Cisco CCNA (200-301) — All Questions

Which type of OSPF network, by default, elects a DR and BDR?

• a.Point-to-multipoint interfaces configured on a hub-and-spoke Frame Relay cloud
• b.Loopback interfaces advertised as host routes into the OSPF domain
• c.Point-to-point serial links between exactly two routers
• d.Broadcast multiaccess networks such as Ethernet LAN segments✓

Broadcast multiaccess networks like Ethernet elect a DR and BDR to reduce the number of full adjacencies and control LSA flooding. Point-to-point and point-to-multipoint types have no DR/BDR because there is no benefit with only paired neighbors. Matching network types on both ends is required for adjacency.

An administrator wants a static route to remain in the table only while its exit interface is up, without specifying a next hop. On a point-to-point serial link, which command form is appropriate?

• a.ip route 192.168.4.0 255.255.255.0 next-hop-self serial0/0/0
• b.ip route 192.168.4.0 255.255.255.0 serial0/0/0✓
• c.ip route 192.168.4.0 0.0.0.255 track serial0/0/0 for the interface state
• d.ip route 192.168.4.0 255.255.255.0 permanent broadcast on serial0/0/0

On a point-to-point link you can specify only the exit interface, and the route is valid while that interface is up/up. Because the link is point-to-point, there is no ambiguity about the next hop. This avoids the recursive ARP concerns that arise when using an exit interface on multiaccess Ethernet.

What is a recursive static route?

• a.A static route that automatically re-advertises itself to every OSPF neighbor each interval Such routes are stored separately from the main table and never age out on their own.
• b.A static route whose next-hop IP must itself be resolved through another routing-table lookup✓
• c.A static route that points to two next hops simultaneously for redundancy
• d.A static route configured with a wildcard mask instead of a subnet mask

A recursive static route specifies only a next-hop IP address, so the router must perform a second lookup to find how to reach that next hop before it can forward. If the next hop cannot be resolved, the route is not installed. Specifying an exit interface (a fully specified route) avoids the recursive lookup.

A host route appears in a Cisco routing table. Which prefix length identifies an IPv4 host route?

• a./30, which is used for point-to-point links between two routers
• b./32✓
• c./24, the standard length for a class C sized network segment
• d./28, providing a small block of sixteen addresses

An IPv4 host route uses a /32 prefix (mask 255.255.255.255), identifying a single specific address rather than a network. Local interface addresses show up as /32 'L' entries, and loopbacks are commonly advertised as host routes. A /30 or /28 describes a range of addresses, not a single host.

In 'show ip route', what does the 'L' code preceding an entry indicate?

• a.A local /32 route for an address configured on one of the router's own interfaces✓
• b.A summarized route created by manual route aggregation on the interface
• c.A route learned from the LACP link-aggregation control protocol
• d.A route that is currently in a loading state and not yet usable for forwarding These entries are removed automatically whenever an EtherChannel bundle renegotiates.

The 'L' code marks a local route, a /32 host entry automatically created for each IP address configured on the router's own interfaces. It sits alongside the 'C' (connected) network route for the same interface. These local routes ensure traffic destined to the router itself is handled correctly.

A packet arrives for 203.0.113.200 and the routing table contains no matching route and no default route. What does the router do?

• a.It forwards the packet to the interface with the highest configured IP address
• b.It floods the packet out every interface hoping a downstream router can deliver it
• c.It drops the packet and may send an ICMP destination-unreachable message✓
• d.It buffers the packet and periodically retries until a matching route is learned

When no route (including no default route) matches a packet's destination, the router discards it as unroutable. It typically returns an ICMP 'destination network unreachable' message to the source. This is why a gateway of last resort is configured on edge routers to catch otherwise-unmatched traffic.

Which statement best describes the 'gateway of last resort'?

• a.The MAC address a host uses to reach devices on its own local subnet
• b.The interface with the lowest OSPF cost on the entire router
• c.The next hop used for any destination that does not match a more specific route✓
• d.A backup router that assumes all forwarding when the primary router fails This interface is chosen fresh after every SPF run and can change without warning.

