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Question 241Question →

Complete the Cisco IOS command below to configure a floating static route for the 172.16.100.0/22 network using the next-hop address 10.254.1.2. The route must serve as a floating backup to a primary path learned via internal EIGRP. Enter the dotted-decimal subnet mask in the first blank and the minimum integer administrative distance value required for backup operation in the second blank.

Fill in the blanks below

ip route 172.16.100.0 10.254.1.2
Show answer & explanation

Answer

blank_1: 255.255.252.0, blank_2: 91
To configure a floating static route in Cisco IOS for the 172.16.100.0/22 prefix, the subnet mask must be specified in dotted-decimal format as 255.255.252.0. Internal EIGRP operates with a default Administrative Distance of 90. To ensure the static route acts strictly as a floating backup—entering the routing table only when the primary EIGRP route is lost—the static route must be assigned an Administrative Distance greater than 90. The minimum integer value that achieves this is 91.

Step-by-Step Solution

1
Convert the CIDR prefix length /22 to a dotted-decimal subnet mask.
A /22 prefix corresponds to 22 contiguous network bits (11111111.11111111.11111100.00000000), which equals 255.255.252.0.
Cisco IOS IPv4 static route syntax requires the subnet mask in dotted-decimal notation.
2
Identify the default Administrative Distance (AD) of internal EIGRP.
Internal EIGRP has a default AD of 90.
A floating static route must have an AD strictly greater than the primary route's AD to remain inactive in the routing table while the primary path is reachable.
3
Calculate the minimum administrative distance for the floating static route.
The minimum integer value greater than 90 is 91.
Assigning an AD of 91 ensures the static route is floating (inactive) relative to EIGRP (AD 90) but activates immediately if the EIGRP route fails.

Key Concept

Floating Static Route Configuration and Administrative Distance
Estimated Time:2m 0s
Question 242Question →

A network administrator executes the following configuration commands on a Cisco router interface connected to an Ethernet switch:

text
R1(config)# interface GigabitEthernet0/1
R1(config-if)# ip ospf network point-to-point

Prior to this change, GigabitEthernet0/1 was operating under the default Cisco IOS OSPF settings for Ethernet interfaces. Which statement accurately describes the effect of this configuration change on OSPF DR/BDR elections and timer values for GigabitEthernet0/1?

Show answer & explanation

Answer: OSPF DR and BDR elections are suppressed on the interface, while the default Hello timer remains 10 seconds.

Answer

OSPF DR and BDR elections are suppressed on the interface, while the default Hello timer remains 10 seconds.
On Cisco routers, Ethernet interfaces default to the Broadcast network type, which elects a Designated Router (DR) and Backup Designated Router (BDR) and uses a 10-second Hello interval. Manually overriding the network type with `ip ospf network point-to-point` instructs OSPF to treat the link as a direct point-to-point connection. As a result, DR and BDR elections are completely suppressed on that interface. Because the standard Hello interval for OSPF Point-to-Point interfaces is also 10 seconds, the Hello timer remains unchanged.

Step-by-Step Solution

1
Identify default OSPF parameters for Ethernet media.
By default, Cisco IOS assigns the OSPF network type 'Broadcast' to Ethernet interfaces, which uses a 10-second Hello timer (40-second Dead timer) and elects a DR/BDR.
Ethernet is multi-access media, requiring DR/BDR to reduce adjacency count.
2
Analyze the impact of the 'ip ospf network point-to-point' command.
Configuring 'point-to-point' changes the network type to Point-to-Point, which does NOT elect a DR/BDR on the interface.
Point-to-Point networks assume only two routers exist on the link, rendering designated routers unnecessary.
3
Determine timer adjustments associated with the Point-to-Point network type.
The Point-to-Point network type in OSPFv2 defaults to a 10-second Hello timer and 40-second Dead timer.
Both Broadcast and Point-to-Point OSPF network types share the same default 10-second Hello / 40-second Dead timer interval.

Key Concept

OSPFv2 Network Types and DR/BDR Suppression
Question 243Question →

An enterprise router R1 learns the internal destination network 10.50.0.0/1610.50.0.0/16 dynamically via OSPF (default Administrative Distance of 110). A network administrator needs to manually configure two IPv4 static routes on R1:
1. A secondary backup (floating) static route to reach 10.50.0.0/1610.50.0.0/16 via the next-hop IP address 192.168.12.2192.168.12.2.
2. A default static route to forward all non-matching IPv4 traffic to the upstream ISP router at next-hop IP 203.0.113.1203.0.113.1.

Which TWO commands must be configured on router R1 to achieve these routing requirements? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: ip route 10.50.0.0 255.255.0.0 192.168.12.2 130; ip route 0.0.0.0 0.0.0.0 203.0.113.1

Answer

The correct commands are 'ip route 10.50.0.0 255.255.0.0 192.168.12.2 130' to establish a floating static route with an Administrative Distance higher than OSPF (110), and 'ip route 0.0.0.0 0.0.0.0 203.0.113.1' to establish a standard default static route using the prefix 0.0.0.0/0.
To create a floating static route, the Administrative Distance specified at the end of the 'ip route' command must be higher than that of the primary routing source. Since OSPF has an AD of 110, setting an AD of 130 guarantees the route will only be installed in the Routing Information Base (RIB) if the primary OSPF route disappears. Additionally, a default static route requires matching any IP address, configured with destination network 0.0.0.0 and subnet mask 0.0.0.0 pointing to the next-hop router address.

