One less reason to adopt IPv6?

Cisco, Microsoft promote DHCPv6 instead of autoconfiguration

"The idea with stateless address-configuration in IPv6 is that you plug a computer into your network, you plug a printer into your network and you can communicate," says Ted Lemon, a DHCP expert and developer for Nominum. "You don't have to set up any servers, and you don't have to manage any servers."

Autoconfiguration will be useful for teleworkers and small branch offices, too. "The classic scenario for autoconfiguration is the dentist's office," Lemon says. "Do you really want to hire an IT guy? That is what stateless address-configuration in IPv6 is for." IPv6's autoconfiguration "is a true advantage for handheld devices. That's where IPv6 gains over IPv4," the UNH-IOL's Winters says.

DHCPv6, on the other hand, provides stateful address-configuration. DHCPv6 servers pass out IP addresses and service information to clients, and both the server and the client retain this information to prevent address conflicts. DHCPv6 lets network managers know the devices connected to the network and their IP addresses. Corporate network managers have grown accustomed to this level of visibility into their networks because they use DHCP with their IPv4 networks. Backers of DHCPv6 say they'll want to keep this visibility into their IPv6 networks. "People want to know who is on their network, and DHCPv6 is the way to do it," Winters says. "IT people understand how DHCP works in IPv4, and the IPv6 version is not that different. It's easy for IT people to wrap their brains around DHCPv6 as opposed to autoconfiguration, which doesn't exist for IPv4."

DHCPv6 became a proposed IETF standard four years ago. It has all the features of DHCPv4, along with some capabilities that make it easier for network managers to renumber networks; that in turn should make it easier to merge networks or switch service providers.

Nominum's Lemon says network managers have a love/hate relationship with DHCP in IPv4 networks. They love it because it gives them control over their networks, but they hate having another network service to manage. "Network managers like the fact that they can assign IP addresses with DHCP, but it's more important that they can see what's on their network. It gives them information about how many devices are on the network and how much usage of the network there is," Lemon says. "It's almost like they have a finger on the pulse of their network if they use DHCP."

To complicate the situation further, there's also a stateless version of DHCPv6. With this feature, network managers can use stateless address-configuration to let clients get their own IPv6 addresses, but they can follow up with a DHCPv6 information request to gather network configuration information and to configure DNS or other servers.

"In low-overhead, low-management deployments, you might want to use this lightweight configuration of DHCPv6," says Ralph Droms, principal engineer with Cisco and one of the chairs of the IETF's Dynamic Host Configuration working group.

Nonetheless, many IPv6 experts now believe that corporations will stick with stateful address-allocation through DHCPv6. "For corporate users, stateless autoconfiguration is not a good selling point for IPv6," Lemon admits. "I think it's a valid selling point for ISPs. If you're a large ISP, stateless autoconfiguration on the customer network is a really good thing because it means you're going to get fewer phone calls. But I think corporate IT departments are going to want the level of information they get out of DHCP."

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Carolyn Duffy Marsan

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