Re: [Gen-art] Gen-art telechat review of draft-ietf-savi-dhcp-32

["Fred Baker (fred)" <[e-mail]>]

> On Feb 10, 2015, at 4:32 PM, Elwyn Davies <[e-mail]> wrote:
> 
> Hi, Fred.
> 
> Thanks for the quick turn around.
> 
> After a quick check, I think we are almost there from my point of view.  Couple of trivia that I spotted:
> 
> The captions of Figures  9, 10 and 14: s/Transit/Transition/

Hmm. Thought I got that.

> s7.9.2: I missed out the "Resulting state" line:
> Add at the end:
>     Resulting state: VERIFY (no change) - if IPv4 DHCPLEASEQUERY "chaddr" address does not match ARP Reply hardware address - or BOUND - otherwise.
> 
> I'll take a slightly slower look tomorrow and get back to you one way or the other by the start of your day (assuming you on PST at the moment).

I (now) have both of these in my copy.

> Cheers,
> Elwyn
> 
> 
> On 10/02/2015 20:58, Fred Baker (fred) wrote:
> > If I say nothing on a comment,
>       you should find a corresponding change
> 
>       > in -33.
> 
>       >
> 
>       > I’m also picking up Alissa’s comments in this same email, as
>       I will
> 
>       > include the updated text and a diff, and ask that reviewers
>       check the
> 
>       > changes made to ensure I have done it correctly and not
>       missed
> 
>       > anything. I imagine we may have another round of discussion
>       resulting
> 
>       > from that. When we agree on this version, I’ll post the
>       draft.
> 
>       >
> 
>       >> On Jan 31, 2015, at 4:31 PM, Elwyn Davies
>       <[e-mail]> <mailto:[e-mail]>
> 
>       >> wrote:
> 
>       >>
> 
>       >>
> 
>       >> I am the assigned Gen-ART reviewer for this draft. For
>       background
> 
>       >> on Gen-ART, please see the FAQ at <
> 
>       >>
>       http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq <http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq>>.
> 
>       >>
> 
>       >> Please wait for direction from your document shepherd or
>       AD before
> 
>       >> posting a new version of the draft.
> 
>       >>
> 
>       >> Document:  draft-ietf-savi-dhcp-32.txt Reviewer:  Elwyn
>       Davies
> 
>       >> Review Date:  2015/01/30 IETF LC End Date:  [2014/08/07]
>       IESG
> 
>       >> Telechat date: 2015/02/05
> 
>       >>
> 
>       >> Summary: I regret to say that although the draft has
>       considerably
> 
>       >> improved since I last reviewed it, there are still a
>       number of
> 
>       >> significant issues that need to be addressed before it
>       can be
> 
>       >> considered ready for the IESG.  My main concern for the
>       technical
> 
>       >> quality of the document is the specification of the Data
>       Snooping
> 
>       >> Process where the state machine is just not properly
>       specified.
> 
>       >> There are numerous more local problems.  I am unsure how
> 
>       >> significant the issue with temporary disconnections if
>       the data
> 
>       >> snooping process has to be used repeatedly on a
>       particular
> 
>       >> attachment point.  The various suggestions on limiting
>       the rate of
> 
>       >> data snooping and the probabilistic back off may mean
>       that the
> 
>       >> disconnection disrupts connections, whereas if the
>       disconnection
> 
>       >> are only a couple of packets long, the usual congestion
>       avoidance
> 
>       >> mechanisms will cover up the gap.  Likewise, in the
>       likely
> 
>       >> deployment scenarios of SAVI-DHCP, fragmented DHCP
>       messages may be
> 
>       >> a non-problem: However the issue should be noted.
>       Previous reviews
> 
>       >> have noted that the attribute setting requirements could
>       be
> 
>       >> contradictory; this has not been fixed, although I think
>       the points
> 
>       >> of conflict have moved.  I have suggested some text to
>       cover the
> 
>       >> necessity for security protection of lease query
>       transactions which
> 
>       >> were also noted previously.
> 
>       >>
> 
>       >> Major issues: =========== None
> 
>       >>
> 
>       >> Minor issues: =========== Temporary disconnections when
>       Data
> 
>       >> Snooping Process is relevant:
> 
>       >>
> -----------------------------------------------------------------------------------------
> 
>       >>
> 
>       >>
> The intention in the Data Snooping process appears to be that when the state reaches BOUND, the state machine 'merges' with the DHCP Snooping Process machine and thereafter responds to snooped DHCP messages as if the BOUND state had been reached purely by snooping DHCP messages.
> >>
> 
>       >> However, there is no guarantee, in the exceptional cases
>       where the
> 
>       >> Data Snooping Process is invoked in the first place, that
>       the SAVI
> 
>       >> device will 'see' any relevant DHCP messages after
>       reaching the
> 
>       >> BOUND state since the lack of such messages is what
>       triggered the
> 
>       >> Data Snooping Process in the first place.  Consequently,
>       there is a
> 
>       >> significant likelihood that when the lease time (derived
>       via lease
> 
>       >> querying) expires, the SAVI device won't have seen any of
>       the DHCP
> 
>       >> messages that would indicate that the lease had been
>       extended.
> 
>       >> The timeout event will therefore trigger the removal of
>       the SAVI
> 
>       >> binding.  Thereafter the messages from the attached
>       device will be
> 
>       >> dropped at least until the Data Snooping Process can kick
>       in again,
> 
>       >> assuming that the attached device still has a lease and
>       the SAVI
> 
>       >> device is still not seeing the DHCP messages.
> 
>       >>
> 
>       >> This will mean that a device managed exclusively by Data
>       Snooping
> 
>       >> will suffer periodic packet loss.  How much of an effect
>       this will
> 
>       >> have on the attached device depends on the probabilistic
>       process
> 
>       >> used to start the Data Snooping Process and the
>       applications being
> 
>       >> run on it.  If only a couple of packets are lost then the
> 
>       >> disconnection will probably be no worse than the effects
>       of
> 
>       >> temporary congestion and the user will likely be
>       unaware.  Longer
> 
>       >> outages could be very irritating, depending on their
>       frequency, and
> 
>       >> would be difficult to diagnose/explain to the user.
> 
>       >>
> 
>       >> One possibility would be to remember that a binding
>       anchor was
> 
>       >> initially set up by data snooping and turn up the Data
>       Snooping
> 
>       >> Probability to one for a period after its lease timed
>       out.  This
> 
>       >> would minimise the disconnection period at the expense of
>       a little
> 
>       >> more complexity.