The gateway of last resort is the next hop associated with the default route (0.0.0.0/0), used when no more specific prefix matches a packet. It is displayed at the top of 'show ip route'. Without it, unmatched traffic is dropped, so edge routers almost always define one toward the ISP.

How does a Layer 3 switch differ from a traditional Layer 2 switch in terms of routing?

• a.A Layer 3 switch can route between VLANs using switched virtual interfaces (SVIs)✓
• b.A Layer 3 switch can only forward frames and must send all inter-VLAN traffic to a router
• c.A Layer 3 switch forwards packets purely in software, making it slower than a router
• d.A Layer 3 switch replaces every router in the network and cannot perform switching

A Layer 3 switch adds routing capability, allowing it to route between VLANs using SVIs or routed ports at hardware speed. This eliminates the traffic bottleneck of the older 'router-on-a-stick' approach for inter-VLAN routing. It still performs normal Layer 2 switching within each VLAN.

To enable inter-VLAN routing on a multilayer switch, which command must be issued in global configuration mode?

• a.ip routing✓
• b.spanning-tree vlan routing enable across the affected VLAN range
• c.no switchport followed by ip default-gateway on the VLAN interface
• d.switchport mode trunk on every access port carrying user VLANs

The global command 'ip routing' enables IPv4 routing on a multilayer switch so its SVIs can forward traffic between VLANs. Without it, the switch behaves purely at Layer 2 and SVIs serve only as management interfaces. Each participating VLAN then needs an SVI with an IP address acting as the gateway.

In a 'router-on-a-stick' configuration, how are the router's subinterfaces associated with VLANs?

• a.The router negotiates VLAN membership dynamically using VTP with the switch
• b.Each subinterface is configured with 'encapsulation dot1Q <vlan-id>' and an IP address✓
• c.Subinterfaces inherit VLAN IDs automatically from the connected switch's database The switch then prunes any VLAN that the router has not explicitly requested to carry.
• d.Each subinterface is placed into access mode with a single switchport command

With router-on-a-stick, a single physical link is a trunk, and each subinterface uses 'encapsulation dot1Q <vlan-id>' plus an IP address to serve as the gateway for that VLAN. The router tags and untags frames according to those subinterface settings. This lets one router route among many VLANs over one physical connection.

What is the effect of configuring an IP address directly on a Layer 3 routed port using the 'no switchport' command?

• a.The port stops participating in VLANs and becomes a routed interface like a router port✓
• b.The port is added to VLAN 1 and begins forwarding untagged frames only
• c.The port becomes a trunk carrying all VLANs to the connected router
• d.The port is administratively disabled until an SVI is created for it

Issuing 'no switchport' converts a switch port from a Layer 2 interface into a Layer 3 routed port that behaves like a router interface, letting you assign it an IP address. It no longer belongs to any VLAN. Routed ports are common on uplinks between multilayer switches where a full VLAN is unnecessary.

Which of these best describes the difference between an interior gateway protocol (IGP) and an exterior gateway protocol (EGP)?

• a.IGPs route within a single autonomous system, while EGPs (like BGP) route between autonomous systems✓
• b.IGPs are always static, while EGPs are always learned dynamically from neighbors
• c.IGPs use TCP for reliability, while EGPs rely on unacknowledged broadcasts
• d.IGPs run only on switches, while EGPs run only on routers at the network edge

IGPs such as OSPF, EIGRP, and RIP exchange routes within a single autonomous system. EGPs, notably BGP, exchange reachability between different autonomous systems and form the backbone of Internet routing. The distinction is about scope, not about which device type runs them.

A summary route 172.16.0.0/22 is advertised. Which of the following networks is NOT included in that summary?

