Examkin

IP Connectivity

493 questions

All types493Multiple choice250Multiple select113Matching25Ordering60Fill in the blank22Short answer23
Question 61Question →

A network administrator is configuring Hot Standby Router Protocol (HSRP) on a Cisco router interface that has already been assigned the physical IPv4 address 192.168.10.1/24. The administrator attempts to execute the command `standby 1 ip 192.168.10.1` on this interface. What is the result of executing this command?

Show answer & explanation

Answer: The router rejects the command because HSRP does not permit assigning a router's physical interface IP address as the virtual IP address.

Answer

The router rejects the command because HSRP does not permit assigning a router's physical interface IP address as the virtual IP address.
In Hot Standby Router Protocol (HSRP), the virtual IP address must be an unused, unique IP address within the local IPv4 subnet. Unlike Virtual Router Redundancy Protocol (VRRP), which allows the virtual IP address to match a physical interface IP address (making that router the IP address owner with priority 255), HSRP explicitly forbids using any member router's physical interface IP address. Attempting to do so in Cisco IOS results in an error message rejecting the command.

Step-by-Step Solution

1
Identify the protocol being configured and the requested virtual IP address.
The protocol is HSRP (v1/v2) and the command `standby 1 ip 192.168.10.1` attempts to use the physical IP address of the local interface (192.168.10.1).
Determining protocol-specific rules for Virtual IP (VIP) assignment is required to evaluate command validity.
2
Recall HSRP IP address assignment constraints.
HSRP requires the virtual IP address to be an unused IP address within the subnet shared by the gateway routers.
HSRP does not support the concept of an IP address owner sharing a physical IP address with the virtual IP address.
3
Determine the Cisco IOS CLI output behavior.
Cisco IOS generates an error indicating that the virtual IP address cannot match the interface IP address and rejects the command.
Executing a standby IP command with the interface's own IP address fails validation.

Key Concept

HSRP Virtual IP Address Assignment Constraints
Question 62Question →

A network administrator is inspecting an IPv4 routing table on a Cisco router to understand how paths to remote networks are chosen. Match each routing table component on the left with its corresponding function or definition on the right.

Click a left item, then click its matching right item

Items

Administrative Distance (AD)
Routing Metric
Next-Hop IP Address
Destination Prefix and Subnet Mask

Matches

Show answer & explanation

Answer

Administrative Distance matches trustworthiness of the route source; Routing Metric matches path cost calculated by a specific protocol; Next-Hop IP Address matches the immediate adjacent router interface address; Destination Prefix and Subnet Mask matches the target network range against which traffic is matched.
Each routing table component serves a distinct role in packet forwarding decisions: Administrative Distance rates protocol trustworthiness, Routing Metric measures path cost for a single protocol, Next-Hop IP specifies the adjacent forwarding device, and Destination Prefix/Mask defines the destination network range.

Step-by-Step Solution

1
Identify the role of Administrative Distance (AD)
AD measures source trustworthiness (lower value = preferred route source)
Different route sources (OSPF, RIP, Static) are compared using AD first.
2
Identify the role of Routing Metric
Metric measures path cost within the same protocol
When multiple routes exist from the same routing protocol, the router uses the lowest metric.
3
Identify the role of Next-Hop IP Address
Refers to the IP address of the adjacent router
Specifies where Layer 2 framing should direct the packet next.
4
Identify the role of Destination Prefix and Subnet Mask
Specifies the target network range
The router compares destination IP addresses against the prefix length using longest prefix match.

Key Concept

Routing Table Components and Roles
Question 63Question →

A network administrator executes the show ip route command on a Cisco router and observes the following routing entry:

O 10.150.1.0/24 [110/20] via 192.168.12.2, 00:10:42, GigabitEthernet0/0

Which component of this routing table entry is represented by the value 110?

Show answer & explanation

Answer: The administrative distance of the route

Answer

The value 110 represents the administrative distance of the route.
In Cisco IOS routing tables, routes learned via dynamic protocols display bracketed values in the format [Administrative Distance / Metric]. The first number, 110, is the administrative distance, which indicates the reliability of the routing source (110 is the default AD for OSPF).

Step-by-Step Solution

1
Examine the bracketed notation [110/20] in the routing table entry.
Identify the standard Cisco routing table notation format [Administrative Distance / Metric].
Cisco IOS displays the administrative distance first, followed by the metric, enclosed in square brackets.
2
Correlate the first value (110) with its corresponding routing component.
110 is identified as the Administrative Distance (AD) for an OSPF-learned route.
Administrative distance measures the trustworthiness of a routing information source.