> 
>       >>
> 
>       >> Note, also that if not all the packets go through the
>       SAVI device,
> 
>       >> those not passing through will not be validated and could
>       have
> 
>       >> spoofed source addresses.
> 
>       >>
> 
>       >> I think these issues should be mentioned even if it is
>       thought they
> 
>       >> do not need any action.
> 
>       >
> 
>       > Yes, a facility designed to drop traffic it believes to be
>       forged
> 
>       > will probably do so from time to time, and a process such as
>       the data
> 
>       > snooping process might do it incorrectly. That said, any time
>       routing
> 
>       > in the network changes (signal fade, loss of a link in an STP
>       network
> 
>       > that causes another link to go active, etc), affected traffic
>       will be
> 
>       > lost. Yes, the data snooping process likely extends that by
>       the RTT
> 
>       > to the DHCP server on the Lease Query, and it’s possible that
>       said
> 
>       > RTT is actually two or three. I should think the application
>       would
> 
>       > have noticed a pause around the routing change and see the
> 
>       > side-effect of SAVI here as a continuation of the same.
> 
>       >
> 
>       >> Fragmented DHCP messages:
>       ---------------------------------------
> 
>       >> The brief mention of draft-ietf-opsec-dhcpv6-shield at
>       the end of
> 
>       >> s4.2.2 triggered a thought about a potential problem for
>       SAVI-DHCP
> 
>       >> that doesn't seem to be considered in the draft.  It is
>       possible
> 
>       >> that the DHCP messages that savi-dhcp has to snoop on
>       might be
> 
>       >> fragmented before they pass through the SAVI device.
>       Unlike the
> 
>       >> scenario in the "shield" draft, it is not sufficient for
>       the SAVI
> 
>       >> device to consider only the first fragment in a v6 DHCP
>       message as
> 
>       >> it needs to know what type of DHCP message is passing by
>       and that
> 
>       >> is not guaranteed to be deducible from the first
>       fragment.  It may
> 
>       >> well not be a frequent occurrence, but it should probably
>       be
> 
>       >> brought out - AFAICS it can apply to both DHCPv4 and
>       DHCPv6 - it
> 
>       >> seems likely that the SAVI device would have to
>       defragment the DHCP
> 
>       >> message in order to analyse it, but I haven't looked into
>       this in
> 
>       >> detail.
> 
>       >
> 
>       > On this, we put a comment into the security considerations
>       (11.8). We
> 
>       > didn’t go into specifying DHCP reassembly (if DHCP is carried
>       in IP,
> 
>       > reassembly is already specified by that), but we note that
>       this is
> 
>       > “left for further study”.
> 
>       >
> 
>       >> s4.1, para 3:
> 
>       >>> Traffic from unprotected links should be checked by
>       an
> 
>       >>> unprotected system or [ RFC2827] mechanisms.
> 
>       >> What does "an unprotected system" imply?  Does "system"
>       mean a
> 
>       >> (SAVI) technique and devices other than the DHCP scheme
>       or just a
> 
>       >> device outside the protection perimeter.   I would have
>       assumed
> 
>       >> that the protection scheme could also be implemented on
>       the (DHCP)
> 
>       >> SAVI device in parallel with the DHCP scheme.  Some
>       different words
> 
>       >> are needed but I am not sure what.
> 
>       >
> 
>       > An unprotected device. We changed the phrase to be precisely
>       as found
> 
>       > in the definitions, and added such a device to the figure
> 
>       > referenced.
> 
>       >
> 
>       >> s4.2.3:
> 
>       >>> If it is FALSE, either the Trust attribute must be
>       TRUE (so that
> 
>       >>> bindings become irrelevant) or another SAVI mechanism
>       such as
> 
>       >>> SAVI-FCFS must be used on the point of attachment.
> 
>       >>>
> 
>       >> Does the protection mechanism *have* to be another SAVI
>       mechanism?
> 
>       >> Would RFC 2827 not be an alternative?
> 
>       >>
> 
>       >> s4.2.3 (DHCP-Snooping Attribute)/s4.2.4 (Data-Snooping
> 
>       >> Attribute)/s4.2.5(Validating Attribute): Last para of
>       s4.2.3:
> 
>       >> Whenever this attribute is set TRUE on a point of
>       attachment, the
> 
>       >> "Validating Attribute" MUST also be set TRUE.
> 
>       >>
> 
>       >> Last para sf s4.2.4: Whenever this attribute is set on an
> 
>       >> attachment, the "Validating Attribute" MUST be set on the
>       same
> 
>       >> attachment.
> 
>       >>
> 
>       >> Last para of s4.2.5:
> 
>       >>
> 
>       >> The expected use case is when SAVI is used to monitor but
>       not
> 
>       >> block unvalidated transmissions.  The network manager, in
>       that
> 
>       >> case, may set the DHCP-Snooping and/or Data-Snooping
>       attribute TRUE
> 
>       >> but the VALIDATING attribute FALSE.
> 
>       >>
> 
>       >> These statements are inconsistent: - s4.2.3 says
>       DHCP-Snooping ==
> 
>       >> TRUE  => Validating == TRUE - s4.2.3 says
>       Data-Snooping == TRUE  =>
> 
>       >> Validating == TRUE - s4.2.5 says DHCP=Snooping == TRUE
>       and/or
> 
>       >> Data-Snooping == TRUE allows VALIDATING to be TRUE or
>       FALSE.
> 
>       >>
> 
>       >> I believe the statements in s4.2.3 and s4.2.4 can be
>       deleted.
> 
>       >>
> 
>       > We did that.
> 
>       >
> 
>       >> s4.2.4, last para:
> 
>       >>> Since some networks require DHCP deployment and
>       others avoid it,
> 
>       >>> there is no obvious universal default value for the
>       Data-Snooping
> 
>       >>> Attribute.  However, note that deployment of SLAAC
>       (and therefore
> 
>       >>> SAVI-FCFS) is generally configuration-free, while the
>       deployment
> 
>       >>> of DHCP involves at minimum the deployment of a
>       server.  Hence,
> 
>       >>> the Data-Snooping Attribute should default to FALSE,
>       and a
> 
>       >>> mechanism should be implemented to conveniently set
>       it to TRUE on
> 
>       >>> all points of attachment for which the Trust
>       attribute is FALSE.
> 
>       >>>
> 
>       >> If this text remains as it is the acronym SLAAC needs to
>       be
> 
>       >> expanded (probably back in s1).