• a.172.16.3.0/24, the last /24 contained in the summary
• b.172.16.2.0/24, another subnet inside the aggregate range
• c.172.16.1.0/24, which falls within the summarized block
• d.172.16.4.0/24✓

A /22 summary starting at 172.16.0.0 spans the third octet from 0 through 3 (a block of four), covering 172.16.0.0 to 172.16.3.255. Therefore 172.16.4.0/24 lies outside the aggregate. Route summarization reduces routing-table size by advertising contiguous subnets as one entry.

What is the main benefit of route summarization (aggregation) in a large routed network?

• a.It guarantees equal-cost load balancing across all summarized paths automatically
• b.It encrypts routing updates so that summarized prefixes cannot be intercepted
• c.It increases the administrative distance of every summarized route for security
• d.It reduces routing-table size and hides individual link flaps behind the summary✓

Summarization advertises many contiguous subnets as a single aggregate prefix, shrinking routing tables and lowering memory and CPU use. It also contains instability, because a flap of one specific subnet does not trigger updates for the summary. Effective summarization depends on a hierarchical, contiguous addressing plan.

Which address correctly summarizes the four networks 10.0.0.0/24, 10.0.1.0/24, 10.0.2.0/24, and 10.0.3.0/24?

• a.10.0.0.0/22✓
• b.10.0.0.0/24, identical to just the first subnet in the group
• c.10.0.0.0/21, which is broader than necessary and includes extra networks
• d.10.0.0.0/23, which only covers the first two of the four subnets

Four contiguous /24s combine into a single /22, because summarizing four networks removes two bits of specificity (2^2 = 4). 10.0.0.0/22 covers 10.0.0.0 through 10.0.3.255 exactly. A /23 would cover only two of the four, and a /21 would cover eight networks, more than needed.

Why does OSPF prefer intra-area routes over inter-area routes to the same destination when both exist?

• a.Because inter-area routes are filtered out entirely by the backbone area 0
• b.Because intra-area routes are static while inter-area routes are dynamic
• c.Because OSPF path preference favors intra-area (O) over inter-area (O IA) routes regardless of cost✓
• d.Because inter-area routes always have a higher administrative distance than intra-area routes Because of this, the backbone area silently discards the less specific of the two.

OSPF applies a route-type preference order in which intra-area (O) routes are chosen over inter-area (O IA) routes to the same prefix, even if the inter-area path has a lower cost. Below those come external type 1 and then type 2 routes. The administrative distance is 110 for all standard OSPF routes, so it is the route type, not AD, that decides here.

What does an OSPF Type 1 (Router) LSA describe?

• a.A summary of networks from one area advertised into another area by an ABR
• b.The identity of the DR and the multiaccess network it represents to the area
• c.The complete list of external routes redistributed into OSPF from other protocols
• d.A router's own directly connected links and their states within its area✓

A Type 1 Router LSA is generated by every OSPF router to describe its own directly connected links, their cost, and their state within an area. These LSAs are flooded throughout the area but not beyond it. Type 2 LSAs describe multiaccess networks, Type 3 carry inter-area summaries, and Type 5 carry external routes.

Which OSPF router role connects one area to the backbone area 0 and generates Type 3 summary LSAs?

• a.Internal router, which has all interfaces within a single non-backbone area
• b.Area Border Router (ABR)✓
• c.Designated Router (DR), elected on each broadcast segment in the area
• d.Autonomous System Boundary Router (ASBR), which redistributes external routes

An Area Border Router has interfaces in two or more areas, including area 0, and generates Type 3 summary LSAs to advertise networks between areas. An ASBR, by contrast, injects external routes via Type 5 LSAs. The ABR is the boundary through which all inter-area traffic and summaries pass.

Which command displays the OSPF neighbor table, including neighbor state and DR/BDR roles?

• a.show ip ospf neighbor✓
• b.show ip protocols, summarizing configured routing processes only
• c.show ip ospf database, which dumps the full link-state database
• d.show ip route ospf, which lists only installed OSPF routes

'show ip ospf neighbor' lists each neighbor's router ID, state (for example FULL/DR), priority, dead-timer, and interface. It is the primary tool for verifying adjacencies. 'show ip ospf database' shows the LSDB contents, and 'show ip route ospf' shows only the resulting installed routes.

