Floating Static Routes

38 questions

Question 21Question

An engineer configures a static backup route on router R1 for remote destination subnet 172.22.50.0/24172.22.50.0/24. The primary path to this subnet is learned dynamically via OSPFv2. During baseline verification, the engineer discovers that traffic destined for 172.22.50.0/24172.22.50.0/24 routes over the backup WAN circuit even though the primary OSPF link is active and in the FULL state. Which configuration issue on router R1 explains why the backup route is active in the routing table?

Show answer & explanation

Answer: The static route was configured without specifying a custom administrative distance, causing it to use the default administrative distance of 1, which beats the OSPF administrative distance of 110.

Answer

The static route was configured without specifying a custom administrative distance, causing it to use the default administrative distance of 1, which beats the OSPF administrative distance of 110.
In Cisco IOS, static routes configured without an explicit administrative distance inherit the default value of 1. Because routers populate the IP routing table by choosing the path with the lowest administrative distance when multiple sources report the same prefix, a static route with AD 1 will take precedence over an OSPF route with AD 110. To act as a floating static route, the static route's administrative distance must be manually set higher than the primary routing protocol's AD (for example, setting AD to 115 or 120).

Step-by-Step Solution

1
Identify the administrative distance (AD) of the primary dynamic routing protocol.
OSPFv2 has a default administrative distance of 110.
Administrative distance measures the trustworthiness of a routing source. Lower values are preferred.
2
Analyze default static route behavior when no administrative distance parameter is specified.
Cisco IOS assigns a default administrative distance of 1 to static routes.
Because 1 is lower than 110, the router chooses the static route as more believable than the OSPF route.
3
Determine the requirement for a floating static route.
To float behind OSPF, the static route must be configured with an administrative distance strictly greater than 110 (e.g., 120).
Omitting the AD parameter causes the static route to become the active primary path instead of a floating backup.

Key Concept

Floating Static Route Administrative Distance Configuration
Estimated Time:2m 0s
Question 22Question

In an enterprise WAN edge topology, router HQ-GW receives a path to subnet 10.80.0.0/1410.80.0.0/14 via a redistributed routing process resulting in an EIGRP External route (default Administrative Distance of 170170). An administrator needs to configure a floating static backup route for destination subnet 10.80.0.0/1410.80.0.0/14 using next-hop IP 192.168.200.1192.168.200.1 over an auxiliary link.

What minimum Administrative Distance integer value must be appended to the Cisco IOS command so that the static route remains dormant until the primary EIGRP External route fails?

Fill in the blanks below

ip route 10.80.0.0 255.240.0.0 192.168.200.1
Show answer & explanation

Answer

171
Cisco IOS routes are populated into the routing table based on Administrative Distance (AD), where lower values indicate higher trustworthiness. EIGRP External routes possess a default AD of 170. For a static route to act as a floating backup (remaining inactive until the primary path fails), its AD must be set higher than the primary path's AD. The minimum integer value greater than 170 is 171.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the primary routing source.
EIGRP External routes have a standard Cisco IOS default AD of 170.
Routing decisions in Cisco IOS select the path with the lowest Administrative Distance.
2
Determine the required Administrative Distance condition for a floating static route.
The floating static route's AD must be strictly greater than 170.
If the static route's AD were less than or equal to 170, it would either override the primary path or cause equal-cost multi-pathing/route instability rather than serving strictly as a backup.
3
Calculate the minimum integer AD required for the static route command.
170 + 1 = 171.
171 is the lowest whole integer value greater than the primary path's AD of 170.

Key Concept

Floating Static Route Administrative Distance Selection
Question 23Question

An enterprise router learns the primary route to network 172.16.50.0/24172.16.50.0/24 via internal BGP (iBGP), which carries a default Administrative Distance of 200200. An administrator wants to configure a floating static backup route pointing to next-hop IP 10.1.1.210.1.1.2. Complete the Cisco IOS command below by entering the minimum administrative distance value required to ensure this route functions strictly as a backup path.

