MPLS Payload Protocol Identifier
draft-xu-mpls-payload-protocol-identifier-08
Network Working Group X. Xu
Internet-Draft Alibaba, Inc.
Intended status: Standards Track H. Assarpour
Expires: June 24, 2021 Broadcom
S. Ma
Mellanox
F. Clad
Cisco Systems, Inc.
December 21, 2020
MPLS Payload Protocol Identifier
draft-xu-mpls-payload-protocol-identifier-08
Abstract
The MPLS label stack has no explicit protocol identifier field to
indicate the protocol type of the MPLS payload. This document
proposes a mechanism for containing a protocol identifier field
within the MPLS packet, which is useful for any new encapsulation
header (e.g., INT metadata) which may need to be encapsulated with an
MPLS header.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 24, 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
Xu, et al. Expires June 24, 2021 [Page 1]
Internet-Draft MPLS Payload Protocol ID December 2020
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Protocol Type Field . . . . . . . . . . . . . . . . . . . . . 3
4. Data Plane Processing of PIL . . . . . . . . . . . . . . . . 4
4.1. Egress LSRs . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. Ingress LSRs . . . . . . . . . . . . . . . . . . . . . . 4
4.3. Transit LSRs . . . . . . . . . . . . . . . . . . . . . . 5
4.4. Penultimate Hop LSRs . . . . . . . . . . . . . . . . . . 5
5. Signaling for PIL Processing Capability . . . . . . . . . . . 5
6. Alternative Approaches . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
9. Security Considerations . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. Normative References . . . . . . . . . . . . . . . . . . 6
10.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
The MPLS label stack has no explicit protocol identifier field to
indicate the protocol type of the MPLS payload. This document
proposes a mechanism for containing a protocol identifier field
within the MPLS packet, which is useful for any new encapsulation
header (e.g., INT metadata) which may need to be encapsulated with an
MPLS header. With this explicit protocol identifier field, there is
no need any more for each new encapsulation header to deal with the
notorious first nibble issue associated with MPLS individually. More
specifically, there is no need to intentionally avoid the first
nibble of each new encapsulation header from being 0100 (IPv4) or
0110 (IPv6) and even worsely misuse the first nibble of each new
encapsulation header as an MPLS payload type field (e.g., MPLS-BIER
[RFC8296]). The tacit permission of misusing the first nibble of
each new encapsulation header as an MPLS payload type field would
exhause the valuable nibble space quickly. Furthermore, there is no
need to insert one additional label indicating the MPLS payload type
when transporting any new encapsulation header over MPLS LSPs (e.g.,
transporting Network Service Header (NSH) [RFC8300] over MPLS LSPs)
Xu, et al. Expires June 24, 2021 [Page 2]
Internet-Draft MPLS Payload Protocol ID December 2020
therefore the signalling for that additional label is not needed
anymore.
To some extent, this situation is much similar to that of the MPLS
reserved label space (a.k.a., the special purpose label space)
[RFC7274] . Due to the concern over the scarcity of the special-
purpose label space , the extended special purpose label concept is
introduced accordingly. Similarily, the IETF MPLS community should
take precautions on the the scarcity of the first nibble of the MPLS
payload before it is too late.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Terminology
This memo makes use of the terms defined in [RFC3032].
3. Protocol Type Field
The encapsulation format for Protocol Type field is depicted as
below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PIL | TC |1| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0| Reserved | Protocol Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
Protocol Identifier Label (PIL): This field contains a special
purpose label with value of <TBD> or an extended special purpose
label [RFC7274] with value of <TBD> which indicates that a
Protocol Type field appears immediately after the bottom of the
label stack.
Traffic Class (TC): The usage of this field is in accordance with
the current MPLS specification [RFC3032].
S: The Bottom of Stack (BoS) field is set since the PIL MUST
always appear at the bottom of the label stack.
Xu, et al. Expires June 24, 2021 [Page 3]
Internet-Draft MPLS Payload Protocol ID December 2020
TTL: The usage of this field is in accordance with the current
MPLS specification [RFC3032].
Reserved MUST be set to 0 and ignored on reception.
Protocol Type: This field indicates the protocol type of the MPLS
payload as per [ETYPES].
Payload: This field contains the MPLS payload which can be an IP
packet, an Ethernet frame, or any other type of payload, e.g.,
Network Service Header (NSH) [RFC8300].
