Thanks Magnus,
I'll consolidate the changes we have agreed so far in the next rev that
I plan to publish later today.
I'll then work on the comments on this email and will send you the
corresponding actions.
Fabio
On 9/20/18 2:39 AM, Magnus Westerlund wrote:
Hi Fabio,
Most of the below text is excellent. Some comments inline for needed
clarifications and additions.
On 9/18/2018 9:52 PM, Fabio Maino wrote:
Hi Magnus,
thanks for your comments.
I think I see the points you are making.
I'll add the section 3.1 below to specify the general transport
requirements for the registration of new LISP-GPE payloads, and I
will introduce two subsections to instantiate those requirements for
Ethernet and NSH (section 4.2 and 4.3 will be moved here). In the
"IANA Considerations" section I'll refer to this new section 3.1 as a
requirement for registration of new encapsulated payload.
"3.1 Payload Specific Transport Interactions
To ensure that protocols that are encapsulated in LISP-GPE will work
well from a transport interaction perspective, the specification of a
new encapsulated payload MUST contain an analysis of how LISP-GPE
SHOULD deal with outer UDP Checksum, DSCP mapping, and Explicit
Congestion Notification (ECN) bits whenever they apply to the new
encapsulated payload.
For IP payloads, section 5.3 of [draft-ietf-lisp-rfc6830bis]
specifies how to handle UDP Checksums encouraging implementors to
consider UDP checksum usage guidelines in section 3.4 of [RFC8085]
when it is desirable to protect UDP and LISP headers against
corruption. Each new encapsulated payloads, when registered with
LISP-GPE, MUST be accompanied by a similar analysis.
Encapsulated payloads may have a priority field that may or may not
be mapped to the DSCP field of the outer IP header (part of Type of
Service in IPv4 or Traffic Class in IPv6). Such new encapsulated
payloads, when registered with LISP-GPE, MUST be accompanied by an
analysis similar to the one performed in Section 3.1.1 of this
document for Ethernet payloads.
Encapsulated payloads may have Explicit Congestion Notification
mechanisms that may or may not be mapped to the outer IP header ECN
field. Such new encapsulated payolads, when registered with LISP-GPE,
MUSTÂ be accompanied by a set of guidelines derived from
[draft-ietf-tsvwg-ecn-encap-guidelines] and [RFC6040].
The rest of this section specifies payload specific transport
interactions considerations for the two new LISP-GPE encapsulated
payloads specified in this document: Ethernet and NSH.
3.1.1 Payload Specific Transport Interactions for Ethernet
Encapsulated Payloads
The UDP Checksum considerations specified in section 5.3 of
[draft-ietf-lisp-rfc6830bis] apply to Ethernet Encapsulated Payloads.
Implementors are encouraged to consider the UDP checksum usage
guidelines in section 3.4 of [RFC8085] when it is desirable to
protect UDP, LISP and Ethernet headers against corruption.
So this is not the necessary documentation of the analysis that
IP/UDP(with zero checksum)/LISP(with GPE)/Ethernet is a safe to use.
There needs to be an analysis here to verify that this protocol
combination do work. You will actually have to discuss how the
Ethernet encapsulation fulfills the requirements listed in Section 4
of RFC 6936.
https://datatracker.ietf.org/doc/rfc7510/ is an example where such an
analysis was included. I would also note the applicability limitations
this has.
Which actually brings up an additional issue for Ethernet
encapsulation. For IP the assumption is that the IP traffic that is
encapsulated is congestion controlled. This assumption is even less
certain when having Ethernet. Thus, some consideration of that issue
is likely needed.
When a LISP-GPE router performs Ethernet encapsulation, the inner
802.1Q [IEEE.802.1Q_2014] priority code point (PCP) field MAY be
mapped from the encapsulated frame to the Type of Service field in
the outer IPv4 header, or in the case of IPv6 the 'Traffic Class'
field as per guidelines provided by [RFC8325].
I don't know enough about IEEE and the various versions of Ethernet
and WLAN here to be certain that 802.1Q PCP's can be mapped directly
to the 802.11 User Priorities discussed in RFC8325. Please investigate
if they are the same, and if they are the same priorities, then make a
explicit statement that they are applicable.
When a LISP-GPE router performs Ethernet encapsulation, the inner
header 802.1Q [IEEE8021Q] VLAN Identifier (VID) MAY be mapped to, or
used to determine the LISP Instance ID field.
3.1.2 Payload Specific Transport Interactions for NSH Encapsulated
Payloads
The UDP Checksum considerations specified in section 5.3 of
[draft-ietf-lisp-rfc6830bis] apply to NSH Encapsulated Payloads.
Implementors are encouraged to consider the UDP checksum usage
guidelines in section 3.4 of [RFC8085] when it is desirable to
protect UDP, LISP, and NSH headers against corruption.
Same as for Ethernet also the NSH header needs to have a documented
analsysis of fulfillment of the requirements.
When a LISP-GPE router performs an NSH encapsulation, DSCP and ECN
values MAY be mapped as specified for the Next Protocol encapsulated
by NSH (namely IPv4, IPv6 and Ethernet)."
