Hi Ben, Thanks for the follow up. Please see answers inline. Regards, Ahmad
> -----Original Message----- > From: Ben Campbell [mailto:b...@estacado.net] > Subject: Re: Gen-ART LC and Telechat Review of > draft-ietf-mext-binding-revocation-10 > > This is a followup on revision 12, since it came out before I > got to revision 11: > > Overall, I think this revision is much better. Most of my > concerns have been addressed, but I have a few minor ones remaining. > > Specific comments: > > > -- Section 10.1, 2nd bullet: > > I don't think we resolved my concern about the SHOULD in the > last sentence. To recap, I think that needs to either be a > MUST, or the draft should offer guidance about the reasoning > for the SHOULD and the consequences of not following it. I'm > picking on this one in particular because it seems like not > sending a BRA when the A bit was set is likely to cause > retransmissions on the part of the initiator. [Ahmad] If the MN does NOT have a binding in its BUL for the HoA address that is included in the Type 2 Routing header, the mobile node should not respond back (that was specifically discussed in details on the wg ml). It is like instructing the MN to delete a session that does not exist. Although, the (A) bit is set, it is up to the mobile node whether to send a BRA or not. I do not believe we need to mandate that via a MUST. I am sure some handset vendors will not like that at all. > > Also, the last sentence does not seem to make grammatical > sense after the edits. Thx, here is the new text, please let me know if you are okay with it. o If the Acknowledge (A) bit is set in the Binding Revocation Indication and its Binding Update List contains an entry for the IP address in the Type 2 routing header, the mobile node MUST send a Binding Revocation Acknowledgement. However, in all other cases when the Acknowledge (A) bit is set in the BRI, the mobile node SHOULD sends a Binding Revocation Acknowledgement following Section 10.2. > > -- Same section, 4th bullet: > > This one still seems to ignore the A bit value. Given the > other edits, am I correct in assuming that you expect a BRA > if the A bit was set, otherwise a silent discard? [Ahmad] I believe we discussed this a little before. It is a fatal error and the MN should never receive a BRI with the (P) bit set. That why this behavior is the same regardless of the (A) bit is set or not. If you feel that some clarification about the (A) bit needs to be added, I can say, ...... regardless if the Acknowledge (A) bit is set or not, the mobile node MUST silently discard the BRI message. > > -- Section 11, (InitMINDelayBRIs) (I think I commented on > this, but can't find the resolution) > > Did you intend for the _default_ to be a range (between .5 > and 1 sec), or did you mean to say the default was 1 second, > and it must not be configured to less than .5 seconds? I > suspect the latter, but it's not clear from the text. [Ahmad] Sure, will fix this as follows: Initial Minimum Delay Between BRI messages (InitMINDelayBRIs) This variable specifies the initial delay timeout in seconds before the revoking mobility entity retransmits a BRI message. The default is 1 second but not to be configured less than 0.5 seconds. > > -- Security Considerations: > > I think there is enough potential for confusion about when > IPSec is required to put some non-normative description of > when it is and isn't required, along with references to the > normative requirements. > [Ahmad] I suppose this is just a comment that does not need clarification or anything like that. Thanks again Ben for your review and comments! > > Thanks! > > Ben. > > > > > > On Sep 5, 2009, at 3:04 AM, Ahmad Muhanna wrote: > > > Hello, > > > > We have updated the draft to address all comments. > > A URL for this Internet-Draft is: > > > http://www.ietf.org/internet-drafts/draft-ietf-mext-binding-revocation > > -1 > > 1.txt > > > > > > In summary, here is a list of the major changes: > > > > 1. Enhanced to the security text mainly under section 6.1. > and section > > 13 (Security Considerations) to address Ben comments. In > addition, we > > eliminated the Security Model section based on Ralph's comment. > > > > 2. Enhanced the text for MAG authorization and