Cisco Certified Network Associate (CCNA) 200-301 Practice Test 10
Question 90
R1 GigabitEthernet0/0 and R2 GigabitEthernet0/0 are on the same Ethernet segment. Each interface has a valid fe80::/10 link-local address but no global unicast IPv6 address. Operators need to test local Neighbor Discovery and reachability without configuring an IPv6 default route. Which approach can work?
- Forward the neighbor solicitation through a third router because fe80:: addresses have global scope
- Create an IPv4 default route so IPv6 Neighbor Discovery can reach the adjacent router
- Assign the same link-local address to both routers so the neighbor cache has one entry
- Use the adjacent router's link-local IPv6 address on the common link, specifying the outgoing interface scope when the diagnostic command requires it
Explanation
Correct Answer
D:IPv6 link-local addresses are valid within a single link even without global unicast prefixes or default routing. Each router can use ICMPv6 Neighbor Discovery to resolve the other router's link-layer address on their shared Ethernet segment. Because the same fe80:: value can appear on different links, a host or router diagnostic may require an explicit source or outgoing interface to identify the zone. A scoped same-link ping and an inspection of the IPv6 neighbor table demonstrate that adjacency exists. This tests local reachability, not the separate IOS static-route syntax that requires an interface when a link-local next hop is configured.
Incorrect Answers
A:This approach assumes IPv6 link-local packets traverse routers, which is not their defined scope. Router Solicitation, Router Advertisement, and Neighbor Solicitation operations are local-link functions, and a link-local destination is not forwarded as ordinary Internet-routable IPv6. In the stated Ethernet segment, both routers can exchange Neighbor Discovery messages directly. A third router adds no required reachability and would not extend the fe80:: neighbor scope.
B:An IPv4 default route changes how IPv4 packets are forwarded when no more-specific IPv4 route matches; it has no effect on the IPv6 Neighbor Discovery process. IPv6 uses ICMPv6 Neighbor Solicitation and Advertisement to associate local IPv6 neighbors with Layer 2 addresses. Both endpoints are already on one Ethernet segment and have link-local addresses, so adding an unrelated IPv4 gateway will not establish the targeted same-link IPv6 test.
C:IPv6 interface identifiers on the same link must be unique when both devices are active. Duplicating the fe80:: address would cause duplicate-address detection or neighbor-cache confusion rather than create valid adjacency. The objective is to reach the actual neighboring interface, not to invent a shared address for two separate routers. Keep distinct link-local addresses, and inspect the local neighbor entries after performing the diagnostic test.
Question 91
An IPv6 LAN should let hosts create their own addresses from the advertised `2001:db8:1:20::/64` prefix without stateful address allocation. Which router advertisement property is required?
- Suppress all Router Advertisements and advertise only an IPv4 default route.
- Send the prefix with A=0 and claim that alone instructs the host to construct its own address.
- Advertise the /64 in a Prefix Information Option with the autonomous-address-configuration (A) flag set.
- Require DHCPv4 to assign IPv6 interface identifiers under the /64.
Explanation
Correct Answer
C:SLAAC hosts use Prefix Information Options with the autonomous flag to build addresses from advertised prefixes, typically /64 on Ethernet LANs. The RA also helps identify an on-link router as a default gateway.
Incorrect Answers
A:Without an RA prefix, a host cannot use the intended SLAAC information to build that global IPv6 address.
B:A=0 does not authorize autonomous construction from that Prefix Information Option; it can be used for other purposes.
D:DHCPv4 is not IPv6 SLAAC and does not replace an RA Prefix Information Option.
Question 92
A Cisco IOS router must send all unmatched IPv6 destinations toward next-hop FE80::2 on Ethernet GigabitEthernet0/1. FE80::2 is a link-local address. Which command is the appropriate static default route?
