IDR Working Group Yao. Liu
Internet-Draft Shaofu. Peng
Intended status: Standards Track ZTE Corporation
Expires: September 8, 2020 March 7, 2020
BGP Extensions for Unified SID in TE Policy
draft-liu-idr-segment-routing-te-policy-complement-00
Abstract
This document defines extensions to BGP in order to advertise Unified
SIDs in SR-TE policies.
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 September 8, 2020.
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.
Liu & Peng Expires September 8, 2020 [Page 1]
Internet-Draft BGP for Unified SID March 2020
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. SR policy with Unified SID . . . . . . . . . . . . . . . . . 2
2.1. BGP Extensions . . . . . . . . . . . . . . . . . . . . . 3
2.2. Head-end Processing . . . . . . . . . . . . . . . . . . . 5
3. Security Considerations . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Normative References . . . . . . . . . . . . . . . . . . 5
5.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Segment Routing [RFC8402] leverages the source routing paradigm. An
ingress node steers a packet through an ordered list of
instructions,called segments.
[I-D.ietf-spring-segment-routing-policy] details the concepts of SR
Policy and steering into an SR Policy.
[I-D.ietf-idr-segment-routing-te-policy] specifies the way to use BGP
to distribute one or more of the candidate paths of an SR Policy to
the headend of that policy.
With increasing requirements for a shortened identifier in a segment
routing network with the IPv6 data plane,
[I-D.mirsky-6man-unified-id-sr] proposed an extension of SRH that
enables the use of a shorter segment identifier, such as 32-bits
Label format SID or 32-bits IP address format SID.
This document defines extensions to BGP in order to advertise Unified
SIDs in SR-TE policies.
Firstly, we focus on how to carry 32-bits IP address format U-SID,
other type of U-SID will be considered in future version.
2. SR policy with Unified SID
As discussed in [I-D.ietf-spring-srv6-network-programming], the node
with the SRv6 capability will maintain its local SID table. A Local
SID is generally composed of two parts, that is, LOC:FUNCT, or may
carry arguments at the same time, that is, LOC:FUNCT:ARGS.
FUNCT indicates the local function of the packet on the node that
generates the LOC.ARGS may contain information related to traffic and
services, or any other information required for executing the
Liu & Peng Expires September 8, 2020 [Page 2]
Internet-Draft BGP for Unified SID March 2020
function.LOC indicates locator. In most cases, other nodes in the
network can forward packets to the node that generates this LOC
according to the corresponding routing table entries.
The controller plane protocol can also use B:N to represent an LOC,
where B is SRv6 SID Locator Block and N to represent node N. In
other words, the structure of a complete SID is B:N:FUNCT:ARGS.
[I-D.ietf-lsr-isis-srv6-extensions] defines the extension of ISIS to
support SRv6, and each node can announce the SID assigned by itself.
In particular, SRv6 SID Structure Sub-Sub-TLV is defined and the
specific structure of the corresponding SID is provided, including
the length of SRv6 SID Locator Block, the length of SRv6 SID Locator
Node, the length of SRv6 SID Function, and the length of SRv6 SID
Arguments.
Similarly, [I-D.ietf-bess-srv6-services] also provide the SID
structure information for L3VPN or EVPN service related SID.
Thus, it can be seen that the existing control plane protocol reveals
a very intuitive method to reduce the size of SRH. That is , under
the specific address planning(the SIDs allocated by all SRv6 nodes
are in the same SRv6 SID Locator Block), SRH only needs to store the
difference between SIDs (N:FUNCT:ARGS), and does not need to contain
the SRv6 SID Locator Block information. In a 128-bit classic SRv6
SID, the highest part is SRv6 SID Locator Block, and the following 32
bits are composed of SRv6 SID Locator Node, SRv6 SID Function and
SRv6 SID Arguments, and the rest bits are zeros.
As for how to obtain the SRv6 SID Locator Block information during
packet forwarding, there are two cases:
1)For the head-end node, when the node sends a packet along the
segment list to the first segment, it already knows the 128-bit
classical SID before truncaturing. The head node copies it directly
to the DA of IPv6 Header, but the SRH carries the 32-bit truncatured
SIDs.
