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Difficulty: HardIPv6 Static Routing

A Cisco router currently learns the active route to destination network 2001:DB8:ACAD:20::/642001:\text{DB8}:\text{ACAD}:20::/64 via OSPFv3 with an administrative distance of 110. An engineer must configure a backup floating static IPv6 route to this remote network. The backup path uses the next-hop router's link-local IPv6 address FE80::2\text{FE80}::2 through the local interface GigabitEthernet0/0/1\text{GigabitEthernet0/0/1}. Which command correctly configures this floating static IPv6 route on the Cisco IOS router?

  1. ipv6 route 2001:db8:acad:20::/64 GigabitEthernet0/0/1 fe80::2 120Answer
  2. B
    ipv6 route 2001:db8:acad:20::/64 fe80::2 120
  3. C
    ipv6 route 2001:db8:acad:20::/64 GigabitEthernet0/0/1 fe80::2 90
  4. D
    ipv6 route 2001:db8:acad:20::/64 GigabitEthernet0/0/1 fe80::2 110

Answer

The command 'ipv6 route 2001:db8:acad:20::/64 GigabitEthernet0/0/1 fe80::2 120' correctly configures the fully specified floating static IPv6 route.
The correct command fully specifies the exit interface alongside the link-local next-hop IPv6 address and sets an administrative distance of 120. In IPv6 static routing, specifying a link-local address as a next hop requires the local exit interface (GigabitEthernet0/0/1). Additionally, configuring an administrative distance greater than OSPFv3's default distance of 110 ensures the static route remains dormant in the routing table until the primary OSPFv3 route fails.

Step-by-Step Solution

1
Identify the requirements for using a link-local IPv6 address as a static route next hop.
Because link-local addresses (FE80::/10) are ambiguous without a scope, Cisco IOS requires fully specified static routes that include both the local exit interface and the link-local next-hop address.
Without the local interface parameter, the router cannot determine which outgoing interface to send traffic to reach the link-local neighbor.
2
Determine the necessary Administrative Distance (AD) for a floating static route.
The AD must be strictly greater than the AD of the primary routing protocol (OSPFv3 default AD is 110). An AD value of 120 is higher than 110.
A floating static route remains inactive in the routing table until the primary route with a lower administrative distance fails.
3
Assemble the complete Cisco IOS IPv6 static route command syntax.
The correct command format is 'ipv6 route <destination-prefix/mask> <exit-interface> <next-hop-link-local-address> <administrative-distance>'.
This guarantees correct forwarding interface binding and proper floating route administrative distance operation.

Key Concept

IPv6 Fully Specified Floating Static Route Configuration
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Topics

IPv6 Static Routing

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