> 
>       >
> 
>       >> However, introducing SLAAC at this point seems
>       inappropriate.
> 
>       >> SAVI-DHCP is specifically stated in s1 to be intended for
>       'pure
> 
>       >> DHCP scenarios'.  Further, it is not at all clear why the
>       issue of
> 
>       >> zero-configuration or otherwise suddenly appears here.  I
>       suggest
> 
>       >> that the second sentence is removed unless there is some
>       really
> 
>       >> good reason that I have missed.
> 
>       >>
> 
>       >> It seems to me that maybe there is something to be said
>       about
> 
>       >> indirectly connected hosts here.
> 
>       >
> 
>       > We removed the statement.
> 
>       >
> 
>       >> Nits/editorial comments: General: Both 'validate' and
>       'check' are
> 
>       >> used in the text.  'Validating' (as in 'Validating
>       Attribute')
> 
>       >> appears to have the specific meaning of ensuring that the
>       IP source
> 
>       >> address is legitimate, whereas 'checking' has a variety
>       of more
> 
>       >> general meanings.  It would be wise to ensure that
>       wherever
> 
>       >> ensuring that the process of ensuring the IP source
>       address is
> 
>       >> legitimate the term 'Validating' is used (possibly with a
>       capital
> 
>       >> letter) and check is used in all other cases.
> 
>       >
> 
>       > We went through, and changed some instances of “validate” to
>       “check”
> 
>       > and vice versa, or added something about a “source address".
>       One
> 
>       > valicates source addresses; one checks other things such as
>       fields in
> 
>       > a DHCP message.
> 
>       >
> 
>       >> General: s/LEASEQUERY_REPLY/LEASEQUERY-REPLY/ (7 places)
>       [There are
> 
>       >> also 8 places where it is already right.]
> 
>       >>
> 
>       >> s1, para 1, first sentence: (has two 'source's) OLD: This
>       document
> 
>       >> describes a fine-grained source IPv4 or IPv6 source
>       address
> 
>       >> validation mechanism. NEW: This document describes a
>       fine-grained
> 
>       >> source address validation mechanism for IPv4 and IPv6
>       packets.
> 
>       >
> 
>       > ack
> 
>       >
> 
>       >> s1, para 1, sentence 4: OLD: assigned to the other
>       attachment
> 
>       >> points or invalid in the network. NEW: assigned to any
>       other
> 
>       >> attachment point in or not associated with the network.
> 
>       >>
> 
>       >> s1, para 1, sentence 6: s/If [RFC2827]/Whereas [RFC2827]/
> 
>       >>
> 
>       >> s1, para 2, sentence 2: s/the header of data packet/on
>       the IP
> 
>       >> header of data packets/
> 
>       >>
> 
>       >> s1, para 2, sentence 3: s/a permanent block/the permanent
> 
>       >> blockage/
> 
>       >>
> 
>       >> s1, para 3: OLD: The appropriate SAVI method must be used
>       in those
> 
>       >> cases. NEW: An alternative SAVI method would have be used
>       in those
> 
>       >> cases.
> 
>       >>
> 
>       >> s1, para 3: s/Besides, this mechanism/This mechanism/
> 
>       >>
> 
>       >> s1, para 3: s/enable a SAVI solution for
>       link-local/deploy an
> 
>       >> alternative SAVI solution for link-local/
> 
>       >>
> 
>       >> s1, last para: OLD: This mechanism works for DHCPv4-only,
> 
>       >> DHCPv6-only, or both DHCPv4 and  DHCPv6. NEW: This
>       mechanism works
> 
>       >> for networks that use DHCPv4 only, DHCPv6 only, or both
>       DHCPv4 and
> 
>       >> DHCPv6.
> 
>       >
> 
>       > ack to all of those.
> 
>       >
> 
>       >> s3, Client-Server messages, 6th bullet:  It would be good
>       to
> 
>       >> distinguish this bullet for example making it a next
>       level sub-list
> 
>       >> with no bullet.
> 
>       >
> 
>       > Unclear. "DHCP Client-Server message” is the fifth bullet,
>       and "DHCP
> 
>       > Server-to-Client message” is the sixth bullet. They are both
>       at the
> 
>       > highest level of list; the next level down lists individual
>       DHCP
> 
>       > messages. ???
> 
>       >
> 
>       >> s3, Direct attachment/Indirect attachment: s/e.g./i.e./
>       (one in
> 
>       >> each entry)
> 
>       >
> 
>       > ack
> 
>       >
> 
>       >> s3, Unprotected link/Protected link: I believe the
>       intention is
> 
>       >> that these are links connected to SAVI devices. Hence:
>       s/that the
> 
>       >> device/that the SAVI device/
> 
>       >
> 
>       > Well, no. The entire point with an unprotected link is that
>       the SAVI
> 
>       > device doesn’t see DHCP messages sent to the interface.
>       Hence, it is
> 
>       > either connected to a non-SVI device, or it is beyond an
>       unprotected
> 
>       > link.
> 
>       >
> 
>       > We changed the word from “upstream/downstream” to
> 
>       > “unprotected/protected” at your request. I you have a better
>       word,
> 
>       > please suggest it.
> 
>       >
> 
>       >> s3, Cut Vertex: s/connected components/connected
>       components in a
> 
>       >> (network) graph/
> 
>       >>
> 
>       >> s3, Cut Vertex; s6.1, para 2; s7.1, 1st and 2nd  bullets:
>       s/DHCP
> 
>       >> snooping process[procedure]/DHCP Snooping Process/
> 
>       >>
> 
>       >> s3, Detection message: "by the Data Snooping Process."  I
>       think
> 
>       >> "by" should be "during" but  could be "that triggers".
> 
>       >
> 
>       > Detection message: a Neighbor Solicitation or ARP message
>       intended by
> 
>       > the Data Snooping Process to detect a duplicate address.
> 
>       >
> 
>       >> s3: The various messages associated with the DHCP lease
>       query
> 
>       >> process are not mentioned here.  It would probably be
>       appropriate
> 
>       >> to add the DHCPv4 DHCPLEASEQUERY and DHCPv6 LEASEQUERY
>       messages to
> 
>       >> the Client-Server set as they will occasionally be used
>       by DHCP
> 
>       >> clients but are mostly used by SAVI devices in this
>       context but
> 
>       >> should be allowed from clients.  On the other hand, it
>       may be
> 
>       >> sensible to have a separate category for the lease query
>       responses
> 
>       >> as treated specially on return flows - I am not quite
>       sure which is
> 
>       >> best. However they are categorized they need to be
>       filtered in the
> 
>       >> same way as Server-to-Client messages and only allowed on
> 
>       >> attachment points that have the Trust or DHCP-Trust
>       attributes.