2)For the transit node, it can obtain the SRv6 SID Locator Block
information from the DA of the received IPv6 packet.
2.1. BGP Extensions
This document defines a new one-bit flag field in the segment-list
sub-TLV [I-D.ietf-idr-segment-routing-te-policy] RESERVED field,
where,
Liu & Peng Expires September 8, 2020 [Page 3]
Internet-Draft BGP for Unified SID March 2020
T: Truncatured-Flag, when set, it indicates the presence of 32-bits
IP address format U-SID(s) in the SR path
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |T| RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// sub-TLVs //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: T-Flag in Segment List sub-TLV
In this document, the Flags field of each segment sub-TLV(type B/I/J/
K) [I-D.ietf-idr-segment-routing-te-policy] is extended to indicate
the block length (BL) and non-block length (NBL) of a 128-bit SID.
Figure 2 uses the type B segment sub-TLV as an example to illustrate
the extended LT field. Other types of segment sub-TLV are similar.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | LT | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 SID (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Length Type Field in Segment sub-TLV
LT: Length Type, 3-bit field with the following values:
000 unknown
001 BL=96bits, NBL=32bits,
010 BL=64bits, NBL=32bits,
011 BL=32bits, NBL=32bits,
Other values are reserved for future use.
It should be noted that NBL represents the length of the Node:Func
that is immediately followed the block.
Liu & Peng Expires September 8, 2020 [Page 4]
Internet-Draft BGP for Unified SID March 2020
2.2. Head-end Processing
Take the length of the short SID as 32 bits as an example.
On the head-end node, if the SR-TE tunnel has enabled the SRv6 SID
compression, and the compression mode is to use 32-bits IPv4 address
U-SID , then it analyzes whether these SIDs are in the same block and
whether the length of Node:Func does not exceed 32 bits based on the
NBL length corresponding to each SID contained in the segment List
received from the controller.
If the above conditions are met, the head-end node uses a 32-bit
short SID optimization SID List for SRH encapsulation.
Note that it can also be the responsibility of the controller to
check if there could use IPv4 address U-SID for the entire SID list,
especially for the inter-domain case. In this case the headend can
simply follow the decision of the controller.
3. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the security considerations discussed in
[I-D.ietf-idr-segment-routing-te-policy].
4. IANA Considerations
TBD
5. References
5.1. Normative References
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P.,
Rosen, E., Jain, D., and S. Lin, "Advertising Segment
Routing Policies in BGP", draft-ietf-idr-segment-routing-
te-policy-08 (work in progress), November 2019.
[I-D.ietf-lsr-isis-srv6-extensions]
Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
Z. Hu, "IS-IS Extension to Support Segment Routing over
IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-05
(work in progress), February 2020.
Liu & Peng Expires September 8, 2020 [Page 5]
Internet-Draft BGP for Unified SID March 2020
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Sivabalan, S., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-06 (work in progress),
December 2019.
[I-D.ietf-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
Matsushima, S., and Z. Li, "SRv6 Network Programming",
draft-ietf-spring-srv6-network-programming-10 (work in
progress), February 2020.
[I-D.mirsky-6man-unified-id-sr]
Cheng, W., Mirsky, G., Peng, S., Aihua, L., Wan, X., Wei,
C., and S. Shay, "Unified Identifier in IPv6 Segment
Routing Networks", draft-mirsky-6man-unified-id-sr-05
(work in progress), February 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>.
5.2. Informative References
[I-D.ietf-bess-srv6-services]
Dawra, G., Filsfils, C., Raszuk, R., Decraene, B., Zhuang,
S., and J. Rabadan, "SRv6 BGP based Overlay services",
draft-ietf-bess-srv6-services-01 (work in progress),
November 2019.
Authors' Addresses
Liu Yao
ZTE Corporation
No. 50 Software Ave, Yuhuatai Distinct
Nanjing
China
Email: liu.yao71@zte.com.cn
Liu & Peng Expires September 8, 2020 [Page 6]
Internet-Draft BGP for Unified SID March 2020
Peng Shaofu
ZTE Corporation
No. 50 Software Ave, Yuhuatai Distinct
Nanjing
China
Email: peng.shaofu@zte.com.cn
Liu & Peng Expires September 8, 2020 [Page 7]