Re: [dhcwg] Genart telechat review of draft-ietf-dhc-rfc3315bis-10

Alissa Cooper <> Tue, 23 January 2018 18:53 UTC

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From: Alissa Cooper <>
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Date: Tue, 23 Jan 2018 13:53:25 -0500
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To: Elwyn Davies <>
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Subject: Re: [dhcwg] Genart telechat review of draft-ietf-dhc-rfc3315bis-10
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Elwyn, thanks for your thorough review. I referenced it in my No Objection ballot.


> On Jan 18, 2018, at 1:00 PM, Elwyn Davies <>; wrote:
> Reviewer: Elwyn Davies
> Review result: Almost Ready
> [This is a Last Call Review, not a telechat review].
> I am the assigned Gen-ART reviewer for this draft. The General Area Review Team
> (Gen-ART) reviews all IETF documents being processed by the IESG for the IETF
> Chair. Please treat these comments just like any other last call comments.
> For more information, please see the FAQ at
> <>;.
> Document: draft-ietf-dhc-rfc3315bis-10
> Reviewer: Elwyn Davies
> Review Date: 2018-01-18
> IETF LC End Date: 2018-01-24
> IESG Telechat date: 2018-01-25
> Summary:  Amost ready.  To the best of my abiity I have done a thorough check
> of the merging of the various earlier documents into the new -bis and the
> incorporation of the various Errata.  All seems to be good from this point of
> view.  I am slightly surprised that two other RFCs (7283 and 8213) were not
> subsumed into this document.  Both are pure updates of 3315 with some important
> improvements and are pretty short in themselves.  I also found that the new
> document did not do a good job on the interactions between relay-agents and
> servers.  Particularly on the processing of options between relays and servers
> and details of reception of Relay-forward messages a little more detail would
> halp naive readers.  Finally the draft has not made much of an effort to
> support possible alternative security algorithms - IETF policy now encourages
> protocols to deal with algorithm flexibility  - DHCPv6 as it stands is pretty
> thoroughly wedded to HMAC-MD5 and would need some (relatively small) IANA
> improvements plus some thought to cope with different algorithms.  There are
> also a fair number of nits, partly due to inconsistent cross referencing in s18.
> Major Issues:
> None
> Minor Issues:
> Non-incorporation of RFC 7283:  Is there a good reason why the update of relay
> agent behaviour (which is apparently of general application across DHCPv6) is
> not incorporated into this document as with several other items?  The update is
> short and would be readily addressed in s19 here.  As it is one is left with 
> another document with some key modifications left around rather than achieving
> the unification aim of this -bis.
> Non-incoporation of RFC 8213:  Similarly regarding use of IPsec for
> server-relay agent comms.
> Definitions of T1 andT2:  I find the definitions of T1 and T2 as replicated in
> many places to be a little confusing.  T1 and T2 are actually time intervals
> rather than absolute times.  I suggest a global substitution as follows: OLD:
> The time at which the client contacts the server NEW: The time interval after
> which the client would be expected to contact the server END
> s6: Might be worth pointing out the pitfalls of defining additional stateful
> services as had to be sorted out with RFC 7550.
> s11.2: [This is not explicitly an issue with this document, but affects its
> usage]  The list of hardware types originally listed for ARP, is now well out
> of date  - in particular it doesn't cover Ethernet interfaces faster than
> 10Mb/s.  Perhas somebody could suggest some updates to Carlos Pignatoro (the
> designated expert).
> s12.2:
>> A client must create at least one distinct
>>   IA_PD.
> Is it not the case that the majority of simple hosts are not concerned with
> IA_PD?  I think this needs qualifying to say that if a client is interested in
> obtaining a prefix, then it has to create an IA_PD.
> s18.3, s18.3.11 and s19, Recording and/or reproduction of the relay address
> chain in servers: I found the lack of description of server handling of
> received messages embedded in relay-forward messages in s18.3 required
> considerable searching to understand what needed to be done, and there is no
> mention of the expectation that the relay address chain would (or at least
> might) need to be recorded to facilitate later generation of Reconfigure
> messages that are originated by the server.  I think it would be helpful to add
> some words about this is in s18.3 as follows: ADD (probably as new para 6, et
> seq):
>   All messages sent from clients may arrive encapsulated in Relay-forward
>   messages. For example, if client C sent a message that was relayed by relay
>   agent A to relay agent B and then to the server, the server would receive
>   the following Relay-forward message to process and, in general, generate an
>   appropriate Relay-reply to be returned to the client:
>      msg-type:       RELAY-FORWARD
>      hop-count:      1
>      link-address:   0
>      peer-address:   A
>      Relay Message option, containing:
>        msg-type:     RELAY-FORWARD
>        hop-count:    0
>        link-address: address from link to which C is attached
>        peer-address: C
>        Relay Message option: <client message>
>                      Figure xx: Relay-forward Example
>   Thus the server MUST record the sequence of link addresses and peer
>   addresses together with their associated hop count values to allow the
>   response to the received message to be relayed through the same relay agents
>   as the original client message (see Section 19.3).  The server may also need
>   to record this information in association with the client's DUID [I think?]