Key Concept

Routing Table Component Interpretation (Administrative Distance vs. Metric)
Question 64Question →

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

text
Codes: C - connected, S - static, O - OSPF, D - EIGRP
Gateway of last resort is not set

D 172.16.10.0/24 [90/2172416] via 10.1.1.1, 00:05:12, GigabitEthernet0/0
O 172.16.10.0/26 [110/20] via 10.1.1.2, 00:12:45, GigabitEthernet0/1
S 172.16.0.0/16 [1/0] via 10.1.1.3
C 172.16.10.128/27 is directly connected, GigabitEthernet0/2

When the router receives an IP packet destined for host 172.16.10.33, which next-hop IP address or interface will be selected to forward the packet?

Show answer & explanation

Answer: 10.1.1.2

Answer

10.1.1.2 via GigabitEthernet0/1 based on Longest Prefix Match (/26).
When forwarding IP packets, a router always evaluates candidate routes using Longest Prefix Match (LPM) first. For the target IP address 172.16.10.33, three candidate routes match: 172.16.0.0/16, 172.16.10.0/24, and 172.16.10.0/26. The OSPF route 172.16.10.0/26 provides the longest matching prefix mask (/26), so the router forwards the packet to next-hop IP 10.1.1.2.

Step-by-Step Solution

1
Identify all candidate routes that match destination IP 172.16.10.33.
Three matching routes exist: 172.16.0.0/16, 172.16.10.0/24, and 172.16.10.0/26. The route 172.16.10.128/27 covers range 172.16.10.128 to 172.16.10.159 and does not match.
Routing decision logic only evaluates routes whose network address and subnet mask encompass the target IP.
2
Compare prefix lengths among all matching candidate routes.
172.16.10.0/26 has a 26-bit prefix match, which is longer (more specific) than /24 and /16.
Longest Prefix Match (LPM) is always the primary criterion used by a router when selecting a route from the routing table.
3
Determine the next-hop associated with the longest prefix match route.
The route 172.16.10.0/26 points to next-hop IP 10.1.1.2.
Administrative Distance and Metric are only evaluated when comparing routes with identical prefix lengths from different sources.

Key Concept

Router Forwarding Decision Logic (Longest Prefix Match Precedence)
Question 65Question →

A network administrator needs to configure a fully specified IPv6 static route on a Cisco router to reach the remote network 2001:DB8:ACAD:1::/642001:\text{DB8}:\text{ACAD}:1::/64 using the neighbor router's link-local address FE80::2\text{FE80}::2 reachable via the local GigabitEthernet0/1\text{GigabitEthernet0/1} interface. Which command correctly configures this route?

Show answer & explanation

Answer: ipv6 route 2001:DB8:ACAD:1::/64 GigabitEthernet0/1 FE80::2

Answer

The command 'ipv6 route 2001:DB8:ACAD:1::/64 GigabitEthernet0/1 FE80::2' correctly configures the fully specified IPv6 static route.
When configuring an IPv6 static route using a link-local address as the next-hop, Cisco IOS mandates a fully specified route that includes both the local exit interface and the link-local address of the adjacent router.

Step-by-Step Solution

1
Identify the mandatory components of an IPv6 static route command with a link-local next hop.
The general syntax requires specifying both the local exit interface and the link-local next-hop address: 'ipv6 route <prefix/mask> <exit-interface> <link-local-address>'.
Because IPv6 link-local addresses (FE80::/10) are only unique on a single local link, Cisco IOS cannot determine which outbound interface to use unless the interface is explicitly defined.
2
Evaluate the specified parameters.
Destination prefix = 2001:DB8:ACAD:1::/64, Exit interface = GigabitEthernet0/1, Next-hop = FE80::2.
Combining these exact parameters in order produces a valid fully specified static route configuration.

Key Concept

Fully specified IPv6 static routes requiring both an exit interface and link-local next-hop address.
Question 66Question →

An engineer configures a next-hop IPv4 static route on a Cisco router using the command `ip route 10.1.2.0 255.255.255.0 192.168.12.2`. Place the processing steps in the correct sequential order from first to last that the router performs when forwarding an incoming packet destined for 10.1.2.4510.1.2.45.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence for packet forwarding with a next-hop static route is: First, match the packet destination IP 10.1.2.4510.1.2.45 to the static route entry pointing to next-hop 192.168.12.2192.168.12.2. Second, perform a recursive lookup in the routing table for 192.168.12.2192.168.12.2 to find the outgoing interface. Third, look up the MAC address of 192.168.12.2192.168.12.2 in the ARP table. Fourth, encapsulate the packet into a Layer 2 frame and transmit it out the egress interface.
When a static route specifies only a next-hop IPv4 address (recursive static route), the router must first identify the static route via longest-prefix match. Next, it performs a recursive RIB lookup on the next-hop IP address to determine the exit interface. After identifying the exit interface, it performs an ARP table lookup to find the next-hop MAC address, and finally encapsulates and transmits the frame.

