Table 2-13 summarizes the advantages and disadvantages of the IPv6 deployment models.
Table 2-13 IPv6 Deployment Model Comparison
| IPv6 Deployment Model | Advantages | Disadvantages |
| Dual-stack model | Tunneling not required. | Network equipment upgrades. |
| Better processing performance. | ||
| IPv4 and IPv6 independent routing, QoS, security, and multicast policies. | ||
| Hybrid model with ISATAP tunnel | Existing network can be leveraged with no upgrades. | IPv6 multicast not supported within ISATAP tunnels. |
| Terminating ISATAP tunnels in the core makes the core appear to be in IPv6 access layer. | ||
| Hybrid model with manually configured tunnels | IPv4 and IPv6 have independent routing, QoS, security, and multicast policies. | Many static tunnels, which makes it difficult to manage. |
| Server block model | Lesser impact on existing network. | Large amounts of tunneling. |
| Flexible when controlling access to IPv6-enabled applications. | Cost of additional equipment. |
Table 2-14 provides simple descriptions of the deployment models. Study this table for the ENSLD 300-420 exam.
Table 2-14 IPv6 Deployment Models
| Model | Description |
| Dual-stack model | All routers and hosts run IPv6 and IPv4. |
| Hybrid model | Uses ISATAP or manually configured tunnels to allow dual-stack clients to connect to dual-stack servers over an IPv4 core. |
| Service block model | Uses ISATAP and manually configured tunnels to a service module. |
IPv6 Comparison with IPv4
This section provides a summary comparison of IPv6 to IPv4. For the ENSLD 300-420 exam, you should be knowledgeable about the characteristics summarized in Table 2-15. Some of the main differences are the use of 128 bits over 32 bits; the use of the Next Header field in IPv6 instead of the Protocol Type field used in IPv4; and the replacement of ARP with IPv6 ND.
Table 2-15 IPv6 and IPv4 Characteristics
| Characteristic | IPv6 | IPv4 |
| Address length | 128 bits | 32 bits |
| Address representation | Hexadecimal | Dotted decimal |
| Header length | Fixed (40 bytes) | Variable |
| Upper-layer protocols | Next Header field | Protocol Type field |
| Link address resolution | ND | ARP |
| Address configuration | SLAAC or stateful DHCP | Stateful DHCP |
| DNS (name-to-address resolution) | AAAA records | A records |
| Interior routing protocols | EIGRPv6, OSPFv3, RIPng, IS-IS for IPv6 | EIGRP, OSPFv2, RIPv2, IS-IS |
| Classification and marking | Traffic Class and Flow Label fields, Differentiated Services Code Point (DSCP) | IP Precedence bits, Type of Service field, DSCP |
| Private addresses | Unique local addresses | RFC 1918 private address space |
| Fragmentation | Sending host only | Sending host and intermediate routers |
| Loopback address | 0:0:0:0:0:0:0:1 | 127.0.0.1 |
| Address scope types | Unicast, anycast, multicast | Unicast, multicast, broadcast |