> 
>       >
> 
>       > ack
> 
>       >
> 
>       >> s4.1, para 1: I assume that a SAVI protection perimeter
>       could
> 
>       >> contain more than one DHCP server (I think the last para
>       of s4.2
> 
>       >> implies this).  In this case s/include a DHCP
>       server/include at
> 
>       >> least one DHCP server/
> 
>       >
> 
>       > In concept, yes. DHCP, however, assumes that there is exactly
>       one
> 
>       > server. If there are multiple servers, they need to make
>       themselves
> 
>       > appear to be one.
> 
>       >
> 
>       >> s4.2.1, para 1:
> 
>       >>> Examples of a trusted binding anchor would be a port
>       to another
> 
>       >>> SAVI device,
> 
>       >>>
> 
>       >> Surely an attachment that is trusted doesn't have a
>       binding anchor
> 
>       >> just because it is trusted - and also because, with
>       multiple source
> 
>       >> addresses expected on the link, a binding anchor is not
>       relevant.
> 
>       >> This is said in the second para of the section! I think
>       s/trusted
> 
>       >> binding anchor/trusted attachment/.
> 
>       >
> 
>       > ack
> 
>       >
> 
>       >> s4.2.1, para 2: Two points: - Presumably the intention is
>       that *no*
> 
>       >> messages from attached devices will be checked - singling
>       out DHCP
> 
>       >> and 'data' messages is confusing - better something like
>       'any
> 
>       >> packets, including DHCP messages' would be better. Also I
>       assume
> 
>       >> that 'checked' is a synonym for 'validated' here (see
>       General point
> 
>       >> above)
> 
>       >
> 
>       > ack
> 
>       >
> 
>       >> - Para 1 of s4.2.6 states that "there is no need to set
>       DHCP-Trust
> 
>       >> to TRUE on an attachment point that sets Trust TRUE   It
>       would be
> 
>       >> clearer if this was made explicit here. I suggest: OLD:
>       SAVI
> 
>       >> devices will not set up bindings for points of attachment
>       with the
> 
>       >> Trust attribute set TRUE; DHCP messages and data packets
>       from
> 
>       >> attached devices with this attribute will not be
>       checked.  If the
> 
>       >> DHCP Server-to-Client messages from attached devices with
>       this
> 
>       >> attribute can trigger the state transitions specified in
>       Section 6
> 
>       >> and Section 7, the corresponding processes in Section 6
>       and Section
> 
>       >> 7 will handle these messages. NEW: SAVI devices will not
>       set up
> 
>       >> bindings for points of attachment with the Trust
>       attribute set
> 
>       >> TRUE; no packets, including DHCP messages, from devices
>       with this
> 
>       >> attribute on their attachments will be validated.
>       However DHCP
> 
>       >> Server-to-Client messages will be snooped on attachment
>       points with
> 
>       >> the Trust attribute set TRUE in the same way as if they
>       had the
> 
>       >> DHCP-Trust attribute set (see Section 4.2.2)
> 
>       >>
> 
>       >> s4.2.2: "ports that are trusted would have it set TRUE."
>       As
> 
>       >> discussed in the previous comment Trust effectively
>       implies
> 
>       >> DHCP-Trust.  Suggest changing this to: NEW: attachment
>       points that
> 
>       >> have Trust set TRUE are implicitly treated as if
>       DHCP-Trust is
> 
>       >> TRUE.
> 
>       >>
> 
>       >> s4.2.5, s8.1: s/VALIDATING/Validating/ (for consistency
>       naming
> 
>       >> attributes)
> 
>       >>
> 
>       >> s4.2.4, para 2: s/Data-Snooping process/Data Snooping
>       Process/
> 
>       >>
> 
>       >> s4.3.1, bullet #2: s/Each SAVI device only need/Each SAVI
>       device
> 
>       >> only needs/
> 
>       >>
> 
>       >> s4.3.1, last para: Add a sentence after sentence 1 to
>       emphasise
> 
>       >> that incoming  DHCP Server-to-Client messages are
>       filtered at the
> 
>       >> boundary.  Suggest: DHCP server response messages
>       incoming across
> 
>       >> the perimeter will be dropped (see Section 8). [Note:
>       This needs to
> 
>       >> be more general as the DHCP Server-to-Client messages do
>       not
> 
>       >> include LEASEQUERY responses and maybe some others.]
> 
>       >>
> 
>       >> s4.3.2, item (4)/Figure 1: The link to Non-SAVI Device 2
>       is marked
> 
>       >> as "protected" in Fig 1 and according to s4.3.2, item(4)
>       it appears
> 
>       >> that the attachment point of this device on  SAVI Device
>       A would
> 
>       >> have Trust set to TRUE.  I would have thought this meant
>       Non-SAVI
> 
>       >> Device 2 was inside the perimeter, but Fig 1 show it
>       outside.
> 
>       >> Please explain what is going on, as some further text may
>       be
> 
>       >> needed.
> 
>       >
> 
>       > I changed the graphic.
> 
>       >
> 
>       >> s4.3.2, last para: OLD: The DHCP-Trust attribute is only
>       TRUE on
> 
>       >> the inside links of the perimeter. NEW: The DHCP-Trust
>       attribute is
> 
>       >> only TRUE on links inside the perimeter.
> 
>       >>
> 
>       >> s4.3.3, para 1: s/guideline/guidelines/
> 
>       >>
> 
>       >> s4.3.5, para 1: s/and the SAVI switch/and the SAVI
>       device/ (as it
> 
>       >> isn't necessarily a switch).
> 
>       >>
> 
>       >> s4.3.5, para 2: s/IP spoofing traffic/spoofed IP traffic/
> 
>       >>
> 
>       >> s4.4, item (1):
> 
>       >>> Address configuration.  For DHCPv4: the client of a
>       SAVI device
> 
>       >>> MUST have an IPv4 address.
> 
>       >>>
> 
>       >> Comparing this with the following words for IPv6, I think
>       this
> 
>       >> ought to be "For DHCPv4: the SAVI device MUST have an
>       IPv4
> 
>       >> address."  Otherwise it is really a non-sequitur, since
>       if DHCPv4
> 
>       >> is being used, presumably the idea is that the client
>       will obtain
> 
>       >> an IPv4 address from the DHCP server - the text implies
>       that it
> 
>       >> needs one even before it gets one via DHCPv4.