defined a default > > mechanism as specified under section 13, Security Considerations. > > > > 3. Addressed Pasi's comments by adding text to clearly specify that > > the current specification uses mobile node identifier > option, MN-ID, > > with subtype 1, as stated mainly under section 5.1. In addition, we > > defined the format of "wild card" NAI as per the use of this > > specification, text under section 8.1.1. > > > > 4. Addressed all the remaining of Ralph's detailed comments > in several > > places of the document. > > > > 5. Clarified that the responder sends BRA only if the > Acknowledge (A) > > bit is set. Text was tweaked in several places. > > > > 6. all nits and editorial comments.... > > > > Please let me know if you still have any issue. > > > > Thanks for all of your comments and help! > > > > Regards, > > Ahmad > > > > > >> -----Original Message----- > >> From: Muhanna, Ahmad (RICH1:2H10) > >> Sent: Thursday, August 27, 2009 1:33 PM > >> To: 'Ben Campbell' > >> Cc: Khalil, Mohamed (RICH2:2S20); sgund...@cisco.com; > >> kchowdh...@starentnetworks.com; pyeg...@juniper.net; General Area > >> Review Team; ietf@ietf.org; Jari Arkko; > marc...@it.uc3m.es; Laganier, > >> Julien > >> Subject: RE: [PART-I] Gen-ART LC and Telechat Review of > >> draft-ietf-mext-binding-revocation-10 > >> > >> Hi, Ben, > >> > >>>> > >>>>> -----Original Message----- > >>>>> > >>>>> Summary: This draft is on the right track, but there are > >>> open issues. > >>>>> Additionally, I have a number of editorial comments. > >>>>> > >>>>> Major issues: > >>>>> > >>>>> -- I think the security considerations need quite a bit of > >>> work. In > >>>>> particular, there is very little guidance on authorization for > >>>>> sending BRI messages. This seem to me have utility for DoS > >>> attacks, > >>>>> particularly with the G bit set. > >>>>> There is mention of reusing existing security associations > >>> if IPSec > >>>>> is used--but no mention of what to do if IPSec is not used. > >>>> [Ahmad] > >>>> Binding Revocation is used between two peers to > >> revoke/terminate a > >>>> mobility session(s) that have been created using an IPv6 > mobility > >>>> protocol signaling (Client Mobile IPv6 or Proxy MIP6). > >> RFC3775 and > >>>> RFC5213, which are the main protocols targeted by this > >>> specification, > >>>> specify that "IPsec SHOULD" be used. On the other hand, > >> there is NO > >>>> other standard track specification which specify other security > >>>> mechanisms to secure the IPv6 mobility signaling. > >>> Therefore, Binding > >>>> Revocation specification assumes the use of whatever security > >>>> mechanism that currently available to secure the IPv6 mobility > >>>> signaling. > >>> > >>> I think there are still a couple of issues here. First, Since the > >>> underlying RFCs only specify IPSec at SHOULD strength, this draft > >>> needs to discuss the consequences of not using it for BRI. > >> Depending > >>> on those consequences, it might be enough to just warn > implementors > >>> that, if you don't use IPSec, certain bad things can happen. > >> [Ahmad] > >> It is NOT expected that BRI/BRA will use a different security > >> mechanism than what is being used for securing IPv6 mobility > >> signaling. Therefore, in order to alert implementors of > the danger if > >> IPsec is NOT used, IMO, that needs to be discussed in related IPv6 > >> mobility specifications, e.g., RFC3775 and RFC5213, which > is already > >> there. On the other hand, it is very difficult to anticipate the > >> criteria of other security mechanisms that would possibly > be used in > >> the future to secure IPv6 mobility signaling and consequently > >> BRI/BRA. > >> > >> > >>> OTOH, it might be that BRI has > >>> greater security risks than for 3775/5213, and you might (for > >>> example) need to strengthen the IPSec requirement for BRI. > >>> > >>> I admit to not being an expert on 3375/5213, so it may be > true that > >>> BRI is no riskier than the underlying technology--but even > >> if that is > >>> true I'd like to see some discussion to support it. > >> [Ahmad] > >> Both IPv6 mobility signaling and BRI/BRA use the same IPv6 layer > >> signaling. I am not sure what impact the underlying > technology has on > >> BRI./BRA