Cisco CCNA (200-301) — All Questions

A router has two routes to 10.1.1.0/24: a static route with administrative distance 1 and an OSPF route with AD 110. Which route is installed in the routing table?

• a.The OSPF route, because OSPF is dynamic
• b.The static route, because it has the lower AD✓
• c.Neither, they conflict and both are rejected
• d.Both routes, load-balanced equally

Administrative distance measures the trustworthiness of a routing source, and the route with the lower AD is preferred. A static route (AD 1) is preferred over an OSPF route (AD 110) to the same destination. The less-trusted OSPF route is kept in the OSPF database but not installed while the static route is valid.

Which command correctly configures a default static route that forwards all unknown-destination traffic to next-hop 203.0.113.1?

• a.ip route 0.0.0.0 0.0.0.0 203.0.113.1✓
• b.ip route 203.0.113.1 0.0.0.0 0.0.0.0
• c.ip default-gateway 203.0.113.1
• d.ip route 203.0.113.1 255.255.255.255 0.0.0.0

A default route uses 0.0.0.0 0.0.0.0 to match any destination, followed by the next-hop address, so 'ip route 0.0.0.0 0.0.0.0 203.0.113.1' is correct. It is the gateway of last resort used when no more specific route matches. The 'ip default-gateway' command only applies to a device that is not routing (ip routing disabled).

In OSPFv2, two routers on the same Ethernet segment fail to form an adjacency. Which mismatch is a common cause?

• a.Different hostnames
• b.Different serial numbers
• c.Different interface descriptions
• d.Different hello/dead timers or mismatched area IDs✓

OSPF neighbors must agree on parameters including hello and dead intervals, area ID, authentication, subnet mask, and MTU to reach the FULL adjacency state. A mismatch in any of these prevents the neighbor relationship from forming. Hostnames and descriptions are cosmetic and do not affect adjacency.

What metric does OSPF use by default to calculate the cost of a link?

• a.Hop count
• b.Delay
• c.Load
• d.Bandwidth (reference bandwidth / interface bandwidth)✓

OSPF calculates cost based on bandwidth, using the formula reference bandwidth (default 100 Mbps) divided by the interface bandwidth. Higher-bandwidth links receive lower costs and are preferred. Because modern links exceed the default reference, engineers often raise the reference bandwidth so faster interfaces are distinguished.

A packet arrives at a router destined for 192.168.5.130. The routing table contains 192.168.5.0/24, 192.168.5.128/25, and 0.0.0.0/0. Which route is used?

• a.192.168.5.0/24
• b.All three simultaneously
• c.0.0.0.0/0
• d.192.168.5.128/25✓

Routers forward using the longest prefix match, meaning the most specific route (the one with the longest matching subnet mask) wins. 192.168.5.130 falls within 192.168.5.128/25 (128-255 range), which is more specific than the /24 or the default route. Longer masks always take precedence regardless of administrative distance across differing prefixes.

Which statement about IPv6 Stateless Address Autoconfiguration (SLAAC) is correct?

• a.Hosts build their own address from the Router Advertisement prefix✓
• b.It uses ARP to learn the gateway
• c.It requires a DHCPv6 server to assign every address
• d.It only works with link-local addresses

With SLAAC, a host listens for Router Advertisement messages, takes the announced /64 prefix, and combines it with a self-generated interface identifier to form a global address without a DHCP server. Neighbor Discovery Protocol (not ARP) provides address resolution and router discovery in IPv6. DHCPv6 is optional and can supplement SLAAC for information like DNS.

What administrative distance does a directly connected route have in a Cisco routing table?

• a.0✓
• b.120
• c.110
• d.1

Directly connected routes have an administrative distance of 0, making them the most trusted source since the router has a live interface on that network. Static routes are AD 1, OSPF is 110, and RIP is 120. Lower AD wins when the same prefix is learned through multiple sources.

What best describes a floating static route?

• a.A static route that is load-balanced with OSPF
• b.A route that changes its next hop automatically
• c.A default route to 0.0.0.0/0
• d.A backup static route configured with a higher administrative distance than the primary route✓

A floating static route is given an AD higher than the primary (often dynamic) route, so it stays out of the routing table until the preferred route fails. When the primary disappears, the floating route floats up and installs, providing automatic backup. It is common for backup WAN links behind a dynamic protocol.

When configuring a static route over a multiaccess Ethernet segment, why is specifying a next-hop IP address preferred over using only the exit interface?

