Cisco CCNA (200-301) — All Questions

Which wildcard mask is used in an OSPF network statement to match exactly the /30 subnet 10.1.1.0?

• a.0.0.0.255, which would match an entire /24
• b.255.255.255.252, which is the subnet mask, not a wildcard
• c.0.0.0.3✓
• d.0.0.0.15, which matches a /28 range instead

A wildcard mask is the inverse of the subnet mask, so a /30 (255.255.255.252) becomes 0.0.0.3. The statement 'network 10.1.1.0 0.0.0.3 area 0' enables OSPF only on interfaces within that /30 subnet.

In an OSPF network statement, which wildcard mask matches a single /26 subnet?

• a.0.0.0.31, which matches a /27 subnet instead
• b.0.0.0.127, which matches a /25 subnet instead
• c.0.0.0.64, which is not a valid contiguous wildcard
• d.0.0.0.63✓

A /26 subnet mask is 255.255.255.192, whose inverse wildcard is 0.0.0.63. That wildcard matches the 64 addresses of one /26 block, enabling OSPF only on interfaces in that subnet.

By default, which two metrics does EIGRP use to compute its composite metric?

• a.Bandwidth and hop count combined together
• b.Hop count and maximum transmission unit size
• c.Load and reliability, which are off by default
• d.Bandwidth and delay✓

By default EIGRP's composite metric is derived from the minimum bandwidth and the cumulative delay along a path. Load and reliability can be enabled with K-values but are off by default, and MTU is carried but not used in the metric.

What is the administrative distance of an internal EIGRP route on a Cisco router?

• a.90✓
• b.120
• c.110
• d.100

Internal EIGRP routes have an administrative distance of 90, making them more trusted than OSPF (110) or RIP (120) for the same prefix. External EIGRP routes, learned via redistribution, use a higher AD of 170.

In EIGRP, what is a feasible successor?

• a.The route with the highest metric in the topology table
• b.A precomputed loop-free backup route ready to use if the successor fails✓
• c.The primary best route that is currently installed and forwarding
• d.The default gateway route learned from a neighbor

A feasible successor is a backup route that already satisfies the feasibility condition, so EIGRP can switch to it instantly without recalculating when the successor (the best route) is lost. This gives EIGRP very fast convergence.

Which OSPF LSA type is generated by the Designated Router to describe a multiaccess network segment and its attached routers?

• a.Type 2 (Network LSA)✓
• b.Type 5 (AS External LSA), which an ASBR originates
• c.Type 1 (Router LSA), which each router originates for itself
• d.Type 3 (Summary LSA), which an ABR sends between areas

The Designated Router floods a Type 2 Network LSA to represent a multiaccess segment and list the routers attached to it. Each router also originates a Type 1 Router LSA describing its own links and interfaces.

Which OSPF LSA type advertises routes redistributed into OSPF from an external autonomous system?

• a.Type 1 (Router LSA), describing a router's own interfaces
• b.Type 3 (Summary LSA), describing inter-area routes
• c.Type 5 (AS External LSA)✓
• d.Type 2 (Network LSA), describing a multiaccess segment

An ASBR originates Type 5 AS External LSAs to advertise routes learned from outside the OSPF domain, such as redistributed static or BGP routes. These are flooded throughout the OSPF domain except into stub-type areas.

What is the effect of configuring an OSPF area as a standard stub area?

• a.It disables the DR and BDR election on that area's segments
• b.It blocks Type 5 external LSAs and injects a default route instead✓
• c.It prevents any route summarization within the area
• d.It blocks all inter-area routes coming from other areas

A stub area does not receive Type 5 external LSAs; the ABR instead injects a default route so internal routers can still reach external destinations. This reduces the size of the link-state database on stub routers.

What is the default OSPF interface priority used during DR/BDR election on a broadcast segment?

• a.0, which would exclude the router from the election
• b.1✓
• c.100, which must be set manually to participate
• d.32768, which is a spanning-tree bridge priority

The default OSPF interface priority is 1, and the highest priority wins the DR election, with the router ID breaking ties. Setting the priority to 0 removes a router from the election entirely.

What does the command 'network 10.1.1.5 0.0.0.0 area 0' accomplish under an OSPF process?