that does not have on BU/BA. > >> > >>> > >>> Second, I think that there is probably more guidance needed on > >>> authorization decisions even if you do use IPSec. For > >> example, do you > >>> assume that any trusted peer can remove any binding? > >> [Ahmad] > >> No. The revoking mobility entity revokes only those mobility > >> session(s) which are registered with it. No mobility node > can revoke > >> a mobility session that is registered with a different trusted > >> mobility node. > >> > >> > >>> Is a trusted peer only allowed to remove bindings that it > >> previously > >>> established using the same SA? > >> [Ahmad] > >> I believe I addressed this via another comment earlier. > The answer is > >> NO. > >> > >>> If an SA is > >>> torn down and a new one established, what authorization gets > >>> inherited, if any? > >> [Ahmad] > >> When the SA is torn down and a new one is established, the > new SA is > >> valid for both BU/BA and BRI/BRA. In other words, the new SA will > >> still have the same SPD which allows the BU/BA and BRI/BRA > messages, > >> etc. If your question is about authorization of Global revocation, > >> that authorization should be done separately. > >> > >>> Do you assume that a peer that is trusted to establish > bindings is > >>> trusted for BRI? > >> [Ahmad] > >> Of course. The node which initiated or granted the registration > >> should have the authority to revoke it. > >> Do you see any problem there? > >> > >>> Do you need to > >>> provision policies around these, and if so what are the > >> moving parts? > >> > >> [Ahmad] > >> The text under the security section was supposed to > capture this. The > >> SPD should be updated to allow MH type of 'Binding Revocation > >> message'. If it is not enough, let us know what is missing > and we can > >> add/modify as needed. > >> > >>> > >>>> > >>>> > >>>>> (Perhaps it is required by the underlying technology? > >>>>> If so, that should be mentioned here.) > >>>> [Ahmad] > >>>> That is not the intention. Please see above. > >>>> > >>>>> You mention that > >>>>> authorization is required if the G-bit is set, but go on to say > >>>>> authorization details are out of scope. I think that this > >>> draft needs > >>>>> to either offer much more guidance on authentication > >> requirements. > >>>> [Ahmad] > >>>> We could introduce a simple default mechanism inline with > >>> what we have > >>>> in RFC5213. > >>> > >>> It's possible that might help--can you point to the > section of 5213 > >>> you have in mind? > >> > >> [Ahmad] > >> Section 4, paragraph 6. > >> > >>> It might also be enough to have > >>> more discussion on what an implementor needs to think about to do > >>> authorization correctly. For example, does it make sense to > >> statically > >>> provision that a trusted peer can remove any binding for > "foo.com"? > >> [Ahmad] > >> Sure, static configuration what RFC5213 has under section 4. > >> However, in our case, is the peer authorized to use Global > Revocation > >> or not. This is not restricted to a certain realm but the > restriction > >> as mentioned above to sessions that is hosted at the revoking > >> mobility node. > >> > >> > >>> Is authorization policy > >>> dynamically determined by prior actions (i.e. a peer can > revoke all > >>> bindings _it_ established for "foo.com", but not bindings > >> that another > >>> device established for "foo.com"? > >> [Ahmad] > >> That is the very fundamental requirement for this protocol. > >> > >>> > >>> Probably more than anything, it would help to discuss the > sort bad > >>> things that this authorization is intended to prevent. > >> > >> [Ahmad] > >> Ok. We can elaborate and add some text here. Thx. > >> > >>> > >>>> > >>>>> It would be helpful if the > >>>>> Security Considerations section discussed the consequences of > >>>>> security failures, possible attacks, etc. > >>>>> > >>>> [Ahmad] > >>>> This specification do not introduce any security threats on > >>> the top of > >>>> what is being discussed in Client MIP6 and Proxy MIP6, > >> RFC3775 and > >>>> RFC5213. > >>> > >>> That's a little hard to believe without some supporting > >> text. Again, > >>> this could be my lack of knowledge of IPv6 mobility > >> talking. But for > >>> example, do RFC3775 