Internet DRAFT - draft-voyer-6man-extension-header-insertion
draft-voyer-6man-extension-header-insertion
Network Working Group D. Voyer, Ed.
Internet-Draft Bell Canada
Intended status: Informational C. Filsfils
Expires: May 24, 2021 D. Dukes, Ed.
Cisco Systems, Inc.
S. Matsushima
Softbank
J. Leddy
Individual Contributor
Z. Li
Huawei
J. Guichard
Futurewei
November 20, 2020
Deployments With Insertion of IPv6 Segment Routing Headers
draft-voyer-6man-extension-header-insertion-10
Abstract
SRv6 is deployed in multiple provider networks.
This document describes the usage of SRH insertion and deletion
within the SR domain and how security and end-to-end integrity is
guaranteed.
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].
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."
Voyer, et al. Expires May 24, 2021 [Page 1]
Internet-Draft SRH Insertion November 2020
This Internet-Draft will expire on May 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
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
2. Deployment Report . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Deployments . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Vendor and Open-Source Support . . . . . . . . . . . . . 3
3. Deployment Experience With SRH Header Operarion . . . . . . . 4
3.1. The SR Domain . . . . . . . . . . . . . . . . . . . . . . 5
4. Baseline Usecase . . . . . . . . . . . . . . . . . . . . . . 5
5. Choosing an SRv6 SID Block . . . . . . . . . . . . . . . . . 6
6. Securing the SR Domain . . . . . . . . . . . . . . . . . . . 7
7. MTU within the SR domain . . . . . . . . . . . . . . . . . . 7
8. VPN with SRv6 . . . . . . . . . . . . . . . . . . . . . . . . 7
9. TILFA with SRv6 . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. SRH Insertion Process . . . . . . . . . . . . . . . . . . 8
9.2. The Penultimate SID of the Inserted SRH is of PSP flavor 9
9.3. MTU-delta . . . . . . . . . . . . . . . . . . . . . . . . 9
10. Security Considerations . . . . . . . . . . . . . . . . . . . 10
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 10
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
13.1. Normative References . . . . . . . . . . . . . . . . . . 10
13.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
[I-D.matsushima-spring-srv6-deployment-status] records multiple SRv6
deployments in multiple networks
Voyer, et al. Expires May 24, 2021 [Page 2]
Internet-Draft SRH Insertion November 2020
In each deployment, traffic traversing an SR domain is encapsulated
in an outer IPv6 header for its journey through the SR domain.
To implement transport services within the SR domain, insertion or
removal of an SRH after the outer IPv6 header is performed. Any
segment within the SRH is strictly contained within the SR domain.
The SR domain always preserves the end-to-end integrity of traffic
traversing it. No extension header is manipulated, inserted or
removed from an inner transported packet. The packet leaving the SR
domain is exactly the same (except for the hop-limit update) as the
packet entering the SR domain.
The SR domain is designed with link MTU sufficiently greater than the
MTU at the ingress edge of the SR domain.
2. Deployment Report
The following deployments are as of November 2019.
2.1. Deployments
Six operators have publicly reported SRv6 deployments with commercial
traffic supported by linerate hardware. Each deployment follows the
network design and SRH add/remove behavior described in this
document.
Softbank
China Telecom
Iliad
China Unicom
CERNET2
MTN Uganda Ltd.
Further information can be found in
[I-D.matsushima-spring-srv6-deployment-status]
2.2. Vendor and Open-Source Support
Eighteen unique implementations of SRv6 are available from multiple
vendors and open source initiatives that support the SRH add/remove
behavior described in this document:
Voyer, et al. Expires May 24, 2021 [Page 3]
Internet-Draft SRH Insertion November 2020
Cisco ASR 9000
Cisco NCS 5500
Cisco NCS 560
Cisco NCS 540
Cisco ASR1000
Huawei ATN
Huawei CX600
Huawei NE40E
Hauwei ME60
Huawei NE5000E
Huawei NE9000
Huawei NG-OLT MA5800
Barefoot Tofino 1 NPU
Barefoot Tofino 2 NPU
Broadcom Jericho 1, 1+
Broadcom Jericho 2
Linux kernel
FD.io VPP
Marvell's Prestera Falcon CX 8500 family
Intel PAC N3000
Further information can be found in
[I-D.matsushima-spring-srv6-deployment-status]
3. Deployment Experience With SRH Header Operarion
Voyer, et al. Expires May 24, 2021 [Page 4]
Internet-Draft SRH Insertion November 2020
3.1. The SR Domain
An SR Domain is defined in [RFC8402].
Section 5.2 of [I-D.ietf-6man-segment-routing-header] further
describes the SR domain as a single system with delegation among
components. It states:
All intra SR Domain packets are of the SR Domain. The IPv6 header
is originated by a node of the SR Domain, and is destined to a
node of the SR Domain.
All inter domain packets are encapsulated for the part of the
packet journey that is within the SR Domain. The outer IPv6
header is originated by a node of the SR Domain, and is destined
to a node of the SR Domain.
