A network administrator is configuring a dual-stack router to support both IPv4 and IPv6 routing. The router is running EIGRP for IPv4 (AS 100) and needs to advertise its directly connected IPv6 networks into EIGRP for IPv6. Which EIGRP configuration mode and command sequence are required to enable EIGRP for IPv6 on an interface and advertise its network?
- Arouter eigrp 100 eigrp router-id 1.1.1.1 address-family ipv6 unicast eigrp router-id 1.1.1.1 network 2001:DB8::/64
- Binterface GigabitEthernet0/0 ipv6 address 2001:DB8::1/64 ipv6 eigrp 100
- Cipv6 router eigrp 100 router-id 1.1.1.1 address-family ipv6 unicast autonomous-system 100 network 2001:DB8::/64
- Drouter eigrp 100 network 192.168.1.0 0.0.0.255 ipv6 router eigrp 100 network 2001:DB8::/64
Show answer & explanationAnswer & explanation
Correct answer: B. interface GigabitEthernet0/0 ipv6 address 2001:DB8::1/64 ipv6 eigrp 100
For EIGRP for IPv6 in Cisco IOS, the routing process (`ipv6 router eigrp <AS>`) is enabled globally, and then EIGRP for IPv6 is enabled directly on the interfaces using `ipv6 eigrp <AS>`. The `network` command under the EIGRP process is not typically used for IPv6; instead, interfaces are explicitly activated. Option B correctly shows enabling EIGRP for IPv6 on a specific interface after the global process is assumed to be configured.
Why the other options are wrong
- A. This uses the `address-family` configuration which is common in newer IOS versions, but the `network` command within `address-family ipv6 unicast` is not the primary way to activate interfaces for EIGRP for IPv6; typically, it's done at the interface level.
- C. This also uses the `address-family` approach and attempts to use a `network` command, but the direct interface command is more common for initial activation and advertisement of connected IPv6 networks in many EIGRPv6 deployments.
- D. This mixes IPv4 and IPv6 network commands incorrectly and uses `network` for IPv6, which is not the standard EIGRPv6 interface activation method.
EIGRP for IPv6 Interface Activation
To enable EIGRP for IPv6 on a Cisco router interface, the `ipv6 eigrp <AS>` command is configured directly under the interface configuration mode.
- Requires `ipv6 unicast-routing` enabled globally.
- `ipv6 router eigrp <AS>` defines the EIGRPv6 process.
- `ipv6 eigrp <AS>` directly activates EIGRPv6 on the interface.
Memory trick: To plug IPv6 into EIGRP, flip the switch directly on the interface.