and/or 5213 already have something a > >> mechanism for > >>> one mobility element to tell another to drop bindings in bulk? > >> > >> [Ahmad] > >> Yes. For example, the client which has multiple Bindings > (referenced > >> by different Binding IDs) could send a single message > >> (de-registration, a BU with lifetime zero) and request the server > >> (HA) to delete all bindings which belong to this Mobile node. > >> > >>> > >>>> > >>>>> > >>>>> > >>>>> Minor issues: > >>>>> > >>>>> -- S3.4.2, paragraph 1: "responds with the appropriate > >> status code > >>>>> by sending a Binding Revocation Acknowledgement message" > >>>>> > >>>>> Always, or just if the A bit is set? > >>>> [Ahmad] > >>>> This section describes the usecase when Global revocation > >> is being > >>>> used by the MAG; there is no normative text in this section. > >>> > >>> Understood (but I had similar questions in the normative > sections). > >>> > >>>> In addition, > >>>> section 10.2.1. which talks about the use of the (G) bit by > >>> the MAG > >>>> and > >>>> indicates that whenever the (G) bit is set the (A) bit MUST > >>> be set, is > >>>> correctly being referenced in this section and mentioned > >>> before the > >>>> text > >>>> quoted above. > >>> > >>> But this text talks about how you form a BRA, not how the > initiator > >>> formed the BRI. Would you expect a responder to just > assume (without > >>> checking) that the A bit was set if it sees a G-bit set? > >>> > >>> There's a lot of interaction between these bit settings > >> that make for > >>> some pretty complicated state transitions. As described, > it expects > >>> the responder to infer the A bit value based on the G-bit > value. It > >>> would be much cleaner to to implement if it were defined so > >> that the > >>> responder always sends a BRA if the A bit is set, and never > >> if it is > >>> not. > >>> > >>> As a thought experiment, how would you recommend an > implementer to > >>> handle the case where a responder got BRI with the G bit > >> set and the A > >>> bit not set? (I'm not asking for the draft to specify > >> that--it's just > >>> a discussion point.) > >>> > >> [Ahmad] > >> Ok. I guess to close on this issue, It is fair to require that the > >> responder send BRA only when the (A) bit is set. > >> Because, also, if the initiator did not set the (A) bit, > it may very > >> well not expecting a BRA and possibly NOT saving the BRI as an > >> outstanding one to start with. Thanks; will make sure that is > >> addressed as a global comment and will make sure that all > places are > >> fixed. > >> > >>>> > >>>>> > >>>>> > >>>>> -S4, paragraph 2: "verify that the mobile access > gateway sending > >>>>> the binding revocation indication message is authorized > >> to invoke > >>>>> global revocation" > >>>>> > >>>>> How does it make such a verification? > >>>> [Ahmad] > >>>> By checking the identity of the MAG if it is authorized > >> for global > >>>> revocation or not. Would a reference to section 9.2.1. makes it > >>>> clearer or you think we need to add more clarification. > >>> > >>> Actually, this is really more of a 9.2.1 issue. (I reviewed things > >>> linearly.) I think a reference here would help, but note I > >> had similar > >>> comments about 9.2.1 further down. > >> [Ahmad] > >> This should be addressed as part of the authorization > clarification. > >> > >>> > >>>>> > >>>>> -- Section 7.2, last paragraph: "If a mobility node receives a > >>>>> Binding Revocation Indication message with a Revocation Trigger > >>>>> value that is NOT in line with the Binding Revocation > Indication > >>>>> message intent, e.g., the Global (G) bit set and the Revocation > >>>>> Trigger field vale is a per-MN specific, the receiving mobility > >>>>> node SHOULD reject the Binding Revocation Indication message by > >>>>> sending a Binding Revocation Acknowledgement message with the > >>>>> Status field set to "Revocation Function NOT Supported"." > >>>>> > >>>>> This paragraph seems to imply some under-specification > >> around how > >>>>> to tell the Revocation Trigger value is not in line with the > >>>>> initiator's intent. > >>>>> > >>>>> Also, do you really mean to send "... not supported"? > >> This really > >>>>> sounds like more of a "bad