Step-by-Step Solution

1
Evaluate incoming packet destination IP against routing table entries.
The destination address 10.1.2.4510.1.2.45 matches static route 10.1.2.0/2410.1.2.0/24 with next-hop 192.168.12.2192.168.12.2.
Routing decisions begin with a longest-prefix match lookup in the RIB.
2
Perform recursive routing lookup for next-hop IP address 192.168.12.2192.168.12.2.
The router identifies the directly connected network prefix and egress interface used to reach 192.168.12.2192.168.12.2.
Static routes configured solely with a next-hop IP require a recursive lookup to identify the exit interface.
3
Resolve Layer 2 destination hardware address via ARP cache lookup for 192.168.12.2192.168.12.2.
The target next-hop MAC address is retrieved for frame header construction.
Ethernet interfaces require the next-hop MAC address to format the data-link layer encapsulation.
4
Encapsulate IPv4 packet into Layer 2 Ethernet frame and send out the egress interface.
The packet is transmitted on the physical wire.
All forwarding requirements (interface and Layer 2 rewrite info) are complete.

Key Concept

IPv4 Static Route Recursive Lookup & Forwarding Process
Estimated Time:1m 30s
Question 67Question →

What prefix and prefix length parameter completes the Cisco IOS command to configure a default IPv6 static route pointing to next-hop address $2001:

\text{db8}:1::2$?

Fill in the blanks below

Router(config)# ipv6 route 2001:db8:1::2
Show answer & explanation

Answer

The correct notation to represent a default route in IPv6 static routing is ::/0.
In IPv6 static routing, ::/0 is the prefix notation for a default route, serving the same function as 0.0.0.0/0 in IPv4.

Step-by-Step Solution

1
Identify the network prefix used to match all possible IPv6 destinations.
The default IPv6 route prefix is written as ::/0.
In IPv6 addressing, :: represents all zeros, and /0 indicates a prefix length of zero bits, matching any destination address.
2
Substitute the default prefix into the Cisco IOS IPv6 static routing command syntax.
The completed command is 'ipv6 route ::/0 2001:db8:1::2'.
The standard command syntax requires 'ipv6 route <destination-prefix/prefix-length> <next-hop-address>'.

Key Concept

IPv6 Default Static Route Configuration
Estimated Time:45s
Question 68Question →

When a Cisco router receives an IP packet, it evaluates several parameters to determine the best route to place into the routing decision process. Place the path selection criteria in the correct sequential order, from the primary (first evaluated) factor to the final tie-breaker factor.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct order of router decision criteria is: 1) Longest Prefix Match, 2) Administrative Distance, 3) Metric, 4) Equal-Cost Multi-Path.
Router forwarding decision logic evaluates parameters in a strict hierarchical order. First, Longest Prefix Match identifies the most specific network prefix for the destination IP address. If multiple routes exist with the exact same prefix length from different protocols, Administrative Distance breaks the tie by choosing the lower value. If multiple candidate routes come from the same routing protocol with identical prefix lengths, the Metric is used as the next tie-breaker. Finally, if prefix length, Administrative Distance, and metric are all identical, Equal-Cost Multi-Path load balancing is performed.

Step-by-Step Solution

1
Determine primary routing lookup criteria
Longest Prefix Match is checked first.
Prefix specificity always takes precedence over AD and metric.
2
Evaluate tie-breaker between different routing protocols for the exact same prefix length
Administrative Distance is compared.
Lower AD indicates a more trustworthy routing source.
3
Evaluate tie-breaker within the same routing protocol
Metric is compared.
Lower metric indicates a lower internal routing protocol cost.
4
Handle identical tie-breaker results
Equal-Cost Multi-Path load balancing is applied.
When all parameters match identically, the router balances traffic across the equal routes.

Key Concept

Router Forwarding Decision Logic Sequence
Question 69Question →

A Cisco router receives an IP packet destined for 10.20.12.15010.20.12.150. Refer to the following routing table output:

text
Codes: C - connected, S - static, D - EIGRP, O - OSPF

Gateway of last resort is 10.1.1.1 to network 0.0.0.0

D 10.20.0.0/14 [90/2172416] via 192.168.1.2, GigabitEthernet0/1
O 10.20.12.0/22 [110/20] via 192.168.1.6, GigabitEthernet0/2
S 10.20.12.0/24 [1/0] via 192.168.1.10, GigabitEthernet0/3
O 10.20.12.128/25 [110/30] via 192.168.1.14, GigabitEthernet0/4
S* 0.0.0.0/0 [1/0] via 10.1.1.1, GigabitEthernet0/0

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

Show answer & explanation

Answer: 192.168.1.14

Answer

The router forwards the packet to next-hop IP 192.168.1.14 because the route 10.20.12.128/25 has the longest prefix match for destination 10.20.12.150.
When forwarding IP packets, a Cisco router always prioritizes the route with the Longest Prefix Match (most specific subnet mask). The destination address 10.20.12.150 falls within the range 10.20.12.128 to 10.20.12.255 defined by 10.20.12.128/25. Because /25 is more specific than /24, /22, /14, or /0, the router uses this route, which forwards to next-hop 192.168.1.14.