Step-by-Step Solution

1
Determine the primary route's Administrative Distance (AD) for network 10.50.0.0/16.
OSPF has a default AD of 110.
Floating static routes must have an AD strictly greater than the active dynamic protocol's AD to remain inactive until primary route failure.
2
Validate the floating static route syntax and AD parameter.
The command syntax 'ip route 10.50.0.0 255.255.0.0 192.168.12.2 130' specifies an AD of 130, which is higher than 110.
AD 130 ensures the static route remains floating in backup mode until OSPF drops the path.
3
Formulate the default static route syntax for all unrouted traffic.
A default route uses destination prefix 0.0.0.0 and subnet mask 0.0.0.0 followed by the next-hop IP 203.0.113.1.
The prefix 0.0.0.0 0.0.0.0 matches any IPv4 address with a 0-bit prefix length.

Key Concept

Floating Static Routes and Default Static Route Syntax
Question 244Question →

A network engineer wants to configure a floating static route to serve as a backup to a primary route learned via OSPF, which has an Administrative Distance of 110. Which Administrative Distance value should be specified in the static route command so that it is only installed in the routing table when the OSPF route fails?

Show answer & explanation

Answer: 120

Answer

The correct administrative distance is 120 because a floating static route must have an administrative distance higher than the primary routing protocol (OSPF AD 110) to remain inactive until the primary route fails.
A floating static route acts as a backup route and is configured with an Administrative Distance higher than that of the primary routing protocol. Since OSPF has an AD of 110, setting the static route's AD to 120 keeps it out of the routing table until the primary OSPF route becomes unavailable.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the primary routing protocol.
The primary route is learned via OSPF, which has a default AD of 110.
Administrative Distance determines route trustworthiness, where a lower AD value is preferred.
2
Determine the required AD relationship for a floating (backup) static route.
The floating static route must be configured with an AD strictly greater than 110.
If the static route has a lower or equal AD, it will be preferred over or compete with the primary OSPF route.
3
Select the valid option that satisfies the backup requirement.
An AD of 120 is greater than 110 and represents standard backup static routing behavior.
120 is higher than 110, ensuring the route stays in floating status until the OSPF route fails.

Key Concept

Floating Static Route Administrative Distance Configuration
Question 245Question →

A Cisco router initializes an OSPFv2 process without a manually configured router ID. The router currently has the following operational interfaces:

- Loopback0: 10.10.10.1/3210.10.10.1/32
- Loopback10: 10.20.20.1/3210.20.20.1/32
- GigabitEthernet0/1: 192.168.100.1/24192.168.100.1/24

What IP address will OSPFv2 automatically select as the router ID?

Show answer & explanation

Answer: 10.20.20.1

Answer

10.20.20.1
When an explicit OSPF router ID is not configured using the 'router-id' command, OSPFv2 selects the highest IPv4 address among all active loopback interfaces. Because loopback interfaces take priority over physical interfaces, the router compares 10.10.10.1 and 10.20.20.1, choosing 10.20.20.1 as the router ID.

Step-by-Step Solution

1
Check if a manual OSPF router ID is configured.
No manual router ID is specified under the OSPF process.
Explicit configuration taking highest precedence is absent.
2
Evaluate active loopback interfaces.
Two active loopback interfaces exist: Loopback0 (10.10.10.110.10.10.1) and Loopback10 (10.20.20.110.20.20.1).
OSPF criteria prioritize active loopback interface IP addresses over active physical interface IP addresses.
3
Determine the highest IP address among active loopback interfaces.
10.20.20.110.20.20.1 is numerically higher than 10.10.10.110.10.10.1.
10.20.20.110.20.20.1 is chosen as the router ID.

Key Concept

OSPFv2 Router ID Election Order
Estimated Time:45s
Question 246Question →

A network administrator initializes an OSPFv2 routing process on a Cisco router without explicitly configuring an OSPF router ID under the router configuration mode. The router displays the following interface status and IP address assignments:

- Loopback0: IP address 10.10.10.1/32, status up, line protocol up
- Loopback1: IP address 192.168.1.1/32, status administratively down, line protocol down
- GigabitEthernet0/0: IP address 172.16.1.1/24, status up, line protocol up
- GigabitEthernet0/1: IP address 192.168.100.1/24, status up, line protocol up

Which IP address will OSPFv2 select as the router ID when the routing process starts?

Show answer & explanation

Answer: 10.10.10.1

Answer

The router will select 10.10.10.1 (Loopback0) as the OSPFv2 Router ID.
OSPFv2 determines its Router ID using a strict three-tier precedence: (1) manual configuration via the 'router-id' command, (2) the highest IPv4 address among active (up/up) loopback interfaces, and (3) the highest IPv4 address among active non-loopback physical interfaces. Because Loopback0 (10.10.10.1) is operational (up/up) and Loopback1 is administratively down, Loopback0 provides the highest active loopback IP address, overriding all physical interface IPs.

Step-by-Step Solution

1
Check for manual configuration
No explicit 'router-id' command was configured under the OSPF process.
Manual configuration always takes highest precedence.
2
Evaluate loopback interfaces
Loopback0 (10.10.10.1) is up/up. Loopback1 (192.168.1.1) is administratively down.
Only active (up/up) interfaces are considered for router ID election.
3
Apply tie-breaking rules for loopback vs physical interfaces
Loopback0 is the only active loopback interface, so its IP address 10.10.10.1 is selected as the Router ID.
Active loopback interfaces are preferred over active physical interfaces regardless of numerical IP address values.