Fill in the blanks below

Router(config)# ip route 172.16.50.0 255.255.255.0 10.1.1.2
Show answer & explanation

Answer

201
A floating static route must be configured with an Administrative Distance (AD) strictly greater than that of the primary route. Since iBGP has a default AD of 200, the static route requires an AD of at least 201 to remain inactive until the primary iBGP route fails.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the primary routing protocol.
The primary path is learned via iBGP, which has a default Administrative Distance of 200200.
Cisco IOS prefers routing information sources with lower Administrative Distance values.
2
Determine the required AD relationship for a floating static backup route.
The static route's administrative distance must be higher than the primary route's AD (>200> 200).
If the static route has an AD lower than or equal to 200200, Cisco IOS will install the static route into the routing table instead of holding it in reserve as a backup.
3
Calculate the minimum integer AD value for the command.
The smallest integer greater than 200200 is 201201.
Specifying 201201 at the end of the `ip route` command sets the static route's AD to 201, keeping it inactive until the iBGP route is removed.

Key Concept

Floating Static Routes and Administrative Distance
Estimated Time:1m 0s
Question 24Question

Complete the Cisco IOS command required to configure a floating static backup route.

Fill in the blanks below

An edge router receives its primary path to destination subnet 172.20.10.0/24172.20.10.0/24 via internal EIGRP, which carries a default Administrative Distance of 9090. A network engineer needs to configure a floating static backup route toward the same destination using next-hop IP 10.1.1.210.1.1.2 with an Administrative Distance of 100100.

What value should be entered to complete the Cisco IOS command below?

`ip route 172.20.10.0 255.255.255.0 10.1.1.2`
Show answer & explanation

Answer

The missing parameter to complete the command is 100.
Appending the integer 100 to the end of the `ip route` syntax sets the static route's Administrative Distance to 100. Because 100 is higher than internal EIGRP's default AD of 90, the router will keep the static route inactive (floating) in the routing table until the primary EIGRP path becomes unavailable.

Step-by-Step Solution

1
Analyze the Cisco IOS static route command structure.
The command syntax is `ip route <prefix> <mask> <next-hop> [distance]`.
The optional trailing integer at the end of the command specifies the Administrative Distance (AD) for the route.
2
Determine the required Administrative Distance value for the floating static route.
The problem specifies an Administrative Distance of 100 for the backup route.
Setting the AD to 100 ensures the static route remains higher (less preferred) than the primary internal EIGRP route (AD 90), causing it to float outside the routing table until the primary path fails.

Key Concept

Floating Static Route Configuration and Administrative Distance
Estimated Time:1m 0s
Question 25Question

A network administrator needs to configure a floating static backup route on a Cisco router to reach the destination subnet 192.168.50.0/24192.168.50.0/24 via the next-hop IP address 10.0.12.210.0.12.2. The primary path to this network is currently dynamically learned via OSPF. Which command correctly configures the floating static route so that it only enters the routing table when the OSPF route fails?

Show answer & explanation

Answer: ip route 192.168.50.0 255.255.255.0 10.0.12.2 120

Answer

The command 'ip route 192.168.50.0 255.255.255.0 10.0.12.2 120' correctly configures the floating static route by setting an administrative distance of 120, which is greater than OSPF's default administrative distance of 110.
The correct command specifies an administrative distance of 120 at the end of the static route definition. Because OSPF has a default administrative distance of 110, Cisco IOS will prefer the OSPF route and keep the static route out of the active routing table (floating) until the OSPF route is removed.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the primary routing protocol.
OSPF has a standard default Administrative Distance of 110 on Cisco IOS devices.
Floating static routes rely on AD comparisons to determine route preference.
2
Determine the required Administrative Distance for the floating static route.
The backup static route must have an AD strictly greater than 110 (e.g., 120).
Cisco routers prefer routes with lower AD values; setting a higher AD keeps the route out of the routing table until the primary route fails.
3
Verify Cisco IOS static route syntax.
The syntax 'ip route <prefix> <mask> <next-hop-ip> <distance>' is satisfied by appending 120 at the end of the command.
Appending an integer after the next-hop address specifies a custom Administrative Distance.

Key Concept

Floating Static Route Administrative Distance Calibration
Estimated Time:1m 0s
Question 26Question

A network administrator is configuring a backup link on a Cisco router for destination network 10.50.0.0/2410.50.0.0/24. The primary path to this network is currently learned via OSPF, which has a default Administrative Distance (AD) of 110110. Which two statements correctly describe the requirements and operational behavior of the floating static route used for this backup path? (Select two.)

Select all that apply

Show answer & explanation

Answer: The administrative distance configured at the end of the static route command must be greater than 110110.; The floating static route will only be installed into the active routing table if the primary OSPF route is removed.