I will also add a paragraph to "Iana Considerations" that says:
"To ensure that protocols that are encapsulated in LISP-GPE will work
well from a transport interaction perspective, the registration of a
new encapsulated payload MUST contain an analysis of how LISP-GPE
SHOULD deal with outer UDP Checksum, DSCP mapping, and Explicit
Congestion Notification (ECN) bits whenever they apply to the new
encapsulated payload. The analysis for the new encapsulated payload
registered in this document is in section 3.1."
Please, let me know if this address your comments.
Thanks,
Fabio
On 8/29/18 2:17 AM, Magnus Westerlund wrote:
Reviewer: Magnus Westerlund
Review result: Not Ready
This document has been reviewed as part of the transport area directorate's
ongoing effort to review key IETF documents. These comments were written
primarily for the transport area directors, but are copied to the document's
authors and WG for their information and to allow them to address any issues
raised.
When done at the time of IETF Last Call, the authors should consider this
review together with any other last-call comments they receive.
Please always [email protected] if you reply to or forward this review.
Issue A.
The reason I state Not Ready has to do with this documents failure to consider
the use of zero checksum for IPv6 when tunneling other things than IP. The none
GPE version is limited to tunnel IP for which the analysis for use of zero
checksum has been done. Each of the new tunneled protocols that are specified
in this document, i.e. ethernet and NHS, will need to perform the analysis if
they are safe to use zero checksum or not, and if not disallow zero checksum
for IPv6/UDP. The documetn also need a requirement in the registration
requirements to perform this analysis and defined if zero checksum is
acceptable or not.
Citing Section 5.3 of draft-ietf-lisp-rfc6830bis
UDP Checksum: The 'UDP Checksum' field SHOULD be transmitted as zero
by an ITR for either IPv4 [RFC0768] and IPv6 encapsulation
[RFC6935] [RFC6936]. When a packet with a zero UDP checksum is
received by an ETR, the ETR MUST accept the packet for
decapsulation. When an ITR transmits a non-zero value for the UDP
checksum, it MUST send a correctly computed value in this field.
When an ETR receives a packet with a non-zero UDP checksum, it MAY
choose to verify the checksum value. If it chooses to perform
such verification, and the verification fails, the packet MUST be
silently dropped. If the ETR chooses not to perform the
verification, or performs the verification successfully, the
packet MUST be accepted for decapsulation. The handling of UDP
zero checksums over IPv6 for all tunneling protocols, including
LISP, is subject to the applicability statement in [RFC6936].
The issue is that when LISP encapsulate other protocols the impact of a
missdelivered tunnel packet to the wrong ETR can have different impacts. As
well as errors in the headers of the encapsulated packet that may be assumed to
be protected by the encapsulating layer. Thus, individual analysis of each
protocol that are tunneled are needed.
B.) 4.2. Type of Service
When a LISP-GPE router performs Ethernet encapsulation, the inner
802.1Q [IEEE.802.1Q_2014] priority code point (PCP) field MAY be
mapped from the encapsulated frame to the Type of Service field in
the outer IPv4 header, or in the case of IPv6 the 'Traffic Class'
field.
Any recommendation about how to perform that mapping? Maybe parts of
https://datatracker.ietf.org/doc/rfc8325/ are relevant in this context.
C. General case of 4.2:
I expect other protocols than Ethernet may have a priority field that may or
may not be mapped to the DSCP field of the tunnel packet.
I would expect that for new protocol registration in the LISP-GPE Next Protocol
Registry should consider this. Thus, it would be good to note that such
considerations are needed and part of what should be evaluated for new
registrations.
D. ECN handling
Section 5.3 of draft-ietf-lisp-rfc6830bis states:
o The 'Explicit Congestion Notification' (ECN) field (bits 6 and 7
of the IPv6 'Traffic Class' field) requires special treatment in
order to avoid discarding indications of congestion [RFC3168].
ITR encapsulation MUST copy the 2-bit 'ECN' field from the inner
header to the outer header. Re-encapsulation MUST copy the 2-bit
'ECN' field from the stripped outer header to the new outer
header.
The above rules may not be applicable for all transport protocols. Thus I think
it is required that one do protocol specific considerations of ECN. TSVWG are
working on recommendations for tunnels handling of ECN here, see:
https://datatracker.ietf.org/doc/draft-ietf-tsvwg-ecn-encap-guidelines/ Thus,
my expectation would be to ensure that the registered protocols have defined
ECN handling, explicitly or by reference. Secondly that registration
requirement states the need for this consideration.
Summary: To ensure that future added protocols that are encapsulated will work
well from a transport interaction perspective there need to be a requirement on
new registration to consider and define how they use zero checksum, any DSCP
mapping and ECN bits. In addition the current document needs to ensure these
things are clearly specified for the encapsulated protocols in this document.
--
Magnus Westerlund
----------------------------------------------------------------------
Network Architecture & Protocols, Ericsson Research
----------------------------------------------------------------------
Ericsson AB | Phone +46 10 7148287
Torshamnsgatan 23 | Mobile +46 73 0949079
SE-164 80 Stockholm, Sweden | mailto:[email protected]
----------------------------------------------------------------------
_______________________________________________
lisp mailing list
[email protected]
https://www.ietf.org/mailman/listinfo/lisp
