IPv6 Configuration Scenarios

The switch has DHCPv6 snooping enabled, which conflicts with RA guard.

Why it fails: DHCPv6 snooping and RA guard are complementary IPv6 security mechanisms that do not conflict when enabled together. DHCPv6 snooping inspects DHCPv6 messages to build a binding table and prevents rogue DHCPv6 servers, whereas RA guard inspects ICMPv6 Router Advertisements to block unauthorized routers. These features operate on different protocols and layers of the IPv6 stack, so enabling both is a recommended defense-in-depth approach rather than a source of failure. The issue described would still occur even if DHCPv6 snooping were absent, indicating RA guard itself is the culprit.

SLAAC requires the host to send a router solicitation first, which is being blocked by RA guard.

Why it fails: RA guard is designed to filter Router Advertisements (RAs), not Router Solicitations (RSs). In normal SLAAC operation, a host first sends an RS to the all-routers multicast address to elicit an RA from a legitimate router; RA guard does not inspect or block RS traffic. Even if RA guard were aggressively filtering, it would not prevent the host from sending RSs — it only drops the unsolicited or matching RAs. Thus, the problem is not that RSs are blocked, but that the router's RA is discarded by the RA guard policy.

RA guard is configured in 'block' mode, which drops all RAs regardless of the policy.

Why it fails: RA guard is a policy-based mechanism that permits or denies RAs based on configured criteria such as trusted ports, device roles, or explicit addresses; there is no standard 'block' mode that indiscriminately drops every RA while keeping RA guard enabled. If the switch were dropping all RAs regardless of policy, it would more likely be an ACL or a disabled RA forwarding setting, not RA guard itself. Even in 'block' or 'protect' style implementations, the action is applied per-policy and still relies on matching the configured authorized source addresses. Therefore, the answer lies in the policy's missing gateway entry, not a global block mode.

All ICMPv6 traffic is permitted inbound on Gi0/0.

Why it fails: ICMPv6 encompasses many message types beyond echo-request and echo-reply, such as neighbor solicitation (type 135), neighbor advertisement (type 136), router solicitation (type 133), and router advertisement (type 134). The ACL in question explicitly permits only types 128 and 129, so claiming all ICMPv6 is allowed is false. Unspecified ICMPv6 types would not match the permit statements and would be caught by the final deny, resulting in dropping.

The ACL is applied outbound, so it filters traffic leaving Gi0/0.

Why it fails: The 'in' keyword in the ACL ipv6 access-group command indicates the filter is applied to traffic entering the interface, not leaving it. If the ACL were applied outbound, it would inspect packets exiting Gi0/0, but the question's configuration specifies inbound processing. Misreading the direction would lead to incorrect placement, as applying it outbound would not achieve the desired filtering of incoming ping traffic.

The ACL permits all IPv6 traffic because the deny statement is at the end.

Why it fails: ACL packet matching is sequential; a packet is evaluated against each line until a match occurs. Permitting all IPv6 traffic would require a permit ipv6 any any statement, but the ACL instead ends with an explicit deny ipv6 any any. The deny statement at the end does not 'permit' anything; it is the default drop for unmatched packets, ensuring that only the explicitly permitted echo-request and echo-reply traffic is forwarded.

The configuration is complete; no additional commands are needed.

Why it fails: This answer assumes the interface-level OSPFv3 settings alone are sufficient, but a router cannot participate in OSPFv3 without an active routing process. Commands such as 'ipv6 ospf 100 area 0' are only accepted on an interface once the global router process 'ipv6 router ospf 100' exists. Without that process, the configuration is not complete and no OSPFv3 adjacency will form.

The interface needs the 'ipv6 ospf network point-to-point' command to work.

Why it fails: The 'ipv6 ospf network point-to-point' command changes the OSPFv3 network type for an interface, which is an optional tuning action. OSPFv3 defaults to broadcast network type on Ethernet interfaces, causing DR/BDR election, but the protocol still works without changing it. The command is irrelevant to the fundamental requirement of first creating the global OSPFv3 process, so its absence does not prevent OSPFv3 from running.

The 'ipv6 unicast-routing' command must be enabled globally.

Why it fails: Although routing IPv6 traffic end-to-end requires 'ipv6 unicast-routing' to actually forward packets, the OSPFv3 routing protocol itself can operate independently of this global switch. On many modern IOS versions, IPv6 unicast routing is enabled by default, and even if it were disabled, OSPFv3 could still establish adjacencies and build its LSDB. The failure described in this scenario is specifically the lack of a router process, not a missing packet-forwarding capability.