Re: [lisp] Tsvart last call review of draft-ietf-lisp-gpe-05

["BRUNGARD, DEBORAH A" <[e-mail]>]

Thanks Magnus for your careful review!

Fabio, on your suggested text below, it is not needed to duplicate this in the IANA section. The IANA section provides guidelines on assignment for IANA, not to future authors - it would not be for IANA to ensure requests for registration provide the proper analysis.

Thanks,
Deborah


From: Fabio Maino <[e-mail]>
Sent: Tuesday, September 18, 2018 3:53 PM
To: Magnus Westerlund <[e-mail]>; [e-mail]
Cc: [e-mail]; [e-mail]; [e-mail]
Subject: Re: Tsvart last call review of draft-ietf-lisp-gpe-05

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, MUST  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.

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].

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.

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 CC [e-mail]<mailto:[e-mail]> 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/<https://urldefense.proofpoint.com/v2/url?u=https-3A__datatracker.ietf.org_doc_rfc8325_&d=DwMDaQ&c=LFYZ-o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=xhv-vipTwtWwg5AcQtMrZCrQA1JAfYXMAgGWqbjj4Aw&s=8gidprIUCfhadFdWi7xlWD0bPsb3dPdfCw9Qf8kdwTI&e=> 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/<https://urldefense.proofpoint.com/v2/url?u=https-3A__datatracker.ietf.org_doc_draft-2Dietf-2Dtsvwg-2Decn-2Dencap-2Dguidelines_&d=DwMDaQ&c=LFYZ-o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=xhv-vipTwtWwg5AcQtMrZCrQA1JAfYXMAgGWqbjj4Aw&s=eyO4c7D3ShNQhaa8oVDqCidHbEp3mW7AkM51duv8Qw4&e=> 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.