> 
>       >>
> 
>       >> s4.4, item (2):  Add "A SAVI device may also require
>       security
> 
>       >> parameters, such as pre-configured keys to establish a
>       secure
> 
>       >> connection for the Lease query process (see [RFC4388,RFC
>       5007]).
> 
>       >> connection
> 
>       >>
> 
>       >> s5, bullet #1: In the light of the discussion in s4.3.5:
>       OLD:
> 
>       >>
> 
>       >> s5, bullet #2 in second set: s/data-snooping/data
>       snooping/ OLD: o
> 
>       >> Binding Anchor(Anchor): the binding anchor, i.e., a
>       physical and/
> 
>       >> or link-layer property of the attachment. NEW: o  Binding
> 
>       >> Anchor(Anchor): the binding anchor, i.e., one or more
>       physical
> 
>       >> and/ or link-layer properties of the attachment.
> 
>       >>
> 
>       >> s5, Figure 4: s/instance/example/ (2 places - sentence
>       before
> 
>       >> figure and caption of figure)
> 
>       >>
> 
>       >> s6.1, sentence 1: s/on the client's point of
>       attachment./via the
> 
>       >> client's point of attachment./
> 
>       >>
> 
>       >> s6.1, sentence 2: s/basis/assumption/
> 
>       >>
> 
>       >> s6.3: It would be worth noting here: "The DHCP message
>       categories
> 
>       >> (e.g., DHCPv4 Discover) defined in Section 3 are used
>       extensively
> 
>       >> in the definitions of events and elsewhere in the state
>       machine
> 
>       >> definition."
> 
>       >>
> 
>       >> s6.3: Possibly add equivalent text to that in s7.4:
> 
>       >>> If an event will trigger the creation of a new
>       binding entry, the
> 
>       >>> binding entry limit on the binding anchor MUST NOT be
>       exceeded.
> 
>       >>
> 
>       >> s6.3.2, EVE_DHCP_LEASEQUERY: It would be worth noting
>       that DHCPv4
> 
>       >> DHCPLEASEQUERY is not used in the DHCP Snooping process
>       to avoid
> 
>       >> confusion with s7.  Also since the LEASEQUERY should have
>       been
> 
>       >> originated by the SAVI Device itself, the destination
>       check should
> 
>       >> verify that the message is directed to this SAVI device
>       - and it
> 
>       >> should not be forwarded once it has been processed here.
> 
>       >>
> 
>       >> s6.3.2:
> 
>       >>> o  Attribute check: ...; the DHCP Client-Server
>       messages should
> 
>       >>> be from attachments with DHCP-Snooping attribute.
> 
>       >>>
> 
>       >>> o  Destination check: the DHCP Server-to-Client
>       messages should
> 
>       >>> be destined to attachments with DHCP-Snooping
>       attribute.  ...
> 
>       >>>
> 
>       >> If I understand correctly, SAVI DHCP will allow devices
>       on
> 
>       >> protected links (e.g., Non-SAVI device 2 in Figure 1) to
>       obtain an
> 
>       >> IP address via DHCP without triggering the binding anchor
>       set up.
> 
>       >
> 
>       > Trusted links, yes. Untrusted protected links *require* the
>       SAVI
> 
>       > device to set up a BST entry, and in the case of a non-SAVI
>       switch,
> 
>       > it would be highly advisable of the binding anchor included
>       both the
> 
>       > port the switch is on and the MAC address of the device using
>       the IP
> 
>       > address. The SAVI Device can’t tell the difference between a
>       switch
> 
>       > requesting an address and a device attached to the switch
>       requesting
> 
>       > an address.
> 
>       >
> 
>       >> The rules cited above would mean that the DHCP
>       interactions for
> 
>       >> these devices would not trigger events, which I think is
>       intended.
> 
>       >> It might be worth making this explicit (assuming I have
>       it
> 
>       >> correct). [Check: Should certain messages of types that
>       might have
> 
>       >> triggered events but didn't, because of the above checks,
>       be
> 
>       >> logged?]
> 
>       >>
> 
>       >> s6.4.1.1: Two issues: - Refers to DHCPv4 Reboot.  This is
>       not a
> 
>       >> message that triggers this event and so should not be
>       mentioned. -
> 
>       >> Should the address in any IA's carried by the DHCPv6
>       Request
> 
>       >> message that can trigger this message also be copied into
>       the BST?
> 
>       >> If so should it also refer to Figure 6?
> 
>       >>
> 
>       >> s6.4.1.2:  Refers to DHCPv4 Request.  This is not a
>       message that
> 
>       >> triggers this event and so should not be mentioned.
> 
>       >>
> 
>       >> s6.4.1.3: Three issues: - Refers to DHCPv4 Request and
>       DHCPv4
> 
>       >> Reboot.  These are not messages that trigger this event
>       and so
> 
>       >> should not be mentioned. - Should the address in any IA's
>       carried
> 
>       >> by the DHCPv6 Solicitation message that can trigger this
>       message
> 
>       >> also be copied into the BST?  If so should it also refer
>       to Figure
> 
>       >> 6?
> 
>       >>
> 
>       >> s6.4.3.7: The LEASEQUERY message is destined for this
>       SAVI device.
> 
>       >> It is not clear where it would be forwarded to (maybe
>       some DHCPv6
> 
>       >> infrastructure on the SAVI device?)
> 
>       >>
> 
>       >> Figure 9 Caption and Figure 10 Caption:
>       s/Transit/Transition/
> 
>       >>
> 
>       >> s6.4.4/Figure 9/Figure 10: Events EVE_DHCP_RENEW and
> 
>       >> EVE_DHCP_REBIND are missing from the table, list and
>       diagram.  They
> 
>       >> should be marked as cycling in the BOUND state.  Putting
>       them in
> 
>       >> here is desirable so that it is consistent with the
>       table/diagrams
> 
>       >> in s7.9 etc.
> 
>       >>
> 
>       >> s7.1, para 1: s/two case when this does not work/two
>       cases when
> 
>       >> this does not work/
> 
>       >>
> 
>       >> s7.1, bullet #1: s/everyone/every one/; s/passing by the
>       SAVI
> 
>       >> device/passing through the SAVI device/
> 
>       >>
> 
>       >> s7.1, bullet #2: s/turns broken/becomes broken/; s/as
>       planned/some
> 
>       >> planned change/
> 
>       >>
> 
>       >> s7.1, para after bullets: OLD: Data Snooping Process
>       prevents
> 
>       >> permanently blocking legitimate traffic in case of these
>       two
> 
>       >> exceptions. NEW: The Data Snooping Process can avoid the
>       permanent
> 
>       >> blocking of legitimate traffic in case one of these two
>       exceptions
> 
>       >> occurs.