request" scenario. > >>>>> > >>>>> Did you mean to capitalize the final "NOT"? > >>>> [Ahmad] > >>>> I thought it was a straight forward combination. If the > >>> Global (G) bit > >>>> is set, the Revocation trigger field value MUST contain > >> one of the > >>>> Global revocation triggers. If the (G) bit is cleared, the > >>> revocation > >>>> trigger MUST contain a per-MN value. Any deviation, means this > >>>> functionality is not supported. > >>>> > >>> > >>> The text indicated those as examples. Are they the only scenarios > >>> where the trigger value can be out of line with the "intent"? > >> [Ahmad] > >> The valid combinations are: > >> > >> Global Revocation==>>> (G) bit set and Revocation Trigger > = a Global > >> revocation trigger. > >> Per-MN Revocation ==>> (G) bit cleared and Revocation Trigger = a > >> per-MN revocation trigger. > >> > >> > >>> I guess > >>> part of my problem is that "intent" is a vague term here. The > >>> important thing is to make sure that all legal combinations are > >>> specified. I think they may be later on (again, reviewing > >> linearly), > >>> but they are scattered around the draft. > >> [Ahmad] > >> The Global Revocation Triggers are defined under section 6.1. > >> > >> > >>>> As far as why having "NOT" in capital letters, some > >> drafts have the > >>>> whole cause value in capital letters, but it is also meant > >>> to say that > >>>> this is a bad request. > >>>> > >>>>> > >>>>> -- Section 7.3: > >>>>> > >>>>> RFC3775 already talks about retransmission for Binding Update > >>>>> messages. Does this really need to be specified separately? > >>>>> > >>>> [Ahmad] > >>>> Yes. It is a separate protocol. > >>> > >>> Okay. > >>> > >>>> > >>>>> -- 2nd paragraph: "SHOULD retransmit" > >>>>> > >>>>> Can you offer guidance on when an implementation might > >> reasonably > >>>>> not do this? (i.e. why not a MUST?) > >>>> [Ahmad] > >>>> Since sending a BRI message is NOT a MUST to start with, > I do not > >>>> believe that the retransmission needs to be mandated as a > >> "MUST". A > >>>> strong recommendation using "SHOULD" gives more > >> flexibility to the > >>>> initiator to retransmit based on the need and the scenario > >>> at hand. In > >>>> addition, I did not see anywhere in RFC3775 or RFC5213 where > >>>> retransmission is mandated. > >>> > >>> A MUST retransmit if you don't get the ack to a BRI does > not in any > >>> way imply MUST send a BRI. > >> [Ahmad] > >> A good point; but in RFC3775 and RFC5213 there is no MUST for > >> retransmission either. > >> For example under section 6.9.4 of RFC5213, it says: > >> > >> " > >> 2. If the mobile access gateway fails to receive a > valid matching > >> response for a registration or re-registration > message within > >> the > >> retransmission interval, it SHOULD retransmit the > message until > >> a > >> response is received. > >> " > >> > >>> > >>> In this case, my concern is that you have two ways to > decide not to > >>> send a retransmission--one is that the value of > BRIMaxRetriesNumber > >>> could be set sufficiently low (zero, I assume) to prevent > >>> retransmissions. The second is that the implementator could > >> choose not > >>> to honor the SHOULD, even if BRIMaxRetriesNumber has a > higher value. > >>> If you want to allow the latter, it would help to have some > >> guidance > >>> (or examples) about scenarios where this would make > sense, and the > >>> consequences of doing it. > >> > >> [Ahmad] > >> I believe 'SHOULD" here is to offer the implementation more > >> flexibility. A simple implementation could interpret 'SHOULD' > >> as always retransmits and moves on and still be compliant to the > >> specification. Others may build more complex logics which > should not > >> be prevented. > >> > >>> > >>>> > >>>>> > >>>>> -- S8.1, 3rd para after bullets: "home agent SHOULD handle this > >>>>> case based on the reason for sending the Binding Revocation > >>>>> Indication message and its local policy" > >>>>> > >>>>> Is this entirely local policy? Is there no guidance to > >> offer about > >>>>> how the "reason for sending" the BRI influences this > >> decision? If > >>>>> it's really just local policy, then I'm not sure you need a > >>>>> normative statement (i.e. you SHOULD