The revised version of draft-ietf-6man-node-req-bis-05.txt contains some new text related to DHC and the RA DNS config option.
In writing the text, I tried to provide more background and guidance regarding DHC vs. RAs. Like it or not, we have the problem today that we are a bit unclear in what our recomendations are to implementors. This has been made worse with 5006bis, as we will now have 2 ways of configuring the DNS. The reality is that both DHCP and SLAAC will be used for address configuration. That said, the choice of which to use is made by the network operator, not the end users. Right now, SLAAC seems to be the default preference for the majority of LANs. But there are also deployment scenarios where DHC is prefered. (Please, can we not debate whether this makes sense and just accept it as fact? - Thanks!) To summarize, the current document - retains SLAAC as a MUST - lists DHC (for address config) as a MAY - makes DHC for other configuration a SHOULD. - lists rfc5006bis (DNS RA Config) as a SHOULD Thoughts? I've included some of the relevant new text below Thomas Current text in document: 6. DHCP vs. Router Advertisement Options for Host Configuration In IPv6, there are two main protocol mechanisms for propagating configuration information to hosts: Router Advertisements and DHCP. Historically, RA options have been restricted to those deemed essential for basic network functioning and for which all nodes are configured with exactly the same information. Examples include the Prefix Information Options, the MTU option, etc. On the other hand, DHCP has generally been preferred for configuration of more general parameters and for parameters that may be client-specific. That said, identifying the exact line on when whether a particular option should be configured via DHCP vs an RA option has not always been easy. Generally speaking, however, there has been a desire to define only one mechanism for configuring a given option, rather than defining multiple (different) ways of configurating the same information. One issue with having multiple ways of configuring the same information is that if a host choses one mechanism, but the network operator chooses a different mechanism, interoperability suffers. For "closed" environments, where the network operator has significant influence over what devices connect to the network and thus what configuration mechanisms they support, the operator may be able to ensure that a particular mechanism is supported by all connected hosts. In more open environments, however, where arbitrary devices may connect (e.g., a WIFI hotspot), problems can arise. To maximize interoperability in such environments hosts may need to implement multiple configuration mechanisms to ensure interoperability. Originally in IPv6, configuring information about DNS servers was performed exclusively via DHCP. In 2007, an RA option was defined, but was published as Experimental [RFC5006]. In 2010, "IPv6 Router Advertisement Options for DNS Configuration" was placed on the Standards Track. Consequently, DNS configuration information can now be learned either through DHCP or through RAs. Hosts will need to decide which mechanism (or whether both) should be implemented. 7. DNS and DHCP ... 7.2. Dynamic Host Configuration Protocol for IPv6 (DHCPv6) - RFC 3315 7.2.1. Managed Address Configuration DHCP can be used to obtain and configure addresses. In general, a network may provide for the configuration of addresses through RAs, DHCP or both. At the present time, the configuration of stateless address autoconfiguraiton is more widely implemented in hosts than address configuration through DHCP. However, some environments may require the use of DHCP and may not support the configuration of addresses via RAs. Implementations should be aware of what operating environment their devices will be deployed. Hosts MAY implement address configuration via DHCP. In the absence of a router, IPv6 nodes using DHCP for address assignment MAY initiate DHCP to obtain IPv6 addresses and other configuration information, as described in Section 5.5.2 of [RFC4862]. 7.2.2. Other Configuration Information IPv6 nodes use DHCP to obtain additional (non-address) configuration. If a host implementation will support applications or other protocols that require configuration that is only available via DHCP, hosts SHOULD implement DHCP. For specialized devices on which no such configuration need is present, DHCP is not necessary. An IPv6 node can use the subset of DHCP (described in [RFC3736]) to obtain other configuration information. 7.2.3. Use of Router Advertisements in Managed Environments Nodes using the Dynamic Host Configuration Protocol for IPv6 (DHCPv6) are expected to determine their default router information and on- link prefix information from received Router Advertisements. 7.3. IPv6 Router Advertisement Options for DNS Configuration - RFC XXXX Router Advertisements have historically limited options to those that are critical to basic IPv6 functioning. Originally, DNS configuration was not included as an RA option and DHCP was the recommended way to obtain DNS configuration information. Over time, the thinking surrounding such an option has evolved. It is now generally recognized that few nodes can function adequately without having access to a working DNS resolver. RFC 5006 was published as an experimental document in 2007, and recently, a revised version was placed on the Standards Track [I-D.I-D.ietf-6man-dns-options-bis]. Implementations SHOULD implement the DNS RA option. -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