> 
>       >>
> 
>       >> s7.1, next to last para: s/a conditional
>       SHOULD/OPTIONAL/;
> 
>       >> s/without the above exceptions/where the exceptions
>       cannot occur/
> 
>       >>
> 
>       >> s7.1, last para:  Mention that the probability of
>       unmatched packets
> 
>       >> triggering the Data Snooping Process should be a
>       configurable
> 
>       >> parameter of implementations.  Presumably the default
>       should be
> 
>       >> zero so it is normally turned off.
> 
>       >>
> 
>       >> s7.2, last para: s/about this process is discussed
>       is/concerning
> 
>       >> this process are discussed in/
> 
>       >>
> 
>       >> s7.3: The way in which the Data Snooping process
>       integrates with
> 
>       >> the DHCP Snooping Process is not explained until the very
>       end of s7
> 
>       >> (in s7.8) and even then very tersely.  I suggest adding
>       the
> 
>       >> following to s7.3: NEW: The Data Snooping Process
>       provides an
> 
>       >> alternative path for binding entries to reach the BOUND
>       state in
> 
>       >> the exceptional cases explained in Section 7.1 when there
>       are no
> 
>       >> DHCP messages that can be snooped by the SAVI device.
> 
>       >>
> 
>       >> In some of the exceptional cases (especially the dynamic
>       topology
> 
>       >> case), by the time the binding has reached the BOUND
>       state the DHCP
> 
>       >> messages may be passing through the SAVI device.  In this
>       case the
> 
>       >> events driven by DHCP messages that are expected in the
>       BOUND state
> 
>       >> in the DHCP Snooping Process may occur and the binding
>       can be
> 
>       >> handled by the DHCP Snooping Process state machine.
> 
>       >>
> 
>       >> In any event, the lease expiry timeout event will occur
>       even if no
> 
>       >> others do. This will cause the binding to be deleted and
>       the state
> 
>       >> to logically return to NO_BIND state.  Either the DHCP or
>       the Data
> 
>       >> Snooping Process will be reinvoked if the lease is still
>       place.  If
> 
>       >> DHCP messages are still not passing through the SAVI
>       device, there
> 
>       >> will be a brief disconnection during which data packets
>       passing
> 
>       >> through the SAVI device will be dropped.  The
>       probabilistic
> 
>       >> initiation of the Data Snooping Process can then take
>       over again
> 
>       >> and return the binding state to BOUND in due course.
> 
>       >>
> 
>       >> s7.4, para 1: s/In addition to EVE_DATA_LEASEQUERY and
> 
>       >> EVE_DHCP_REBIND,/In addition to EVE_DHCP_RENEW and
> 
>       >> EVE_DHCP_REBIND,/
> 
>       >>
> 
>       >> s7.4, para 1:  To make the BOUND state consistent with
>       the DHCP
> 
>       >> Snooping Process case, the events EVE_DHCP_RELEASE,
> 
>       >> EVE_DHCP_DECLINE, EVE_DHCP_REPLY, and EVE_DHCP_LEASEQUERY
>       should
> 
>       >> also be processed in the BOUND state.  The actions in the
>       BOUND
> 
>       >> state can be explained by a reference to s6.4.3 rather
>       than having
> 
>       >> to repeat them in s7.
> 
>       >>
> 
>       >> s7.5-s7.7:  The textual description of the actions is not
>       an
> 
>       >> accurate representation of the evolution of the state
>       machine,
> 
>       >> primarily because the sending of the second neighbour
>       detection and
> 
>       >> second lease query messages is shown in the wrong state.
>       This
> 
>       >> means that the detection messages would not be received
>       in the
> 
>       >> expected states.  The way to fix this is to define three
> 
>       >> "functions" (as is normally done for state machines).
>       The
> 
>       >> functions would subsume the text about sending ARP/DAD
>       messages in
> 
>       >> s7.5.1, the text about sending lease queries in s7.6.1
>       and sending
> 
>       >> ARP requests in s7.7.1.  A third intermediate state is
>       needed to
> 
>       >> handle the three response messages or timeouts from the
>       three
> 
>       >> remote messages.  As it stands, the actions after an
>       UNMATCH event
> 
>       >> (s7.5.1) involve transmitting messages and waiting for
>       responses or
> 
>       >> timeouts.  The text is unclear exactly when the
>       transition to the
> 
>       >> DETECTION state occurs, and the EVE_ENTRY_EXPIRE actions
>       in
> 
>       >> DETECTION (s7.6.1) do not handle the retransmission of
>       the ARP/DAD
> 
>       >> requests (see s7.5.1) but set about sending lease
>       queries.  The BST
> 
>       >> needs an expire counter entry to simplify the number of
>       states.
> 
>       >> The sequence (for v4) needs to go something like:
>       [NO_BIND] UNMATCH
> 
>       >> recd and decided to act [NO_BIND] Set expiry count ->
>       0; Send ARP;
> 
>       >> Set timeout to  DETECTION_TIMEOUT; Transition to
>       [DETECTION]
> 
>       >> [DETECTION] CONFLICT recd => abort and discard
>       binding; Transition
> 
>       >> to [NO_BIND] [DETECTION] EXPIRY: Increment expiry count;
>       if count
> 
>       >> == 1: Send ARP; Set timeout to  DETECTION_TIMEOUT; Remain
>       in state
> 
>       >> [DETECTION]; else if count ==2: Send lease query; Set
>       timeout to
> 
>       >> LEASEQUERY_DELAY; set count to 0; Transition to state
>       [RECOVERY]
> 
>       >> ... and similar in state RECOVERY.. an extra state is
>       needed to
> 
>       >> handle the ARP etc after successful lease query.
> 
>       >>
> 
>       >> s7.5.1:
> 
>       >>> This local conflict process SHOULD be performed.  If
>       it is not
> 
>       >>> performed, the state of the entry is set to RECOVERY,
>       the
> 
>       >>> lifetime is set to 2*MAX_LEASEQUERY_DELAY, and the
>       lease query
> 
>       >>> process specified in the following section will be
>       performed
> 
>       >>> directly.