Key Concept

OSPFv2 Router ID election precedence logic
Question 247Question →

A network administrator is configuring static routing on Cisco router Branch-R1 to reach remote subnet 2001:db8:3c4d:15::/642001:\text{db8}:3\text{c4d}:15::/64. The routing design requires a primary path using next-hop global unicast address 2001:db8:3c4d:12::22001:\text{db8}:3\text{c4d}:12::2, and a floating static backup path using link-local next-hop address fe80::2\text{fe80}::2 reachable via interface GigabitEthernet0/0/1. Which two commands must be configured on Branch-R1 to fulfill these requirements? (Select two.)

Select all that apply

Show answer & explanation

Answer: ipv6 route 2001:db8:3c4d:15::/64 2001:db8:3c4d:12::2; ipv6 route 2001:db8:3c4d:15::/64 GigabitEthernet0/0/1 fe80::2 130

Answer

The correct commands are 'ipv6 route 2001:db8:3c4d:15::/64 2001:db8:3c4d:12::2' for the primary route and 'ipv6 route 2001:db8:3c4d:15::/64 GigabitEthernet0/0/1 fe80::2 130' for the floating static backup route.
For the primary path, specifying the destination IPv6 prefix and the global unicast next-hop address provides sufficient forwarding information to the routing table. For the backup path, using a link-local IPv6 address requires a fully specified route format that explicitly includes the exit interface (GigabitEthernet0/0/1), combined with an administrative distance greater than 1 (such as 130) so that it functions as a floating backup route.

Step-by-Step Solution

1
Identify the proper syntax for a primary IPv6 static route using a global unicast next-hop address.
The command syntax is 'ipv6 route <destination-prefix/prefix-length> <global-unicast-next-hop>'. This maps to 'ipv6 route 2001:db8:3c4d:15::/64 2001:db8:3c4d:12::2'.
Global unicast addresses are uniquely identifiable across interfaces, so specifying an exit interface is optional.
2
Identify the mandatory components when configuring a fully specified IPv6 static route with a link-local next-hop address.
Because link-local addresses (fe80::/10) are reused across multiple physical links, Cisco IOS demands both the local exit interface and the link-local address.
Without the local exit interface, the router cannot determine which physical link to transmit packets on to reach fe80::2.
3
Determine the administrative distance requirement for a floating static route.
Assign an administrative distance higher than the primary route's default AD of 1 (e.g., 130).
A higher administrative distance ensures the route remains inactive in the IPv6 routing table until the primary route fails.

Key Concept

IPv6 Static Route Syntax and Link-Local Next-Hop Requirements
Question 248Question →

A network administrator needs to configure a backup floating static route for destination network 10.30.0.0/16 via next-hop IP 192.168.10.2. The primary route to this destination is learned via internal EIGRP, which has a default administrative distance of 90. What is the minimum administrative distance value that must be specified at the end of the command to ensure the route acts as a backup?

Fill in the blanks below

`Router(config)# ip route 10.30.0.0 255.255.0.0 192.168.10.2 `
Show answer & explanation

Answer

91
To configure a floating static route, the administrative distance (AD) appended to the end of the `ip route` command must be higher than the AD of the primary route. Because internal EIGRP has an administrative distance of 90, the minimum integer value required to make the static route act as a backup is 91.

Step-by-Step Solution

1
Identify the administrative distance (AD) of the primary routing protocol.
Internal EIGRP has a default Administrative Distance of 90.
Floating static routes rely on administrative distance values to determine route preference in the Cisco IOS routing table.
2
Determine the required administrative distance for the backup static route.
The floating static route must have an AD strictly greater than 90.
A route with a lower AD is always preferred. Standard static routes have a default AD of 1, which would override EIGRP if not changed.
3
Calculate the minimum integer value.
The lowest integer greater than 90 is 91.
Setting the AD to 91 ensures EIGRP is preferred under normal operations while allowing the static route to take over if EIGRP fails.

Key Concept

Floating Static Route Administrative Distance Configuration
Question 249Question →

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

Gateway of last resort is 192.168.10.1 to network 0.0.0.0

S* 0.0.0.0/0 [1/0] via 192.168.10.1
D 172.20.0.0/16 [90/307200] via 10.1.1.2, 02:14:10, GigabitEthernet0/0
O 172.20.100.0/24 [110/20] via 10.2.2.2, 01:45:12, GigabitEthernet0/1
R 172.20.100.32/27 [120/2] via 10.3.3.2, 00:12:05, GigabitEthernet0/2

When the router receives an IP packet with a destination address of 172.20.100.50172.20.100.50, to which next-hop IP address and interface will the router forward the packet?

Show answer & explanation

Answer: 10.3.3.2 via GigabitEthernet0/2, because 172.20.100.32/27 provides the longest matching subnet mask for the destination IP address.