In other words, all packets within the SR domain have a source and
destination address within the SR Domain.
The SR domain is secured as per Section 5.1 of
[I-D.ietf-6man-segment-routing-header] and no external packet can
enter the domain with a destination address equal to a segment of the
domain.
In other words, no node outside the SR domain may send packets to,
nor make direct use of, segments within the SR domain.
4. Baseline Usecase
The following abstract illustration shows the SR Domain, how traffic
is encapsulated when traversing the SR domain, and (in subequent
sections) how an SRH is inserted and processed for a packet
traversing the SR domain. It is representative of all deployments in
Section 2.1.
Voyer, et al. Expires May 24, 2021 [Page 5]
Internet-Draft SRH Insertion November 2020
+ * * * * * * * * * * * * * * * * * * * * +
* *
[1]----[3]--------[5]----------------[6]---------[4]---[2]
* | | *
| |
* | | *
[7]----------------[8]
* *
+ * * * * * * * SR Domain * * * * * * * +
Figure 1
o 3 and 4 are SR Domain edge routers
o 5, 6, 7, and 8 are all SR Domain routers
o 1 and 2 are hosts outside the SR Domain
Since all inter domain packets are encapsulated for the part of the
packet journey that is within the SR Domain, a packet sent from 1 and
destined to 2 is encapsulated in an outer IP v6 header between nodes
3 and 4.
5. Choosing an SRv6 SID Block
Without revealing the specifics of each deployment, the following
well-known technique can be used:
Obtain a GUA block from the respective registry (e.g.
PPPP:PPP0::/28)
Sub-allocate a block for SID allocation (e.g.
PPPP:PPPB:BB00::/40)
Allocate a /64 SID locator to each node in the domain that needs
to provide network instruction (e.g. node 4 gets
PPPP:PPPB:BB00:0004::/64 as a SID locator)
Vendors and operators have automated the process of locator
selection, the details of which are outside the scope of this
document.
Voyer, et al. Expires May 24, 2021 [Page 6]
Internet-Draft SRH Insertion November 2020
6. Securing the SR Domain
The security measures defined in
[I-D.ietf-6man-segment-routing-header] Section 5.1 are applied.
Protection level 1: filter external traffic entering the SR domain.
For example, node 4 (on its interface from node 2) applies an ingress
ACL that drops any packet with DA within the PPPP:PPPB:BB00::/40
block.
Protection level 2: filter internal traffic. For example, node 4 (on
its interface from node 6) applies an ingress ACL that drops any
packet with DA in PPPP:PPPB:BB00:0004::/64 block if SA is not within
the block PPPP:PPP0::/28
Vendors and operators have automated the application of these
protection levels, the details of which are outside the scope of this
document.
7. MTU within the SR domain
The deployments, Section 2.1, leverage the extensively used practice
of ensuring an MTU within the domain is bigger than the MTU on the
external links of the domain.
More specifically, the MTU difference (MTU-Delta) is designed to be
larger than the maximum encapsulation overhead deemed required by the
deployment.
The exact number is operator specific and is outside the scope of
this document. Some indications on how to plan this are provided in
the following sections.
Any packet exceeding the MTU of a link generates an IPv6 ICMP error
message "packet too big" back to the source of the packet.
8. VPN with SRv6
The deployments involve the creation of commercial SRv6-based VPN
traffic as described in [I-D.ietf-bess-srv6-services].
The salient point to note is that no SRH needs to be inserted to
realize an SRv6 VPN service.
The ingress PE encapsulates the inner packet in an outer header and
sets the outer DA to the END.DT/DX SID signaled by the egress PE.
Voyer, et al. Expires May 24, 2021 [Page 7]
Internet-Draft SRH Insertion November 2020
MTU-Delta must be >= 40 bytes to allow for the outer IPv6
encapsulation without fragmentation.
9. TILFA with SRv6
The deployments involve the delivery of sub-50msec TILFA protection
to the commercial SRv6-based VPN traffic transported by the operator
network [I-D.ietf-rtgwg-segment-routing-ti-lfa].
In these deployments, when a failure is detected, the Point of Local
Repair (PLR) inserts an SRH implementing the precomputed TILFA backup
path.
The following salient points are discussed:
SRH insertion process
The penultimate SID of the inserted SRH is of PSP flavor
MTU-delta planning
9.1. SRH Insertion Process
When an SRH is inserted by an intermediate node it walks the IPv6
header chain to the first header after the IPv6 header and inserts
the SRH prior to that header.
+---------------+------------
| IPv6 header | IPv4 header
| VPN Service |
| Next Header = |
| IPv4 |
+---------------+------------
^-SRH insertion here
Figure 2
An SR Policy headend within the SR domain inserts an SRH as follows:
1. Determine where to insert the SRH.
2. Copy the destination address from the IPv6 header to Segment
List[0] of the SRH to be inserted. This ensures the original
destination address is restored upon execution of the final
segment in the inserted SRH.
3. Increase the IPv6 header payload length field by the length in
bytes of the inserted SRH.