• a.Because it disables ARP
• b.So the router can resolve the next hop's Layer 2 (MAC) address via ARP✓
• c.Because it uses less memory
• d.Because exit interfaces are not supported on Ethernet

On multiaccess links like Ethernet, specifying only an exit interface makes the router assume every destination is directly connected, forcing ARP for each remote address (proxy ARP reliance). Providing the next-hop IP lets the router ARP for that single gateway and forward correctly. On point-to-point links, an exit interface alone is unambiguous.

If no router ID is manually configured, how does OSPF choose its router ID?

• a.The highest loopback IP, or if none, the highest active interface IP✓
• b.The device's base MAC address
• c.The lowest interface IP address
• d.The highest physical interface IP only, ignoring loopbacks

OSPF selects the router ID in this order: a manually configured router-id, then the highest IP among active loopback interfaces, then the highest IP among active physical interfaces. Loopbacks are preferred because they never go down. Best practice is to set the router-id explicitly for stability and predictability.

In a multi-area OSPF design, which area must all other areas connect to (directly or via a virtual link)?

• a.Any area of the lowest number
• b.A stub area
• c.Area 0 (the backbone)✓
• d.Area 1

OSPF requires a backbone, Area 0, to which all other areas must attach so inter-area routing information passes through it. This hub-and-spoke area design prevents routing loops between areas. If an area cannot physically touch Area 0, a virtual link can bridge it through a transit area.

On a broadcast multiaccess OSPF segment, what does OSPF elect to reduce the number of adjacencies?

• a.A Designated Router (DR) and Backup Designated Router (BDR)✓
• b.A VTP server
• c.A root bridge
• d.A gateway of last resort

On broadcast and non-broadcast multiaccess networks, OSPF elects a DR and BDR so routers form full adjacencies only with them instead of every neighbor, cutting down LSA flooding overhead. Election favors the highest OSPF interface priority, then the highest router ID. Point-to-point links need no DR/BDR.

Using OSPF's default reference bandwidth of 100 Mbps, what is the cost of a 10 Mbps Ethernet link?

• a.1
• b.10✓
• c.0
• d.100

OSPF cost equals the reference bandwidth divided by the interface bandwidth: 100 Mbps / 10 Mbps = 10. A 100 Mbps link would compute to a cost of 1. Because all links at or above 100 Mbps default to cost 1, engineers often raise the reference bandwidth so gigabit and faster links are differentiated.

In the output of 'show ip route', which code identifies a route learned via OSPF?

• a.C
• b.D
• c.S
• d.O✓

In the routing table legend, 'O' marks OSPF-learned routes, 'S' marks static routes, 'C' marks directly connected networks, and 'D' marks EIGRP routes. Recognizing these codes lets you quickly determine how each destination was learned when verifying connectivity or troubleshooting path selection.

What is the role of the default gateway configured on an end host?

• a.It is the router address the host uses to reach destinations on other subnets✓
• b.It stores the host's ARP cache
• c.It assigns the host its IP address
• d.It resolves DNS names to IP addresses

The default gateway is the IP address of a local router interface that a host sends packets to whenever the destination is on a different subnet. The host compares the destination against its own subnet; if it is remote, the frame is addressed to the gateway's MAC. Without a valid gateway, off-subnet communication fails.

A packet is destined for 10.0.0.66. The routing table has 10.0.0.0/8, 10.0.0.0/24, and 10.0.0.64/29. Which route forwards the packet?

• a.10.0.0.64/29✓
• b.0.0.0.0/0
• c.10.0.0.0/8
• d.10.0.0.0/24

The router uses longest prefix match, choosing the most specific route that contains the destination. 10.0.0.64/29 covers addresses .64 through .71, which includes .66, and its /29 is longer (more specific) than the /24 or /8. The most specific match always wins regardless of how each route was learned.

Which OSPF neighbor state indicates that two routers have fully synchronized their link-state databases?

• a.2-WAY
• b.FULL✓
• c.EXSTART
• d.INIT

The FULL state means the neighbors have exchanged and synchronized their complete link-state databases and can route through each other. INIT and 2-WAY are early stages of neighbor discovery, and EXSTART/EXCHANGE occur while databases are being compared. On multiaccess links, non-DR routers stay 2-WAY with each other, which is normal.

On which OSPF network type is no DR/BDR election performed?

• a.Broadcast
• b.Multiaccess Ethernet
• c.Point-to-point✓
• d.Non-broadcast (NBMA)

Point-to-point network types (such as serial links or point-to-point subinterfaces) have only two routers, so a DR/BDR would add no value and none is elected. Broadcast and NBMA multiaccess types do elect a DR/BDR to control flooding. Matching network types and timers on both ends is required for adjacency.