do whatever you choose to > >>>>> do...) > >>>> > >>>> [Ahmad] > >>>> The intention here is to make sure that the home agent take in > >>>> consideration the reason for sending the BRI, i.e., > >>> Revocation Trigger > >>>> value and NOT to handle all of the BRI cases by applying > a single > >>>> reaction. For example, if the Revocation Trigger value > >> indicate an > >>>> administrative reason, then the HA probably have a lot of > >>> options for > >>>> handling such a case. On the other hand, an inter-MAG handover > >>>> Revocation Trigger value would probably require a more careful > >>>> consideration. > >>> > >>> A note to that effect would be helpful. > >> [Ahmad] > >> Sure, thx. > >> > >>> > >>>> > >>>>> > >>>>> -- Last para: "SHOULD NOT" > >>>>> > >>>>> Why not MUST NOT? > >>>> [Ahmad] > >>>> > >>>> The problem we are trying to avoid here is: if we use "MUST NOT" > >>>> then we > >>>> need to specify the behavior of the receiving node in case it > >>>> receives a BRI with all of the BID(s) included. Considering such > >>>> case > >>> as an error > >>>> scenario is probably not the best way. Allowing it, then > >> it is not > >>>> "MUST NOT" anymore. > >>> > >>> On the contrary, it's not necessary to describe what the > >> responder has > >>> to do for every possible violation of MUST level > >> requirements by the > >>> initiator. But it _is_ necessary to do that for violations > >> of SHOULD > >>> level requirements, because that is much more likely to > >> happen. So by > >>> making this a SHOULD you've created more work on the part of the > >>> responder than if it were a MUST. > >>> > >>> OTOH, if it really doesn't matter to the responder one way > >> or another, > >>> then I'm not sure you need either. > >>> > >>> BTW, It's not necessary for the responder to treat every MUST > >>> violation by the sender as an error--Postel's law should > >> applies here. > >>> I suspect the real requirement is that the _receiver_ MUST > >> ignore any > >>> BIDs if present, right? > >> > >> [Ahmad] > >> No. > >> In this case, the mobile node may have registered multiple > bindings, > >> i.e., multiple care-of addresses for the same HoA. > >> Each bindings is assigned one Binding ID. Let us assume > that the MN > >> has BIDs(1, 2, 3, and 4) just for the sake of this discussion. > >> > >> The home agent may send a BRI with [BIDs (1,4)], this > means ONLY BIDs > >> (1 & 4) are being revoked. 2 & 3 still active. > >> The home agent may send a BRI with [BIDs (1, 2, 3, & 4)] to revoke > >> all of these 4 Bindings (In this case ALL Bindings). > >> Well, this is NOT recommended, the HA could have sent a > BRI with NO > >> BID(s) and accomplish the same result. > >> > >>> > >>>> > >>>>> > >>>>> -- S 10.1.1, third bullet: "MUST send a Binding Revocation > >>>>> Acknowledgement" > >>>>> > >>>>> So the G bit and the revocation trigger field value of > "per-peer > >>>>> policy" is enough to require a BRA? Wouldn't this only > >> apply when > >>>>> the A bit is set? (I know the initiator may have been > >> required to > >>>>> set the A bit, but it seems wrong to expect the > >> responder to infer > >>>>> that.) > >>>> [Ahmad] > >>>> This case a little similar to the "SHOULD NOT" case above. > >>> If the (A) > >>>> bit is NOT set, what the receiving node should do. The > >>> intention is > >>>> for > >>>> the MAG (responder) in the case of (G) revocation to always > >>> send the > >>>> BRA > >>>> message. > >>> > >>> This goes back to my previous comment. You require the > responder to > >>> make complex decisions on whether to send a BRA, based on > >> the A-bit, > >>> the G-bit, the responder role, etc. It would make life much easier > >>> (read: less error prone) for the implementor if you could > make this > >>> entirely dependent on a single flag. > >> [Ahmad] > >> Will fix this as pointed earlier. > >> > >>> > >>>> > >>>>> > >>>>> -- S 11.1, bullet 2: "SHOULD send a Binding Revocation > >>>>> Acknowledgement" > >>>>> > >>>>> Can you document reasons why a responder might not send > the BRA, > >>>>> and the consequences thereof? In particular, are there > scenarios > >>>>> where the initiator might go into retries because the responder > >>>>> chose not to send a BRA? > >>>> [Ahmad] > >>>> Sure. > >>>> In