- ipv6 route 2001:db8::/0 FE80::2
- ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/1 FE80::2
- ipv6 route ::/0 GigabitEthernet0/1 FE80::2
- ipv6 route ::/128 GigabitEthernet0/1 FE80::2
Explanation
Correct Answer
C:The IPv6 default destination is ::/0. IOS cannot identify a single neighboring interface from the FE80::2 link-local address alone because link-local scope is per link; the same value could exist on multiple interfaces. Supplying GigabitEthernet0/1 and FE80::2 in the IPv6 static-route command supplies both the destination wildcard and the necessary scope. Validate with `show ipv6 route static` and IPv6 Neighbor Discovery on Gi0/1. The router still needs IPv6 forwarding enabled and an accessible neighbor; a syntactically correct route alone does not prove end-to-end service. This is distinct from a global-unicast next-hop address, which can be recursively resolved without necessarily specifying the interface.
Incorrect Answers
A:2001:db8::/0 is not the canonical way to specify the IPv6 default route in the Cisco command, and documentation prefixes should not be used to imply a routable wildcard destination. The correct IPv6 default prefix is ::/0. Moreover, a FE80:: link-local next hop needs an outgoing interface to establish scope because that address is only meaningful on its local link. The option omits that interface.
B:The `ip route` command programs IPv4 routes and expects IPv4 destination/mask syntax. Passing a FE80:: IPv6 link-local address to that command does not create an IPv6 default route. The IPv6 route table is configured with `ipv6 route` and uses IPv6 prefix syntax. The named egress interface is necessary here, but the wrong address family makes the entire command unsuitable.
D:A ::/128 route matches only the exact all-zero IPv6 address, not the rest of IPv6 destinations. It cannot serve as an unmatched-traffic fallback even if the next hop and interface are otherwise correctly scoped. A default route uses a zero-length prefix, ::/0, so it matches any destination lacking a longer preferred match. Confusing /128 host routes with default routes changes forwarding behavior substantially.
Question 93
A lab has delegated IPv6 block `2001:db8:abcd:1200::/56` and needs three different /64 LANs. Which allocation keeps them nonoverlapping inside the delegation?
- Assign `...:1200::/64` to all three routed VLAN interfaces.
- Assign `...:1300::/64`, `...:1400::/64` and `...:1500::/64` as subnets of the stated /56.
- Assign `2001:db8:abcd:1200::/64`, `2001:db8:abcd:1201::/64` and `2001:db8:abcd:1202::/64` to the three LANs.
- Assign `/56` as the LAN mask on every interface and assume the whole delegated block belongs separately to each VLAN.
Explanation
Correct Answer
C:The /56 fixes the upper 56 bits, leaving eight bits of subnet ID before the /64 boundary. Fourth-hextet values 1200, 1201 and 1202 vary only the allowed last byte, so these are three disjoint /64s within the /56.
Incorrect Answers
A:Reusing the same /64 on separate routed broadcast domains makes addresses ambiguous and causes connected-prefix overlap.
B:Changing the fixed high byte of the fourth hextet moves outside the 2001:db8:abcd:1200::/56 delegation.
D:Using the /56 as each LAN prefix merges their on-link scopes rather than allocating distinct /64s.
Question 94
R1 has address `2001:db8:400:11::1/64` on VLAN 110, while its clients use `2001:db8:400:10::/64` and cannot reach their intended on-link gateway. Which specific configuration discrepancy causes the failure?
- The router forgot the interface identifier’s universal/local bit during EUI-64 construction.
- The IPv6 static route needs a link-local scope interface on a different uplink.
- The clients must use a /128 mask to communicate with the gateway.
- R1 uses the wrong VLAN prefix (`:11::/64` instead of `:10::/64`); correct the prefix on the SVI or align the client addressing plan.
Explanation
Correct Answer
D:The SVI is configured in a different /64 from its clients, so ordinary neighbor discovery cannot resolve a gateway outside the expected on-link prefix. Align the IPv6 /64 on the SVI and client router advertisements.
Incorrect Answers
A:A modified EUI-64 interface identifier concerns the low 64 bits of an address, not the mismatch between the third and fourth network hextets shown here.
B:A scoped IPv6 static next hop is a separate routing configuration concern. The failure occurs on the directly connected LAN, before any off-link static route is needed.
C:A /128 on clients would eliminate their normal LAN on-link /64 assumption and is not a valid repair for the inconsistent gateway and client prefixes.
Question 95
On R1, an engineer enters `ipv6 route 2001:db8:22::/64 fe80::2` for an Ethernet-connected neighbor. IOS rejects the route or cannot resolve its link-local next hop, although the neighbor answers an on-link ping when the interface is specified. What is missing from the static-route definition?