Before forwarding an IPv4 packet onto an Ethernet segment, what does a router use ARP to determine?

• a.The administrative distance of the route
• b.The DNS name of the destination
• c.The subnet mask of the destination
• d.The MAC address of the next hop✓

To build the Layer 2 frame, the router must know the MAC address that corresponds to the next-hop IP address, and ARP provides that IP-to-MAC resolution. The result is cached in the ARP table to avoid repeated lookups. In IPv6, Neighbor Discovery replaces ARP for this function.

Which link-state routing protocol is used to route IPv6 networks?

• a.RIPv2
• b.EIGRP for IPv4
• c.OSPFv3✓
• d.OSPFv2

OSPFv3 is the link-state protocol that supports IPv6, mirroring OSPFv2 concepts like areas, LSAs, and SPF while running over IPv6 and using link-local addresses for adjacencies. OSPFv2 and RIPv2 are IPv4-only, and EIGRP has a separate IPv6 address family. IPv6 also supports static routing for simple designs.

Under what condition will OSPF install multiple routes to the same destination and load-balance across them?

• a.When the routes have equal cost (metric)✓
• b.When the routes have different administrative distances
• c.OSPF never load-balances
• d.When one of the routes is static

OSPF performs equal-cost multipath (ECMP) load balancing, installing up to a configurable maximum of routes only when they share the same lowest cost to the destination. Traffic is then distributed across those equal paths. If costs differ, only the lowest-cost path is installed; OSPF does not do unequal-cost balancing like EIGRP.

A packet's destination matches only the 0.0.0.0/0 entry in the routing table. How is it handled?

• a.It is forwarded using the gateway of last resort✓
• b.It is buffered until a more specific route appears
• c.It is broadcast on all interfaces
• d.It is dropped as unroutable

The 0.0.0.0/0 route is the default route, also called the gateway of last resort, used when no more specific prefix matches the destination. The router forwards the packet toward the configured default next hop, typically an upstream/Internet router. Without a default route, an unmatched packet would be dropped.

What is the fundamental difference between a routing protocol and a routed protocol?

• a.There is no practical difference; the two terms are interchangeable synonyms used by different vendors
• b.A routed protocol elects the root bridge, while a routing protocol builds the spanning tree across the switched network
• c.A routing protocol carries user data end to end, while a routed protocol only advertises administrative distances between neighbors Cisco groups both under the same heading in every version of the exam blueprint.
• d.A routing protocol (such as OSPF) exchanges reachability information to build the routing table, while a routed protocol (such as IP) carries user data✓

A routing protocol like OSPF, EIGRP, or RIP dynamically exchanges network reachability so routers can build and maintain their routing tables. A routed (or routable) protocol such as IPv4 or IPv6 is the protocol that actually carries user traffic across those learned paths. One learns the paths; the other travels them.

A router must forward a packet to 10.20.30.40. It has matching entries for 10.0.0.0/8, 10.20.0.0/16, and 10.20.30.0/24. Which entry is selected?

• a.All three are used together in a round-robin load-sharing arrangement
• b.10.20.30.0/24✓
• c.10.20.0.0/16, because a /16 balances specificity and summarization
• d.10.0.0.0/8, because the classful boundary always takes priority over subnets

Forwarding always uses the longest prefix match, meaning the entry with the greatest number of matching mask bits. Here 10.20.30.0/24 matches 24 bits and is more specific than the /16 or /8, so it is chosen. Prefix length is compared before administrative distance or metric when the prefixes differ.

Which three sources can populate a Cisco router's IPv4 routing table?

• a.Spanning-tree BPDUs, CDP neighbor advertisements, and ARP table entries combined
• b.Directly connected networks, static routes, and dynamic routing protocols✓
• c.Only statically configured routes entered by an administrator at the console
• d.Only dynamic routing protocols such as OSPF, EIGRP, and RIP running on the device

A routing table is built from directly connected interfaces (code C/L), manually configured static routes (code S), and routes learned from dynamic protocols like OSPF or EIGRP. Directly connected routes appear automatically once an interface has an IP address and is up/up. ARP and CDP operate at other layers and do not create routing-table entries.

In 'show ip route', a route is displayed as 'O 192.168.9.0/24 [110/65] via 10.1.1.2'. What does the number 65 represent?

• a.The number of hops separating this router from the 192.168.9.0 network
• b.The interface index of the outgoing interface used to forward the traffic
• c.The administrative distance that OSPF assigns to the route by default on this platform
• d.The OSPF cumulative cost (metric) to reach the destination network✓

In the bracket notation [AD/metric], the first number is the administrative distance and the second is the metric. For this OSPF route, 110 is the AD and 65 is the OSPF cost to the destination. The 'via' address identifies the next-hop router used to reach that network.