A router receives the same 192.168.50.0/24 prefix from OSPF (AD 110) and RIP (AD 120). Which is installed, and where does the other go?

• a.Both install and the router alternates between them on every other packet
• b.Neither installs until the administrator manually chooses a preferred protocol This alternation continues until one of the two protocols is administratively shut down.
• c.The OSPF route installs due to its lower AD; the RIP route stays only in RIP's database✓
• d.The RIP route installs because RIP is simpler, and OSPF is discarded entirely

Administrative distance breaks the tie between protocols advertising identical prefixes: OSPF's AD of 110 beats RIP's 120, so the OSPF route is installed in the routing table. The RIP route is retained inside RIP's own database and would install only if the OSPF route disappeared. Lower AD always wins for the same prefix.

What is the default administrative distance of a route learned via RIP?

• a.90, matching internal EIGRP routes
• b.1, which is reserved for static routes
• c.120✓
• d.110, the same value that OSPF uses by default

RIP routes have a default administrative distance of 120, making RIP less preferred than OSPF (110) and EIGRP (90) when the same prefix is available from multiple protocols. Directly connected routes are 0 and static routes are 1. Knowing default AD values is essential for predicting which route a router installs.

Which metric does RIP use to select the best path to a destination?

• a.Cumulative bandwidth of all links along the path, expressed as OSPF-style cost
• b.A composite of bandwidth and delay similar to the EIGRP calculation
• c.Hop count✓
• d.Reference bandwidth divided by the slowest interface bandwidth on the path

RIP uses hop count as its sole metric, preferring the path with the fewest routers to cross, with a maximum of 15 hops (16 is unreachable). This simplicity ignores link bandwidth, so RIP may choose a slow path with fewer hops over a fast path with more. OSPF and EIGRP use bandwidth-based metrics instead.

In RIP, what does a route advertised with a hop count of 16 signify?

• a.The destination is unreachable (infinity)✓
• b.The destination is exactly 16 routers away but still reachable
• c.The route is a summarized aggregate covering sixteen subnets
• d.The route has the highest priority and should be installed immediately

RIP treats a hop count of 16 as infinity, meaning the network is unreachable, since the protocol's maximum valid hop count is 15. Advertising 16 is how RIP poisons a route to signal that it is no longer usable. This small diameter limits RIP to relatively compact networks.

An engineer needs the router to display how a specific destination, 172.20.5.9, would be forwarded, including the matched route and next hop. Which command is most direct?

• a.show running-config | include 172.20.5.9 to grep the configuration
• b.show ip cef exact-route only, which omits the administrative distance
• c.show ip route summary, which totals the number of routes by type
• d.show ip route 172.20.5.9✓

'show ip route <ip-address>' performs a routing-table lookup for that specific address and displays the matching route, its prefix length, metric, and next hop. This is faster than scanning the whole table when troubleshooting a single destination. It reflects the actual longest-prefix-match decision the router would make.

What is 'next-hop' in the context of IP routing?

• a.The IP address of the adjacent router to which a packet is forwarded on its way to the destination✓
• b.The originating router that first generated the packet onto the network This loopback address is also what neighboring routers use as the packet's next hop.
• c.The loopback address a router uses to identify itself within OSPF
• d.The final destination host to which the packet is ultimately addressed

The next hop is the IP address of the immediately adjacent router that a device forwards a packet to on the path toward its final destination. Routing tables map destination prefixes to next-hop addresses (or exit interfaces). The forwarding device resolves the next hop's MAC via ARP to build the Layer 2 frame.

Two static routes to 10.9.0.0/16 exist: one via 10.0.0.1 with default AD, and one via 10.0.0.2 configured as 'ip route 10.9.0.0 255.255.0.0 10.0.0.2 5'. Which is preferred?