Step-by-Step Solution

1
Identify all candidate routes that encompass the destination IP address 10.20.12.150.
Candidate routes are 10.20.0.0/14, 10.20.12.0/22, 10.20.12.0/24, 10.20.12.128/25, and 0.0.0.0/0.
The router evaluates destination IP bit alignment against subnet masks of all known routes.
2
Compare the prefix lengths of all matching candidate routes.
Prefix lengths are /14, /22, /24, /25, and /0. The route 10.20.12.128/25 has the longest prefix mask (/25).
Routers use the Longest Prefix Match (LPM) logic first before considering Administrative Distance or Metric.
3
Select the next-hop IP associated with the longest prefix match route.
The route 10.20.12.128/25 points to next-hop 192.168.1.14.
Longest prefix match determines the exact routing entry used for forwarding.

Key Concept

Longest Prefix Match (LPM) precedence in IP forwarding decision logic.
Question 70Question →

A network engineer is configuring Virtual Router Redundancy Protocol (VRRP) on a router interface that has been assigned the physical IPv4 address 10.1.1.1/2410.1.1.1/24. The engineer enters the command `vrrp 1 ip 10.1.1.1`. Which statement correctly describes the operational result of configuring the physical interface IP address as the VRRP virtual IP address?

Show answer & explanation

Answer: VRRP accepts the configuration, allowing the router to become the IP address owner with a priority automatically set to 255.

Answer

VRRP accepts the configuration, allowing the router to become the IP address owner with a priority automatically set to 255.
In VRRP, an engineer can assign the physical interface IP address as the virtual IP address. When this is done, the router becomes the IP address owner and its priority is automatically assigned as 255, making it the active Master router for that VRRP group.

Step-by-Step Solution

1
Identify the protocol and command syntax specified in the scenario.
The scenario uses VRRP (`vrrp 1 ip 10.1.1.1`) where the virtual IP address matches the primary physical interface IP address (10.1.1.110.1.1.1).
Understanding protocol-specific rules regarding virtual IP address assignment is essential.
2
Evaluate VRRP operational rules for IP address ownership.
RFC 5798 / VRRP standards state that if a router's physical interface IP address is configured as the VRRP virtual IP address, that router becomes the IP address owner.
VRRP permits virtual IP reuse, unlike HSRP which enforces separate virtual IP addresses.
3
Determine the resulting priority value for the IP address owner.
The IP address owner in VRRP automatically receives the highest possible priority value of 255.
This guarantees that the owner router will always become the Master router when functional.

Key Concept

VRRP IP Address Ownership and Priority Assignment
Question 71Question →

A Cisco router receives an IPv4 packet destined for host 10.200.15.42. The router inspects its routing table and finds the following entry routes:

text
O 10.200.15.0/24 [110/20] via 172.16.1.1, GigabitEthernet0/0/1
S 10.200.0.0/16 [1/0] via 172.16.2.1, GigabitEthernet0/0/2
D 10.200.15.32/28 [90/307200] via 172.16.3.1, GigabitEthernet0/0/3
B 10.200.15.40/30 [200/0] via 172.16.4.1, GigabitEthernet0/0/4

Which next-hop IP address and outgoing interface will the router select to forward the packet?

Show answer & explanation

Answer: 172.16.4.1 via GigabitEthernet0/0/4 because the 10.200.15.40/30 route has the longest prefix match.

Answer

The router forwards the packet to next-hop 172.16.4.1 via interface GigabitEthernet0/0/4 because the 10.200.15.40/30 prefix offers the longest prefix match.
When a router receives an IP packet, it compares the destination IP address (10.200.15.42) against all entries in its routing table. The matching entries cover the following ranges:
- 10.200.0.0/16 (/16)
- 10.200.15.0/24 (/24)
- 10.200.15.32/28 (/28: 10.200.15.32 to 10.200.15.47)
- 10.200.15.40/30 (/30: 10.200.15.40 to 10.200.15.43)

Because 10.200.15.42 falls within the /30 range, and /30 is the most specific prefix (longest prefix match), the router selects the entry pointing to 172.16.4.1 via GigabitEthernet0/0/4. Administrative Distance is not evaluated across different prefix lengths.