this bullet it says that if the mobile node receives a > >>> BRI message > >>>> and the MN has an entry for the binding defined in the > >> received BRI, > >>>> then the MN MUST send a BRA. In other words, if the MN > >> successfully > >>>> process the BRI and still track this binding and still able > >>> to send a > >>>> BRA, then it MUST send a BRA. In all other circumstances, > >>> e.g., the MN > >>>> no longer tracking this binding, the MN received the BRI > >> and before > >>>> processing the battery went down and no BRA is sent > >> anyway, etc. The > >>>> whole idea is to make sure that the mandate on the > mobile node is > >>>> reasonable and within the mobile node abilities to send a BRA. > >>>> Otherwise, we would like to offer the mobile node a > >>> reasonable excuse. > >>> > >>> I don't think one needs to worry about scenarios such as "battery > >>> failed" in deciding to make a requirement a MUST or a > SHOULD. If we > >>> did, it would not be possible to have _any_ MUSTs. > >>> > >>> In this particular case, not sending the BRA appears to > do harm, in > >>> that it may induce unnecessary retransmissions on the > sender's part. > >>> > >>> > >>> > >>>> > >>>>> > >>>>> -- same paragraph: "In all cases, the mobile node MUST follow > >>>>> Section 11.2" > >>>>> > >>>>> Do you really mean "in all cases"? This seems to > contradict the > >>>>> SHOULD in the previous sentence, and the "If the A bit is set" > >>>>> condition in the first sentence in the paragraph. > >>>> > >>>> [Ahmad] > >>>> Yes. The bullet correctly reference section 11.2 which says: > >>>> > >>>> " > >>>> 11.2. Sending Binding Revocation Acknowledgement > >>>> > >>>> When the mobile node receives a Binding Revocation > >> Indication from > >>>> its home agent, the mobile node processes the received Binding > >>>> Revocation Indication as in Section 11.1. If the mobile > node is > >>>> required to send a Binding Revocation Acknowledgement > message in > >>>> response to the received Binding Revocation Indication, > >> the mobile > >>>> node sends a packet to its home agent containing a Binding > >>>> Revocation Acknowledgement according to the procedure in Section > >> 7.1 and the > >>>> following: > >>>> " > >>>> > >>>> The key text is: "If the mobile node is required to send a > >>> BRA.." That > >>>> requirement is defined in the bullet you reference under > >>> section 11.1. > >>> > >>> So this is really an editorial issue then. The problem is in the > >>> phrase "in all cases". Putting "all cases" here, then a > loophole of > >>> "if required" in the referenced section is confusing. I propose > >>> changing the sentence to say something to the effect of: > >>> > >>> "In all cases where the MN sends a BRA, it MUST do so > according to > >>> section 11.1" > >> [Ahmad] > >> Sure, will adopt this text. > >> > >>> > >>>> > >>>>> > >>>>> -- Bullet 3: "mobile node MUST send" > >>>>> > >>>>> Even if A bit is not set? > >>>> > >>>> [Ahmad] > >>>> Please see response to the comment about processing the BRI > >>> when the > >>>> (G) > >>>> bit is set, as described above. > >>> > >>> ... and please see my response. > >> [Ahmad] > >> Will be resolved as mentioned above. > >> > >>> > >>>> > >>>>> > >>>>> -- same bullet: "mobile node SHOULD send a Binding Revocation > >>>>> Acknowledgement with the status field set to "Binding Does NOT > >>>>> Exist"" > >>>>> > >>>>> Even if A bit is not set? > >>>> [Ahmad] > >>>> :) > >>>> As you said earlier, it is inferred that is being set but > >>> if it is not > >>>> being set, we need to specify the behavior of the MN. In > >>> this case, it > >>>> is very important for the MN to send a BRA message and > >> inform the HA > >>>> that since BRI did not have the HoA IPv4 option, the MN can not > >>>> identify the impacted binding. This is to give the HA an > >> indication > >>>> that it needs to resend BRI with the HoA IPv4 option included. > >>> > >>> See my previous response about it being better to make explicit > >>> decisions on the A bit rather than inferences due to > other bits. In > >>> this particular case, the sender has _already_ violated a > >> MUST if it > >>> didn't set the A-bit. (And I assume that if it did not set > >> the A bit, > >>> it probably isn't