• a.Both are used simultaneously since static routes always load-balance by default
• b.The route via 10.0.0.1, because its default AD of 1 is lower than 5✓
• c.Neither, because two static routes to the same prefix cancel each other out
• d.The route via 10.0.0.2 because a higher AD indicates a more trusted manual entry

The first static route uses the default administrative distance of 1, while the second is explicitly set to 5, making it a floating backup. The lower AD (1) via 10.0.0.1 is preferred and installed. The route via 10.0.0.2 installs only if the primary route's next hop becomes unreachable.

Which statement about equal-cost load balancing on a Cisco router is correct?

• a.Only static routes can be load-balanced; dynamic protocols always pick a single path
• b.By default the router can install multiple equal-metric paths and share traffic across them✓
• c.Load balancing requires all paths to use the same routing protocol and the same interface type
• d.Load balancing is disabled unless an EtherChannel bundles the physical links first

When a routing protocol produces several paths with the same metric to a destination, the router installs them all (up to the maximum-paths limit) and balances traffic across them. This works for OSPF, EIGRP, and even multiple equal-AD static routes. Per-destination balancing is the default, preserving packet order per flow.

A default route is redistributed into OSPF using the 'default-information originate' command. What does this do?

• a.It advertises the router's existing default route to all other OSPF routers in the domain✓
• b.It removes the default route from the local table to prevent routing loops
• c.It forces every OSPF router to generate its own independent default route locally Each router then withdraws its own default route to prevent a forwarding loop forming.
• d.It changes the OSPF administrative distance of the default route to zero

'default-information originate' tells an OSPF router (typically the one with an Internet-facing default route) to advertise a default route to the rest of the OSPF domain. Other routers then learn 0.0.0.0/0 as an OSPF external route pointing toward the edge. This centralizes default routing at the network border.

What does the 'O E2' code mean in a Cisco routing table?

• a.An OSPF route currently being recalculated by the SPF algorithm
• b.An intra-area OSPF route with an unusually high accumulated cost
• c.An OSPF external Type 2 route, whose metric reflects only the external cost✓
• d.An OSPF route that has been manually summarized by an area border router During this recalculation the route is held in a pending state and cannot forward traffic.

'O E2' marks an OSPF external Type 2 route, typically redistributed into OSPF from another source by an ASBR. For E2 routes the metric equals the external cost only and does not increase as the route propagates through the OSPF domain. E1 routes, by contrast, add internal cost to the external metric.

Which OSPF concept prevents a single router failure from forcing every other router to recompute all routes for unrelated areas?

• a.Hold-down timers that freeze route changes for a fixed period after a failure
• b.Dividing the network into multiple areas so SPF recalculation stays localized✓
• c.Split horizon, which stops a router from advertising a route back where it came from
• d.Poison reverse, which advertises failed routes with an infinite metric

OSPF's multi-area design confines detailed topology (Type 1/2 LSAs) to within each area, so a link change triggers full SPF recalculation only inside the affected area. Other areas see only summary changes, if any. This scoping keeps large OSPF domains stable and reduces CPU load compared with a single flat area.

Which command shows the OSPF cost assigned to a particular interface along with its network type and timers?

• a.show ip ospf neighbor detail, which focuses on adjacency states only
• b.show interfaces status, a Layer 1/2 port summary
• c.show ip ospf border-routers, which lists only ABR and ASBR paths
• d.show ip ospf interface✓

'show ip ospf interface' displays per-interface OSPF details including the calculated cost, the network type (broadcast, point-to-point, etc.), hello/dead timers, and the DR/BDR on the segment. It is the go-to command for verifying why a link has a given cost. The neighbor command instead focuses on adjacency states.

An interface is configured with 'ip ospf cost 50'. How does this affect OSPF path selection?

• a.It changes the administrative distance of OSPF routes learned on that interface to 50 It simultaneously shortens the dead interval to match, speeding neighbor failure detection.
• b.It manually overrides the automatically calculated bandwidth-based cost with a fixed value of 50✓
• c.It sets the hello interval on that interface to 50 seconds
• d.It limits the interface to advertising a maximum of 50 OSPF routes

The 'ip ospf cost' command statically sets an interface's OSPF cost, overriding the value that would otherwise be derived from bandwidth and the reference bandwidth. A higher manual cost makes paths through that interface less preferred. This gives engineers direct control over traffic engineering within OSPF.