Answer

The router forwards the packet to next-hop 10.3.3.2 via interface GigabitEthernet0/2 because 172.20.100.32/27 is the longest prefix match.
When a router makes a forwarding decision, it evaluates all matching routes in the routing table and selects the route with the most specific (longest) subnet mask. The destination IP 172.20.100.50 matches four routes in the routing table: 0.0.0.0/0, 172.20.0.0/16, 172.20.100.0/24, and 172.20.100.32/27 (range 172.20.100.32 to 172.20.100.63). Because /27 has the highest number of matching network bits, the router selects 172.20.100.32/27 and forwards the packet to next-hop 10.3.3.2 out GigabitEthernet0/2.

Step-by-Step Solution

1
Identify all candidate routes matching the destination IP address 172.20.100.50172.20.100.50.
0.0.0.0/00.0.0.0/0 (/0), 172.20.0.0/16172.20.0.0/16 (/16), 172.20.100.0/24172.20.100.0/24 (/24), and 172.20.100.32/27172.20.100.32/27 (/27) all cover 172.20.100.50172.20.100.50.
The range for 172.20.100.32/27172.20.100.32/27 is 172.20.100.32172.20.100.32 to 172.20.100.63172.20.100.63, which includes host .50.50.
2
Compare the prefix lengths of all matching routes.
Prefix lengths are /0, /16, /24, and /27.
The router forwarding engine always selects the matching route with the most specific (longest) prefix mask.
3
Select the route with the maximum prefix length.
Route 172.20.100.32/27172.20.100.32/27 has the longest prefix match (/27).
Administrative Distance (AD) and metric are ignored when routes have different prefix lengths; Longest Prefix Match (LPM) takes strict priority.

Key Concept

Longest Prefix Match (LPM) Rule
Question 250Question →

A Cisco router's IPv4 routing table contains the following entries:

text
Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 5 subnets, 3 masks
O 10.180.0.0/14 [110/65] via 192.168.12.2, 00:04:12, GigabitEthernet0/0/1
D 10.180.0.0/16 [90/307200] via 192.168.10.2, 01:15:04, GigabitEthernet0/0/0
S 10.180.32.0/19 [1/0] via 192.168.15.1, GigabitEthernet0/0/3
O IA 10.180.40.0/22 [110/120] via 192.168.14.2, 00:10:05, GigabitEthernet0/0/2

When a packet destined for IP address 10.180.42.100 arrives at the router, which route entry will the router select to forward the packet?

Show answer & explanation

Answer: The OSPF inter-area route to 10.180.40.0/22 because it provides the longest prefix match for the destination address.

Answer

The router will select the OSPF inter-area route to 10.180.40.0/22 because 10.180.42.100 matches that route with a /22 prefix length, which is the longest matching prefix.
The destination address 10.180.42.100 matches multiple entries in the routing table. Cisco routers evaluate forwarding decisions using the Longest Prefix Match rule, which prioritizes the route with the longest subnet mask length regardless of administrative distance or metric. The route 10.180.40.0/22 covers range 10.180.40.0 to 10.180.43.255, giving a 22-bit matching prefix, which is longer than /19, /16, or /14.

Step-by-Step Solution

1
Determine which routing table entries match the destination IP 10.180.42.100.
Destination 10.180.42.100 falls into 10.180.0.0/14 (10.180.0.0 - 10.183.255.255), 10.180.0.0/16 (10.180.0.0 - 10.180.255.255), 10.180.32.0/19 (10.180.32.0 - 10.180.63.255), and 10.180.40.0/22 (10.180.40.0 - 10.180.43.255). All four routes are valid matches.
Before making forwarding decisions, the router identifies all routes matching the destination IP address.
2
Compare the prefix lengths of all matching routes to apply the Longest Prefix Match rule.
The prefix lengths are /14, /16, /19, and /22. The longest (most specific) prefix length is /22.
The fundamental routing lookup logic in Cisco IOS prefers the route with the most specific mask (longest subnet mask / highest number of prefix bits).
3
Select the route corresponding to the longest prefix match.
The entry 'O IA 10.180.40.0/22 [110/120] via 192.168.14.2' is selected.
Administrative Distance and metric are completely ignored when comparing routes of different prefix lengths.

Key Concept

Longest Prefix Match Rule in Cisco Routing Tables
Question 251Question →

A network administrator needs to configure a secondary floating default route on router Edge-2 toward an upstream ISP. The primary default route is learned dynamically via OSPFv3 with a administrative distance of 110. The backup route must forward all unmatched traffic out local interface GigabitEthernet0/1 to the ISP router's link-local next-hop address fe80::250:56ff:fea1:2b3c using an administrative distance of 130. Complete the global configuration command required on router Edge-2 to create this fully specified floating default static route.

Fill in the blanks below

ipv6 route GigabitEthernet0/1 fe80::250:56ff:fea1:2b3c
Show answer & explanation

Answer

The first blank requires '::/0' to designate the default IPv6 prefix, and the second blank requires '130' to set the administrative distance for the floating static route.
An IPv6 default static route uses the prefix '::/0'. When using a link-local address (fe80::/10) as a next-hop, Cisco IOS requires specifying the local exit interface alongside the link-local address because link-local addresses are scope-bound to a specific link. To make the static route a floating backup path behind OSPFv3 (AD 110), an administrative distance parameter of 130 is added to the end of the global configuration command syntax: 'ipv6 route <prefix/length> <exit-interface> <next-hop-address> [administrative-distance]'.