waiting for a BRA--otherwise it is > doubly broken). > >>> Is it really that important for it to get the BRA under those > >>> circumstances? > >> [Ahmad > >> Will resolve as mentioned earlier above. > >> > >>> > >>>> > >>>>> > >>>>> -- Bullet 4: "MUST silently discard the Binding Revocation > >>>>> Indication message" > >>>>> > >>>>> Even if A bit is set? > >>>> [Ahmad] > >>>> In other words, this is a fatal error. When the (P) bit is > >>> set, the MN > >>>> binding is for a proxy MIPv6 binding which SHOULD never be > >>> sent to the > >>>> MN but to a MAG. In this case, the MN should silently > discard the > >>>> message. > >>>> > >>>>> > >>>>> -- S11.1, last paragraph: "could be used by the mobile node to > >>>>> define what action" > >>>>> > >>>>> I think this could use some more guidance, if you expect > >> consistent > >>>>> behavior across implementations. > >>>>> > >>>> [Ahmad] > >>>> Thanks. This probably was intentionally left like it is > >>> because, it is > >>>> probably very difficult to get all implementations to agree on a > >>>> common behavior. However, the text was meant as a reminder to > >>> implementations > >>>> in order to take that in consideration. > >>> > >>> Okay. > >>> > >>>> > >>>> > >>>>> -- S 11.2, 2nd bullet: "The mobile node MUST set the > >> Status field > >>>>> to an appropriate value. The mobile node sets the Status > >> field to > >>>>> success to reflect that it has received the Binding Revocation > >>>>> Indication and acknowledge that its IP connectivity with > >> its home > >>>>> agent has been revoked" > >>>>> > >>>>> I think this is under-specified. In particular, is the > >> mobile node > >>>>> allowed to set failure status values? > >>>> [Ahmad] > >>>> Yes, it could. E.g., if the MN received a BRI with > >>> Revocation Trigger > >>>> value set to: a non supported value or "8 Possible > >> Out-of Sync BCE > >>>> State", the MN could send a BRA with status code set to failure. > >>> > >>> Okay--I think adding a sentence or two that at least > >> indicates that it > >>> sends a successful status on success, and sends an > >> appropriate error > >>> status if an error occurs would help. > >> [Ahmad] > >> Sure, will add a note to that extent. > >> > >>> > >>>> > >>>>> > >>>>> -- S 12: "BRI Maximum Number of Retries" > >>>>> > >>>>> Why do you have both a max number of retries _and_ a max > >> timeout? I > >>>>> gathered from previous sections that retries stop after > >> the backoff > >>>>> hits max_brack-timeout. Did I read that wrong? > >>>> [Ahmad] > >>>> May be the name is misleading. What the "Maximum BRA > >>> TIMEOUT" means is > >>>> the MAX time the initiator waits before it retransmits. > >> Here is the > >>>> text, please let me know if you have any suggestions for > >>> modification. > >>>> > >>>> " > >>>> Maximum BRA TIMEOUT (MAX_BRACK_TIMEOUT) > >>>> > >>>> This variable specifies the maximum delay timeout in seconds > >>>> before the revoking mobility entity retransmits a > >> BRI message. > >>>> The default is 2 seconds. > >>>> " > >>>> > >>> > >>> So it's the maximum interval between any two > >> retransmission, not the > >>> maximum time before retransmissions stop, right? That is, > once you > >>> reach MAX_BRACK_TIMEOUT you stop backing-off, but you may > >> continue to > >>> send retransmissions at an interval of MAX_BRACK_TIMEOUT > until you > >>> reach max retries? If so, it might be useful to add > >> something to the > >>> effect of: > >>> > >>> "Once the interval between retransmissions reaches > >> MAX_BRACK_TIMEOUT, > >>> the exponential back-off will cease. If the total number of > >>> retransmissions has not yet reached BRIMaxRetriesNumber, > the sender > >>> will continue to retransmit at intervals of > >> MAX_BRACK_TIMEOUT it does > >>> so." > >> [Ahmad] > >> Sure. Thx. > >> > >>> > >>>> I will respond to the rest of the comments separately in > >>> order to make > >>>> it easier for audience to follow. > >>>> Many thanks again for the detailed comments. > >>>> > >>>> Regards, > >>>> Ahmad > >>> > >>> Thanks! > >> [Ahmad] > >> Thanks to your detailed review! > >> > >>> > >>> Ben. > >>> > > _______________________________________________ Ietf mailing list Ietf@ietf.org https://www.ietf.org/mailman/listinfo/ietf
