200-301 Question #511: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. Which IPv6 configuration is required for R17 to successfully ping the WAN interface on R18? A. B. C. D.

Options

• AR17# ! no ip domain lookup ip cef ! interface FastEthernet0/0 no ip address duplex auto speed auto ipv6 address 2001:DB8:3::201/64 ! interface FastEthernet1/0 no ip address duplex auto speed auto ipv6 address 2001:DB8:2::201/64 ! no cdp log mismatch duplex ipv6 route 2001:DB8:4::/64 2001:DB8:5::101 !
• BR17# ! no ip domain lookup ip cef ipv6 unicast-routing ! interface FastEthernet0/0 no ip address duplex auto speed auto ipv6 address 2001:DB8:2::201/64 ! interface FastEthernet1/0 no ip address duplex auto speed auto ipv6 address 2001:DB8:3::201/64 ! no cdp log mismatch duplex ipv6 route 2001:DB8:4::/64 2001:DB8:3::301 !
• CR17# ! no ip domain lookup ip cef ipv6 cef ! interface FastEthernet0/0 no ip address duplex auto speed auto ipv6 address 2001:DB8:2::201/64 ! interface FastEthernet1/0 no ip address duplex auto speed auto ipv6 address 2001:DB8:3::201/64 ! no cdp log mismatch duplex ipv6 route 2001:DB8:4::/64 2001:DB8:4::302 !
• DR17# ! no ip domain lookup ip cef ipv6 unicast-routing ! interface FastEthernet0/0 no ip address duplex auto speed auto ipv6 address 2001:DB8:2::201/64 ! interface FastEthernet1/0 no ip address duplex auto speed auto ipv6 address 2001:DB8:3::201/64 ! no cdp log mismatch duplex ipv6 route 2001:DB8:4::/64 2001:DB8:2::201 !

Explanation

Option B is correct because it includes ipv6 unicast-routing (required on Cisco routers to forward IPv6 packets between interfaces), assigns the correct addresses to the right interfaces (Fa0/0 on 2001:DB8:2::/64, Fa1/0 on 2001:DB8:3::/64), and uses a valid next-hop address (2001:DB8:3::301) that resides on R17's directly connected Fa1/0 segment — pointing toward R18's WAN network (2001:DB8:4::/64).

Option A fails on two counts: it omits ipv6 unicast-routing entirely (so the router won't route IPv6 at all), and the static route's next-hop (2001:DB8:5::101) doesn't appear to be on any directly connected subnet.

Option C fails because ipv6 cef alone does not enable IPv6 routing — ipv6 unicast-routing is the required global command; additionally, the static route's next-hop (2001:DB8:4::302) is inside the destination network itself, which is invalid unless that network is directly connected.

Option D fails because the static route's next-hop (2001:DB8:2::201) is R17's own Fa0/0 address — a router cannot use its own interface as a next-hop for a remote destination, creating a routing loop.

Memory tip: On Cisco, think of ipv6 unicast-routing as the "master switch" — without it, your router is just an IPv6 host. Also remember: next-hop addresses must live on a directly connected segment, never in the destination network or on your own interfaces.

No community discussion yet for this question.