Examkin

IPv4 Static Routing

89 questions

All types89Multiple choice45Multiple select21Ordering23
Question 81Question →

A Cisco router's IPv4 routing table contains four active static routes to various destination networks:

- `ip route 0.0.0.0 0.0.0.0 192.168.1.4`
- `ip route 10.10.0.0 255.255.0.0 192.168.1.1`
- `ip route 10.10.4.0 255.255.255.0 192.168.1.2`
- `ip route 10.10.4.16 255.255.255.240 192.168.1.3 110`

When the router receives an IP packet destined for 10.10.4.2510.10.4.25, which next-hop IP address will the router select to forward the packet?

Show answer & explanation

Answer: 192.168.1.3

Answer

192.168.1.3 is selected because 10.10.4.16/28 provides the longest matching subnet mask for the destination address 10.10.4.25.
When a router makes a packet forwarding decision, it compares the destination IP address (10.10.4.2510.10.4.25) against all installed routes in its routing table and selects the route with the most specific match (longest subnet mask). The destination address falls into the subnet 10.10.4.16/2810.10.4.16/28 (10.10.4.1610.10.4.16 to 10.10.4.3110.10.4.31). Since /28/28 is longer than /24/24, /16/16, and /0/0, the router selects this entry and forwards the packet to next-hop 192.168.1.3192.168.1.3. Administrative Distance is irrelevant during the actual lookup phase of already-installed routes.

Step-by-Step Solution

1
Analyze the destination IPv4 address against all routing table entries
Destination 10.10.4.25 matches four routes: 0.0.0.0/0, 10.10.0.0/16, 10.10.4.0/24, and 10.10.4.16/28 (range 10.10.4.16 - 10.10.4.31).
Routing lookup evaluates all routes installed in the routing table to find candidates.
2
Apply the Longest Prefix Match (LPM) rule to select the forwarding route
The /28 subnet mask is longer and more specific than /24, /16, or /0.
Routers always forward packets based on the longest matching prefix length regardless of Administrative Distance.
3
Determine the next-hop IPv4 address associated with the selected route
The 10.10.4.16/28 route points to next-hop 192.168.1.3.
The packet is forwarded to the next-hop IP associated with the winning prefix match.

Key Concept

Longest Prefix Match forwarding decision logic in IPv4 Routing
Question 82Question →

A Cisco router receives an IPv4 packet destined for host 192.168.2.50192.168.2.50. The router's routing table contains a static route configured as `ip route 192.168.2.0 255.255.255.0 10.1.1.2`. Which sequence correctly orders the internal packet processing and recursive routing lookup steps executed by the router from first to last?

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct order of steps for processing a packet requiring a recursive static route lookup is: First, match the destination IP address against the routing table using longest prefix match. Second, extract the static route entry pointing to next-hop IP 10.1.1.2. Third, perform a recursive lookup for 10.1.1.2. Fourth, resolve the egress interface to GigabitEthernet0/1 via the connected route. Fifth, perform ARP resolution for 10.1.1.2 and encapsulate/forward the frame out GigabitEthernet0/1.
The correct sequence begins with comparing the incoming packet's destination IP address against the routing table using longest prefix matching. Upon matching the static route for 192.168.2.0/24, the router retrieves the next-hop IP address (10.1.1.2). Because the static route was configured with only a next-hop IP address rather than an exit interface, the router must execute a second (recursive) lookup to resolve how to reach 10.1.1.2. The recursive lookup matches a directly connected route (10.1.1.0/24 on GigabitEthernet0/1), establishing the outbound interface. Finally, ARP resolves the MAC address corresponding to 10.1.1.2, allowing the router to encapsulate and transmit the frame.

Step-by-Step Solution

1
Perform initial routing table lookup for destination IP 192.168.2.50192.168.2.50.
Matches static route prefix `192.168.2.0/24` based on longest prefix match.
Routers evaluate incoming packet destinations against all active routes in the routing table to find the best match.
2
Extract the next-hop IP address 10.1.1.210.1.1.2 from the matched static route.
Determines that packets must be sent toward next-hop IP address 10.1.1.210.1.1.2.
When a static route points to an IP address rather than an interface, the router must identify where to send the traffic next.
3
Execute a recursive lookup in the routing table for IP 10.1.1.210.1.1.2.
Searches for an active routing entry covering IP 10.1.1.210.1.1.2.
The router needs to determine which exit interface connects to the network containing next-hop address 10.1.1.210.1.1.2.
4
Resolve next-hop IP 10.1.1.210.1.1.2 to connected subnet route `10.1.1.0/24` on GigabitEthernet0/1.
Identifies GigabitEthernet0/1 as the physical outbound interface.
The recursive process ends when the next-hop IP resolves to a directly connected interface.
5
Perform ARP resolution for 10.1.1.210.1.1.2 and transmit frame.
Encapsulates packet in Ethernet frame with next-hop MAC address and transmits out GigabitEthernet0/1.
Layer 3 packet processing concludes with Layer 2 address resolution and frame transmission out the designated egress interface.