Answer

The floating static route must be configured with an administrative distance higher than the primary routing protocol's AD (greater than 110 for OSPF), and it will only populate the routing table when the primary OSPF route is removed.
A floating static route serves as a backup path by assigning an Administrative Distance (AD) higher than that of the primary routing protocol (OSPF AD = 110). Because Cisco IOS prefers routes with lower AD values, the floating static route is held in inactive standby and is only placed into the active routing table when the primary OSPF route disappears.

Step-by-Step Solution

1
Identify the primary routing protocol and its default Administrative Distance (AD).
The primary route is OSPF, which carries a default AD of 110110.
Administrative Distance determines the trustworthiness of routing sources in Cisco IOS.
2
Determine the required AD for the floating static route to function as a backup.
The static route AD must be set to a value higher than 110110 (such as 120120).
Lower AD values are preferred. Setting a higher AD ensures the static route is ignored as long as the OSPF route is present in the routing table.
3
Analyze how Cisco IOS installs the floating static route into the routing table.
The floating static route remains inactive in configuration until the OSPF route fails or is withdrawn, at which point the router installs the backup static route.
A router only installs the route with the lowest AD for a given prefix into the active routing table.

Key Concept

Floating Static Route Administrative Distance and Failover Mechanics
Estimated Time:1m 30s
Question 27Question

An edge router receives the primary route to remote destination network 10.10.0.0/1610.10.0.0/16 via external BGP (eBGP) from ISP-1 using default settings. The network administrator attempts to configure a floating static backup route toward ISP-2 using the command `ip route 10.10.0.0 255.255.0.0 192.168.1.2 15`. Which behavior will be observed on the router regarding this destination?

Show answer & explanation

Answer: The static route immediately replaces the eBGP route as the primary active route in the routing table because its Administrative Distance of 15 is lower than the default eBGP Administrative Distance of 20.

Answer

The static route immediately replaces the eBGP route as the primary active route in the routing table because its Administrative Distance of 15 is lower than the default eBGP Administrative Distance of 20.
In Cisco IOS, lower Administrative Distance values take precedence. The default Administrative Distance for external BGP (eBGP) is 20. Because the static route was configured with an explicit Administrative Distance of 15, the router considers it more reliable than the eBGP route. As a result, the static route becomes the primary active path in the routing table rather than remaining an inactive backup.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the primary routing protocol.
The primary route is learned via external BGP (eBGP), which has a default Cisco IOS Administrative Distance of 2020.
Administrative Distance indicates the trustworthiness of a routing source.
2
Analyze the configured Administrative Distance of the static route.
The trailing argument in `ip route 10.10.0.0 255.255.0.0 192.168.1.2 15` specifies an Administrative Distance of 1515.
The optional metric value at the end of the `ip route` syntax overrides the default static route AD of 1.
3
Compare the AD values to determine routing table selection.
Since 15<2015 < 20, the static route is considered more believable than the eBGP route.
Routers select the route with the lowest Administrative Distance when multiple sources advertise the exact same prefix length.

Key Concept

Floating Static Route Administrative Distance Precedence
Question 28Question

A network engineer is configuring a backup static route on a Cisco router for the destination network 10.100.4.0/2410.100.4.0/24. The primary path to this network is currently learned dynamically via internal EIGRP, which uses a default Administrative Distance of 9090. The engineer needs the static route to remain inactive in the routing table unless the EIGRP path fails. Which command correctly configures this floating static route?

Show answer & explanation

Answer: ip route 10.100.4.0 255.255.255.0 192.168.12.2 130

Answer

The command specifying an administrative distance of 130 correctly configures the floating static route.
A floating static route requires an Administrative Distance (AD) value higher than that of the primary route protocol. Because internal EIGRP uses a default AD of 90, specifying an AD of 130 ensures the static route remains out of the IP routing table until the primary EIGRP route fails.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the primary routing protocol.
Internal EIGRP has a default AD of 90.
Floating static routes rely on AD precedence to remain dormant while the primary path is operational.
2
Determine the required Administrative Distance for the floating static route.
The static route must be assigned an AD value strictly greater than 90 (e.g., 130).
Cisco IOS prefers routes with lower AD values. Assigning an AD higher than 90 ensures the static route is installed into the routing table only if the EIGRP route is withdrawn.
3
Evaluate the syntax options for the correct trailing AD value.
The command 'ip route 10.100.4.0 255.255.255.0 192.168.12.2 130' correctly appends the custom AD 130.
It successfully creates a floating static backup route.

