU values are advertised inside DBD headers, an MTU mismatch (1500 bytes on R1 vs. 1400 bytes on R2) causes the router with the lower MTU to ignore incoming DBD packets. As a result, Master/Slave election and DBD sequence number synchronization fail, leaving the neighbor relationship stuck in the ExStart state.

Adım Adım Çözüm

1
Analyze OSPF Hello packet processing and initial state transitions
Hello parameters (Area ID, Subnet Mask, Hello/Dead timers, Authentication) match between R1 and R2, allowing the routers to pass the Init state and transition into the 2-Way state.
MTU values are not contained or evaluated within OSPF Hello packets.
2
Evaluate Database Description (DBD) packet negotiation during ExStart
Upon transitioning to the ExStart state, routers exchange Database Description (DBD) packets to elect a Master/Slave relationship and negotiate sequence numbers. The configured interface MTU is explicitly included in the Interface MTU field of the DBD header.
OSPF requires matching interface MTUs to ensure Database Description packets carrying Link-State Advertisements can be exchanged without fragmentation issues.
3
Determine the impact of the MTU mismatch
R2 receives a DBD packet from R1 advertising an MTU of 1500 bytes, which exceeds R2's interface MTU of 1400 bytes. Consequently, R2 drops the packet, causing Master/Slave negotiation to stall endlessly in the ExStart state.
Without ip ospf mtu-ignore enabled, any mismatch in advertised MTU prevents completion of DBD packet exchange.

Anahtar Kavram

OSPF Neighbor States and MTU Mismatch Behavior
Soru 234Soru →

An engineer is troubleshooting an OSPFv2 neighbor adjacency issue between two directly connected routers. Which two parameters must match on the interconnecting interfaces for an OSPFv2 neighbor relationship to successfully form? (Select TWO.)

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: Area ID; Hello and Dead timer intervals

Cevap

The parameters that must match for OSPFv2 neighbor adjacency formation are Area ID and Hello and Dead timer intervals.
For two routers to establish an OSPFv2 neighbor adjacency, several parameters exchanged in Hello packets must match: Area ID, Hello and Dead timers, subnet mask/subnet ID, and authentication settings. Area ID and Hello/Dead timers are mandatory matching parameters.

Adım Adım Çözüm

1
Identify OSPFv2 Hello packet parameter requirements for neighbor formation.
OSPF Hello packets contain parameters that must match (Area ID, Subnet Mask, Hello/Dead timers, Authentication, MTU) and parameters that must be unique (Router ID).
Matching parameters ensure both routers agree on common network boundaries and operational timings.
2
Evaluate local vs global OSPF settings.
The OSPF Process ID is locally significant to the router, and the Router ID must be unique per router.
Process IDs do not affect protocol negotiation across links, while duplicate Router IDs cause protocol conflicts.

Anahtar Kavram

OSPFv2 Neighbor Adjacency Requirements
Soru 235Soru →

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

text
Gateway of last resort is not set

192.168.10.0/24 is variably subnetted, 4 subnets, 3 masks
O 192.168.10.0/24 [110/20] via 10.1.1.1, 00:05:12, GigabitEthernet0/0
D 192.168.10.0/26 [90/307200] via 10.1.1.2, 00:12:45, GigabitEthernet0/1
S 192.168.10.0/27 [1/0] via 10.1.1.3
O E2 192.168.10.16/28 [110/20] via 10.1.1.4, 00:01:10, GigabitEthernet0/2

Which next-hop IPv4 address will the router select to forward a packet with a destination IP address of 192.168.10.20?

Cevabı ve açıklamayı göster

Cevap: 10.1.1.4

Cevap

The router will select the next-hop address 10.1.1.4.
When a router receives a packet, it compares the destination IP address against all entries in its routing table and selects the route with the longest matching prefix (most specific subnet mask). In this scenario, the destination address 192.168.10.20 matches 192.168.10.0/24, 192.168.10.0/26, 192.168.10.0/27, and 192.168.10.16/28. The /28 route is the most specific match (28 bits), so the router uses its specified next-hop address, 10.1.1.4.

Adım Adım Çözüm

1
Determine which subnet ranges contain the destination IP address 192.168.10.20.
The destination address 192.168.10.20 falls within 192.168.10.0/24 (.0 - .255), 192.168.10.0/26 (.0 - .63), 192.168.10.0/27 (.0 - .31), and 192.168.10.16/28 (.16 - .31).
All four routes in the routing table match the destination address.
2
Compare the prefix lengths of all matching routes to apply the Longest Prefix Match rule.
The prefix length of /28 (28 subnet bits) is longer than /27, /26, and /24.
The router always prioritizes the route with the most specific match (longest subnet mask / prefix length), regardless of administrative distance or routing protocol source.
3
Identify the next-hop IPv4 address associated with the /28 matching entry.
The route for 192.168.10.16/28 specifies the next-hop address 10.1.1.4.
The router forwards packets matching this prefix to 10.1.1.4 out GigabitEthernet0/2.