Step-by-Step Solution

1
Identify all candidate routes in the routing table that encompass the destination IPv4 address 10.200.15.42.
Candidate routes are 10.200.0.0/16, 10.200.15.0/24, 10.200.15.32/28 (range 10.200.15.32–10.200.15.47), and 10.200.15.40/30 (range 10.200.15.40–10.200.15.43). All four entries match the destination address.
Before comparing routing metrics or administrative distance, the router identifies every route that includes the target IP address within its range.
2
Apply the Longest Prefix Match (LPM) rule to choose among matching entries.
Prefix lengths are /16, /24, /28, and /30. The /30 route has the longest mask length (30 set subnet bits).
Cisco IOS packet forwarding decision logic prioritizes prefix specificity above all other metrics, including Administrative Distance and routing protocol metrics.
3
Determine the next-hop IP and outgoing interface from the winning route entry.
The entry 10.200.15.40/30 points to next-hop 172.16.4.1 via GigabitEthernet0/0/4.
The router uses the next-hop parameters specified by the chosen LPM entry to perform Layer 2 frame encapsulation and egress transmission.

Key Concept

Longest Prefix Match (LPM) Rule
Estimated Time:1m 15s
Question 72Question →

A Cisco router receives an IPv4 packet destined for 10.25.8.1210.25.8.12. The router inspects its routing table and finds the following matching route entries:

text
S 10.25.0.0/16 [1/0] via 172.16.1.1
O 10.25.8.0/23 [110/30] via 172.16.2.1
D 10.25.8.0/27 [90/2170112] via 172.16.3.1
S* 0.0.0.0/0 [1/0] via 172.16.0.1

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

Show answer & explanation

Answer: 172.16.3.1

Answer

The router will forward the packet to next-hop 172.16.3.1 based on the longest prefix match rule.
The destination IP address 10.25.8.12 falls within the subnet range of 10.25.8.0/27 (10.25.8.0 to 10.25.8.31). Because /27 has the largest prefix length among all matching routes (/27 > /23 > /16 > /0), the router uses this route and forwards the packet to 172.16.3.1.

Step-by-Step Solution

1
Evaluate which subnet prefixes match the destination IP address 10.25.8.12.
The destination address 10.25.8.12 matches 10.25.0.0/16, 10.25.8.0/23 (range 10.25.8.0–10.25.9.255), 10.25.8.0/27 (range 10.25.8.0–10.25.8.31), and 0.0.0.0/0.
Before making a forwarding decision, all matching routing entries must be identified.
2
Compare the prefix lengths of all matching routes to determine the most specific route.
The prefix length of /27 is longer (more specific) than /23, /16, and /0.
Cisco routers always prefer the route with the longest prefix match (most specific subnet mask), regardless of administrative distance or routing protocol metric.
3
Identify the next-hop address associated with the longest prefix route entry.
The entry 10.25.8.0/27 specifies the next-hop address 172.16.3.1.
The forwarding engine forwards the traffic out to the next-hop specified by the winning route.

Key Concept

Longest Prefix Match (LPM) Rule
Question 73Question →

A network administrator needs to configure an IPv6 static route on a Cisco IOS router to reach the destination prefix 2001:db8:1:10::/642001:\text{db8}:1:10::/64. Which of the following commands represent valid IPv6 static route configurations? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: ipv6 route 2001:db8:1:10::/64 2001:db8:1:1::2; ipv6 route 2001:db8:1:10::/64 GigabitEthernet0/0 fe80::1

Answer

The valid IPv6 static route commands are 'ipv6 route 2001:db8:1:10::/64 2001:db8:1:1::2' (directly specifying a global unicast next-hop) and 'ipv6 route 2001:db8:1:10::/64 GigabitEthernet0/0 fe80::1' (fully specifying both the exit interface and the link-local next-hop address).
Valid Cisco IOS IPv6 static route configurations require the 'ipv6 route' keyword followed by the destination prefix. The next hop may be specified either as a global unicast IPv6 address directly, or as a link-local IPv6 address provided that the local exit interface is also explicitly specified.

Step-by-Step Solution

1
Verify correct command prefix keyword for IPv6 static routing
Cisco IOS requires 'ipv6 route' rather than 'ip route'.
The 'ip route' command is strictly used for configuring IPv4 static routes.
2
Evaluate next-hop syntax with global unicast addresses
A global unicast IPv6 address can be configured directly as a next hop without specifying an exit interface.
Global unicast addresses are globally unique and routable across network interfaces.
3
Evaluate next-hop syntax with link-local addresses
A link-local next-hop address (fe80::/10) requires specifying the local exit interface alongside the address.
Link-local addresses are only valid on their specific local link, making the command ambiguous to the router if the exit interface is omitted.