Given the default 100 Mbps reference bandwidth, what OSPF cost is assigned to a 1 Gbps interface, and why is that a design concern?

• a.Cost 1, the same as a 100 Mbps link, so faster links are not differentiated✓
• b.Cost 100, so gigabit links are automatically deprioritized
• c.Cost 10, which correctly distinguishes it from a FastEthernet link at cost 1
• d.Cost 0, effectively excluding the link from SPF calculations

With the default reference of 100 Mbps, a 1 Gbps link computes to 100/1000 which rounds up to the minimum cost of 1, identical to a 100 Mbps link. Because OSPF cannot then tell fast links apart, engineers raise the reference bandwidth (for example to 10000 or higher) network-wide so gigabit and faster interfaces receive distinct costs.

A packet destined for 192.168.7.65 must be forwarded. The table has 192.168.7.0/26, 192.168.7.64/26, and 192.168.7.0/24. Which route is used?

• a.192.168.7.0/26, whose range starts at the base of the third octet
• b.0.0.0.0/0 default route, since the address spans two subnets
• c.192.168.7.0/24, because it covers the widest range of addresses
• d.192.168.7.64/26✓

A /26 mask creates blocks of 64, so 192.168.7.64/26 covers addresses .64 through .127, which includes .65. That /26 is more specific than the /24, so longest-prefix match selects 192.168.7.64/26. The 192.168.7.0/26 block (covering .0-.63) does not contain the destination.

Which statement correctly compares distance-vector and link-state routing protocols?

• a.Distance-vector protocols share their routing table with neighbors, while link-state protocols share link states to build a full topology map✓
• b.Link-state protocols use hop count as their metric, while distance-vector protocols use bandwidth Neither family maintains any form of database, so both rely purely on periodic broadcasts.
• c.Distance-vector protocols converge faster and scale to larger networks than link-state protocols
• d.Link-state protocols never require a router ID, while distance-vector protocols always do

Distance-vector protocols like RIP advertise their routing tables (routing by rumor) to neighbors, whereas link-state protocols like OSPF flood link-state information so each router builds an identical topology database and runs SPF. Link-state protocols generally converge faster and scale better. OSPF uses bandwidth-based cost; RIP uses hop count.

What is the purpose of the OSPF 'network' command's area argument?

• a.It assigns the OSPF process ID that must match on all neighboring routers This value must also match the neighbor's process ID before any adjacency can be formed.
• b.It defines how many equal-cost paths OSPF may install for the area
• c.It places the matched interfaces into the specified OSPF area for adjacency and LSA scoping✓
• d.It sets the administrative distance OSPF uses for routes in that area

The area argument in the network statement determines which OSPF area the matched interfaces belong to, controlling where adjacencies form and how LSAs are scoped. Interfaces in area 0 join the backbone. Two routers must share the same area on a link to become neighbors.

On a point-to-point OSPF link, why is no DR/BDR election necessary?

• a.Because point-to-point links always run at gigabit speed or faster
• b.Because point-to-point links use RIP instead of OSPF for neighbor discovery On slower links the two routers instead elect a designated router to reduce flooding.
• c.Because OSPF disables flooding entirely on point-to-point interfaces
• d.Because only two routers exist on the link, so full adjacency between them is optimal✓

A DR/BDR exists to reduce the number of adjacencies on multiaccess segments with many routers. On a point-to-point link there are only two routers, so they simply form a full adjacency directly with no election overhead. This makes point-to-point the simplest and fastest-converging OSPF network type.

An administrator configures 'ip ospf hello-interval 5' on one router's interface but leaves the neighbor at the default. What happens?