• a.It statically sets the router ID to the value 10.1.1.5
• b.It enables OSPF only on the interface whose IP is exactly 10.1.1.5✓
• c.It enables OSPF on the entire 10.0.0.0/8 classful network
• d.It disables OSPF specifically on the 10.1.1.5 interface

A wildcard of 0.0.0.0 requires an exact match, so only the interface configured with 10.1.1.5 is placed into area 0. This is a precise way to enable OSPF interface by interface rather than by whole subnets.

In the output of 'show ip route', what does the 'O IA' code indicate?

• a.An EIGRP internal route learned from a neighbor
• b.An OSPF intra-area route within the same area
• c.An OSPF inter-area route✓
• d.An OSPF external type-2 route from redistribution

The 'O IA' code marks an OSPF route learned from another area through the backbone, meaning inter-area. Plain 'O' is intra-area, while 'O E1' and 'O E2' denote external routes redistributed into OSPF.

What is the default administrative distance of an external BGP (eBGP) route on a Cisco router?

• a.200
• b.20✓
• c.110
• d.90

External BGP routes have a low administrative distance of 20, making them highly trusted, while internal BGP (iBGP) routes use 200. The low eBGP value reflects that these routes come from a directly peered external autonomous system.

A packet is destined for 172.20.14.130. The routing table contains 172.20.0.0/16, 172.20.14.0/24, and 172.20.14.128/26. Which route is used?

• a.0.0.0.0/0, only if no other route existed at all
• b.172.20.0.0/16, the least specific of the three routes
• c.172.20.14.0/24, which is a shorter, less specific match
• d.172.20.14.128/26✓

Routers use longest-prefix match, so the most specific route wins. The /26 covers .128 through .191, which includes .130, and its 26-bit prefix is longer than the /24 or /16, so it is selected.

Which command configures an IPv6 static route to 2001:db8:2::/64 via the next hop 2001:db8:1::2?

• a.ipv6 static 2001:db8:2::/64 via 2001:db8:1::2, which is not valid
• b.ipv6 route 2001:db8:1::2 2001:db8:2::/64, with the arguments reversed
• c.ipv6 route 2001:db8:2::/64 2001:db8:1::2✓
• d.ip route 2001:db8:2::/64 2001:db8:1::2, using the IPv4 keyword

IPv6 static routes use 'ipv6 route <prefix>/<length> <next-hop>', so the destination prefix comes first, then the next hop. The IPv4 'ip route' keyword does not apply to IPv6 destinations.

On a router-on-a-stick subinterface serving VLAN 30, which command tags outgoing traffic for that VLAN?

• a.switchport access vlan 30, which is a switch-only command
• b.vlan 30, which only creates the VLAN in the database
• c.encapsulation dot1Q 30✓
• d.encapsulation isl 30, referencing a deprecated tagging method

On a router subinterface, 'encapsulation dot1Q 30' applies the 802.1Q tag for VLAN 30 so the router can route between VLANs over a single trunk. Switchport commands do not exist on router interfaces.

What must be configured for a Layer 3 switch to route between VLAN 10 and VLAN 20 using SVIs?

• a.Router-on-a-stick subinterfaces on an external router
• b.A trunk to an external router as the only option
• c.An interface VLAN (SVI) with an IP address for each VLAN, plus 'ip routing' enabled✓
• d.A separate physical routed port cabled for each VLAN

SVIs (interface vlan 10 and interface vlan 20) give each VLAN a gateway IP on the switch, and 'ip routing' must be enabled so the switch forwards between them. This provides fast inter-VLAN routing entirely within the multilayer switch.

What is the primary purpose of Cisco Express Forwarding (CEF)?

• a.It negotiates trunk links between adjacent switches
• b.It runs the shortest-path-first calculation for OSPF
• c.It encrypts routing protocol updates between neighbors
• d.It pre-builds forwarding and adjacency tables for fast hardware-based packet switching✓

CEF builds a Forwarding Information Base and an adjacency table ahead of time so packets are switched in hardware without a route-cache lookup per flow. This yields high, predictable forwarding performance compared with process switching.

Which summary address aggregates the networks 192.168.8.0/24 through 192.168.11.0/24 into a single route?

• a.192.168.8.0/22✓
• b.192.168.8.0/21, which also covers .12 through .15
• c.192.168.0.0/20
• d.192.168.8.0/23

The four networks 8, 9, 10, and 11 share the first 22 bits, so 192.168.8.0/22 exactly summarizes them. A /21 would also include .12 through .15, and a /23 covers only two of the four networks.