Step-by-Step Solution

1
Identify the destination prefix notation for an IPv6 default static route.
The default route covering all IPv6 destinations is represented by '::/0'.
In IPv6 prefix notation, ::/0 represents all possible IPv6 destinations, equivalent to 0.0.0.0 0.0.0.0 in IPv4.
2
Verify link-local next-hop syntax requirements.
The exit interface GigabitEthernet0/1 precedes the link-local address fe80::250:56ff:fea1:2b3c.
Link-local addresses (fe80::/10) are only unique on the local link segment. Cisco IOS mandates specifying the egress interface when using a link-local address as a next-hop.
3
Determine the administrative distance needed for floating route behavior.
Append '130' to the end of the command.
To float behind an active OSPFv3 route (AD 110), the static route's administrative distance must be higher than 110. The scenario specifies an AD of 130.

Key Concept

IPv6 Fully Specified Floating Static Default Route Syntax
Estimated Time:1m 30s
Question 252Question →

An enterprise router receives an internal EIGRP route for the summary prefix 172.16.0.0/16 (Administrative Distance 90) and learns a specific path for subnet 172.16.10.0/24 via OSPF (Administrative Distance 110). A network engineer attempts to configure a backup floating static route for destination 172.16.10.0/24 using the command `ip route 172.16.10.0 255.255.255.0 192.168.1.2 100`. Under normal operating conditions while all links remain fully operational, which routing behavior will occur for traffic sent to host 172.16.10.50?

Show answer & explanation

Answer: The router routes traffic using the static route via next-hop 192.168.1.2 because its Administrative Distance of 100 is lower than the OSPF route's Administrative Distance of 110.

Answer

Traffic to host 172.16.10.50 will be forwarded using the static route via next-hop 192.168.1.2 because its configured Administrative Distance of 100 is lower than OSPF's Administrative Distance of 110.
For identical prefix lengths (/24), the router compares Administrative Distance (AD) values to determine which route enters the routing table. OSPF has a default AD of 110. Since the configured static route has an AD of 100, which is lower than 110, Cisco IOS selects the static route as the active primary path. Consequently, traffic destined for 172.16.10.50 is immediately forwarded via next-hop 192.168.1.2.

Step-by-Step Solution

1
Evaluate the prefix lengths available for the destination address 172.16.10.50.
Two prefix lengths match: /16 (EIGRP summary) and /24 (OSPF and static). The longest prefix match rule prioritizes the /24 subnet over the /16 summary.
Cisco routers always select the most specific route (longest subnet mask) first during packet forwarding lookup.
2
Compare the Administrative Distance (AD) values of competing routes for the 172.16.10.0/24 destination.
The OSPF route has a default AD of 110, while the configured static route has an AD of 100.
When multiple sources offer a route to the exact same prefix, Cisco IOS selects the route with the lowest Administrative Distance to install into the Routing Information Base (RIB).
3
Determine the operational status of the floating static route.
Because AD 100 < AD 110, the static route is active in the routing table immediately, preempting the primary OSPF route rather than acting as a floating backup.
A floating static route must have an AD set strictly higher than the primary route (e.g., AD 115 or higher) to remain dormant until the primary route fails.

Key Concept

Floating Static Route Administrative Distance Selection
Question 253Question →

A Cisco router receives an IPv4 packet destined for host 192.168.10.45192.168.10.45, which matches a static route configured strictly with a next-hop IP address (10.0.0.210.0.0.2) rather than an exit interface. Arrange the operational steps in the exact sequence the router executes to process, resolve, and forward this packet.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence of router operation steps is: Extract the destination IPv4 address (192.168.10.45192.168.10.45), search the IPv4 RIB using Longest Prefix Match, identify the next-hop IPv4 address (10.0.0.210.0.0.2), perform a recursive lookup to resolve the exit interface, and consult the ARP table to encapsulate and transmit the packet.
When a Cisco router receives an IPv4 packet, it extracts the destination IP address from the packet header (192.168.10.45192.168.10.45). Next, it evaluates its routing table (RIB) using Longest Prefix Match (LPM) to find the most specific route entry. Upon finding the static route, it identifies that the destination is reached via next-hop IP 10.0.0.210.0.0.2. Because the static route was configured without specifying an egress interface, the router must perform a recursive lookup in the routing table to determine which directly connected interface reaches 10.0.0.210.0.0.2. Once the exit interface is resolved, the router queries its ARP cache to map 10.0.0.210.0.0.2 to a Layer 2 MAC address, re-encapsulates the packet into a new Layer 2 frame, and transmits it out the interface.

Step-by-Step Solution

1
Packet Ingress and Header Parsing
Destination IPv4 address 192.168.10.45192.168.10.45 is extracted.
The router needs the destination IPv4 address to perform a routing lookup.
2
RIB Query via Longest Prefix Match
The static route entry best matching 192.168.10.45192.168.10.45 is selected.
Routing decisions in Cisco IOS prioritize routes with the longest prefix length.
3
Next-Hop Extraction
Next-hop IPv4 address 10.0.0.210.0.0.2 is retrieved from the static route entry.
The router identifies that the traffic must be sent to 10.0.0.210.0.0.2 before reaching the final destination.
4
Recursive Route Resolution
Next-hop 10.0.0.210.0.0.2 is resolved to a directly connected exit interface.
Static routes configured solely with next-hop IP addresses require a second routing lookup to identify the physical outbound interface.
5
Layer 2 Resolution & Encapsulation
ARP table maps 10.0.0.210.0.0.2 to its destination MAC address, the packet is encapsulated into a Layer 2 frame, and forwarded.
The router must encapsulate the IP packet into a valid Ethernet frame using the exit interface and next-hop MAC address.