Key Concept

IPv4 Static Route Recursive Lookup Process
Estimated Time:1m 30s
Question 83Question →

An administrator is configuring IPv4 static routes on a Cisco IOS router connected to adjacent networks via both point-to-point serial and multiaccess Ethernet interfaces. Which two statements correctly describe the behavior of these IPv4 static route configurations? (Select two.)

Select all that apply

Show answer & explanation

Answer: Configuring a static route specifying only an Ethernet exit interface forces the router to resolve destination IP addresses using ARP, increasing ARP table size and processing overhead.; Configuring a static route specifying only a next-hop IP address requires the router to perform a recursive lookup in the routing table to identify the outgoing interface.

Answer

The correct statements are that specifying only an Ethernet exit interface forces the router to resolve destination host IPs using ARP (increasing processing and memory load), and specifying only a next-hop IP address requires a recursive lookup in the routing table to determine the egress interface.
Specifying only an Ethernet exit interface causes the router to issue ARP requests for every destination IP address, inflating the ARP table. Specifying only a next-hop IP address forces the router to perform a recursive routing lookup to identify the appropriate outbound interface.

Step-by-Step Solution

1
Analyze static route next-hop IP resolution behavior
Identified that next-hop static routes require a recursive lookup step
When a route specifies only a next-hop IP address, the router must search its routing table again to find the interface through which that next-hop address is reachable.
2
Analyze static route exit-interface behavior on multiaccess networks
Identified that specifying only an exit interface on Ethernet causes excessive ARP requests
On multiaccess segments, omitting the next-hop IP causes the router to treat every remote destination host IP as directly attached to the local link, triggering ARP resolution for each destination.
3
Evaluate administrative distance for route selection
Identified that an administrative distance of 110 does not take precedence over OSPF
OSPF uses a default administrative distance of 110. To override an OSPF route, a static route must have a lower administrative distance (e.g., default AD of 1).

Key Concept

IPv4 Static Routing Next-Hop Resolution and Exit Interface Selection
Question 84Question →

A network engineer is configuring a static route on a Cisco router interface connected to a broadcast multiaccess Ethernet network. If the engineer configures the command using only the egress interface (e.g., `ip route 10.20.30.0 255.255.255.0 GigabitEthernet0/0`) without specifying a next-hop IPv4 address, which network behavior or operational issue will occur?

Show answer & explanation

Answer: The router treats the destination subnet as directly connected and generates an ARP request for every destination IP address, leading to high CPU load and ARP table bloat.

Answer

The router treats the destination prefix as a directly connected subnet on the Ethernet segment and attempts to perform an ARP lookup for every host IP address in that destination network.
When an IPv4 static route on a broadcast multiaccess Ethernet interface specifies only the exit interface, Cisco IOS considers the destination prefix directly connected. Consequently, the router attempts to resolve the MAC address for every individual destination IP address in that subnet via ARP requests. This leads to severe ARP table growth, high CPU usage, and dependence on Proxy ARP.

Step-by-Step Solution

1
Analyze the static route syntax used on a multiaccess broadcast interface.
The command specifies an exit interface (`GigabitEthernet0/0`) instead of a next-hop IPv4 address.
On point-to-point links (like HDLC/PPP serial), an exit interface is sufficient because there is only one possible recipient. On multiaccess Ethernet networks, multiple devices share the segment.
2
Determine how the router processes packet forwarding for an exit-interface-only static route on Ethernet.
The router considers the target subnet directly connected to `GigabitEthernet0/0`.
To forward a packet, the router must encapsulate it into an Ethernet frame requiring a destination MAC address. Because no next-hop IP was defined, the router broadcasts an ARP request asking for the MAC address of the final destination IP address.
3
Identify the operational consequences of this configuration.
Excessive ARP traffic, enlarged ARP table size, and elevated CPU utilization occurs.
Every unique destination IPv4 address triggers a separate ARP request. Unless Proxy ARP is enabled on the downstream gateway, traffic will fail completely; if Proxy ARP is enabled, the router's ARP table fills with individual host entries.

