1. RFC 4477 DHCP: Dual-Stack Issues Speaker: Ching-Chen Chang Date:20070514

2. Outline Introduction Dual-Stack Issues Potential Solutions Conclusion

3. Introduction(1/2) A new DHCP specification for IPv6 has been designed and published as DHCPv6. In early IPv6 deployments, a dual-stack of operation is typically used. The document is about operating DHCP in a mixed IPv4 and IPv6 environment within a single administrative domain.

4. Introduction(2/2) In a dual-stack environment a node will need to obtain both IPv4 and IPv6 configuration settings 。  IPv4 address  IPv6 address  NTP server (Network Time server)  DNS server  NIS server (Network Information server)  DNS search path

5. Dual-Stack Issues(1/3) Handing Multiple Responses  Handling configuration information that may be gathered from multiple sources. Different Administrative Management  Ipv4 and Ipv6 services may not be administered by the same organization or people.  This poses the problems for consistency of data. Multiple Interfaces  Whether the settings are per interface or per node.

6. Dual-Stack Issues(2/3) DNS Load Balancing  Responses from different DHCP and DHCPv6 servers may take such configuration problematic, if the knowledge of the load balancing is not available to both servers. DNS Search Path Issues  Different protocol with different domain name.

7. Dual-Stack Issues(3/3) Protocol startup sequence  It may be possible that one protocol is shut down or started while the system is running. DHCP option variation  Some sites may choose to use IPv4–mapped addresses in DHCPv6-based options.

8. Potential Solutions(1/3) Separate DHCP Servers  Run DHCP and DHCPv6 servers.  The client could merge information received from both, or choose a version first.  The information could be generated from a single database instance supporting both DHCP and DHCPv6 protocols for consistency.  One possible solution is to have per-host preferences, or an ordered list of preferences.

9. Potential Solutions(2/3) Single DHCPv6 Servers  The use of both servers may also lead to some redundancy.  One solution may be to allow DHCP for IPv4 to be completely replaced by DHCPv6 with additional IPv4 information options, for dual-stack nodes.  Requiring the listing of a mix of IPv4 and IPv6 addresses for option.

10. Potential Solutions(3/3) Optimizing for failure with lists of addresses  Clients has no way to “try a different server”.  It’s easier to solve this in the combined-DHCP- server case than in the two-server case. Administrative and other areas  Whether separate manual configuration files

11. Conclusion The IETF dhc WG reached a strong consensus t o adopt the two0server approach, rather than a combined single server. Future work is required to determine best practice for merging information from multiple servers.