4. Data Plane Processing of PIL
4.1. Egress LSRs
Suppose egress LSR Y is capable of processing the Protocol Type field
contained in MPLS packets. LSR Y indicates this to all ingress LSRs
via signaling (see Section 5). LSR Y MUST be prepared to deal with
both packets with an imposed Protocol Type field and those without;
the PIL will distinguish these cases. If a particular ingress LSR
chooses not to impose a Protocol Type field, LSR Y's processing of
the received label stack (which might be empty) is as if LSR Y chose
not to accept Protocol Type field. If an ingress LSR X chooses to
impose the Protocol Type field, then LSR Y will receive an MPLS
packet constructed as follows: <Top Label (TL), Application Label
(AL), PIL> <Protocol Type field> <remaining MPLS payload>. Note that
here the TL could be replaced with an IP-based tunnel [RFC4023] and
the AL is optional. LSR Y recognizes TL as the label it distributed
to its upstream LSR and pops the TL (note that the TL may be an
implicit null label, in which case it doesn't appear in the label
stack and LSR Y MUST process the packet starting with the AL label
(if present) and/or the PIL.) LSR Y recognizes the PIL with S bit
set. LSR Y then processes the Protocol Type field, which will
determine how LSR Y processes the MPLS payload.
4.2. Ingress LSRs
If an egress LSR Y indicates via signaling that it can process the
Protocol Type field, an ingress LSR X can choose whether or not to
insert it into the MPLS packet destined for LSR Y. The ingress LSR X
MUST NOT insert the Protocol Type field into that MPLS packet unless
the egress LSR X has explicitly announced that it could process it.
The steps that ingress LSR X performs to insert the Protocol Type
field are as follows:
Xu, et al. Expires June 24, 2021 [Page 4]
Internet-Draft MPLS Payload Protocol ID December 2020
1. On an incoming packet, identify the application to which the
packet belongs and determine whether the Protocol Type field
needs to be added to the incoming packet.
2. For packets requiring the insertion of the Protocol Type field,
prepend the Protocol Type field to the existing MPLS payload;
then, push the PIL on to the label stack with the S bit set.
3. Push the application label (AL) label (if required) on to the
label stack.
4. Push the EL and the ELI labels [RFC6790] on to the label stack
(if required).
5. Determine the top label (TL) and push it on to the label stack.
6. Determine the output interface and send the packet out.
4.3. Transit LSRs
Transit LSRs MAY operate with no change in forwarding behavior. If a
transit LSR recognizes the PIL and the subsequent Protocol Type
field, it MAY be allowed to do some additional value-added
processing, such as MPLS payload inspection, on the received MPLS
packet containing the PIL and the Protocol Type field.
4.4. Penultimate Hop LSRs
No change is needed at penultimate hop LSRs.
5. Signaling for PIL Processing Capability
TBD.
6. Alternative Approaches
As illustrated in Section 3 and Section 4, the existence of the
Protocol Type field immediately after the MPLS label stack is
indicated by inserting the PIL into an MPLS packet. Alternatively,
by setting the first nibble of the 4-octet entry containing the
Protocol Type field to a dedicated value (e.g., 1111), the existence
of the Protocol Type field could be indicated as well (see Figure 2).
In this way, there is no need to insert additional label(s) (i.e.,
the PIL) into an MPLS packet. As for which approach should be
selected in the end, it depends on a wide-scope discussion within the
IETF.
Xu, et al. Expires June 24, 2021 [Page 5]
Internet-Draft MPLS Payload Protocol ID December 2020
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bottom Label | TC |1| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 1 1| Reserved | Protocol Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2
7. Acknowledgements
TBD.
8. IANA Considerations
A special purpose label with value of <TBD> or an extended special
purpose label with value of <TBD> for the PIL needs to be assigned by
the IANA
9. Security Considerations
TBD.
10. References
10.1. Normative References
[ETYPES] The IEEE Registration Authority, "IEEE 802 Numbers", 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
10.2. Informative References
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[RFC4023] Worster, T., Rekhter, Y., and E. Rosen, Ed.,
"Encapsulating MPLS in IP or Generic Routing Encapsulation
(GRE)", RFC 4023, DOI 10.17487/RFC4023, March 2005,
<https://www.rfc-editor.org/info/rfc4023>.
Xu, et al. Expires June 24, 2021 [Page 6]
Internet-Draft MPLS Payload Protocol ID December 2020
[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/info/rfc6790>.
[RFC7274] Kompella, K., Andersson, L., and A. Farrel, "Allocating
and Retiring Special-Purpose MPLS Labels", RFC 7274,
DOI 10.17487/RFC7274, June 2014,
<https://www.rfc-editor.org/info/rfc7274>.
[RFC8296] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
for Bit Index Explicit Replication (BIER) in MPLS and Non-
MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
2018, <https://www.rfc-editor.org/info/rfc8296>.
[RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
"Network Service Header (NSH)", RFC 8300,
DOI 10.17487/RFC8300, January 2018,
<https://www.rfc-editor.org/info/rfc8300>.
Authors' Addresses
Xiaohu Xu
Alibaba, Inc.
Email: 13910161692@qq.com
Hamid Assarpour
Broadcom
Email: hamid.assarpour@broadcom.com
Shaowen Ma
Mellanox
Email: mashaowen@gmail.com
Francois Clad
Cisco Systems, Inc.
Email: fclad@cisco.com
Xu, et al. Expires June 24, 2021 [Page 7]