Key Concept

Recursive Static Route Lookup and Packet Forwarding Sequence
Question 254Question →

Router R1 connects an enterprise edge network to two service providers, ISP-A and ISP-B. The primary default path is dynamically learned from ISP-A via eBGP, which assigns an Administrative Distance (AD) of 2020. A network engineer needs to configure a floating static default route toward ISP-B through next-hop IP 198.51.100.1198.51.100.1 as a redundant backup path that will remain inactive in the routing table until the primary eBGP path fails. Which Cisco IOS command correctly achieves this objective?

Show answer & explanation

Answer: ip route 0.0.0.0 0.0.0.0 198.51.100.1 25

Answer

The command 'ip route 0.0.0.0 0.0.0.0 198.51.100.1 25' correctly specifies a default route with an Administrative Distance higher than the primary eBGP AD of 20, ensuring it remains inactive until link failure.
A floating static route acts as a backup path and must remain inactive in the Routing Information Base (RIB) until the primary route fails. Because the primary route is dynamically learned via eBGP with an Administrative Distance (AD) of 20, the static backup route must be explicitly configured with an AD value strictly greater than 20. The option specifying 'ip route 0.0.0.0 0.0.0.0 198.51.100.1 25' correctly applies an AD of 25 to the default network 0.0.0.0/0, ensuring it functions strictly as a backup.

Step-by-Step Solution

1
Identify the primary route source and its administrative distance.
Primary default route is learned via eBGP, which has an Administrative Distance of 2020.
Floating static routes must be assigned an Administrative Distance higher than the primary protocol's AD.
2
Determine the correct IPv4 default static route prefix and mask syntax.
Default route destination is represented as '0.0.0.0 0.0.0.0'.
A quad-zero prefix and mask match any destination network not explicitly matched by more specific routes.
3
Select the appropriate Administrative Distance for the backup floating route.
Specify an Administrative Distance greater than 2020 (e.g., 2525).
Setting the AD to 2525 keeps the static route hidden from the Routing Information Base (RIB) while the primary eBGP route (AD 2020) is active.

Key Concept

Floating Static Route Administrative Distance Selection
Question 255Question →

A network administrator initializes OSPFv2 on a Cisco router named R1. The router has the following interface states and IP addresses configured prior to starting the OSPF process:

- Interface GigabitEthernet0/0: IP address 172.16.10.1/24 (Up/Up)
- Interface GigabitEthernet0/1: IP address 192.168.1.254/24 (Up/Up)
- Interface Loopback0: IP address 10.1.1.1/32 (Up/Up)
- Interface Loopback1: IP address 10.2.2.1/32 (Administratively Down)

The administrator enables OSPF process 1 without explicitly setting a router ID. After OSPF initializes, the administrator enters `router-id 1.1.1.1` under the `router ospf 1` process configuration prompt and changes Loopback1 to the Up/Up state. No further commands are entered.

Which two statements correctly describe the resulting OSPF Router ID behavior on router R1? (Select two.)

Select all that apply

Show answer & explanation

Answer: The active OSPF Router ID remains 10.1.1.1 until the OSPF process is reset or restarted.; Executing the clear ip ospf process command is required to apply 1.1.1.1 as the active OSPF Router ID.

Answer

The active OSPF Router ID remains 10.1.1.1 until the process is reset, and executing the clear ip ospf process command is required to apply 1.1.1.1 as the active OSPF Router ID.
When OSPF process 1 initializes without an explicit router-id configured, it evaluates active interfaces. Loopback1 is administratively down, so Loopback0 (10.1.1.1) is chosen as the active OSPF Router ID. OSPF Router ID election is non-preemptive, meaning subsequent configuration changes—such as configuring a manual router-id or enabling a higher IP loopback interface—will not change the active Router ID immediately. The statement indicating that the active Router ID remains 10.1.1.1 until reset and the statement indicating that executing 'clear ip ospf process' is required to activate 1.1.1.1 are both correct.

Step-by-Step Solution

1
Determine initial Router ID election upon starting OSPF process 1.
Loopback0 (10.1.1.1/32) is selected because it is the highest IP among active (up/up) loopback interfaces. Loopback1 is administratively down and ignored.
OSPF Router ID tie-breaker order is: 1) Manual router-id command, 2) Highest IP among active loopbacks, 3) Highest IP among active physical interfaces.
2
Analyze the impact of issuing 'router-id 1.1.1.1' on a running OSPF process.
The command is saved to running-config, but the active Router ID remains 10.1.1.1.
OSPF Router ID selection in Cisco IOS is non-preemptive. Changes do not take effect dynamically while the process is actively running.
3
Analyze the impact of bringing Loopback1 (10.2.2.1) to Up/Up state.
The active Router ID is unaffected.
Interface state changes after initialization do not preempt an established active OSPF Router ID.
4
Identify the required action to activate the new router-id command.
Executing 'clear ip ospf process' in EXEC mode resets the OSPF process and applies 1.1.1.1.
Clearing the OSPF process forces re-evaluation, allowing the manually configured router-id command (highest priority) to take effect.