Voyer, et al. Expires May 24, 2021 [Page 8]
Internet-Draft SRH Insertion November 2020
If the resulting payload length exceeds 2^16 bytes generate an
ICMP "Packet To Big" error message to the source with an MTU of
2^16 minus the length in bytes of the SRH and discard the packet.
Note: this does not occur in reported deployments given the MTU
design constraint.
4. Set the SRH next header field to the value in the next header
field of the header that will precede the SRH.
5. Set the next header field of the header that will precede the SRH
to the routing extension header (43)
6. Set the IPv6 destination address to the first segment in the
segment list of the SRH to be inserted. This segment may or may
not be present in the SRH depending on the use of a reduced SRH,
see section 4.1.1 of [I-D.ietf-6man-segment-routing-header].
7. Insert the SRH into the packet at the location it should be
inserted and resubmit the packet to the IPv6 module for
transmission to the new destination.
9.2. The Penultimate SID of the Inserted SRH is of PSP flavor
The TILFA protection service is essentially a transparent service: it
seeks to make the loss of a link, node or SRLG invisible to the
transport service. It is also a very transient service as it only
lasts a few hundreds of msec while the IGP converges.
Consistent with this transparent service definition, the deployments
leverage a TILFA computation that ensures that the penultimate SID of
the inserted SRH is of PSP flavor.
9.3. MTU-delta
The vendors reporting the listed deployments have collectively
deployed TILFA in tens of SR-MPLS networks, in 6 SRv6 networks and
have simulated their SRv6 algorithm in tens of collected real
topologies. The inferred experience is that the probability that a
TILFA backup path requires more than 2 SRv6 SIDs is very rare.
MTU-Delta must be >= 80 bytes.
40 bytes (VPN service)
+ 8 (SRH) (TILFA)
+ 2 * 16 (2 TILFA SID's)
Voyer, et al. Expires May 24, 2021 [Page 9]
Internet-Draft SRH Insertion November 2020
The maximum encapsulation size of any node within the SR domain is
limited to a specific value, this maximum is used to calculate the
maximum link MTU of interfaces ingress to the SR domain.
10. Security Considerations
Section 6 describes the method of securing the SR domain in the
deployments listed.
All security considerations discussed in
[I-D.ietf-6man-segment-routing-header] are equally applicable when an
SRH insertion is performed.
11. IANA Considerations
This document doesn't introduce any IANA request.
12. Contributors
The authors would like to thank the following for their
contributions: Robert Raszuk, Stefano Previdi, Stefano Salsano,
Antonio Cianfrani, David Lebrun, Olivier Bonaventure, Prem
Jonnalagadda, Milad Sharif, Hani Elmalky, Ahmed Abdelsalam, Arthi
Ayyangar, Dirk Steinberg, Wim Henderickx.
13. References
13.1. Normative References
[I-D.ietf-6man-segment-routing-header]
Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", draft-ietf-6man-segment-routing-header-26 (work in
progress), October 2019.
[I-D.ietf-bess-srv6-services]
Dawra, G., Filsfils, C., Talaulikar, K., Raszuk, R.,
Decraene, B., Zhuang, S., and J. Rabadan, "SRv6 BGP based
Overlay services", draft-ietf-bess-srv6-services-05 (work
in progress), November 2020.
[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>.
Voyer, et al. Expires May 24, 2021 [Page 10]
Internet-Draft SRH Insertion November 2020
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
13.2. Informative References
[I-D.ietf-rtgwg-segment-routing-ti-lfa]
Litkowski, S., Bashandy, A., Filsfils, C., Decraene, B.,
Francois, P., Voyer, D., Clad, F., and P. Camarillo,
"Topology Independent Fast Reroute using Segment Routing",
draft-ietf-rtgwg-segment-routing-ti-lfa-04 (work in
progress), August 2020.
[I-D.matsushima-spring-srv6-deployment-status]
Matsushima, S., Filsfils, C., Ali, Z., Li, Z., and K.
Rajaraman, "SRv6 Implementation and Deployment Status",
draft-matsushima-spring-srv6-deployment-status-09 (work in
progress), November 2020.
Authors' Addresses
Daniel Voyer (editor)
Bell Canada
Canada
Email: daniel.voyer@bell.ca
Clarence Filsfils
Cisco Systems, Inc.
Belgium
Email: cfilsfil@cisco.com
Darren Dukes (editor)
Cisco Systems, Inc.
Ottawa
Canada
Email: ddukes@cisco.com
Voyer, et al. Expires May 24, 2021 [Page 11]
Internet-Draft SRH Insertion November 2020
Satoru Matsushima
Softbank
Japan
Email: satoru.matsushima@g.softbank.co.jp
John Leddy
Individual Contributor
USA
Email: john@leddy.net
Zhenbin Li
Huawei
China
Email: lizhenbin@huawei.com
James Guichard
Futurewei
USA
Email: james.n.guichard@futurewei.com
Voyer, et al. Expires May 24, 2021 [Page 12]