Key Concept

Floating Static Routes and Administrative Distance
Question 29Question

Company router R1 currently reaches the remote subnetwork 192.168.50.0/24192.168.50.0/24 via internal EIGRP, which has a default Administrative Distance of 90. A network administrator wants to configure a backup floating static route to 192.168.50.0/24192.168.50.0/24 through the next-hop IP address 172.16.1.2. The floating route must remain inactive in the routing table until the primary EIGRP path becomes unavailable. Which Cisco IOS command correctly configures this floating static route?

Show answer & explanation

Answer: ip route 192.168.50.0 255.255.255.0 172.16.1.2 95

Answer

The command 'ip route 192.168.50.0 255.255.255.0 172.16.1.2 95' correctly configures the floating static route.
A floating static route functions as a backup route by configuring an Administrative Distance (AD) higher than that of the primary routing source. Internal EIGRP has a default AD of 90. Configuring the static route with an AD of 95 ensures that Cisco IOS keeps the static route inactive in the routing table during normal conditions, activating it only if the primary EIGRP path fails.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the primary routing source.
Internal EIGRP has a default Administrative Distance of 9090.
Floating static routes rely on administrative distance values to determine primary vs. backup paths.
2
Determine the required Administrative Distance for the backup floating static route.
The administrative distance must be set to a value greater than 9090 (such as 9595).
Cisco IOS prefers routes with lower administrative distance values. Setting a value higher than 9090 keeps the static route out of the routing table while the EIGRP route is active.
3
Construct the static route CLI command including the destination IP, subnet mask, next-hop IP, and trailing AD parameter.
The resulting command is 'ip route 192.168.50.0 255.255.255.0 172.16.1.2 95'.
The trailing numeric argument defines the custom administrative distance for the static route.

Key Concept

Floating Static Route Configuration and Administrative Distance
Question 30Question

A network administrator needs to configure a floating static route on router R1 to serve as a backup path for the 192.168.100.0/24192.168.100.0/24 network. The primary path to this destination is currently learned dynamically via OSPF, which uses a default Administrative Distance of 110110. Which TWO statements correctly describe the requirements and operational behavior for this floating static route configuration?

Select all that apply

Show answer & explanation

Answer: The floating static route must be configured with an Administrative Distance value greater than 110.; The floating static route will only be installed into the routing table when the primary OSPF route disappears from the routing table.

Answer

The floating static route must be configured with an Administrative Distance greater than 110, and it will only be installed into the routing table after the primary OSPF route is removed.
A floating static route acts as an inactive backup line that only takes effect when the primary path goes down. Because Cisco IOS evaluates route preference using Administrative Distance (where lower is preferred), the backup static route must be configured with an AD higher than the primary protocol's AD (in this case, higher than OSPF's default AD of 110). Consequently, the backup route stays inactive in the background and is only installed into the IP routing table when the primary OSPF route is withdrawn.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the primary routing protocol.
OSPF has a default AD of 110.
Administrative Distance defines route trustworthiness; lower values are preferred.
2
Determine the AD requirement for a backup (floating) static route.
The backup route AD must be strictly greater than 110 (e.g., 120).
If the AD were equal or lower, the router would prefer or load balance with the static route, preventing it from functioning strictly as a backup.
3
Analyze how Cisco IOS handles routing table selection with floating static routes.
The floating static route remains hidden from the routing table as long as the OSPF route (AD 110) exists.
When the primary OSPF route fails and is removed, the floating static route becomes the best available path for that destination prefix and is installed into the active routing table.

Key Concept

Floating Static Route AD Requirements and Routing Table Selection
Question 31Question

An enterprise edge router receives its primary route to the 172.20.10.0/24172.20.10.0/24 destination network via OSPF, which uses a default Administrative Distance of 110110. A network administrator must configure a floating static backup route targeting next-hop IP address 192.168.12.2192.168.12.2 that will remain inactive in the routing table unless the primary OSPF route becomes unavailable. Which Cisco IOS command accomplishes this objective?