Key Concept

IPv6 Static Route Command Syntax and Link-Local Next-Hop Requirements
Question 74Question →

An administrator examines an IPv4 routing table entry on a Cisco router:

`D 192.168.50.0/24 [90/2170112] via 10.1.1.2, 00:04:12, GigabitEthernet0/1`

Which two statements correctly describe the components of this routing entry? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: The value 90 represents the administrative distance of the route source.; The IP address 10.1.1.2 identifies the next-hop router address to forward packets destined for 192.168.50.0/24.

Answer

The correct statements are that the value 90 represents the administrative distance of the route source, and the IP address 10.1.1.2 identifies the next-hop router address for forwarding packets.
In a Cisco IP routing table entry formatted as `[AD/Metric] via Next-Hop`, the first number inside the square brackets (90) is the administrative distance, which reflects the trustworthiness of EIGRP routes. The IP address following 'via' (10.1.1.2) represents the next-hop forwarding address.

Step-by-Step Solution

1
Parse the bracketed numbers [90/2170112] in the routing table output.
The first number inside the brackets (90) is the Administrative Distance (AD), and the second number (2170112) is the Metric (cost).
Cisco IOS routing tables always display route metrics in the standard format [Administrative Distance / Metric].
2
Identify the next-hop address following the 'via' keyword.
The IP address 10.1.1.2 is identified as the next-hop router IP.
The 'via' field specifies the neighboring router interface to which packets matching the prefix must be sent.
3
Interpret the source code prefix 'D'.
'D' represents EIGRP dynamic routing protocol, not a static route.
The routing table legend uses 'S' for static routes and 'D' for EIGRP routes.

Key Concept

Interpretation of Cisco IP routing table entry components including administrative distance, metric, next-hop address, and route source codes.
Estimated Time:45s
Question 75Question →

A network administrator needs to configure a static route on a Cisco router to reach destination network 2001:DB8:ABCD:10::/642001:\text{DB8}:\text{ABCD}:10::/64. The adjacent router's link-local address is FE80::2:1\text{FE80}::2:1 and the local outbound interface is GigabitEthernet0/0. Which Cisco IOS command correctly configures this IPv6 static route?

Show answer & explanation

Answer: ipv6 route 2001:DB8:ABCD:10::/64 GigabitEthernet0/0 FE80::2:1

Answer

The command 'ipv6 route 2001:DB8:ABCD:10::/64 GigabitEthernet0/0 FE80::2:1' correctly configures the static route.
When configuring an IPv6 static route using a link-local next-hop address, Cisco IOS requires specifying the local exit interface because link-local addresses are ambiguous and exist on every interface. The correct syntax specifies the exit interface followed by the link-local address.

Step-by-Step Solution

1
Identify destination prefix and next-hop type
Destination prefix is 2001:DB8:ABCD:10::/642001:\text{DB8}:\text{ABCD}:10::/64, and next-hop is link-local FE80::2:1\text{FE80}::2:1.
Link-local addresses are non-routable outside the local link segment.
2
Apply Cisco IOS fully specified static route rule
Because link-local addresses are ambiguous across multiple interfaces, the exit interface GigabitEthernet0/0 must be included before the next-hop address.
Cisco IOS requires syntax: `ipv6 route <prefix/mask> <exit-interface> <next-hop-address>` when using link-local addresses.

Key Concept

Fully Specified IPv6 Static Route Syntax using Link-Local Next-Hop
Estimated Time:45s
Question 76Question →

A network administrator is troubleshooting an OSPFv2 neighbor relationship between two directly connected Cisco routers. Command-line interface output indicates that the neighbor relationship is persistently stuck in the ExStart state. Which configuration mismatch is the primary cause of this specific neighbor state condition?

Show answer & explanation

Answer: Interface Maximum Transmission Unit (MTU) size

Answer

Interface Maximum Transmission Unit (MTU) size
During OSPF adjacency negotiation, routers pass through Init and 2-Way before entering ExStart. In ExStart, master/slave roles are determined using Database Description (DBD) packets, which contain the interface MTU size. If the interface MTUs between neighbor interfaces do not match, the router receiving DBDs with a higher MTU drops them, causing the neighbor state to remain stuck in ExStart.

Step-by-Step Solution

1
Analyze OSPF Hello packet verification parameters.
Parameters verified in Hello packets include Area ID, Hello/Dead timers, Subnet Mask, and Authentication. A mismatch in any of these parameters causes Hello packets to be ignored, leaving neighbors in the Down state.
Interface MTU is not checked during the initial Hello packet exchange.
2
Trace adjacency progression into the ExStart state.
Because initial Hello parameters match, the routers establish two-way communication (2-Way) and progress to ExStart to begin Database Description (DBD) packet negotiation.
ExStart is the state where master/slave roles and initial Database Description sequence numbers are negotiated.
3
Identify the parameter evaluated during DBD packet exchange.
DBD packets carry the configured interface MTU value. If one router receives a DBD packet specifying an MTU larger than its own configured interface MTU, it drops the packet.
Dropping DBD packets prevents sequence number acknowledgment, trapping the neighbor relationship in the ExStart/Exchange state.