>   in case it is needed to send a Reconfigure message at a later time unless
>   the server has been configured with addresses that can be used to send
>   Reconfigure messages (see Section 18.3.11). For messages that are not
>   encapsulated in a Relay-forward message responses will be sent to the source
>   address of the received message; this source address becomes the destination
>   of the Relay-reply message in the case of Relay-forward messages (see
>   Sections 18.3.10 and 18.3.11).
> s19:  The treatment of additonal options in communications between relay-agents
> and servers is extremely sketchy.  It appears that extensive use is now made of
> this capability which was hardly envisaged when RFC 3315 was written.  I think
> it would be helpful to include a little more information about how this
> capability is used and maybe pointers to a couple of examples in other RFCs
> that represent common usages.
> s20.4: Possibility of using alternative HMAC algorithms? Whilst it appears that
> HMAC-MD5 is still adequate and not significantly compromised, the draft does
> not make much provision for possible alternatives  (there are  no registries
> for alternative parameters in the authentication option (Section 21.11) and s20
> is restricted to HMAC-MD5.
> Nits/editorial:
> General: Conventionally tables are given titles and numbers.
> s1, para 1: Might be worth adding in a second sentence to clarify the reason
> for the relay agents: "The basic operation of DHCP provides configuration for
> clients connected to the same link as the server."
> s1, para 4: s/provide only/deliver nothing but/
> s1, para 4: Mention that the stateless mode was defined in RFC 3736.
> s1.1:  It would be helpful to indicate that all the various Errata have been
> processed and point at
>  Appendix A for complete listing of changes.
> s1.1, next to last sentence: s/errate filled/errata filed/
> s1.1, last sentence: s/aforementioned/the aforementioned/
> s3, para 1:  The main IPv6 specification is now RFC 8200 rather than RFC 2460 
> [idnits gets very upset!]
> s3, para 2: s/address scope/address scopes/
> s4.2: The term "encapsulated option" is used in several places in this draft
> and defined in [RFC7227]. It would be good to have a brief introduction here as
> well as a pointer to Section 9 of RFC 7227.
> s4.2, "binding":  Probably worth notng that IA* and DUID are defined later in
> s4.2.
> s4.2, "relaying": Add "typically conected to different links".
> s4.2, "Singleton option": s/a the/a/
> s5.3:
> OLD:
> The client then performs the earlier described two message exchange.
> NEW:
> The client then performs the two message exchange as described earlier.
> s6.1, para 1, 2nd sentence: s/Stateless may be used/Stateless DHCP may be used/
> s6.3, para 3: s/hence use/hence the use/ (2 places)
> s6.3, para 4: s/provided prefixes/provisioned with prefixes/
> s6.5, para 1: Is the reference to RFC 3041 essential?  RFC 4941 obsoletes it.
> [and idnits enquires]
> s6.6, para 3: s/to request larger prefix/to request a larger prefix/
> s7.2: The references for the DHCP ports at
> are currently associated with  Jim Bound. Unfortunately Jim has passed on many
> years ago.  I suggest asking IANA to update the references to this new RFC. 
> Also the TCP port numbers are reserved for DHCP and are used in other DHCPv6
> functions (e.g., RFC5460 but there is no allocation reference. )
> ss9.1/9.2: What options might one get along with the encapsulated message?  If
> so where are they processed?  See the Minor Issue raised against s19 above.
> s11.2, para 1:  The reference for hardware types probably ought to be RFC 5494
> and it would handy to add in the IANA page address
> (
> As mentioned in Minor Issues, relevant hardware types for higher speed
> Ethernets (and potentially other types) are missing from this list.
> s14.2:  T1 and T2 are time intervals: s/time(s)/time interval(s)/g
> s15: It would help to indicate that specific values for the various
> retransmission parameters for each message type are given in the sections
> 18.2.x and use default values taken from the table in s7.6.  Suggest adding
> after list of variables: ADD:
>   Specfic values for each of these parameters relevant to the usages of the
>   various messages are given in the sub-sections of  Section 18.2 using values
>   defined in the table in Section 7.6.  The selection algorithm for RAND is
>   common across all message transmissions.
> s17.2, para 2: s/(ISP network)/(typically, connected to an ISP network)/
> s18, Fig9:  Would client always send request to non-selected server?  And would
> it renew/release on non-selected server?
> s18 (multiple places):  In many places the first reference to an option in a
> subsection is accompanied by a pointer to the part of s21 that defines it
> (Good!).  However this is not consistent.  I have picked up several cases where
> the reference is missing but there may be others.  Please check and make it
> consistent.  However, in the case of Client Identifier and Server Identifier
> options and the IA options, they appear so many times that it might be worth
> just adding a paragraph about the identifiers with the reference pointers in
> Section 18.
> s18.1:
>> For a rationale of this
>>   approach, see Section 4.2 of [RFC7550].