Key Concept

Static Route Exit Interface vs. Next-Hop IP on Multiaccess Broadcast Networks
Question 85Question →

An administrator is configuring a secondary IPv4 static route on router R1 to reach network 10.50.0.0/1610.50.0.0/16 via next-hop 192.168.2.2192.168.2.2. A primary static route to the same destination network via next-hop 192.168.1.2192.168.1.2 already exists in the active configuration with default settings. The secondary route must serve strictly as a backup and only enter the routing table if the primary path fails. Which Cisco IOS command should be configured on router R1?

Show answer & explanation

Answer: ip route 10.50.0.0 255.255.0.0 192.168.2.2 10

Answer

The correct command is `ip route 10.50.0.0 255.255.0.0 192.168.2.2 10`.
The command configuring an administrative distance of 10 creates a floating static route. Because Cisco IOS static routes default to an administrative distance of 1, setting the backup route's distance to 10 ensures it remains inactive until the primary route fails.

Step-by-Step Solution

1
Identify the administrative distance of the existing primary static route.
Standard static routes configured without an explicit distance parameter use a default administrative distance (AD) of 11.
Administrative distance determines route trustworthiness in the Cisco IOS routing table.
2
Determine the required administrative distance for a floating static backup route.
The backup route must have an AD strictly greater than 11 (such as 1010).
Routes with higher AD values are ignored by the routing engine until all lower-AD routes for the identical prefix become unreachable.
3
Construct the Cisco IOS static route command syntax incorporating the distance parameter.
Syntax: `ip route <prefix> <mask> <next-hop> <distance>`. Applying parameters yields `ip route 10.50.0.0 255.255.0.0 192.168.2.2 10`.
Appending an administrative distance higher than 11 creates a floating static route.

Key Concept

Floating static routes rely on configuring an Administrative Distance higher than the primary routing source so that the backup route remains dormant in the configuration until the primary route drops out of the routing table.
Estimated Time:1m 30s
Question 86Question →

A network administrator needs to configure and verify a floating static route for destination network 172.16.20.0/24172.16.20.0/24 via next-hop IP 10.2.2.210.2.2.2 on a Cisco router. The primary path to this network is currently learned dynamically via EIGRP with an Administrative Distance of 9090. Place the configuration and verification steps in the correct sequential order from first to last.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequential process is: Enter global configuration mode -> Configure the floating static route with AD 100 -> Verify the routing table to ensure the route is inactive during normal operation -> Shut down the primary interface to trigger failover -> Re-verify the routing table to confirm the floating static route becomes active.
The correct order follows standard Cisco IOS workflow: configuring global settings first, adding the floating static route with an AD higher than EIGRP (90), verifying that the route is inactive during normal operation, simulating a link failure by shutting down the primary interface, and finally verifying that the floating static route takes over as the active path in the routing table.

Step-by-Step Solution

1
Enter global configuration mode
The CLI prompt changes to global configuration mode (`Router(config)#`).
Static routing commands (`ip route`) can only be entered in global configuration mode.
2
Configure the backup static route
The floating static route with Administrative Distance 100 is written to the running configuration.
Configuring an Administrative Distance of 100 ensures the static route has a higher distance than EIGRP (AD 90), keeping it out of the routing table during normal operation.
3
Verify initial routing table state
The output of `show ip route` lists only the EIGRP route for 172.16.20.0/24172.16.20.0/24.
Cisco IOS selects routes with the lowest Administrative Distance for the Routing Information Base (RIB); thus, the floating static route must remain hidden while EIGRP is healthy.
4
Simulate primary path failure
The primary interface enters the administratively down state, invalidating and removing the primary EIGRP route from the RIB.
Interface shutdown removes dependent routes, prompting the router to evaluate alternative routes for the destination.
5
Verify post-failover routing table state
The output of `show ip route` shows 172.16.20.0/24172.16.20.0/24 reachable via static route next-hop 10.2.2.210.2.2.2.
With the primary route removed, the floating static route becomes the best remaining path and is installed into the active routing table.

Key Concept

Floating static route configuration, administrative distance precedence, and failover verification.
Estimated Time:1m 30s
Question 87Question →

A Cisco router receives an IPv4 packet destined for 172.16.10.45172.16.10.45. Place the routing table lookup and packet forwarding 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 forwarding sequence begins with parsing the packet header to extract the destination IP, searching the routing table using longest prefix match logic, selecting the most specific matching prefix, identifying the next-hop IP or exit interface, and finally encapsulating the packet into a Layer 2 frame for egress transmission.
The correct order follows standard Cisco IOS router packet forwarding logic: extracting the destination IPv4 address, evaluating routing table prefixes, applying the longest prefix match (LPM) rule to select the best route, resolving the next-hop IP address or exit interface, and performing Layer 2 frame encapsulation prior to egress.