Key Concept

OSPF Neighbor States and MTU Mismatch Impact
Estimated Time:1m 0s
Question 77Question →

An administrator executes the command `show ip route` on a Cisco router and observes the following routing table entry:

`O 10.40.0.0/24 [110/50] via 172.16.1.2, 00:15:30, GigabitEthernet0/0`

Which component of the routing table entry is represented by the numerical value 50 inside the brackets?

Show answer & explanation

Answer: The metric (cost) of the route to the destination network

Answer

The numerical value 50 inside the brackets represents the metric (cost) of the route to the destination network.
In Cisco IOS routing tables, bracketed values following a destination network prefix use the standard format `[Administrative Distance / Metric]`. In the given output `[110/50]`, `110` is the default Administrative Distance for OSPF routes, and `50` is the calculated cost metric to reach network `10.40.0.0/24`.

Step-by-Step Solution

1
Identify the standard bracket notation in Cisco IPv4 routing table output.
The bracketed syntax is defined as `[Administrative Distance / Metric]`.
Cisco routers display the trustworthiness (AD) and path cost (metric) together inside square brackets immediately after the network prefix.
2
Parse the bracketed values `[110/50]` from the OSPF route entry.
The first number `110` is the OSPF Administrative Distance, and the second number `50` is the route metric.
Separating the position of each number identifies `50` as the metric/cost value calculated by OSPF.

Key Concept

Routing Table Components: Administrative Distance vs. Metric
Estimated Time:45s
Question 78Question →

A network administrator is configuring static routing on router R1 to forward traffic to the destination network 2001:DB8:CAFE:5::/642001:\text{DB8}:\text{CAFE}:5::/64. The egress interface on R1 is GigabitEthernet0/0/0, which connects directly to router R2. Router R2's connected interface has a global unicast address of 2001:DB8:LAB:1::2/642001:\text{DB8}:\text{LAB}:1::2/64 and a link-local address of FE80::2\text{FE80}::2. Which command correctly configures a static route on R1 using R2's link-local address as the next hop?

Show answer & explanation

Answer: ipv6 route 2001:DB8:CAFE:5::/64 GigabitEthernet0/0/0 FE80::2

Answer

The command 'ipv6 route 2001:DB8:CAFE:5::/64 GigabitEthernet0/0/0 FE80::2' correctly specifies both the local exit interface and the neighbor's link-local next-hop address.
In Cisco IOS, IPv6 static routes using a link-local address as the next-hop MUST be fully specified by including both the local exit interface and the neighbor's link-local IPv6 address. The command specifying both GigabitEthernet0/0/0 and FE80::2 meets this requirement.

Step-by-Step Solution

1
Identify the destination prefix and prefix length.
The target destination network is 2001:DB8:CAFE:5::/642001:\text{DB8}:\text{CAFE}:5::/64.
The first argument of an IPv6 static route in Cisco IOS is always the destination IPv6 prefix/prefix-length.
2
Determine the next-hop requirements when using a link-local address.
Link-local addresses (FE80::/10) are bound strictly to a specific link (interface).
Because the same link-local address can exist on multiple interfaces of the same router, the router cannot determine which egress interface to use unless the exit interface is explicitly stated in the command.
3
Construct the complete fully specified IPv6 static route command.
'ipv6 route 2001:DB8:CAFE:5::/64 GigabitEthernet0/0/0 FE80::2'
This includes the destination prefix, the local interface (GigabitEthernet0/0/0), and the neighbor's link-local address (FE80::2).

Key Concept

IPv6 Static Route Link-Local Next-Hop Syntax Requirement
Estimated Time:1m 30s
Question 79Question →

A Cisco router receives an IPv4 unicast packet destined for 10.150.45.6710.150.45.67. The router's Routing Information Base (RIB) and Forwarding Information Base (FIB) contain multiple overlapping routes, static entries, and dynamic routing protocol paths. In what exact sequence does the router evaluate routing parameters and process the packet from ingress lookup to physical egress forwarding? Arrange the steps in the correct chronological order from first to last.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct evaluation sequence for router forwarding decision logic is: 1) Longest Prefix Match evaluation, 2) Administrative Distance tie-breaking for identical prefixes across different protocols, 3) Metric tie-breaking for identical prefixes within the same protocol, 4) ARP lookup for next-hop MAC address resolution, and 5) Layer 2 encapsulation rewrite, TTL decrement, checksum update, and frame transmission.
The router forwarding process follows a strict hierarchy: Longest Prefix Match (LPM) is evaluated first across all routes in the routing table. If multiple routes from different protocol sources share the exact same prefix length, Administrative Distance (AD) breaks the tie. If multiple routes from the same protocol share the exact same prefix length, protocol metric breaks the tie. Once the best route and next-hop are chosen, the router resolves the next-hop MAC via ARP/NDP, updates IP header fields (TTL decrement by 1 and checksum update), rewrites the Layer 2 header, and transmits the frame out the egress interface.