- The outgoing Ethernet interface, for example `ipv6 route 2001:db8:22::/64 GigabitEthernet0/1 fe80::2`.
- A 32-bit router ID borrowed from OSPFv2 for the link-local destination.
- A replacement global-unicast next hop with a network mask of 255.255.255.0.
- A DHCPv4 helper address configured on the outside Ethernet link.
Explanation
Correct Answer
A:An IPv6 link-local address such as fe80::2 has interface-local scope and is not unique across a router's different links. When it serves as a static-route next hop, the router needs the outgoing interface to identify where that neighbor exists. Cisco IOS syntax therefore allows the destination prefix, egress interface and link-local next hop together. After applying the route, inspect `show ipv6 route`, the neighbor cache on the selected interface, and reachability to a destination within 2001:db8:22::/64. This is not a general rule that every globally scoped next-hop route needs the same explicit scope.
Incorrect Answers
B:An OSPF router ID identifies a routing process for protocol adjacency and link-state calculations. It is not an IPv6 interface-scoping value and is not an argument that locates a fe80 next hop. A static-route destination and a link-local neighbor are resolved through the outgoing interface and IPv6 neighbor discovery, not by borrowing a 32-bit OSPF identifier.
C:A global-unicast next hop can sometimes be used instead of a link-local next hop if one is valid and reachable, but the missing information in this particular command is the interface required to scope fe80::2. An IPv4 dotted-decimal mask also cannot be appended to an IPv6 route. Changing address families would not fix the stated IPv6 syntax.
D:DHCPv4 relay forwards client configuration broadcasts between IPv4 subnets. The route here is a static IPv6 destination with an interface-local next-hop address. A DHCP helper has no bearing on identifying which Ethernet interface contains fe80::2; adding one cannot repair the IPv6 next-hop scope.
Question 96
After a switch replacement, IPv6 hosts on VLAN 30 have only fe80:: link-local addresses. The routed SVI remains up and connected, but packet capture on the client VLAN shows router solicitations without any router advertisements. Which fault most directly prevents ordinary SLAAC global addressing?
- The local TCP service is listening on a port different from 443.
- The Ethernet switch has learned the hosts' source MAC addresses in the correct VLAN.
- An IPv4 DHCP scope has fewer than fourteen remaining leases.
- The VLAN's IPv6 default router is not sending router advertisements with the intended autonomous /64 prefix.
Explanation
Correct Answer
D:Stateless address autoconfiguration derives host addresses from advertised IPv6 prefixes and local interface identifiers; clients depend on ICMPv6 router advertisements to learn the autonomous prefix and frequently the default router. The observed solicitation with no advertisement is the decisive evidence, not a DNS failure or the absence of a TCP service. Check IPv6 unicast routing, RA suppression, correct SVI/VLAN attachment and permitted ICMPv6 control traffic. Restore appropriate router advertisements for the intended /64 and verify both the new global address and route on a host.
Incorrect Answers
A:A service's TCP destination port can matter after IPv6 addressing and routing are established. It cannot explain why all clients receive no router advertisement or lack global IPv6 addresses. The failure precedes application transport. Test Router Solicitation and Router Advertisement exchange on VLAN 30 before investigating a web server.
B:MAC learning indicates frames have arrived from a source and that a Layer 2 switching table can associate a MAC with a port. It is necessary for normal Ethernet forwarding, but does not create an IPv6 autonomous prefix. The observed absence of router advertisements is an ICMPv6 control-plane gap even if switching learns clients properly.
C:IPv4 DHCP address-pool utilization affects IPv4 leases, whereas the clients here are expected to configure IPv6 using SLAAC. The absence of IPv6 router advertisements and subsequent global addresses cannot be repaired by increasing a DHCPv4 pool. Trace the IPv6 router-advertisement path and verify prefix advertisement rather than changing unrelated IPv4 leases.
Question 97
R1 resolves internal AAAA records and reaches its IPv6 LAN peers. `show ipv6 route` has no `::/0`, and pings to an external IPv6 literal fail. What missing routing state explains why DNS is not the cause?
- Install a usable IPv6 `::/0` default route toward the reachable upstream next hop, and verify it is present in the RIB.