Show answer & explanation

Answer: ip route 172.20.10.0 255.255.255.0 192.168.12.2 120

Answer

The command 'ip route 172.20.10.0 255.255.255.0 192.168.12.2 120' correctly configures the backup floating static route.
The correct command specifies an Administrative Distance of 120 at the end of the syntax. Because 120 is higher than the default OSPF distance of 110, Cisco IOS keeps this static route out of the routing table as long as the OSPF route is active. If the OSPF route fails and is withdrawn, the floating static route with AD 120 becomes the best available path and is inserted into the routing table.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the primary dynamic routing protocol.
OSPF has a default Administrative Distance of 110.
Floating static routes rely on AD values to determine route preference.
2
Determine the required Administrative Distance for the floating static route.
The static route AD must be strictly greater than 110 (e.g., 120).
Routers select routes with the lowest AD. Setting a higher value keeps the static route inactive while OSPF is healthy.
3
Construct the Cisco IOS static route command syntax.
The syntax is 'ip route <prefix> <mask> <next-hop> <distance>'. Placing 120 at the end sets the floating distance.
Specifying 120 at the end of the command overrides the default static AD of 1.

Key Concept

Floating Static Routes and Administrative Distance
Question 32Question

A router receives routes to the destination network 10.50.0.0/1610.50.0.0/16 via internal EIGRP (Administrative Distance 9090). An engineer intends to create a floating static route as a backup path and executes the command `ip route 10.50.0.0 255.255.0.0 192.168.12.2 80`. Which outcome occurs as a direct result of this configuration?

Show answer & explanation

Answer: The newly configured static route immediately replaces the EIGRP route in the routing table because its Administrative Distance of 8080 is lower than 9090.

Answer

The newly configured static route immediately replaces the EIGRP route in the routing table because its Administrative Distance of 80 is lower than 90.
Cisco routers use Administrative Distance (AD) to evaluate route trustworthiness when multiple sources learn paths to identical prefixes. Internal EIGRP has a default AD of 90. Configuring a static route with an AD of 80 makes it more preferred than EIGRP because a lower AD value indicates higher priority. As a result, the static route preempts the EIGRP route immediately in the routing table rather than functioning as a backup.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the existing primary route.
Internal EIGRP has a default AD of 9090.
Administrative Distance is used by Cisco IOS to select the best path when multiple routing sources supply routes to the same destination.
2
Analyze the configured AD of the static route command `ip route 10.50.0.0 255.255.0.0 192.168.12.2 80`.
The trailing value 8080 sets the static route's AD to 8080.
The default static route AD is 11, but appending a number at the end overrides the default AD value.
3
Compare the two AD values to determine routing table selection.
Since 80<9080 < 90, the static route is considered more trustworthy than EIGRP.
Lower AD values are preferred. To make a static route a floating backup, its AD must be higher than the primary protocol (e.g., AD of 95 or higher).

Key Concept

Floating Static Route Administrative Distance Requirements
Question 33Question

A network engineer needs to configure a floating static route on Cisco router R1 for destination subnet 10.10.20.0/2410.10.20.0/24 via next-hop IP 192.168.1.2192.168.1.2. The route must serve as a backup to an existing OSPF path, which has a default Administrative Distance of 110110. The engineer decides to set the backup route's Administrative Distance to 130130.

Complete the Cisco IOS global configuration command below by filling in the missing trailing Administrative Distance value.

Fill in the blanks below

R1(config)# ip route 10.10.20.0 255.255.255.0 192.168.1.2
Show answer & explanation

Answer

The trailing Administrative Distance value required to complete the command is 130.
Specifying 130 at the end of the `ip route` command assigns an Administrative Distance higher than the primary OSPF route's AD of 110. This keeps the route out of the routing table during normal operation and activates it only when the primary path is removed.

Step-by-Step Solution

1
Identify the standard Cisco IOS syntax for a static route.
The basic command syntax is `ip route <prefix> <mask> <next-hop> [distance]`.
Placing an optional integer value at the end of the static route command assigns a custom Administrative Distance.
2
Determine the requested Administrative Distance value for the floating static route.
The specified Administrative Distance value is 130.
Setting the AD to 130 ensures it is higher than OSPF's default AD of 110, keeping the static route floating in reserve until the OSPF route fails.

Key Concept

Floating Static Route CLI Syntax and Administrative Distance
Estimated Time:1m 0s
Question 34Question

An enterprise router receives a primary path for the prefix 192.168.50.0/24192.168.50.0/24 via OSPF. An engineer attempts to configure a floating static backup route using the command `ip route 192.168.50.0 255.255.255.0 10.0.0.2 105`. However, after entering the command, the routing table immediately replaces the OSPF path with the static route. What is the cause of this behavior?