Step-by-Step Solution

1
Perform destination IP lookup using Longest Prefix Match (LPM).
The router identifies all matching subnet routes and selects the route entry with the highest number of matching network bits (most specific mask length).
LPM supersedes lower Administrative Distance values or routing metrics. A /28/28 route will always be chosen over a /24/24 route regardless of whether the /24/24 is static or connected.
2
Compare Administrative Distance (AD) if multiple sources present identical prefix masks.
The route from the source with the lowest AD (e.g., Static 11 vs. OSPF 110110) is preferred.
AD measures route source believability and only arbitrates between identical prefix masks from different routing processes.
3
Compare routing protocol metrics for ties within the same protocol.
The path with the lowest metric (cost, hop count, composite metric) is selected for RIB insertion.
Metrics only compare routes of the exact same prefix length learned via the same routing protocol algorithm.
4
Perform Layer 2 address resolution for the resolved next-hop address.
The router locates the next-hop IPv4 address in the ARP cache to retrieve its target MAC address.
Layer 3 forwarding decision requires binding the IP next-hop to a physical Layer 2 destination MAC address.
5
Execute packet header modifications and physical transmission.
The IPv4 TTL is decremented by 11, header checksum recalculated, source MAC updated to egress interface MAC, destination MAC updated to next-hop MAC, and the frame is serialized onto the wire.
Routers act as Layer 3 boundaries and must rebuild the Layer 2 frame header for each routed hop.

Key Concept

Router Forwarding Decision Logic and Longest Prefix Match Hierarchical Precedence
Question 80Question →

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

text
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

Gateway of last resort is 10.4.4.4 to network 0.0.0.0

O 172.16.32.0/20 [110/20] via 10.1.1.1, 00:10:05, GigabitEthernet0/0
D 172.16.35.64/28 [90/307200] via 10.2.2.2, 00:05:12, GigabitEthernet0/1
S 172.16.35.64/26 [1/0] via 10.3.3.3
C 172.16.35.0/24 is directly connected, GigabitEthernet0/2
S* 0.0.0.0/0 [1/0] via 10.4.4.4

The router receives an ingress IPv4 packet with a destination address of 172.16.35.73. Which statements accurately describe the router forwarding decision for this packet? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: The router forwards the packet to next-hop IP 10.2.2.2 via GigabitEthernet0/1 because the route to 172.16.35.64/28 provides the longest prefix match.; The router bypasses the static route to 172.16.35.64/26 despite its lower Administrative Distance because Administrative Distance is only compared among routes with identical prefix lengths.

Answer

The router forwards the packet to next-hop IP 10.2.2.2 via GigabitEthernet0/1 because 172.16.35.64/28 is the longest prefix match, and it ignores lower administrative distances on shorter prefixes because AD is only evaluated when prefix lengths are equal.
When forwarding an IPv4 packet, a Cisco router evaluates the Forwarding Information Base using Longest Prefix Match (LPM) as the primary criteria. For destination address 172.16.35.73, the route 172.16.35.64/28 (host range 172.16.35.64 to 172.16.35.79) has a 28-bit prefix length, making it more specific than the /26 static route, the /24 directly connected subnet, or the /20 OSPF route. Administrative Distance (AD) is only evaluated when multiple routing protocols install identical network prefixes into the routing table, so the router does not consider the lower AD of the static route.

Step-by-Step Solution

1
Identify all candidate routes matching destination IP 172.16.35.73
Candidate routes are 172.16.32.0/20, 172.16.35.0/24, 172.16.35.64/26, 172.16.35.64/28, and 0.0.0.0/0.
The destination host IP 172.16.35.73 falls within the IP address range of all these configured route subnets.
2
Determine the Longest Prefix Match (LPM) among candidates
172.16.35.64/28 has the longest prefix mask length (/28 = 28 bits).
Cisco IOS forwarding logic always selects the route with the most specific subnet mask matching the target destination.
3
Evaluate Administrative Distance and Metric applicability
Administrative Distance and Metric are not compared across different prefix lengths.
AD is only used when multiple routing protocols offer routes to the exact same network prefix length.

Key Concept

Router Forwarding Decision Logic (Longest Prefix Match Rule)
PreviousPage 4 / 25Next