Hi Jari, I think we are converging here as well. If there are no other comments, we will update the draft based on your review. See below:
On Sep 2, 2011, at 2:40 PM, Jari Arkko wrote: > Jonathan, > > Please see below. I think we are converging. The main remaining discussion > item below is the description of what the border router does. > >>> > Here are my comments in more detail: >>> > >>> >> Datagrams being forwarded within a RPL domain MUST include a RPL >>> >> Option. For datagrams sourced within a RPL domain, the RPL Option >>> >> MAHui,Y be included in the datagram itself. >>> > >>> > I'm not sure I understand the difference or its motivation. Do you really >>> > mean that a packet might not have the option until it hits the first >>> > router? Or are you just talking about something that happens internally >>> > on a host, but on the wire all packets would still have the option? Also, >>> > since the tunnel (or something else) is used to include the option for >>> > datagrams sourced outside the RPL domain, wouldn't it be easier to just >>> > say this: >>> > >>> > "Datagrams sent between nodes within an RPL domain MUST include an RPL >>> > Option." >>> >>> Agree. >>> > > OK I spoke too quickly on the comment above. In fact, the RPL Option is not required when a RPL Source Route Header exists. With SRH, there is no potential for loops, so the RPL Option is not required. How about the following text? "Datagrams sent between nodes within a RPL domain MUST include a RPL Option or RPL Source Route Header. Datagrams MAY include both a RPL Option and a RPL Source Route Header." >>> >> For datagrams sourced >>> >> outside a RPL domain, IPv6-in-IPv6 tunneling, as specified in >>> >> [RFC2473 <http://tools.ietf.org/html/rfc2473>] SHOULD be used to >>> >> include a RPL Option. >>> > >>> > This text should be aligned with whatever conclusion we will have for the >>> > issue that I raised with the other document. >>> >>> Agree. See my response to your other review. >>> > > OK > >>> >>> >> To help avoid IP-layer fragmentation, the RPL Option has a maximum >>> >> size of RPL_OPTION_MAX_SIZE octets and links within a RPL domain >>> >> SHOULD have a MTU of at least 1280 + 44 (outer IP header, Hop-by-Hop >>> >> Option header, Option header) + RPL_OPTION_MAX_SIZE + (additional >>> >> extension headers or options needed within RPL domain). >>> >> >>> > >>> > There's a same MTU issue here as in the other document. >>> >>> Agree. See my response to your other review. >>> > > I have a text suggestion on the other thread now., We will add the suggested text in the next revision. >>> >> The action taken by using the RPL Option and the potential set of >>> >> sub-TLVs carried within the RPL Option MUST be specified by the RFC >>> >> of the protocol that use that option. No TLVs are defined in this >>> >> document. >>> >> >>> > >>> > I think you should define the behavior when a node encounters a sub-TLV >>> > that it does not recognize. E.g., ignore and move on to the next sub-TLV. >>> > Or do you want a stricter policy? In any case, for future extensions it >>> > will be necessary to know how they are treated by legacy RPL nodes. >>> >>> Yes, we need to define the behavior. I'm comfortable with specifying an >>> skip-over-and-continue policy for unknown sub-TLVs. >>> > > OK > >>> >> In very specific cases, IPv6-in-IPv6 tunneling may be undesirable due >>> >> to the added cost and complexity required to process and carry a >>> >> datagram with two IPv6 headers. [I-D.hui-6man-rpl-headers >>> >> <http://tools.ietf.org/html/draft-ietf-6man-rpl-option-03#ref-I-D.hui-6man-rpl-headers>] >>> >> describes >>> >> how to avoid using IPv6-in-IPv6 tunneling in such specific cases and >>> >> the risks involved. >>> >> >>> > >>> > Again, the same comments as in the other draft. Please delete this >>> > paragraph. >>> >>> Agree. >>> > > OK > > >>> >>> >> For datagrams exiting the RPL domain, RPL Border Routers MUST remove >>> >> the RPL Option from the datagram. If the RPL Option was included >>> >> using tunneled mode and the RPL Border Router serves as the tunnel >>> >> end-point, removing the outer IPv6 header serves to remove the RPL >>> >> Option as well. Otherwise, the RPL Border Router assumes that the >>> >> RPL Option was included using transport mode and MUST remove the RPL >>> >> Option from the IPv6 Hop-by-Hop Option header. >>> >> >>> > >>> > The part about removing the RPL option even in a non-tunneled case >>> > relates to the issue of supporting that particular mode of operation. >>> > >>> > But in addition, I wonder if you should write the above text not in terms >>> > of packet modification operations but rather in terms of forwarding >>> > decision outcomes. Like this, for instance: >>> > >>> > "For datagrams destined to the RPL Border Router the router processes the >>> > packet in the usual way. For instance, if the RPL Option was included >>> > using tunneled mode and the RPL Border Router serves as the tunnel >>> > end-point, the router removes the outer IPv6 header, at the same removing >>> > the RPL Option as well. Datagrams destined elsewhere within the same RPL >>> > domain are forwarded to the right interface. Datagrams destined outside >>> > the RPL domain are dropped." >>> >>> The intent was to allow operation where a device within the RPL domain >>> could source a packet destined outside the RPL domain and not use >>> tunneling. In