One less reason to adopt IPv6?

Cisco, Microsoft promote DHCPv6 instead of autoconfiguration

For a decade, IPv6 proponents have pushed this upgrade to the Internet's main communications protocol because of its three primary benefits: a gargantuan address space, end-to-end security, and easier network administration through automatic device configuration.

Now it turns out that one of these IPv6 benefits -- autoconfiguration -- may not be such a boon for corporate network managers. A growing number of IPv6 experts say that corporations probably will skip autoconfiguration and instead stick with DHCP, which has been updated to support IPv6.

Autoconfiguration vs. DHCPv6 has become a point of contention among IPv6 proponents. As recently as last month, the IETF -- the standards body that created IPv6 and DHCPv6 -- held a lively online debate about rethinking autoconfiguration in light of DHCPv6.

"This is a widely discussed issue. Which is better: DHCPv6 or autoconfiguration?" says Timothy Winters, software engineering manager at the University of New Hampshire's Inter Operability Lab. The UNH-IOL operates Moonv6, the world's largest IPv6 test bed.

Winters sees the commercial software industry starting to back DHCPv6 because of the additional controls and tracking and debugging features it provides. "Moonv6 tried to run DHCPv6 testing two and a half years ago, and we only had two or three companies that did servers and software," he says. "A year later, we had 14 companies...We've definitely seen the DHCPv6 implementations explode."

The biggest backer of DHCPv6 is Cisco, which has supported DHCPv6 in its IOS since 2003, and also supports it in Cisco Network Register (CNR). The company says the next version of CNR, expected out by early 2008, will feature parity between DHCPv4 and DHCPv6. "From a security standpoint and for information assurance, network managers all still want visibility into their networks," says Dave West, director of field operations for Cisco's Federal Center of Excellence. "We believe the demand is going to be there for DHCPv6."

Microsoft is starting to support DHCPv6, too. Microsoft Vista's IPv6 implementation supports DHCPv6, although its earlier IPv6 support in Windows XP did not. Microsoft says Windows Server 2008 will support DHCPv6 as well.

On the other side of the debate are such DNS and DHCP appliance vendors as Infoblox, BlueCat Networks and InfoWeapons, which aren't supporting DHCPv6 yet. (InfoWeapons says it will support stateless and stateful DHCPv6 autoconfiguration in a new version of its SolidDNS product that's expected out this month.) "We have not seen a tremendous amount of demand for DHCPv6," says Cricket Liu, vice president of architecture at Infoblox. "We don't see a ton of companies champing at the bit to implement IPv6. And where they will be prodded to because [the American Registry for Internet Numbers] starts issuing only IPv6 addresses, they'll use IPv6 externally and they'll still use network address translation internally. So we don't see an opportunity for DHCPv6."

Autoconfiguration vs. DHCPv6

IPv6 addresses are 128 bits long, compared to IPv4's 32-bit addresses. Because they're so large, these addresses will be difficult for network administrators to memorize and type into applications. That's why it's important how network managers assign and manage IPv6 addresses.

With IPv6, network managers can choose between the stateless address-autoconfiguration built into IPv6 and stateful address configuration using DHCPv6.

IPv6's default mode is stateless address-autoconfiguration, which is supposed to provide true plug-and-play connectivity for network devices. With autoconfiguration, a device automatically receives an IP address and doesn't need to contact a server for one. This is made possible through several features of IPv6 including router advertisements, neighbor discovery and duplicate-address detection. The autoconfiguration approach is easier for network managers and less taxing for the network, backers say. That's why it's likely to be used for mobile devices and home networks.

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Carolyn Duffy Marsan

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