300-410 ENARSI: Implementing Cisco Enterprise Advanced Routing and ServicesDemo

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QuestionQ472

Infrastructure Security

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Refer to the exhibit. An engineer configured and connected Router2 to Router1. The link came up, but Router2 could not establish a Telnet connection to Router1’s IPv6 address, 2001:DB8::1.

Which configuration enables Router2 to establish a Telnet connection to Router1?

  • A ipv6 unicast-routing
  • B permit ICMPv6 on access list INGRESS for Router2 to obtain IPv6 address
  • C permit ip any any on access list EGRESS2 on Router1
  • D IPv6 address on GigabitEthernet0/0
Explanation

Router2's GigabitEthernet0/0 has no static IPv6 address - it relies on 'ipv6 address autoconfig' (SLAAC). Autoconfig can only work if Router2 receives Router Advertisements from Router1, but those RAs are sourced from a link-local (FE80::) address and are dropped by Router2's inbound INGRESS filter (which only permits sources in 2001:DB8::/64), so Router2 never obtains an address in the 2001:DB8::/64 subnet and cannot reach 2001:DB8::1. The reliable, lab-verified fix is to configure a static IPv6 address on GigabitEthernet0/0 (choice D); Router2 then has a directly connected address in the same /64 and can Telnet Router1 immediately, and the INGRESS list already permits the 2001:DB8::/64 return traffic. Option C (EGRESS2) is an IPv4-only ACL and irrelevant to IPv6; option A alone would not help because the RA would still be blocked by INGRESS. This item is debated between B (permit ICMPv6) and D, but D deterministically resolves it.

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