this case, we would like to simply remove the option at the >>> border router rather than drop the packet. Do you see cases where removing >>> the option is unacceptable? >>> > > I don't know. > > But maybe it doesn't matter. If we don't have other alternative > encapsulations than tunneling, the point is moot. And I'm not sure we do. The > two drafts really only describe the tunneling case. Even if you source a > packet from an RPL domain and want to send it to an outside destination, > you'll still have to use both the routing header and the option, no? I agree. As mentioned above, if the packet already includes a RPL routing header, it does not also need to include the RPL option. >>> >> 6. Usage of the RPL Option >>> >> >>> >> The RPL Option is only for use within a RPL domain. RPL routers MUST >>> >> process and include the RPL Option when forwarding datagrams to other >>> >> nodes within the RPL domain. Routers on the edge of a RPL domain >>> >> MUST remove the RPL Option when forwarding datagrams to nodes outside >>> >> the RPL domain. >>> > >>> > What is it that this section says that is not already covered by sections >>> > 2 and 5: >>> > >>> > Sect 2: Datagrams being forwarded within a RPL domain MUST include a RPL >>> > Option. >>> > >>> > Sect 5: ... serves as the tunnel end-point, removing the outer IPv6 >>> > header serves to remove the RPL Option as well. Otherwise, the RPL >>> > Border Router assumes that the RPL Option was included using transport >>> > mode and MUST remove the RPL Option from the IPv6 Hop-by-Hop Option >>> > header. >>> >>> Agree. Will remove the redundant text. >>> > > OK > >>> >>> >> This option may be used to mount several potential attacks since >>> >> routers may be flooded by bogus datagram containing the RPL option. >>> >> It is thus RECOMMENDED for routers to implement a rate limiter for >>> >> datagrams using the RPL Option. >>> > >>> > Please open this up a bit. What specific danger does flooding by bogus >>> > datagrams and RPL options cause? What would be the default settings for >>> > the rate limiter? >>> >>> The option contains information that can affect the operation of RPL. For >>> example, an inconsistent Rank value can cause a RPL router to reset its >>> trickle timer. >>> >>> After some careful thought, I'm not sure specifying a default setting for a >>> rate limiter is the best approach. Determining what is acceptable vs. >>> unacceptable can vary greatly between different deployments and >>> environments. But rather than rate limiting, how about the following: >>> >>> This option may be used to mount several potential attacks since >>> routers may be flooded by bogus datagrams containing the RPL >>> option. In particular, an inconsistent Rank value can cause a RPL >>> router to reset its DIO Trickle timer. Thus, it is RECOMMENDED >>> that a RPL router monitor triggers caused by receiving a RPL >>> option and log conditions when the average rate is higher than >>> expected. >>> > > I like your description of the problem. But given the possibility of some DIO > timer issues, wouldn't it be prudent to actually have some kind of rate > limiting? Maybe not rate limiting of packets with this option, but rate > limiting of packets causing a trigger to happen? How about the following text? "In order to avoid any unacceptable impact on network operations, an implementation MAY allow a limit to be placed on the number of triggers caused by receiving a RPL option, and MAY allow a limit to be placed on the rate of messages sent by a specific neighbor. It MAY also allow logging an error or sending a notification when a rate threshold is reached." >>> >>> >> Opt Data Len: 8-bit field indicating the length of the option, in >>> >> octets, excluding the Option Type and Opt Data Len fields. >>> >> >>> >> Down 'O': 1-bit flag as defined in Section 11 of >>> >> [I-D.ietf-roll-rpl >>> >> <http://tools.ietf.org/html/draft-ietf-6man-rpl-option-03#ref-I-D.ietf-roll-rpl>]. >>> >> >>> >> Rank-Error 'R': 1-bit flag as defined in Section 11 of >>> >> [I-D.ietf-roll-rpl >>> >> <http://tools.ietf.org/html/draft-ietf-6man-rpl-option-03#ref-I-D.ietf-roll-rpl>]. >>> >> >>> >> Forwarding-Error 'F': 1-bit flag as defined in Section 11 of >>> >> [I-D.ietf-roll-rpl >>> >> <http://tools.ietf.org/html/draft-ietf-6man-rpl-option-03#ref-I-D.ietf-roll-rpl>]. >>> >> >>> >> RPLInstanceID: 8-bit field as defined in Section 11 of >>> >> [I-D.ietf-roll-rpl >>> >> <http://tools.ietf.org/html/draft-ietf-6man-rpl-option-03#ref-I-D.ietf-roll-rpl>]. >>> >> >>> >> SenderRank: 16-bit field as defined in Section 11 of >>> >> [I-D.ietf-roll-rpl >>> >> <http://tools.ietf.org/html/draft-ietf-6man-rpl-option-03#ref-I-D.ietf-roll-rpl>]. >>> >> >>> >> Values within the RPL Option are expected to change en-route. >>> > >>> > This specification needs to describe what the behavior of a router is >>> > with the content of the option. I think this is easy, you should just add >>> > to the end: "The processing shall follow the rules described in Section >>> > 11.2 of [roll-rpl]. >>> >>> Agree. >>> >>> > As an aside, the entire Section 11 is marked in roll-rpl as >>> > non-normative. I don't think that's actually right as far as 11.2 goes, >>> > because it contains tons of MUSTs and SHOULDs. Perhaps you want to fix >>> > that in AUTH48... >>> >>> Right. >>> > OK Thanks. -- Jonathan Hui -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