Anahtar Kavram

Longest Prefix Match Rule
Soru 236Soru →

Three Cisco routers (R1, R2, and R3) are connected to the same Layer 2 Ethernet switch on the 10.1.1.0/24 subnet and configured in OSPFv2 Area 0. Router R1 completes OSPF initialization first and is successfully elected as the Designated Router (DR). To optimize resource utilization, the network administrator explicitly configures the interface command `ip ospf priority 0` on GigabitEthernet0/0 on both R2 and R3.

After all OSPF processes converge, what neighbor state will be displayed when issuing the `show ip ospf neighbor` command on router R2 specifically for the neighbor entry corresponding to router R3?

Cevabı ve açıklamayı göster

Cevap: 2WAY/DROTHER

Cevap

The neighbor state between R2 and R3 will be 2WAY/DROTHER.
On a broadcast multiaccess network (such as Ethernet), routers only establish FULL adjacencies (exchanging link-state databases) with the Designated Router (DR) and Backup Designated Router (BDR). Routers configured with an OSPF priority of 0 cannot become DR or BDR (they remain DROTHERs). When two DROTHER routers discover each other via Hello packets, they verify bi-directional communication and remain stably in the 2WAY/DROTHER state.

Adım Adım Çözüm

1
Analyze OSPF interface priority settings for R2 and R3.
Setting 'ip ospf priority 0' disables a router from participating in DR/BDR election, forcing both R2 and R3 into DROTHER status on the broadcast network.
Routers with an OSPF priority of 0 can never become a DR or BDR.
2
Evaluate OSPF adjacency requirements on broadcast multiaccess networks.
Full adjacencies are formed only between DROTHER routers and the DR/BDR. Routers that are both DROTHERs form relationships that stop at 2-WAY state.
This behavior minimizes flooding overhead and database synchronization traffic on multiaccess media.
3
Determine the output of the show command on R2 for R3.
The neighbor relationship successfully reaches bi-directional communication, yielding a state of 2WAY/DROTHER.
Both routers hear each other's Hellos (2-WAY), but neither router is a DR or BDR, so no LSA exchange takes place between them.

Anahtar Kavram

OSPF Adjacency Formation on Multiaccess Networks and Priority 0 Behavior
Soru 237Soru →

Refer to the following command output from Router R1 on a multiaccess Ethernet network:

text
R1# show ip ospf interface GigabitEthernet0/0
GigabitEthernet0/0 is up, line protocol is up
Internet Address 192.168.10.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 1
Transmit Delay is 1 sec, State DROTHER, Priority 0
Designated Router (ID) 3.3.3.3, Interface address 192.168.10.3
Backup Designated Router (ID) 2.2.2.2, Interface address 192.168.10.2

The administrator attempts to force R1 to become the Designated Router (DR) by assigning it the highest Router ID on the segment (10.10.10.10) and resetting the OSPF process. However, R1 remains in the DROTHER state. Why did R1 fail to participate in the DR/BDR election?

Cevabı ve açıklamayı göster

Cevap: The OSPF interface priority on R1 is set to 0, which explicitly excludes the router from participating in DR/BDR elections regardless of its Router ID.

Cevap

R1 cannot become the Designated Router because its OSPF interface priority is configured as 0, which makes the interface ineligible to participate in DR/BDR elections.
In OSPFv2 multiaccess networks (such as Broadcast), DR/BDR elections evaluate interface priority first. A router with an interface priority of 0 is strictly excluded from becoming a DR or BDR and will always remain a DROTHER, regardless of how high its Router ID or interface IP address is.

Adım Adım Çözüm

1
Examine the output of 'show ip ospf interface GigabitEthernet0/0'.
Identify that R1 has an OSPF Priority of 0 and a State of DROTHER.
Interface priority determines DR/BDR election eligibility.
2
Evaluate the effect of OSPF interface priority 0.
Recognize that a priority value of 0 explicitly prevents a router from ever becoming a DR or BDR.
OSPF rules dictate that any interface with priority 0 remains permanently in the DROTHER state regardless of Router ID or interface IP address.

Anahtar Kavram

OSPF Priority 0 Exclusion in DR/BDR Selection
Soru 238Soru →

An administrator is implementing a floating static route on a Cisco IOS router to act as a backup path for a primary route learned dynamically via internal EIGRP (Administrative Distance 90) to the destination subnet 10.100.50.0/2410.100.50.0/24. The administrator executes the following command:

`ip route 10.100.50.0 255.255.255.0 172.16.1.2 90`

While the primary EIGRP route remains active, traffic destined for 10.100.50.0/2410.100.50.0/24 is unexpectedly load-shared across both the dynamic route and the static route. Which configuration change will ensure that the static route functions exclusively as a backup route?

Cevabı ve açıklamayı göster

Cevap: Reconfigure the static route with an administrative distance greater than 90.

Cevap

Reconfigure the static route with an administrative distance greater than 90.
For a static route to act as a floating backup route, its administrative distance must be configured higher than the administrative distance of the primary route. Since internal EIGRP uses an AD of 90, configuring the static route with an AD of 90 causes both routes to share the same administrative distance, resulting in unexpected dual-path active insertion. Assigning an AD greater than 90 keeps the static route out of the routing table until the primary EIGRP route fails.