> 
>       >>>
> 
>       >> Under what circumstances would the local conflict process
>       not be
> 
>       >> performed? If the sequence noted above is used, the lease
>       query
> 
>       >> process can be triggered by  setting the expiry count to
>       0 and
> 
>       >> sending the lease query request before transitioning to
>       state
> 
>       >> RECOVERY.
> 
>       >>
> 
>       >> s7.6.1, item (1): s/A list of authorized DHCP servers are
>       kept/A
> 
>       >> list of authorized DHCP servers is kept/
> 
>       >>
> 
>       >> s7.8/s7.9/Figure 13/Figure 14: s/Transit/Transition/ (4
>       places)
> 
>       >>
> 
>       >> s8: The filtering of DHCP messages needs to apply to the
>       various
> 
>       >> lease query and lease query response messages.  The
>       relevant
> 
>       >> messages need to be either added to the appropriate one
>       from
> 
>       >> Client-Server and server-to-Client category, or a new
>       category
> 
>       >> created and mentioned with the existing categories (see
>       comment on
> 
>       >> s3 above).
> 
>       >>
> 
>       >> s9.1, para 2: s/attribute can be found/attributes can be
>       found/
> 
>       >>
> 
>       >> s9.2, para 1: s/discard legitimate/to discard
>       legitimate/;
> 
>       >> s/Purely/Simply/; s/is of/is a/; s/considerable/may cause
> 
>       >> considerable/ s9.2, last para: OLD: Immediately after
>       reboot, the
> 
>       >> SAVI device SHOULD restore binding states from the
>       non-volatile
> 
>       >> storage.  The system time of save process MUST be
>       stored.  After
> 
>       >> rebooting, the SAVI device MUST check whether each entry
>       has been
> 
>       >> obsolete by comparing the saved lifetime and the
>       difference between
> 
>       >> the current time and time when the binding entry is
>       established.
> 
>       >> NEW Immediately after reboot, the SAVI device SHOULD
>       restore the
> 
>       >> binding states from the non-volatile storage.   Using the
>       time when
> 
>       >> each binding entry was saved, the SAVI device should
>       check whether
> 
>       >> the entry has become obsolete by comparing the saved
>       lifetime and
> 
>       >> the difference between the current time and time when the
>       binding
> 
>       >> entry was established. Obsolete entries which would have
>       expired
> 
>       >> before the reboot MUST be removed.
> 
>       >>
> 
>       >> s11.2:  This section adds additional
>       states/events/actions into the
> 
>       >> state machine.  The link-down event and its consequences
>       aren't
> 
>       >> really a security consideration.
> 
>       >
> 
>       > As noted there, there is a case. If a device departs and the
>       binding
> 
>       > state is maintained, another system can mimic it by
>       recreating in
> 
>       > itself the binding anchor information. If the state is not
> 
>       > maintained, it may need to be to be recovered using the Data
>       Snooping
> 
>       > process. This comment suggests that the trade-off may be best
>       handled
> 
>       > by keeping the state momentarily to see if it is simply a
>       signal fade
> 
>       > issue.
> 
>       >
> 
>       >> s11.3: I am unclear how the processes described could
>       lead to
> 
>       >> multiple binding anchors being established on the same
>       SAVI device.
> 
>       >> Could you quote an example please?  I am unsure how a
>       client with
> 
>       >> multiple attachments could be using the same address on
>       each of
> 
>       >> them.
> 
>       >
> 
>       > We may need to discuss this with my Chinese colleagues.
> 
>       >
> 
>       >> s11:  As discussed on various previous occasions, lease
>       query
> 
>       >> operations are considered security sensitive [RFC5007]
>       [RFC4388].
> 
>       >> It is recommended that an IPsec channel is opened to
>       carry out
> 
>       >> lease query enquiries.   However, since the number of
>       SAVI devices
> 
>       >> and DHCP servers/relays in a typical network is
>       relatively small
> 
>       >> and they will all be under the control of a single
>       administrative
> 
>       >> authority, keying material can be prepositioned out of
>       band and
> 
>       >> used as necessary by SAVI devices that know the addresses
>       of the
> 
>       >> DHCP entities.  This needs to be described in an extra
>       section in
> 
>       >> s11.  It may also be the case that in some circumstances,
>       the SAVI
> 
>       >> protection itself could be considered sufficient to
>       obviate the
> 
>       >> need for using IPsec channels - however, that needs to be
>       discussed
> 
>       >> and  I suggest that the authors consult with a security
>       expert
> 
>       >> (i.e., not me) to decide what is appropriate.
> 
>       >
> 
>       > We now have a note on configuration that the SAVI device may
>       need
> 
>       > keying information. I remain at a loss to say why the
>       reference to
> 
>       > 4388/5007 didn’t cover this, why it needs to be stated here
>       and not
> 
>       > any of the other requirements noted in 4388/5007, and why it
>       has a
> 
>       > different requirement level (MUST vs RECOMMENDED) from
>       4388/5007.
> 
>       > Recall that significant cain is raised when
> 
>       > draft-ietf-v6ops-mobile-device-profile increases the
>       requirement
> 
>       > levels from those in RFCs 6434 and 7066; what makes this
>       different?
> 
>       > Hence, I have not added commentary (that seems superfluous)
>       to
> 
>       > section 11.
> 
>       >
> 
>       >
> 
>       > From Alissa:
> 
>       >>
> 
>       >>
>       ----------------------------------------------------------------------
> 
>       >>
> 
>       >>
> DISCUSS:
> >>
>       ----------------------------------------------------------------------
> 
>       >>
> 
>       >>
> 
>       >>
> I have one point I'd like to discuss that shouldn't be hard to resolve.
> >>
> 
>       >> = Section 4.3.4 = "In common deployment practice, the
>       traffic from
> 
>       >> the unprotected network is treated as trustworthy, which
>       is to say
> 
>       >> that it is not filtered.  ...
> 
>       >>
> 
>       >> To configure such a perimeter, at minimum the DHCP
>       messages from
> 
>       >> unprotected networks MUST be ensured to be trustworthy.
>       Achieving
> 
>       >> this is beyond the scope of this document."
> 
>       >>
> 
>       >> The first sentence says that trustworthy == not filtered,
>       then the
> 
>       >> later sentence says that messages MUST be ensured to be
> 
>       >> trustworthy. The implication could be that messages MUST
>       not be
> 
>       >> filtered, but that seems backwards. On the other hand, it
>       doesn't
> 
>       >> seem right to have a normative requirement that messages
>       be
> 
>       >> "ensured to be trustworthy" somehow, using some
>       unspecified
> 
>       >> mechanism, without really explaining what counts as
>       trustworthy. I
> 
>       >> would suggest deleting the second paragraph altogether
>       unless it
> 
>       >> can be made meaningful for a network operator.