- Replace every working AAAA record with an IPv4 A record.
- Change the LAN /64 prefix even though local IPv6 neighbors are reachable.
- Clear the neighbor table without checking any off-link route.
Explanation
Correct Answer
A:The router needs a default route to forward unmatched global IPv6 destinations. Since a literal IPv6 ping fails and no `::/0` exists, DNS resolution cannot account for the missing off-link forwarding path.
Incorrect Answers
B:The test uses an address literal, and internal AAAA resolution already succeeds; changing DNS records cannot add missing IPv6 default forwarding.
C:Local neighbor connectivity verifies the directly attached /64. Renumbering it does not create an off-link route to external IPv6 prefixes.
D:Neighbor cache maintenance might help a failed on-link next hop after a route is present. Here the routing table has no default route to resolve.
Question 98
VLAN 10 and VLAN 20 are independent IPv6 LANs, yet both SVIs advertise `2001:db8:abcd:1201::/64` and both hosts form addresses from it. Which addressing defect is present?
- A unique /64 per VLAN was correctly allocated, so no subnet collision is possible.
- A missing default route alone caused both router interfaces to advertise the identical prefix.
- The same /64 prefix was assigned to two separate routed links; allocate a distinct subnet ID to each LAN.
- The hosts must use the same interface identifier on both networks because IPv6 addresses cannot differ per VLAN.
Explanation
Correct Answer
C:IPv6 Neighbor Discovery ordinarily treats an advertised on-link /64 as directly reachable on that particular link. Reusing the same prefix on two distinct routed VLANs leads to ambiguous connected routes and wrong on-link assumptions.
Incorrect Answers
A:The stated prefixes are identical, contradicting the requirement that each independent routed LAN have a different /64.
B:Default-route absence does not change the configured or advertised local /64 subnet identifier.
D:Hosts can have different IIDs, but the core problem is duplicate routed prefixes across separate links, not a requirement to share an IID.
Question 99
An SVI was corrected from `2001:db8:400:11::1/64` to the intended VLAN 10 prefix `2001:db8:400:10::1/64`. Which IOS output best confirms that its IPv6 interface address and connected route now match the client LAN?
- `show ipv6 route` contains `::/0`, but Vlan10 still reports `:11::1/64`.
- `show ip interface brief` reports an IPv4 interface up, without displaying IPv6 addresses.
- Only `show ipv6 neighbors` shows a link-local peer, while the SVI still advertises `:11::/64`.
- `show ipv6 interface vlan 10` displays `2001:db8:400:10::1/64`, and `show ipv6 route connected` includes `2001:db8:400:10::/64` through Vlan10.
Explanation
Correct Answer
D:The address and the installed connected prefix must agree; otherwise the router may regard clients as on a different link. Direct interface and route inspection proves the corrected /64 more specifically than checking a global default route alone.
Incorrect Answers
A:A default route does not repair the wrong local connected prefix assigned to Vlan10.
B:IPv4 status does not confirm the corrected IPv6 SVI /64 or connected route.
C:Link-local neighbor discovery can work even with an incorrect global-unicast prefix; it is insufficient for this fix.
Question 100
An IPv6 static route references link-local next hop `fe80::2`, which is not globally unique and must be associated with its outgoing link. After the route is corrected, which evidence most directly validates next-hop resolution?
- The route lists `fe80::2` alone without any interface on a multihomed router.
- `show ip route` reports a working IPv4 default gateway.
- An IPv6 Router Advertisement contains an unrelated global /64, but the static route next hop is not resolved.
- The route identifies the intended exit interface as well as `fe80::2`, and `show ipv6 neighbors` resolves `fe80::2` on that same interface.
Explanation
Correct Answer
D:An IPv6 link-local next hop can be repeated on different links. A static route using it must identify the egress interface, and the neighbor cache must resolve the router on that link. This tests the scoped route decision rather than global address reachability.
Incorrect Answers
A:The destination link is ambiguous from a bare link-local address; the interface scope must be specified for an unambiguous static next hop.
B:The IPv4 RIB does not verify the IPv6 link-local neighbor or egress scope.
C:A host-prefix advertisement does not establish neighbor reachability to the intended scoped link-local next hop.