Key Concept

OSPFv2 Router ID Selection Precedence and Non-Preemptive Behavior
Question 256Question →

A network administrator needs to configure reliable static default routing on a Cisco IOS router by tying a primary static route to an IP SLA probes object, ensuring that the route is automatically withdrawn if the target becomes unreachable. Arrange the operational and CLI configuration steps in the correct chronological order from establishing the probe metric to static route activation.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct chronological sequence is: (1) Define and schedule the IP SLA probe instance, (2) Create the object tracking process monitoring IP SLA reachability, (3) Configure the static route bound to the track object ID, and (4) Verify probe success leading to tracking state UP and RIB installation.
The correct sequence follows the mandatory dependency hierarchy in Cisco IOS: first, the IP SLA engine must be defined and scheduled to generate active probes; second, a tracking object must be constructed to translate probe results into a boolean UP/DOWN status; third, the IPv4 static route must be configured with the `track` keyword; and finally, once the tracking object confirms reachability (UP state), the router installs the static route into the routing table (RIB).

Step-by-Step Solution

1
Configure and schedule the IP SLA ICMP Echo probe operation.
The router begins sending ICMP echo packets to target IP 203.0.113.1203.0.113.1.
Tracking objects require an active underlying probe instance to supply reachability status.
2
Bind the IP SLA operation to a tracking object ID using `track <id> ip sla <ops-number> reachability`.
Tracking object status changes to UP when SLA probe responses are received successfully.
Static routes cannot monitor IP SLA probes directly; they must reference a tracking object.
3
Apply the `ip route` global configuration command specifying the next-hop IP and the `track <id>` parameter.
The static route is created in conditional status linked to tracking object state.
Adding the `track` keyword instructs Cisco IOS to conditionally evaluate RIB placement.
4
Cisco IOS processes the UP status of the tracking object and writes the route to the routing table.
The default static route becomes active in the RIB with Administrative Distance 11.
RIB installation occurs only when the tracked object returns a valid UP reachability state.

Key Concept

IPv4 Static Route Object Tracking with IP SLA
Question 257Question →

A Cisco router initializes an OSPFv2 routing process without an explicitly configured router ID. The router currently has the following operational interfaces and statuses:

- Loopback 0: 10.254.254.1/24 (Administratively Down / Down)
- Loopback 1: 172.16.40.1/24 (Up / Up)
- Loopback 2: 172.16.100.1/24 (Up / Up)
- GigabitEthernet0/0: 192.168.10.1/24 (Up / Up)

What IP address will be selected as the OSPFv2 router ID for this router?

Show answer & explanation

Answer: 172.16.100.1

Answer

172.16.100.1
When no manual router ID is configured, OSPFv2 selects the highest IPv4 address among active (up/up) loopback interfaces. Loopback 0 is administratively down, so it is ignored. Between the operational loopbacks (172.16.40.1 and 172.16.100.1), 172.16.100.1 is the highest IP address.

Step-by-Step Solution

1
Check for an explicitly configured router ID under the OSPF process.
No manual 'router-id' command is configured.
Explicit configuration takes highest priority in OSPF router ID election.
2
Evaluate active (up/up) loopback interfaces.
Loopback 1 (172.16.40.1) and Loopback 2 (172.16.100.1) are active. Loopback 0 (10.254.254.1) is administratively down and ignored.
Inactive interfaces cannot be used for router ID election, and active loopbacks take priority over physical interfaces.
3
Select the highest IP address among the active loopback interfaces.
172.16.100.1 is selected because 172.16.100.1 is greater than 172.16.40.1.
OSPF selects the numerically highest IPv4 address among operational loopback interfaces.

Key Concept

OSPFv2 Router ID Election Order
Question 258Question →

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

text
Gateway of last resort is 172.16.1.1 to network 0.0.0.0

D 10.50.0.0/16 [90/2170112] via 192.168.12.2, GigabitEthernet0/0
O 10.50.10.0/24 [110/20] via 192.168.23.2, GigabitEthernet0/1
S 10.50.10.16/28 [1/0] via 192.168.34.2
O 10.50.10.16/30 [110/10] via 192.168.45.2, GigabitEthernet0/3
S* 0.0.0.0/0 [1/0] via 172.16.1.1

The router receives a packet destined for IPv4 address 10.50.10.1810.50.10.18. Which two statements correctly describe how the router processes this packet? (Select two.)

Select all that apply

Show answer & explanation

Answer: The router forwards the packet to next-hop 192.168.45.2 out interface GigabitEthernet0/3 because 10.50.10.16/30 has the longest matching subnet mask.; Administrative distance is not compared because the matching routes have different prefix lengths.

Answer

The router forwards the packet to next-hop 192.168.45.2 out GigabitEthernet0/3 because 10.50.10.16/30 provides the longest prefix match, and administrative distance is not evaluated across different prefix lengths.
When a router receives an IP packet, it compares the destination IP address against all entries in its routing table. The rule of Longest Prefix Match (LPM) states that the entry with the highest number of matching network bits (longest subnet mask) is selected. Here, 10.50.10.16/30 matches 30 bits of the address 10.50.10.18, making it the most specific match. Administrative Distance is only compared when identical destination prefixes are learned via different protocols; because prefix lengths differ here, AD is not evaluated.