> 
>       >
> 
>       > I removed the comment. The primary point is that such stuff
>       is out of
> 
>       > scope.
> 
>       >
> 
>       >>
>       ----------------------------------------------------------------------
> 
>       >>
> 
>       >>
> COMMENT:
> >>
>       ----------------------------------------------------------------------
> 
>       >>
> 
>       >>
> 
>       >>
> In general I question whether calling the procedures in this document
> >> "snooping" is prudent. I
>       would have thought something like
> 
>       >> "checking" or "verification" would have less baggage.
> 
>       >
> 
>       > That could be a long discussion. I’m with you in theory. This
>       is in
> 
>       > fact the language that has been used throughout the lifetime
>       of the
> 
>       > draft, since 2009. Changing it at this point seems very late
>       in the
> 
>       > game. For the version, I’m leaving it unchanged.
> 
>       >
> 
>       >> = Section 3 = In the definitions of Unprotected link and
>       Protected
> 
>       >> link, what does it mean for a device to "see" a DHCP
>       message to a
> 
>       >> host?
> 
>       >
> 
>       > The DHCP message goes through the attached equipment. I
>       changed the
> 
>       > wording. See if it works better for you.
> 
>       >
> 
>       >> = Section 4.1 = "Traffic from unprotected links should be
>       checked
> 
>       >> by an unprotected system or [RFC2827] mechanisms.  The
>       generation
> 
>       >> and deployment of such a mechanism is beyond the scope of
>       this
> 
>       >> document."
> 
>       >>
> 
>       >> I see a few problems with this text. In the first
>       sentence I don't
> 
>       >> understand the idea that a check would be performed by a
>       system
> 
>       >> _or_ a mechanism. What about a system that employs the
>       mechanism
> 
>       >> specified in BCP 38?
> 
>       >
> 
>       > “BCP 38” and “RFC 2827” differ in what way?
> 
>       >
> 
>       > Recall, BTW, that BCP 38 differs from SAVI in a fundamental
>       way. BCP
> 
>       > 38 is about a filter applied by an upstream network to
>       traffic from
> 
>       > its customer, and is about the prefix used by the customer.
>       SAVI is
> 
>       > about something done in the switch that a host connects to,
>       in the
> 
>       > SAME network, and is about the *address* used by a specific
>       host. BCP
> 
>       > 38 doesn’t protect a network from itself, only from other
>       networks.
> 
>       > SAVI protects a network from itself. One could argue that a
>       network
> 
>       > that implements SAVI throughout doesn’t require BCP 38
>       upstream, as
> 
>       > it will never generate messages that BCP 38 would drop. One
>       can’t say
> 
>       > anything like that about a network protected by BCP 38 not
>       needing
> 
>       > internal protection.
> 
>       >
> 
>       >> Furthermore, the text implies that there are cases where
>       BCP 38
> 
>       >> doesn't apply, which seems to undercut the actual
>       guidance provided
> 
>       >> in BCP 38. This is further reinforced by the second
>       sentence that
> 
>       >> indicates that the generation of a new mechanism (to
>       replace BCP
> 
>       >> 38? it's not clear) is beyond the scope of this document.
>       It's also
> 
>       >> redundant to say that deployment is beyond the scope of
>       the
> 
>       >> document -- deployment is beyond the scope of all
>       protocol specs.
> 
>       >> And I'm unclear on whether "unprotected system" means the
>       same
> 
>       >> thing as "unprotected device" as defined in Section 3.
> 
>       >
> 
>       > I think you have not understood the statement of the section.
>       Maybe
> 
>       > you can help me reword that better.
> 
>       >
> 
>       > Here’s the concept. I have two switching domains. They might
>       or might
> 
>       > not have a router between them; for sake of argument, let’s
>       imagine
> 
>       > they do. They do have separate DHCP service - the addresses
>       in one
> 
>       > domain come from DHCP server 1 and go through that domain,
>       and the
> 
>       > addresses in the other come from DHCP server 2 and go through
>       the
> 
>       > other domain. The switch I’m thinking hard about right now is
>       in the
> 
>       > first domain, and the second domain is “somewhere else”, at
>       least
> 
>       > topologically. I can protect systems in the first domain,
>       because the
> 
>       > DHCP messages from DHCP Server 1 go through it and are
>       therefore
> 
>       > visible to the switches. From my perspective, I have done
>       good things
> 
>       > for the second domain as well; if I can now not present a
>       threat to
> 
>       > myself, I can’t hurt anyone else either. But I don’t know
>       that about
> 
>       > the second domain - traffic coming from there might have
>       crossed the
> 
>       > great unwashed backbone, for example. Sure, I can say (BCP 38
>       applied
> 
>       > in reverse) that my traffic came from the backbone, the
>       backbone gave
> 
>       > me a default route, and therefore that traffic all matches
>       said
> 
>       > default route. That doesn’t tell me much about whether
>       anything is
> 
>       > spoofed or not; I just don’t know, and have no way of
>       knowing.
> 
>       >
> 
>       > What this is saying is that if I have no way to validate
>       addresses
> 
>       > from a neighboring domain, I have no way to validate them;
>       that’s the
> 
>       > point of “out of scope". I can earnestly hope that the
>       neighboring
> 
>       > domain implements BCP 38 or SAVI, but I may not have control
>       over
> 
>       > that either. That’s a problem I can’t solve in this domain.
> 
>       >
> 
>       >> I think both sentences could be replaced with the
>       following: "The
> 
>       >> mechanism specified in RFC 2827 is required in those
>       cases."
> 
>       >
> 
>       > Well, maybe. But it might also be a SAVI mechanism in the
>       neighboring
> 
>       > network. And then there’s the reverse BCP 38 thing - traffic
>       arrived
> 
>       > from the backbone. What does that actually tell me about its
>       source
> 
>       > addresses? I’m a great believer in BCP 38 where it makes
>       sense. I
> 
>       > would be very hesitant to require it where it doesn't.
> 
>       >
> 
>       >> = Section 7.1 = "This is the case stands when the SAVI
>       device is
> 
>       >> persistently on the path(s)"
> 
>       >>
> 
>       >> I think the "stands" is extraneous?
> 
>       >
> 
>       > removed it.
> 
>       >
> 
>       >> s/one feasible link-layer paths/one feasible link-layer
>       path/
> 
>       >>
> 
>       >>
>