[dhcwg] Review of the draft-cui-dhc-dhcpv6-prefix-length-hint-issue-01
Marcin Siodelski <msiodelski@gmail.com> Tue, 03 November 2015 01:04 UTC
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From: Marcin Siodelski <msiodelski@gmail.com>
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Subject: [dhcwg] Review of the draft-cui-dhc-dhcpv6-prefix-length-hint-issue-01
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Hello, I have read the version -01 of the document. It is important to clarify the behavior of the requesting/delegating router behavior with respect to prefix-length hints. A couple of comments below. The document is structured in a way that makes it hard to match the issues with the solutions for them. For example: section 3.1 focuses on issues in handling prefix length hint in case of the Solicit. It doesn't provide a solution, though. The solution is provided in section 4.1, i.e. a couple of sections down the road. This makes me scroll back and forth to find out "how did they deal with this problem?". I'd suggest that the issue and the solution is provided in the same section. See how RFC7550 is structured. Abstract "DHCPv6 Prefix Delegation [RFC3633] allows a client to include a prefix-length hint value in the IA_PD option to indicate a preference for the size of the prefix to be delegated..." According to the terminology used in RFC3633, the "client" is referred to as "requesting router". Admittedly, when we merged the RFC3633 into the RFC3633 into RFC3315bis we unified the terminology and we also refer to the node having a function of requesting router as a client. However, since this document refers to the RFC3633, it would be better to use the original terminology in the abstract and then mention that further in this document whenever the "client" term is used it refers to the requesting router. On the other hand, if the document will not be incorporated into the RFC3315bis, perhaps it is simply better to stick to requesting router/delegating router terminology. 3.1. Creation of Solicit Message by the Client "The Solicit message allows a client to ask servers for addresses and configuration parameters." It is a bit odd that addresses are specifically mentioned in the context of this draft, which discusses the issues pertaining to prefix delegation. 4.1. Creation of Solicit Message by the Client " When the client wants the same prefix back from the server, it should include the prefix value in the "IPv6 prefix" field of the IA_PD Prefix option, and the length of the prefix in the "prefix-length" field. This is an indication to the server that the client wants the same prefix back." At this point there is a possibility that the lease that the client remembers and which it includes in the hint is not available anymore. Perhaps it has been allocated to another requesting router. Therefore the server considerations in 4.2. could be a bit more specific what to do in such case. The section 4.2. currently says that the server should try to provide a prefix of a specific length, regardless of the prefix recorded from previous interactions. In fact, if the requesting router is sending a non-zero prefix as a hint the server could try to allocate this prefix in the first place. If it is unavailable, it should use the prefix length hint and use that to allocate a different prefix. 4.3. Receipt of Advertise Message by the Client This text should be revised against the RFC7550. The text currently recommends that the client, unsatisfied with prefixes provided, should do Solicit but use the IA_NAs with available addresses. First of all, this section discusses Advertise message processing when the server hasn't committed addresses for the client, so technically the client can't use them until it does Request-Reply. Also, doing Request-Reply (and then Renew) for IA_NAs and Solicit for IA_PDs at the same time, requires two state machines on the client side. The RFC7550 solves those issues already by allowing to accept some bindings and continue requesting other bindings in the Renew/Rebind. This section should probably refer to RFC7550 to describe the case when the client doesn't get the prefixes it is satisfied with. 4.4. Creation of Renew/Rebind Message by the Client The client willing to obtain another prefix would typically include a different IA_PD (with different IAID). The IA_PD may contain no prefix option or it may contain a prefix option with a prefix-length hint. Again, see RFC7550. Using the same IA_PD to renew existing prefix and request another one is probably not a good idea. Marcin
- [dhcwg] Review of the draft-cui-dhc-dhcpv6-prefix… Marcin Siodelski
- Re: [dhcwg] Review of the draft-cui-dhc-dhcpv6-pr… tianxiang li