Show answer & explanation

Answer: The static route was assigned an administrative distance of 105, which is lower than the default OSPF administrative distance of 110.

Answer

The static route was assigned an administrative distance of 105, which is lower than the default OSPF administrative distance of 110.
Cisco IOS selects routes based on Administrative Distance (AD), where lower AD values indicate higher trustworthiness. Default OSPF has an AD of 110. Because the engineer configured the static route with an AD of 105, it is lower than OSPF's AD of 110. Consequently, the router prefers the static route and installs it into the routing table immediately, preventing it from functioning as a backup route. A proper floating static route for OSPF must be configured with an AD greater than 110 (such as 120).

Step-by-Step Solution

1
Identify the default Administrative Distance (AD) for the primary routing protocol (OSPF).
OSPF has a default AD of 110.
Cisco IOS uses AD values to determine route trustworthiness when multiple routing sources offer paths to the exact same destination.
2
Evaluate the AD assigned to the static route in the command `ip route 192.168.50.0 255.255.255.0 10.0.0.2 105`.
The trailing value 105 configures the static route AD to 105.
The optional numeric argument at the end of a static route statement specifies its administrative distance.
3
Compare the static route AD against the primary OSPF route AD.
Because 105<110105 < 110, the static route has a lower (more preferred) AD than OSPF.
Lower AD values take precedence in routing table installation. To act as a floating static backup, the static route AD must be configured with a value strictly greater than the primary protocol AD (e.g., AD > 110).

Key Concept

Floating Static Route Administrative Distance Requirements
Question 35Question

A network administrator intends to deploy a floating static route on router R1 as a backup path for the internal network 172.16.50.0/24172.16.50.0/24. The primary path to this destination is currently learned through internal EIGRP (default Administrative Distance of 9090). During initial testing, the administrator notices that traffic destined for 172.16.50.0172.16.50.0 is immediately taking the static backup path across interface GigabitEthernet0/2, even though the primary EIGRP neighbor relationship remains active and healthy. Which two issues could cause the static route to be preferred over the active EIGRP route? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: The administrator configured the floating static route with an Administrative Distance of 8080.; The static route was configured using a destination prefix of 172.16.50.0/25172.16.50.0/25 instead of 172.16.50.0/24172.16.50.0/24.

Answer

The static route is preferred over the primary EIGRP route if the static route was configured with an Administrative Distance of 80 (which is lower than EIGRP's default Administrative Distance of 90) or if the static route was configured with a more specific subnet mask of /25 (which takes precedence due to the Longest Prefix Match rule).
A floating static route functions as a backup path only when its Administrative Distance (AD) is strictly higher than that of the primary routing protocol (internal EIGRP default AD = 90). Configuring an AD of 80 causes the static route to preempt EIGRP. Additionally, routers prioritize routes based on Longest Prefix Match before AD; configuring a /25 route creates a more specific entry than the /24 EIGRP route, forcing traffic onto the static path.

Step-by-Step Solution

1
Evaluate the role of Administrative Distance (AD) in route selection.
Cisco IOS routing tables prioritize routes with lower AD values. Internal EIGRP has a default AD of 90. If a static route is configured with AD 80, it overrides the EIGRP route.
Floating static routes must have an AD higher than the primary routing protocol to stay in standby mode.
2
Evaluate the forwarding decision order between Longest Prefix Match and AD.
Routers first match packets using the longest (most specific) network prefix mask. A /25 prefix is more specific than a /24 prefix.
If the destination mask is /25, the router selects that route prior to comparing AD against the /24 EIGRP route.

Key Concept

Floating Static Route Administration and Prefix Matching
Estimated Time:1m 30s
Question 36Question

A network engineer is configuring a floating static route on a Cisco router to serve as a backup path for destination network 172.20.10.0/24 via next-hop IP 10.1.1.2. The primary route to this network is currently learned via eBGP, which has a default administrative distance of 20. The engineer needs to assign an administrative distance of 25 to the backup route so that it only enters the routing table if the primary route fails. What value should complete the configuration command?

Fill in the blanks below

ip route 172.20.10.0 255.255.255.0 10.1.1.2
Show answer & explanation

Answer

25
In Cisco IOS, a floating static route is created by appending a numerical administrative distance at the end of the `ip route` command. Specifying 25 configures the static route with an administrative distance higher than eBGP (AD 20), ensuring it remains floating (inactive) until the primary route drops out of the routing table.