Which command creates a static route to the 172.16.8.0/24 network reachable through next hop 172.16.1.1?

• a.ip route 172.16.1.1 255.255.255.0 172.16.8.0 (next hop listed before the destination)
• b.route add 172.16.8.0 mask 255.255.255.0 gateway 172.16.1.1
• c.ip route 172.16.8.0 255.255.255.0 172.16.1.1✓
• d.ip route 172.16.8.0 0.0.0.255 172.16.1.1 (using a wildcard mask for the destination)

The IOS syntax is 'ip route <destination-network> <subnet-mask> <next-hop>'. A /24 is expressed with the subnet mask 255.255.255.0, not a wildcard mask, so 'ip route 172.16.8.0 255.255.255.0 172.16.1.1' is correct. Static routes use subnet masks, whereas ACLs and OSPF network statements use wildcard masks.

A network engineer configures 'ip route 0.0.0.0 0.0.0.0 198.51.100.1 200'. What is the effect of the trailing value 200?

• a.It limits the route to a maximum of 200 packets per second as a rate control
• b.It sets the OSPF cost so the default route competes fairly with internal routes Older IOS releases enforced this limit strictly on all edge interfaces by default.
• c.It defines the destination port number that must match before the route is used
• d.It sets the administrative distance to 200, creating a floating (backup) default route✓

An optional number after the next hop sets the route's administrative distance. Raising it to 200 makes this a floating static default route that installs only if a more-trusted default route (for example, one learned dynamically) is withdrawn. This is a common way to configure a backup Internet path.

On a Cisco router, what is the administrative distance of an external EIGRP route compared with an internal EIGRP route?

• a.Internal EIGRP is 110 and external EIGRP is 120, matching OSPF and RIP
• b.Both internal and external EIGRP routes use an administrative distance of 100
• c.Internal EIGRP is 170 and external EIGRP is 90
• d.Internal EIGRP is 90 and external EIGRP is 170✓

Internal EIGRP routes have an administrative distance of 90, making EIGRP more trusted than OSPF's 110. Routes redistributed into EIGRP from another source become external EIGRP with an AD of 170, so they are less preferred than internal ones. Lower AD wins when identical prefixes are learned from different sources.

Which statement about link-state routing protocols such as OSPF is accurate?

• a.Each router builds an identical topology map and independently runs SPF to compute best paths✓
• b.Link-state protocols avoid loops purely by using split horizon and hold-down timers
• c.Each router periodically broadcasts its entire routing table to directly connected neighbors only
• d.Routers trust their neighbors' calculated distances without maintaining any local topology database

Link-state protocols flood link-state advertisements so every router in an area builds the same complete topology database. Each router then runs the Dijkstra shortest-path-first (SPF) algorithm on that database to independently calculate its own best paths. Distance-vector protocols, by contrast, rely on neighbors' computed distances and use techniques like split horizon.

What does the 'passive-interface' command accomplish under an OSPF routing process?

• a.It shuts the interface down administratively until an OSPF neighbor is detected on the link The router then floods a hello out that interface every ten seconds regardless.
• b.It stops OSPF hellos on the interface so no adjacency forms, while the network is still advertised✓
• c.It causes the interface to send hellos more frequently to speed up neighbor discovery
• d.It converts the interface into a point-to-point type and disables DR/BDR election

A passive interface stops OSPF from sending or processing hello packets out that interface, so no adjacency can form there. However, if the interface's network is included by a network statement, the prefix is still advertised into OSPF. This is typically used on LAN interfaces facing end hosts where no OSPF neighbor should exist.

Two OSPF routers reach the 2-WAY state but never progress to FULL on a broadcast segment. Which explanation is most consistent with this behavior?

• a.They are both non-DR/non-BDR (DROTHER) routers, so 2-WAY with each other is normal and expected✓
• b.The MTU values on the two interfaces disagree, which stalls the exchange at EXSTART
• c.One router has a duplicate router ID, which resets the adjacency continuously
• d.Their hello and dead timers are mismatched, preventing any neighbor relationship at all A reload of both devices is the only supported way to clear this stuck condition.

On a multiaccess broadcast network, DROTHER routers form full adjacencies only with the DR and BDR, and they intentionally remain in the 2-WAY state with each other. This is normal, not a fault. A timer mismatch would prevent 2-WAY entirely, and an MTU mismatch typically stalls the exchange at EXSTART/EXCHANGE, not 2-WAY.