> I think the rationale is in s4.3 of RFC 7550.   IMO I think I would have copied
> the rationale across - it is short and 7550 is being obsoleted.
> s18.2, para 3:  The reference to RFC 7550 does not appear to add any value and
> since this doc is obsoleting RFC 7550 I think the ref should be removed.
> s18.2, para 5: s/Server Unicast option Section 21.12/Server Unicast option (see
> Section 21.12)/
> s18.2.1, para 6: s/IA Prefix options/IA Prefix options (see Section 21.22)/
> s18.2.1, para 10: s/descynronize/desynchronize/
> s18.2.1, para 12 (after retransmit parameters): s/Rapid Commit option/Rapid
> Commit option (see Section 21.14)/
> s18.2.3, para 5: s/IA Address options/IA Address options (see Section 21.6)/
> s18.2.4, para 1: s/IA Address options/IA Address options (see Section 21.6)/,
> s/IA Prefix options/IA Prefix options (see Section 21.22)/
> s18.2.9, para 8: s/The client MUST process SOL_MAX_RT and INF_MAX_RT
> options/The client MUST process SOL_MAX_RT and INF_MAX_RT options (see Sections
> 21.24 and 21.25)/
> s18.2.10, para 2: (same as last comment)
> s18.2.10, para 6: s/Client FQDN option/Client FQDN option [RFC4704]/
> s18.2.10.1:
>>   -  Record T1 and T2 times, if appropriate for the IA type.
> The T1 and T2 'times' received in the message are (as mentioned above) are
> actually intervals:  The client needs to convert these to absolute times in
> some way (may of course be by setting an interval timer running!) but should
> the interval just run from the time of receipt of the message - or something
> more complicated?  This should be noted here.
> s18.2.10.1, para 19 (I think):
>>   -  Sends a Renew/Rebind if any of the IAs are not in the Reply
>>      message, but in this case the client MUST limit the rate at which
>>      it sends these messages, to avoid the Renew/Rebind storm.
> The term Renew/Rebind storm is used here just once and without definition.  I
> am sure that I can see that one might happen but I think the circumstances
> envisioned need to be spelled out. Maybe already are at the end of s18.2.12?
> s18.3, para 5: s/Option Request option/Option Request option (see Section 21.7)/
> ss18.3.1, 18.3.3, 18.3.5, para 1 in each case: s/regardless if/regardless of
> whether/
> s18.3.2, para 6: s/Status Code option/Status Code option (see Section 21.13)/
> s18.3.2, para 11: s/Reconfigure Accept option/Reconfigure Accept option (see
> Section21.20)/
> s18.3.3, last para: s/Status Code option/Status Code option (see Section 21.13)/
> s18.3.4, para 9: s/Status Code option/Status Code option (see Section 21.13)/
> s18.3.5, para 8: s/Status Code option/Status Code option (see Section 21.13)/
> s18.3.7, para 4: s/Status Code option/Status Code option (see Section 21.13)/
> s18.3.8, para 4: s/Status Code option/Status Code option (see Section 21.13)/
> s18.3.9, para 3: s/Reconfigure Accept option/Reconfigure Accept option (see
> Section 21.20)/
> s18.3.9, para 4: s/Option Request option/Option Request option (see Section
> 21.7)/
> s18.3.10, para 2: s/Interface-id option/Interface-id option (see Section 21.18)/
> s18.3.11, para 2: Provide a pointer to Section 20 for DHCP Authentication.
> s18.2.11, para 5: I suggested in the Minor Issues that some text be added  to
> s18 regarding collection of addressing information for use with Reconfigure
> messages.  If this is done, a pointer back to this text would be useful here.
> s18.4, para 1:  s/Server Unicast option/Server Unicast option (see Section
> 21.12)/
> s18.4, para 2: s/Status Code option/Status Code option (see Section 21.13)/
> s19.1, para 1:  As mentioned above (in Minor Issues), I don't see why the
> essence of RFC 7283 is not incorporated into this document.
> s20.3: Does there need to be a registry for RDM values?
> s21: Including a general statement that general numeric values are encoded as
> unsigned integers would be helpful - this is not done consistently through the
> options at present.
> s21.4, last para: s/is taken to ("infinity")/is taken to mean "infinity"/  I
> think this para would be more useful as the third last para, i.e., moved up two
> paras to just after > The values in the T1 and T2 >    fields are the number of
> seconds until T1 and T2.
> s21.8: The pref_value should be specified as an unsigned integer.
> s24: It would probably good to take on the allocations of well-known ports as
> owned by this document (see comment of s7.2)  For future proofing of
> authentication, it might be desirable to start registries for some of the  DHCP
> Authentication parameters.
> s24, Note (4) on Table 1:  Need to make RFC8156 an informative ref.
> s27.1:  RFC 7083 is being obsoleted... making it a normative reference is not
> allowed.
> s27.2: I would say that RFC 8213 needs to be normative unless (as I would
> recommend) the text is brought into this document, in which case it is
> unnnecessary.
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