[netext] Review of draft-ietf-netext-pd-pmip-01.txt
Carlos Jesús Bernardos Cano <cjbc@it.uc3m.es> Tue, 28 February 2012 18:51 UTC
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From: Carlos Jesús Bernardos Cano <cjbc@it.uc3m.es>
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Date: Tue, 28 Feb 2012 19:51:34 +0100
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Subject: [netext] Review of draft-ietf-netext-pd-pmip-01.txt
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Hi, As promised in the last meeting, I've reviewed draft-ietf-netext-pd-pmip-01.txt. Here are my comments: - I think the goals of the document should be more clear, as 3 different concepts are involved: DHCPv6 Prefix Delegation, Proxy Mobile IPv6 and NEMO. Actually, I think this is not an easy problem to solve, because the scenario described in the document is not really a NEMO one (I'll explain this better below). - The abstract says: "This document specifies an extension to Proxy Mobile IPv6 protocol for supporting network mobility using DHCPv6-based Prefix Delegation.". This is not very aligned with the title of the document, which seems to suggest that the document just specifies how to delegate prefixes using DHCPv6 in PMIPv6 (but in reality the document does more than this). - The abstract also says: "DHCPv6 Prefix Delegation can be used to assign a prefix or prefixes to a mobile router for use on the links in the mobile network as specified in [RFC6276] but not supported in Proxy Mobile IPv6.". RFC6276 is for use with the Network Mobility Basic Support protocol (RFC 3963), but the draft does not consider NEMO at all, as what is called "Mobile Router" does not have any IP mobility support at all. Therefore, any link between RC3963/RFC6275 and the draft may lead to confusion, IMHO. - In the Introduction (and in the rest of the document), the term Mobile Router (MR) is used, though it is not accurate, as RFC3963 tends to implicitly assume that an MR implements the NEMO BS protocol (e.g., "A Mobile Router has a unique Home Address through which it is reachable when it is registered with its Home Agent."). However, in the draft, it is mentioned that "The specification assumes that a MR is a regular IPv6 router without extension for mobility managements.", so I think it's better not to call this "router" MR. - I'd rewrite the Introduction to make the problem scope clearer. I needed to read the whole document to get the full picture (it was not clear to me when I was reading the intro). - I'd avoid using normative text (like MUST) in the intro. - In Section 3.1, the document starts mixing the terms MN and MR, which again, is a source of potential misunderstandings. For example, it says "The MR (as a RR) MUST either obtain the Home Network Prefix (HNP) before initiating the DHCPv6-PD procedure or in case of stateful address configuration simultaneously while configuring the Mobile Node Home Address (MN-HoA)." - I don't see why the MR should support the Prefix Exclude Option. - In Section 3.2: "If the network mobility service needs to be offered to the mobile node, the mobile access gateway MUST set the Mobile Router Flag (R) when sending the Proxy Binding Update (PBU) message to the LMA.". I think this cannot be done, as RFC3963 states that "The Mobile Router Flag is set to indicate to the Home Agent that the Binding Update is from a Mobile Router.". Therefore, if the "R" bit is set, that means that the (P)BU is sent by an MR implementing RFC3963 (which is not the case here), unless this draft is updating RFC3963. - In Section 3.3.1, the terms "MN" and "MR" are again mixed, which makes it complex to follow. - Another, IMHO, source of potential misleading, is the use of the MNP option, which again is tightly related to the RFC3963. Not sure if it'd be good to define a new option for this. For example, the HNP and MNP options are exactly the same format-wise, but we have two different options (types) because it is better not to overload too much them. - In Section 3.4.2, it says: "On receiving a packet from the bi-directional tunnel established with the MR's LMA, the MAG MUST use the destination address of the inner packet to forward it on the interface where the destination MNP is hosted." --> does this mean that the packet is not decapsulated and then routed, but routed based on the inner packet destination address? If so, this seems very weird to me. I guess the tunnel ends at the MAG, like in regular PMIPv6 for a host. In that case, I'd say that some additional text about forwarding considerations on the MAG is missing (e.g., the MAG has to add a route for the "MNP" via the "MR"). - In Section 3.5.2, it says: "In order to receive those packets, the LMA MUST advertise a connected route into the routing infrastructure for the MR's MNP(s).". I guess the "advertisement" is not really mandatory (no need of using MUST there), as what is required is that the LMA anchores the prefix, right? - I'd say that the Security Considerations section may benefit from additional text. I have not thought of that carefully, but at least some examples of the SPD and SAD entries used to protect the signaling could be helpful (e.g., as used in RFC6276). This is just a first batch of comments. I think the document needs an update and further revisions. Regarding the document's scope, I think it's very important to make it clear. For example, as it is now, a rader could think that this document addresses the problem I tried to describe in draft-bernardos-netext-pmipv6-nemo-ps-01, but this is not the case. While writing that draft I learned/suffered myself how difficult is to clearly explain the problem. In case it is not clear, I'm supportive of the problem described in draft-ietf-netext-pd-pmip-01. I'm just trying to help here, so don't take my comments as negative ones. Thanks, Carlos -- Carlos Jesús Bernardos Cano http://www.netcom.it.uc3m.es/ GPG FP: D29B 0A6A 639A A561 93CA 4D55 35DC BA4D D170 4F67
- [netext] Review of draft-ietf-netext-pd-pmip-01.t… Carlos Jesús Bernardos Cano
- Re: [netext] Review of draft-ietf-netext-pd-pmip-… Alexandru Petrescu