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Difficulty: Very hardIPv6 Static Routing

A network engineer must configure path redundancy on a Cisco IOS router for reaching the remote IPv6 prefix 2001:db8:4000:50::/642001:\text{db8}:4000:50::/64. The primary path must forward packets through interface GigabitEthernet0/0/1 using the next-hop router's link-local IPv6 address fe80::2\text{fe80}::2. The secondary backup path must forward packets toward the global unicast next-hop IPv6 address 2001:db8:1000:20::22001:\text{db8}:1000:20::2 only if the primary path fails. Which TWO Cisco IOS commands are required to satisfy these requirements?

  1. ipv6 route 2001:db8:4000:50::/64 GigabitEthernet0/0/1 fe80::2Answer
  2. ipv6 route 2001:db8:4000:50::/64 2001:db8:1000:20::2 130Answer
  3. C
    ipv6 route 2001:db8:4000:50::/64 fe80::2
  4. D
    ipv6 route 2001:db8:4000:50::/64 GigabitEthernet0/0/2 2001:db8:1000:20::2

Answer

The correct configuration requires both the command specifying the local exit interface alongside the link-local next-hop address ('ipv6 route 2001:db8:4000:50::/64 GigabitEthernet0/0/1 fe80::2') and the command defining a higher administrative distance for the backup route ('ipv6 route 2001:db8:4000:50::/64 2001:db8:1000:20::2 130').
The combination of using a fully-specified route syntax for link-local next-hops ('GigabitEthernet0/0/1 fe80::2') and appending an elevated Administrative Distance of 130 for the global unicast backup path ensures that link-local scoping syntax rules are respected and that the backup route remains floating until primary path failure.

Step-by-Step Solution

1
Analyze link-local IPv6 static routing requirements.
Link-local addresses (fe80::/10) are only unique per link. Cisco IOS cannot determine which interface to send traffic through if only a link-local next-hop address is provided. Therefore, the exit interface MUST be specified when using a link-local next-hop.
Ensures proper outgoing interface binding for link-scoped IPv6 destinations.
2
Analyze floating static route AD requirements.
To configure a floating static route as a secondary backup path, an Administrative Distance (AD) higher than default static routes (AD 1) must be explicitly appended to the command (e.g., AD 130).
Prevents the secondary route from populating the IPv6 routing table while the primary route is active.

Key Concept

IPv6 Static Route Syntax & Floating Static Administrative Distance
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Topics

IPv6 Static Routing

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