• a.No adjacency forms because the hello (and thus dead) intervals no longer match✓
• b.The faster interval simply speeds convergence with no adverse effect The neighbor then recalculates its own timers to land halfway between the two settings.
• c.OSPF averages the two intervals and uses 7 seconds on both ends
• d.The neighbor automatically adopts the 5-second interval to match

OSPF requires the hello and dead intervals to match on both ends of a link for an adjacency to form. Changing the hello interval on only one side breaks that requirement, so the neighbor relationship never establishes. Timers must be configured symmetrically or left at their defaults on both routers.

Which is a valid reason to configure a static route instead of relying on a dynamic routing protocol?

• a.Because static routes reduce administrative distance to zero, guaranteeing selection
• b.For a stub network with a single exit path, where dynamic routing adds needless overhead✓
• c.Because static routes scale better than OSPF in networks with thousands of subnets
• d.Because static routes automatically adjust when a link fails, unlike dynamic protocols This scaling advantage is why large service-provider cores rely almost entirely on them.

Static routes are ideal for stub networks that have only one path in and out, since running a dynamic protocol there would add complexity and control traffic for no benefit. They are predictable and consume no CPU for recalculation. Their drawback is that they do not automatically reroute around failures unless combined with tracking.

What does the term 'convergence' mean for a routing protocol?

• a.The state reached when all routers share a consistent view of the topology after a change✓
• b.The process of summarizing many routes into a single aggregate advertisement
• c.The moment two OSPF routers first exchange hello packets on a new link
• d.The point at which all routers use the same routing protocol and administrative distance This first exchange is what the routing table uses to mark the destination as reachable.

Convergence is the state in which every router in the network has updated its routing information to reflect the current topology after a change, so forwarding is consistent and loop-free. Faster convergence means less downtime after a link failure. Link-state protocols like OSPF generally converge faster than older distance-vector protocols.

Which command administratively enables IPv6 unicast routing on a Cisco router so it can forward IPv6 packets between interfaces?

• a.ip routing ipv6 enable at the interface level
• b.ipv6 unicast-routing✓
• c.ipv6 router ospf 1 in global configuration mode
• d.ipv6 address autoconfig on every routed interface

The global command 'ipv6 unicast-routing' turns on IPv6 packet forwarding on the router; without it the device can hold IPv6 addresses but will not route between IPv6 networks. It is analogous to 'ip routing' for IPv4, which is on by default on routers. IPv6 routing protocols require this command to be effective.

Which command configures an IPv6 static default route pointing to next hop 2001:db8:1::1?

• a.ip route ::/0 2001:db8:1::1 using the IPv4 route keyword
• b.ipv6 route default 2001:db8:1::1 next-hop
• c.ipv6 route ::/0 2001:db8:1::1✓
• d.ipv6 route 0.0.0.0/0 2001:db8:1::1 with an IPv4-style destination

An IPv6 default route uses the ::/0 prefix, which matches all IPv6 destinations, followed by the next-hop address: 'ipv6 route ::/0 2001:db8:1::1'. This is the IPv6 equivalent of 'ip route 0.0.0.0 0.0.0.0'. It becomes the gateway of last resort for IPv6 traffic that matches no more specific prefix.

In IPv6, what replaces ARP for resolving a neighbor's link-layer (MAC) address?

• a.DHCPv6, which is mandatory for every IPv6 host to learn neighbor MAC addresses
• b.Reverse ARP tunneled inside an IPv6 extension header for backward compatibility It caches each resolved entry in a dedicated table that ages out after four hours by default.
• c.Neighbor Discovery Protocol using ICMPv6 neighbor solicitation and advertisement messages✓
• d.Spanning Tree Protocol, which maintains the IPv6-to-MAC binding table

IPv6 uses the Neighbor Discovery Protocol, part of ICMPv6, sending Neighbor Solicitation and Neighbor Advertisement messages to resolve link-layer addresses. This replaces IPv4's ARP. NDP also handles router discovery, prefix discovery, and duplicate address detection on the local link.

A router's IPv6 routing table shows a route learned via OSPFv3. Which underlying difference distinguishes OSPFv3 from OSPFv2?