Adım Adım Çözüm

1
Analyze the administrative distance of the primary routing protocol.
Internal EIGRP has a default administrative distance of 90.
Administrative distance determines route preference in the Cisco IOS Routing Information Base (RIB).
2
Evaluate the current static route configuration.
The configured static route explicitly sets an administrative distance of 90, matching EIGRP's administrative distance.
When two routes to the exact same prefix have equal administrative distances, the router treats them as equally trustworthy, leading to unexpected traffic load-sharing or tie-breaking behavior.
3
Determine the requirement for a floating static route.
A floating static route must have an administrative distance strictly higher than the primary route's AD (e.g., 91 or 130).
This guarantees the static route remains inactive in the RIB until the primary dynamic route is removed.

Anahtar Kavram

Floating Static Route Administrative Distance Calibration
Soru 239Soru →

Match each component or prefix notation from a Cisco IOS routing table output to its correct technical characteristic or forwarding behavior.

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Öğeler

Code prefix 'D EX' in: D EX 192.168.50.0/24 [170/2578560] via 10.1.1.2
Bracketed notation '[110/65]' in: O 10.1.4.0/24 [110/65] via 10.1.12.1
Prefix '192.168.10.0/28' vs '192.168.10.0/24' when forwarding to 192.168.10.14
Code prefix 'C' in: C 172.16.1.0/24 is directly connected, GigabitEthernet0/0

Eşleşmeler

Cevabı ve açıklamayı göster

Cevap

Each routing table notation matches its corresponding definition based on Cisco IOS routing table syntax and path determination rules: 'D EX' matches external EIGRP with AD 170, '[110/65]' matches AD 110 and metric 65, the '/28' prefix matches the Longest Prefix Match rule, and 'C' matches a directly connected network with AD 0.
Each routing table component directly corresponds to Cisco IOS routing table syntax and path determination logic. 'D EX' signifies EIGRP external routes (AD 170); bracketed numbers '[110/65]' display Administrative Distance followed by Metric; destination matching favors the longest subnet mask (/28 over /24); and 'C' represents directly connected routes with an AD of 0.

Adım Adım Çözüm

1
Analyze routing table protocol codes
Identify 'D EX' as EIGRP External (AD 170) and 'C' as Connected (AD 0).
Cisco IOS routing tables use specific legend codes to indicate how routes were learned.
2
Interpret numerical brackets [AD/Metric]
Confirm '[110/65]' represents Administrative Distance 110 (OSPF) and a cost metric of 65.
The first number in brackets is always the Administrative Distance and the second is the route metric.
3
Apply forwarding logic to destination lookup
Determine that the /28 route is selected over /24 because 28 matching bits exceeds 24 matching bits.
Longest prefix matching (LPM) is the fundamental rule evaluated before comparing administrative distance or metric.

Anahtar Kavram

Interpretation of Cisco IOS Routing Table Components and Forwarding Decision Logic
Soru 240Soru →

A network administrator needs to configure an IPv6 static route on router R1 to forward traffic to the remote network 2001:db8:10:20::/642001:\text{db8}:10:20::/64. The next-hop router's interface has a link-local address of fe80::212:79ff:fe34:5678\text{fe80}::212:79\text{ff}:\text{fe34}:5678 connected to R1's local interface GigabitEthernet0/0/1. Which Cisco IOS command correctly provisions this static route?

Cevabı ve açıklamayı göster

Cevap: ipv6 route 2001:db8:10:20::/64 GigabitEthernet0/0/1 fe80::212:79ff:fe34:5678

Cevap

The command 'ipv6 route 2001:db8:10:20::/64 GigabitEthernet0/0/1 fe80::212:79ff:fe34:5678' correctly configures the fully specified IPv6 static route.
The command correctly uses the Cisco IOS syntax for a static route pointing to a link-local address: 'ipv6 route <prefix/length> <exit-interface> <link-local-address>'. Because link-local IPv6 addresses (FE80::/10) are valid only on the local link, the local exit interface must be explicitly stated.

Adım Adım Çözüm

1
Identify the target destination prefix and length.
Destination prefix is 2001:db8:10:20::/642001:\text{db8}:10:20::/64.
The prefix specifies the remote network to be added to the IPv6 routing table.
2
Evaluate the next-hop address type.
The next-hop address fe80::212:79ff:fe34:5678\text{fe80}::212:79\text{ff}:\text{fe34}:5678 is a link-local IPv6 address (starts with FE80::/10).
Link-local addresses require explicit egress interface identification because they are bound to a specific link.
3
Apply Cisco IOS IPv6 static route command syntax for link-local next hops.
Syntax must be: 'ipv6 route <prefix/length> <exit-interface> <link-local-next-hop>'.
Cisco IOS requires the local exit interface (GigabitEthernet0/0/1) immediately following the prefix and preceding the link-local address.

Anahtar Kavram

IPv6 Static Routing with Link-Local Next Hop
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