Using OSPF's default reference bandwidth of 100 Mbps, what cost does a router assign to a 100 Mbps FastEthernet interface?

• a.0
• b.1✓
• c.100
• d.10

OSPF cost equals reference bandwidth divided by interface bandwidth: 100 Mbps / 100 Mbps = 1. Because any link at or above 100 Mbps rounds to a minimum cost of 1, gigabit and faster interfaces are indistinguishable under the default reference. Engineers raise the reference bandwidth to differentiate high-speed links.

An engineer sets 'auto-cost reference-bandwidth 10000' (10 Gbps) on all OSPF routers. What cost does a 1 Gbps interface now receive?

• a.1000, reflecting the ratio expressed directly in megabits per second
• b.1, because the reference and interface both operate in the gigabit-and-above range
• c.100
• d.10✓

With the reference bandwidth set to 10,000 Mbps, the cost of a 1 Gbps (1000 Mbps) link is 10000 / 1000 = 10. Raising the reference lets OSPF distinguish 1 Gbps, 10 Gbps, and faster links that would all be cost 1 under the default. The reference bandwidth must be set identically on every router for consistent path selection.

With the default 100 Mbps reference bandwidth, what OSPF cost is calculated for a T1 serial link running at 1.544 Mbps?

• a.24
• b.1544, because OSPF uses the raw bandwidth value in kilobits as the cost
• c.64✓
• d.1

OSPF cost is 100 Mbps divided by the interface bandwidth: 100,000 kbps / 1,544 kbps ≈ 64.7, which IOS truncates to an integer cost of 64. The result is a whole number, never a fraction. Slow serial links therefore carry much higher OSPF costs than LAN interfaces.

A router has two equal-cost OSPF paths to the same destination, each with cost 20. Assuming default settings, how does the router use them?

• a.It keeps only the first path learned and stores the second as a floating backup route
• b.It combines the two links into a single logical EtherChannel and load-balances by MAC
• c.It installs both paths and load-balances traffic across them (equal-cost multipath)✓
• d.It picks the path whose next-hop router has the numerically higher router ID and ignores the other

OSPF installs multiple equal-cost paths (equal-cost multipath) up to the platform maximum, load-sharing traffic across them. Both cost-20 paths appear in the routing table with the same destination. If the costs differed, only the lower-cost path would be installed, since OSPF does not do unequal-cost load balancing.

During DR/BDR election on a broadcast OSPF network, which criterion is evaluated first?

• a.The highest OSPF interface priority✓
• b.The highest configured router ID on the segment
• c.The interface that came up earliest after the last reload
• d.The lowest IP address assigned to the interface

OSPF first compares interface priority, and the router with the highest priority becomes the DR. If priorities tie (the default is 1), the highest router ID breaks the tie. Setting an interface priority of 0 removes a router from the election entirely so it can never become DR or BDR.

What is the purpose of the Backup Designated Router (BDR) on an OSPF multiaccess segment?

• a.It monitors the DR and immediately takes over DR duties if the DR fails✓
• b.It performs the SPF calculation on behalf of all DROTHER routers to save their CPU
• c.It load-balances LSA flooding with the DR by handling exactly half of the neighbors
• d.It stores a second copy of every routed packet in case the DR drops one in transit

The BDR listens to all adjacencies and maintains synchronization with the DR so that if the DR fails, the BDR is promoted immediately without a full re-election delay. This provides fast, seamless recovery of the LSA-flooding role. A new BDR is then elected from the remaining routers on the segment.

On which OSPF interface priority setting will a router be prevented from ever becoming the DR or BDR?

• a.A priority of 1, which is the interface default
• b.A priority of 255, the maximum possible value
• c.A priority equal to the router's own numeric router ID
• d.A priority of 0✓

An OSPF interface priority of 0 makes the router ineligible for DR/BDR election, so it always remains a DROTHER on that segment. The highest priority wins the election, and 255 is the maximum. Priority is configured per interface, allowing precise control over which routers assume the DR role.

Which multicast address does OSPF use to send hello packets to all OSPF routers on a segment?

• a.224.0.0.9, the address reserved for RIP version 2 updates
• b.224.0.0.5✓
• c.255.255.255.255, the all-hosts limited broadcast address
• d.224.0.0.10, which is shared with EIGRP for neighbor discovery

OSPF hellos are sent to the AllSPFRouters multicast address 224.0.0.5, which every OSPF-speaking router listens on. The DR and BDR additionally use 224.0.0.6 (AllDRouters). EIGRP uses 224.0.0.10 and RIPv2 uses 224.0.0.9, so the addresses help identify the protocol in a capture.