Step-by-Step Solution

1
Identify all matching routes for the destination IP address 10.50.10.18.
The address matches four specific prefixes: 10.50.0.0/16, 10.50.10.0/24, 10.50.10.16/28, and 10.50.10.16/30, as well as the default route 0.0.0.0/0.
Before making a forwarding decision, a router evaluates all active entries in the routing table to find candidate routes.
2
Determine the Longest Prefix Match (LPM) among the candidate routes.
The prefix 10.50.10.16/30 has a 30-bit mask length, which is longer than /28, /24, /16, or /0.
A Cisco router always selects the route with the most specific (longest) subnet mask first, regardless of administrative distance or metric.
3
Verify if Administrative Distance (AD) comparisons are necessary.
Administrative distance comparison is bypassed because the prefix lengths of the matching routes differ.
Administrative distance is only evaluated when a router learns about the exact same destination prefix and mask length from multiple routing sources.

Key Concept

Router Forwarding Decision Logic and Longest Prefix Match
Question 259Question →

An enterprise edge router receives a primary internal route for destination prefix 10.50.0.0/1610.50.0.0/16 via Internal EIGRP (Administrative Distance 90) and a primary default route for 0.0.0.0/00.0.0.0/0 via external BGP (eBGP, Administrative Distance 20). A network administrator needs to configure floating static routes to serve as automatic failover backups for both destinations. Which TWO configuration statements correctly specify the Administrative Distance requirements for these static routes to operate strictly as floating backups? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: The floating static route backing up destination 10.50.0.0/1610.50.0.0/16 must be configured with an Administrative Distance value greater than 90.; The floating static route backing up destination 0.0.0.0/00.0.0.0/0 must be configured with an Administrative Distance value greater than 20.

Answer

The floating static route for 10.50.0.0/16 must have an Administrative Distance greater than 90, and the floating static route for 0.0.0.0/0 must have an Administrative Distance greater than 20.
Cisco IOS routing table selection prioritizes routes with lower Administrative Distance (AD). For a static route to function as a 'floating' backup, its AD must be manually configured to a value higher than that of the active primary routing protocol (Internal EIGRP AD 90, eBGP AD 20). This ensures the static route remains untracked in the routing table until the primary route's AD source is lost.

Step-by-Step Solution

1
Identify the default Administrative Distance (AD) of the primary routing protocols.
Internal EIGRP has a default AD of 90; external BGP (eBGP) has a default AD of 20.
Cisco IOS selects routes with the lowest Administrative Distance when multiple sources provide routes to the same destination.
2
Determine the required AD for floating static backup routes.
Backup route AD for EIGRP must be > 90 (e.g., 95). Backup route AD for eBGP must be > 20 (e.g., 25).
A floating static route must remain out of the routing table while the primary protocol is active, which requires the static route to have a higher numerical AD than the primary route.

Key Concept

Floating Static Route Administrative Distance Requirements
Question 260Question →

An enterprise Cisco router displays the following IPv4 routing table output:

text
Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 4 subnets, 4 masks
O 10.45.0.0/16 [110/65] via 192.168.1.1, 01:15:02, GigabitEthernet0/0
D 10.45.12.0/22 [90/2172416] via 192.168.2.1, 00:42:10, GigabitEthernet0/1
S 10.45.12.0/24 [1/0] via 192.168.3.1
C 10.45.12.128/25 is directly connected, GigabitEthernet0/2

Which two statements correctly describe how the router processes traffic destined to 10.45.12.15010.45.12.150 and interpret its routing table components? (Select two.)

Select all that apply

Show answer & explanation

Answer: The router forwards the packet out interface GigabitEthernet0/2 because 10.45.12.128/25 provides the longest prefix match for destination 10.45.12.150.; The bracketed numbers [110/65] in the OSPF route entry represent an Administrative Distance of 110 and a route Metric of 65.

Answer

The router egresses traffic out GigabitEthernet0/2 based on the longest prefix match rule (10.45.12.128/25), and the notation [110/65] defines an Administrative Distance of 110 and a Metric of 65.
Traffic destined to 10.45.12.150 matches multiple entries in the routing table, but 10.45.12.128/25 has the longest prefix length (25 bits), making GigabitEthernet0/2 the elected forwarding interface. Additionally, standard Cisco routing table syntax formats protocol entries as [Administrative Distance / Metric], meaning [110/65] indicates an AD of 110 and an OSPF metric of 65.

Step-by-Step Solution

1
Analyze candidate destination matching prefixes for destination IP 10.45.12.150.
The destination address 10.45.12.150 matches 10.45.0.0/16, 10.45.12.0/22, 10.45.12.0/24, and 10.45.12.128/25 (range 10.45.12.128 to 10.45.12.255).
All four subnet ranges encompass IP address 10.45.12.150.
2
Apply the Longest Prefix Match (LPM) forwarding rule.
Prefix length /25 is longer (more specific) than /24, /22, and /16. Thus, route C (10.45.12.128/25) is chosen, forwarding traffic directly out GigabitEthernet0/2.
Routers always prioritize prefix length over Administrative Distance and metric when determining the forwarding path.
3
Decode the standard Cisco routing table notation components.
For entry 'O 10.45.0.0/16 [110/65]', the first value inside brackets represents Administrative Distance (110) and the second value represents Metric/Cost (65).
This is the mandatory syntax used by Cisco IOS/IOS-XE to display route trustworthiness and path cost.

Key Concept

Routing Table Components and Longest Prefix Match Decision Logic
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