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Document: draft-ietf-opsawg-capwap-alt-tunnel-10
Reviewer: Paul Kyzivat
Review Date: 2017-12-11
IETF LC End Date: 2017-12-13
IESG Telechat date: TBD
Summary:
This draft is on the right track but has open issues, described in the
review.
(Thanks for fixing most of the issues I raised in the previous round.)
Issues:
Major: 0
Minor: 7
Nits: 1
(1) MINOR:
In Section 1.3, if this document is intended to serve as a *historical*
reference, then why isn't then intended status "Historic" rather than
"Experimental"?
(2) MINOR:
Section 3 contains:
Since AC can configure a WTP with more than one AR available for the
WTP to establish the data tunnel(s) for user traffic, it may be
useful for the WTP to communicate the selected AR. To enable this,
the IEEE 802.11 WLAN Configuration Response may contain the AR list
element containing the selected AR.
But "IEEE 802.11 WLAN Configuration Response" is not defined in this
version of the document. Seems like this may be a dangling reference
from a prior version.
(3) MINOR:
In Section 3.1, Figure 6 shows Tunnel-Type1 occupying the first 16 bits
of a 32 bit value, and Tunnel-Type (2..N) all occupying the 2nd 16 bits
of that value. That doesn't work for N>2. I *presume* that the intent is
that this be an array of 16 bit values in network order starting with
Tunnel-Type1, but that is not what it says. Needs some work.
(4) MINOR:
In Section 3.3 I find the wording of the usage unclear in the following:
The Alternate Tunnel Failure Indication message element is sent by
the WTP to inform the AC about the status of the Alternate Tunnel.
It MAY be included in the CAPWAP Station Configuration Request
message. ...
It is the way "MAY" is used here that causes me confusion, as if there
is some other way to achieve this goal. Perhaps the following would be
clearer:
The WTP MAY include the Alternate Tunnel Failure Indication message
in a CAPWAP Station Configuration Request message to inform the AC
about the status of the Alternate Tunnel.
(5) MINOR:
In Section 4.2 I find the usage of the term "Access Router (LMA)
Information Element" confusing. I find no definition of this as a
distinct thing, so I gather the intent is that this is a particular
usage of "Access Router Information Element". I think this would be
clearer to remove "(LMA)" from Figure 10.
(6) MINOR:
Section 5.2 uses "ARs" and "ARs information" in ways that are unclear
and improper grammar. IIUC "AR" in this document means "Access Router",
and so "ARs" should mean "Access Routers". It is used that way once in
section 3.3, and once in 5.2. But several other usages in 5.2 are
different, and seem to be intended to refer to "Access Router
Information Elements". I suggest the following change:
OLD
... If there are more than one ARs
information provided by the AC for reliability reasons, the same
Tunnel DTLS Policy (see Figure 14) is generally applied for all
tunnels associated with the ARs. Otherwise, Tunnel DTLS Policy MUST
be bonding together with each of the ARs, then WTP will enforce the
independent tunnel DTLS policy for each tunnel with a specific AR.
NEW
... If, for reliability reasons, the AC has provided more than one
AR address in the Access Router Information Element, the same
Tunnel DTLS Policy (see Figure 14) is generally applied for all
tunnels associated with those ARs. Otherwise, Tunnel DTLS Policy
MUST be bonded together with each of the Access Router Information
Elements, and the WTP will enforce the independent tunnel DTLS policy
for each tunnel with a specific AR.
In addition the mechanics of this "bonding" aren't entirely clear. This
seems to be covered by:
A: If A bit is set, there is an AR information associated with the
DTLS policy. There may be an array of pairs binding DTLS policy
information and AR information contained in the Tunnel DTLS Policy
Element. Otherwise, the same Tunnel DTLS Policy (see Figure 14) is
generally applied for all tunnels associated with the ARs configured
by the AC.
The above says "There may be an array of pairs". How is the array
encoded and how is its length specified? I'm guessing you intend:
When A=0:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Tunnel DTLS Policy Element Type| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |A|D|C|R|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
When A=1:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Tunnel DTLS Policy Element Type| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |A|D|C|R|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR Information .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |A|D|C|R|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR Information .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |A|D|C|R|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR Information .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where the number of repeats is equal to the number of AR addresses
previously specified.
This needs to be made much clearer. ISTM it would be cleaner to forget
the flag, and simply say this is always a list, where the last element
has no AR Information and provides options for any address not
previously mentioned. (But this isn't an option if it is documenting
existing usage.)
In Figure 9, I gather that "AR Information" means "Access Router
Information Element", and in this context it must be restricted to a
single address, and must be the address of one of previously specified
AR addresses. If so, please say this explicitly.
(7) MINOR:
Section 5.3 has a similar construction to that in 5.2, with the same
issues and should get a comparable fix.
(8) NIT:
IdNits reports that the reference to RFC2460 in section 5.6 is obsolete.
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