Step-by-Step Solution

1
Identify the administrative distance of the primary route protocol.
The primary path is learned via eBGP, which has a default administrative distance of 20.
A floating static route must be configured with an administrative distance higher than the primary path so it remains inactive until failure.
2
Determine the trailing numerical argument for the Cisco IOS static route command.
Appending 25 to the end of the `ip route` syntax sets the administrative distance of the static route to 25.
Cisco IOS uses the optional trailing distance parameter in the `ip route <prefix> <mask> <next-hop> [distance]` command syntax.

Key Concept

Floating Static Route Configuration and Administrative Distance
Question 37Question

An administrator intends to deploy a floating static route on router R1 to serve as a backup path for internal network 10.100.50.0/2410.100.50.0/24, which is primarily learned via Internal EIGRP (administrative distance 90). Following the configuration, traffic immediately shifts to the secondary link despite the primary link remaining fully operational.

Which configuration mistake caused the static route to preempt the primary EIGRP route in the routing table?

Show answer & explanation

Answer: The static route was assigned an administrative distance value lower than 90, causing it to take precedence over the EIGRP route.

Answer

The static route was assigned an administrative distance value lower than 90, causing it to take precedence over the EIGRP route.
Cisco IOS routers evaluate Administrative Distance (AD) to determine which routing source to trust when multiple sources offer routes to the exact same destination prefix. Lower AD values are preferred. Internal EIGRP has a default AD of 90. For a static route to serve as a floating backup, its AD must be configured to a value strictly greater than 90 (e.g., 95 or 130). If the administrator configures an AD lower than 90 (or omits the AD parameter, which defaults to 1), the static route will be preferred over EIGRP and immediately installed into the routing table as the active route.

Step-by-Step Solution

1
Analyze the primary routing protocol's Administrative Distance (AD).
Internal EIGRP has a default AD of 90.
Cisco IOS selects routes with the lowest administrative distance when multiple sources advertise the identical destination network prefix.
2
Determine the requirement for a floating static route to act as a backup.
The floating static route must have an AD strictly greater than 90 so it stays out of the routing table while EIGRP is active.
If the configured static route has an AD lower than 90 (or defaults to 1), the router prefers the static route over EIGRP immediately.
3
Identify the cause of immediate preemption.
Assigning an AD lower than 90 caused the router to install the static route into the routing table over the active EIGRP route.
Routes with lower administrative distance values take administrative preference in the Cisco IOS routing table installation process.

Key Concept

Administrative Distance Precedence in Floating Static Routes
Question 38Question

Router R1 learns the destination network 10.50.0.0/1610.50.0.0/16 dynamically via internal EIGRP, which has a default Administrative Distance (AD) of 90. A network administrator wants to configure a floating static route pointing to next-hop 192.168.12.2192.168.12.2 to serve as a backup path when the EIGRP route fails. Which two conditions or behaviors apply to this floating static route implementation? (Select two.)

Select all that apply

Show answer & explanation

Answer: The floating static route must be configured with an Administrative Distance value greater than 90.; The floating static route will be placed into the active routing table only when the primary EIGRP route is removed.

Answer

To configure a functional floating static route for an EIGRP primary path, the static route must specify an Administrative Distance greater than 90 (the default EIGRP AD). Consequently, the backup route will only be installed into the active routing table when the lower-AD EIGRP route disappears.
A floating static route acts as a backup mechanism by using an Administrative Distance (AD) higher than that of the primary route (in this case, EIGRP AD of 90). Cisco IOS populates the active routing table with the lowest AD available; thus, the static route stays out of the routing table until the primary route fails and is withdrawn.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the primary routing protocol.
Internal EIGRP has a default AD of 90.
Floating static routes rely on AD comparison to remain dormant until the primary route fails.
2
Determine the required Administrative Distance for the backup floating static route.
The static route's AD must be set higher than 90 (e.g., 95 or 130).
If configured with a lower AD (such as 80 or 1), the static route would override the EIGRP path during normal operation.
3
Analyze how Cisco IOS handles routing table selection for multiple sources.
Only the path with the lowest AD is placed in the active routing table.
The floating static route remains inactive in the background and is only installed when the EIGRP prefix is removed due to network failure.

Key Concept

Floating Static Routes and Administrative Distance
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