Step-by-Step Solution

1
Parse packet header
Destination IPv4 address extracted
The router requires the destination address to perform a routing lookup.
2
Perform routing table lookup
Candidate matching routes identified
The routing table contains network prefixes that must be checked against the destination IP.
3
Apply Longest Prefix Match (LPM)
Select most specific route entry
When multiple routes match the destination, the prefix with the most matching leading bits (longest subnet mask) is selected.
4
Resolve forwarding details
Determine next-hop IP address or egress interface
The selected route specifies the exact forwarding path towards the destination.
5
Layer 2 Encapsulation and Egress
Frame transmitted out the outbound interface
Layer 2 headers (such as Ethernet MAC headers) are constructed based on next-hop ARP table resolution before physical transmission.

Key Concept

IPv4 Routing Table Lookup and Longest Prefix Match Forwarding Logic
Question 88Question →

An enterprise router learns the path to a remote subnet 192.168.100.0/24192.168.100.0/24 through EIGRP, which operates with a default administrative distance of 9090. A network engineer needs to configure a backup IPv4 static route to reach this subnet using the next-hop IPv4 address 10.0.5.210.0.5.2 so that the backup route remains inactive until the primary EIGRP path fails. Which Cisco IOS command correctly configures this floating static route?

Show answer & explanation

Answer: ip route 192.168.100.0 255.255.255.0 10.0.5.2 95

Answer

The command 'ip route 192.168.100.0 255.255.255.0 10.0.5.2 95' correctly specifies a static route with an administrative distance higher than EIGRP's default AD of 90.
The correct command uses the syntax 'ip route 192.168.100.0 255.255.255.0 10.0.5.2 95'. Because an administrative distance of 95 is higher than EIGRP's default AD of 90, the router keeps this static route in reserve as a floating backup until the primary EIGRP path becomes unavailable.

Step-by-Step Solution

1
Identify the primary routing protocol's Administrative Distance (AD)
EIGRP internal routes have an AD of 90.
Floating static routes require an administrative distance strictly higher than the active primary routing source.
2
Determine the required AD for the floating static route
An administrative distance value greater than 90 (such as 95) is required.
Routes with lower AD values are preferred in the IP routing table. Setting AD > 90 ensures the route stays hidden until the primary route disappears.
3
Verify Cisco IOS static route syntax
Syntax: 'ip route <prefix> <mask> <next-hop-ip> [distance]'.
The subnet mask must be written in standard dotted-decimal format (255.255.255.0), followed by the next-hop IP and the custom AD value.

Key Concept

Floating Static Route Administrative Distance Selection
Question 89Question →

A network administrator is configuring IPv4 static routes on router R1 to reach destination network 10.88.0.0/1610.88.0.0/16. The primary path must forward traffic to the next-hop IP address 192.168.50.2192.168.50.2. A secondary path must act as a floating static backup route using the point-to-point interface Serial0/1/0, forwarding traffic only if the primary path becomes unavailable. Which TWO commands must be configured on router R1 to achieve this objective?

Select all that apply

Show answer & explanation

Answer: ip route 10.88.0.0 255.255.0.0 192.168.50.2; ip route 10.88.0.0 255.255.0.0 Serial0/1/0 130

Answer

The correct configurations are the command defining the primary static route using next-hop IP address 192.168.50.2 with the default administrative distance of 1, and the command defining the floating static backup route via interface Serial0/1/0 with an administrative distance elevated to 130.
The primary path to 10.88.0.0/1610.88.0.0/16 is defined using the next-hop IPv4 address 192.168.50.2, which inherits the default static route Administrative Distance (AD) of 1. To configure a floating static backup route, an explicit AD value strictly greater than the primary route's AD (such as 130) must be appended at the end of the command string. Additionally, point-to-point interfaces like Serial0/1/0 are valid exit interface choices for static routing.

Step-by-Step Solution

1
Determine the primary route configuration.
Syntax: 'ip route 10.88.0.0 255.255.0.0 192.168.50.2'.
Standard IPv4 static routes default to an Administrative Distance (AD) of 1 when no distance parameter is specified at the end of the command.
2
Determine the backup floating static route configuration.
Syntax: 'ip route 10.88.0.0 255.255.0.0 Serial0/1/0 130'.
A floating static route requires an administrative distance higher than the primary route's AD (which is 1). Specifying an AD of 130 ensures it remains out of the routing table until the primary path goes down.

Key Concept

IPv4 Static Route Syntax and Floating Static Administrative Distance
PreviousPage 5 / 5
IPv4 Static Routing Practice Questions — Cisco CCNA — Page 5 | Examkin