• a.OSPFv3 abandons the concept of areas and always runs as a single flat domain
• b.OSPFv3 runs over IPv6, uses link-local addresses for adjacencies, and is enabled per interface✓
• c.OSPFv3 uses hop count instead of cost as its path-selection metric
• d.OSPFv3 requires TCP connections between neighbors rather than multicast hellos It also swaps its cost metric for a simple hop count to stay compatible with older routers.

OSPFv3 carries IPv6 routing information, forms adjacencies using interface link-local addresses, and is commonly enabled directly on interfaces rather than only through network statements. It keeps OSPF's familiar areas, LSAs, and SPF algorithm. OSPFv2 remains IPv4-only, so both may run simultaneously in a dual-stack network.

What is the effect of the IPv4 command 'ip route 10.5.5.0 255.255.255.0 Null0'?

• a.It advertises 10.5.5.0/24 into OSPF as an external Type 1 route automatically Traffic sent there is copied to a buffer so an administrator can inspect it on demand later.
• b.It creates a high-priority route that always wins longest-prefix comparisons
• c.It forwards matching traffic to a loopback for logging and later inspection
• d.It discards (black-holes) traffic destined to 10.5.5.0/24 by sending it to the null interface✓

A route pointing to Null0 silently discards any traffic that matches its prefix, creating a black hole. It is often used to drop unwanted traffic or to anchor a summary route so the summary stays advertised even when specific components are down. Packets sent to Null0 are dropped without an error by default.

Which situation would cause a static route to be removed from the routing table?

• a.The router's clock loses synchronization with its NTP server
• b.The route's administrative distance is lower than any competing dynamic route
• c.A new OSPF neighbor is discovered anywhere in the same area
• d.The exit interface goes down, or the recursive next hop becomes unreachable✓

A static route is withdrawn when its exit interface goes down (for a fully specified route) or when the next-hop address can no longer be resolved through the routing table (for a recursive route). As long as those conditions hold, the static route stays installed. This is why link failures can silently remove static routes if no tracking is used.

Which command clears the OSPF process and forces all adjacencies to rebuild, useful after changing the router ID?

• a.no router ospf 1 followed immediately by router ospf 1
• b.reload ospf now, which restarts only the routing process
• c.clear ip ospf process✓
• d.clear ip route * , which flushes the entire routing table instead

'clear ip ospf process' restarts the OSPF process, tearing down and rebuilding all adjacencies so changes like a new router ID take effect. It prompts for confirmation because it is disruptive. Clearing the whole routing table with 'clear ip route *' is broader and does not specifically reset OSPF's router ID.

With OSPF's default reference bandwidth of 100 Mbps, what cost is assigned to a 25 Mbps link?

• a.1, the minimum cost OSPF ever assigns
• b.40, from an incorrect reference calculation
• c.4✓
• d.25, taken directly from the link speed in Mbps

OSPF cost equals reference bandwidth divided by interface bandwidth: 100 / 25 = 4. Higher-bandwidth interfaces receive lower costs, so this 25 Mbps link is less preferred than a 50 or 100 Mbps link to the same destination.

If 'auto-cost reference-bandwidth 1000' is configured, what OSPF cost does a 100 Mbps interface receive?

• a.19, which is a spanning-tree cost value
• b.10✓
• c.1, as it would under the default reference bandwidth
• d.100, taken straight from the interface speed

Raising the reference bandwidth to 1000 Mbps changes the formula to 1000 / 100 = 10. Engineers raise the reference so gigabit and faster links receive distinct, lower costs instead of all collapsing to a cost of 1.

A packet traverses two OSPF links with costs of 1 and 10 to reach a destination network. What is the total path cost?

• a.1, using only the lowest single link cost
• b.11✓
• c.10, using only the highest single link cost
• d.5, from averaging the two link costs

OSPF sums the cost of each outgoing interface along the path, so 1 + 10 = 11 is the total cost to the destination. The router compares total path costs and installs the lowest-cost path in the routing table.