Use EIGRP for IPv6 in large geographic IPv6 networks. EIGRP’s diameter can scale up to 255 hops, but this network diameter is not recommended. EIGRP authentication can be used instead of IPv6 authentication.
EIGRP for IPv6 can be used in site-to-site WANs and IPsec VPNs. In the enterprise campus, EIGRP can be used in data centers, server distribution, building distribution, and the network core.
EIGRP’s DUAL algorithm provides for fast convergence and routing loop prevention. EIGRP does not broadcast its routing table periodically, so there is no large network overhead. The only constraint is that EIGRP for IPv6 is restricted to Cisco routers.
EIGRP in the Data Center
When EIGRP is used in the data center (DC), several design considerations are important. Because DCs will have many different services, networks, and applications, you should design for summarizing data center subnets, just as you would do in wide-area networking. Furthermore, it is a good idea to advertise a default route into the DC from the aggregation layer. This way, you do not have to advertise all global network routes into the DC.
EIGRP for IPv6 Summary
The characteristics of EIGRP for IPv6 are as follows:
EIGRP for IPv6 uses the same characteristics and functions as EIGRP for IPv4.
- EIGRP for IPv6 is a hybrid routing protocol (a distance-vector protocol that has link-state protocol characteristics).
- EIGRP for IPv6 uses Next Header protocol 88.
- EIGRP for IPv6 routes IPv6 prefixes.
- The default composite metric uses bandwidth and delay.
- You can factor load and reliability into the metric.
- EIGRP for IPv6 sends partial route updates only when there are changes.
- EIGRP for IPv6 supports MD5 authentication.
- EIGRP for IPv6 uses DUAL for loop prevention and fast convergence.
- By default, EIGRP for IPv6 uses equal-cost load balancing. Unequal-cost load balancing is possible with the variance command.
- The administrative distances are 90 for EIGRP internal routes, 170 for EIGRP external routes, and 5 for EIGRP summary routes.
- EIGRP for IPv6 uses IPv6 multicast FF02::A for EIGRP updates.
- EIGRP for IPv6 enables high scalability and can be used in large networks.
A CCNP should understand EIGRP-specific characteristics and benefits. Table 3-10 provides a summary for reference.
Table 3-10 EIGRP Protocol Characteristics
| Characteristic | EIGRP Support |
| Distance vector or link state | Hybrid: distance-vector routing protocol with link-state characteristics |
| Convergence | Fastest convergence with DUAL for a loop-free topology |
| Classless or classful | Classless routing protocol, supports VLSM |
| Scalability | Highly scalable, supports large networks |
| Multiprotocol support | Supports IPv4, IPv6, and legacy protocols such as IPX and AppleTalk |
| Multicast address for updates | 224.0.0.10 for IPv4; FF02::A for IPv6 |