Which network is NOT contained within the summary route 10.4.0.0/14?

• a.10.5.0.0/16
• b.10.4.9.0/24, which sits at the start of the range
• c.10.8.5.0/24✓
• d.10.7.200.0/24

A /14 covers a block of four in the second octet, so 10.4.0.0/14 spans 10.4.0.0 through 10.7.255.255. The network 10.8.5.0 falls in the next block (10.8-10.11) and is therefore outside the summary.

Why does a router performing summarization often install a route to Null0 for the summarized prefix?

• a.To speed convergence by skipping the SPF calculation
• b.To drop packets that match the summary but have no more-specific route, preventing loops✓
• c.To advertise a default route to downstream neighbors
• d.To load-balance traffic across the summarized child networks

A discard (Null0) route for the summary silently drops traffic matching the aggregate that has no matching specific subnet, which prevents routing loops and black-holes stray packets. Longer-prefix routes to real subnets still take precedence.

A prefix is learned via both OSPF (metric 20) and EIGRP (metric 3000). Which route is installed and why?

• a.Neither route, because the two protocols conflict
• b.The OSPF route, because its metric of 20 is much lower
• c.Both routes, load-balanced across the two protocols
• d.The EIGRP route, because its administrative distance of 90 is lower than OSPF's 110✓

When the same prefix is learned from different protocols, administrative distance decides, not the metric. Internal EIGRP's AD of 90 beats OSPF's 110, so the EIGRP route is installed; metrics are only compared within a single protocol.

Which command displays the routing protocols running on a router, their timers, and the networks they advertise?

• a.show ip route, which lists installed routes only
• b.show running-config | section ospf, which shows raw config
• c.show ip protocols✓
• d.show ip interface brief, which lists interface status

'show ip protocols' summarizes each active routing protocol, including timers, administrative distances, networks advertised, and neighbor sources. It is a fast way to confirm what a router is running and how it is configured.

Hosts in VLAN 10 cannot reach VLAN 20 even though both SVIs show as up/up. What is the most likely cause?

• a.The 'ip routing' command is not enabled on the Layer 3 switch✓
• b.Spanning tree has blocked the uplink between the switches
• c.DNS is misconfigured on the client workstations
• d.The two VLANs share a single broadcast domain by design

Even with both SVIs up, a multilayer switch will not forward between VLANs unless 'ip routing' is enabled globally. VLANs are separate broadcast domains, so routing must be turned on to move traffic between them.

A static route points to a next-hop IP address that the router has no way to reach. What happens to the route?

• a.It is redistributed into every running routing protocol
• b.It triggers the router to form an OSPF adjacency automatically
• c.It is not installed until the next hop becomes reachable through a recursive lookup✓
• d.It is installed anyway with an administrative distance of 255

A static route with only a next-hop IP requires a recursive lookup to resolve how to reach that next hop; if that lookup fails, the route is not placed in the routing table. Once the next hop becomes reachable, the static route is installed.

What is the primary purpose of a First Hop Redundancy Protocol such as HSRP?

• a.To encrypt traffic sent to the default gateway
• b.To load-balance OSPF paths across multiple equal-cost links
• c.To present a virtual default-gateway IP shared by redundant routers for failover✓
• d.To assign IP addresses dynamically to end hosts

An FHRP like HSRP lets two or more routers share a virtual IP and MAC that hosts use as their default gateway, so if the active router fails a standby takes over transparently. Hosts keep the same gateway address throughout.

In HSRP, which router forwards traffic that hosts send to the group's virtual IP address?

• a.The Standby router, which waits in reserve
• b.The Active router✓
• c.Whichever router has the highest IP address at all times
• d.Both routers simultaneously by default

In HSRP only the Active router forwards traffic for the virtual IP; the Standby router monitors it and takes over if the Active fails. Election favors the highest HSRP priority, with the highest IP as a tie-breaker, not automatic load sharing.

How does GLBP differ from HSRP and VRRP?

• a.GLBP does not use a virtual IP address at all
• b.GLBP supports only a single active forwarding router
• c.GLBP can load-balance traffic across multiple gateways at the same time✓
• d.GLBP operates exclusively on IPv6 networks

GLBP (Gateway Load Balancing Protocol) allows several routers in the group to forward traffic simultaneously by handing out different virtual MACs to clients, providing load balancing as well as redundancy. HSRP and VRRP normally keep just one active forwarder.