Internet DRAFT - draft-mirsky-6man-unified-id-sr
draft-mirsky-6man-unified-id-sr
Network C. Weiqiang
Internet-Draft China Mobile
Intended status: Standards Track G. Mirsky
Expires: 29 March 2022 Ericsson
P. Shaofu
L. Aihua
ZTE Corporation
G. Mishra
Verizon Inc.
25 September 2021
Unified Identifier in IPv6 Segment Routing Networks
draft-mirsky-6man-unified-id-sr-10
Abstract
Segment Routing architecture leverages the paradigm of source
routing. It can be realized in a network data plane by prepending
the packet with a list of instructions, a.k.a. segments. A segment
can be encoded as a Multi-Protocol Label Switching (MPLS) label, IPv4
address, or IPv6 address. Segment Routing can be applied in the MPLS
data plane by encoding segments in the MPLS label stack. It also can
be applied to the IPv6 data plane by encoding a list of segment
identifiers in IPv6 Segment Routing Extension Header (SRH). This
document extends the use of the SRH to unified segment identifiers
encoded, for example, as MPLS label or IPv4 address, to compress the
SRH, and support more detailed network programming and interworking
between SR-MPLS and SRv6 domains.
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 29 March 2022.
Weiqiang, et al. Expires 29 March 2022 [Page 1]
Internet-Draft Unified Identifier SRv6 September 2021
Copyright Notice
Copyright (c) 2021 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 . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions used in this document . . . . . . . . . . . . 3
1.1.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . 3
1.1.2. Requirements Language . . . . . . . . . . . . . . . . 4
2. Segment Routing Extension Header: Benefits and Challenges . . 4
3. Unified SIDs in IPv6 Segment Routing Extension Header . . . . 4
4. Operations with Unified Segment Identifier . . . . . . . . . 6
4.1. Procedures of 32bits MPLS Label within SRH . . . . . . . 7
4.1.1. Packet Forwarding Based on UET-MPLS U-SID . . . . . . 8
4.2. Procedures of 32bits IP Address within SRH . . . . . . . 9
4.2.1. Packet Forwarding Based on UET-32 U-SID . . . . . . . 10
5. The Use Case of Unified Segment Identifier . . . . . . . . . 11
5.1. Nesting Interworking Between SR-MPLS and SRv6 Using Binding
U-SID . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.2. Flat Interworking Between Different UET Domains Using
Mixing U-SID . . . . . . . . . . . . . . . . . . . . . . 15
5.2.1. UET Capability Advertisement . . . . . . . . . . . . 15
5.2.2. SRv6 SID Allocated per UEC . . . . . . . . . . . . . 16
5.2.3. Packets Forwarding Procedures . . . . . . . . . . . . 17
6. Control Plane in Support of Unified SID . . . . . . . . . . . 21
7. SRH with U-SID Pseudo-code . . . . . . . . . . . . . . . . . 22
8. U-SID supporting SRv6 programming . . . . . . . . . . . . . . 23
9. Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . 24
10. Implementation Considerations . . . . . . . . . . . . . . . . 24
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
12. Security Considerations . . . . . . . . . . . . . . . . . . . 24
13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 24
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25
15. Normative References . . . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
Weiqiang, et al. Expires 29 March 2022 [Page 2]
Internet-Draft Unified Identifier SRv6 September 2021
1. Introduction
Segment Routing architecture [RFC8402] leverages the paradigm of
source routing. It can be realized in a network data plane by
prepending the packet with a list of instructions, a.k.a. segment
identifiers (SIDs). A segment can be encoded as a Multi-Protocol
Label Switching (MPLS) label, IPv4 address, or IPv6 address. Segment
Routing can be applied in MPLS data plane by encoding 20-bits SIDs in
MPLS label stack [RFC8660]. It also can be applied to IPv6 data
plane by encoding a list of 128-bits SIDs in IPv6 Segment Routing
Extension Header (SRH) [RFC8754].
This document extends the use of the SRH [RFC8754] to unified
identifiers encoded as MPLS label or IPv4 address to support more
detailed network programming and interworking between SR-MPLS and
SRv6 domains.
1.1. Conventions used in this document
1.1.1. Acronyms
SR: Segment Routing
SRH: Segment Routing Extension Header
MPLS: Multiprotocol Label Switching
SR-MPLS: Segment Routing using MPLS data plane
SID: Segment Identifier
IGP: Interior Gateway Protocol
DA: Destination Address
ILM: Incoming Label Map
FEC: Forwarding Equivalence Class
FTN: FEC-to-NHLFE map
OAM: Operation, Administration, and Maintenance
TE: Traffic Engineering
SRv6: Segment Routing in IPv6
U-SID: Unified Segment Identifier
Weiqiang, et al. Expires 29 March 2022 [Page 3]
Internet-Draft Unified Identifier SRv6 September 2021
PSP: Penultimate Segment Popping
FIB: Forwarding Information Base
UET: U-SID Encapsulation Type
UEC: U-SID Encapsulation Capability
1.1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Segment Routing Extension Header: Benefits and Challenges
Many functions related to Operation, Administration, and Maintenance
(OAM) require identification of the SR tunnel ingress and the path,
constructed by segments, between the ingress and the egress SR nodes.
Combination of IPv6 encapsulation [RFC8200] and SRH [RFC8754],
referred to as SRv6, comply with these requirements while it is
challenging when applying SR in MPLS networks, also referred to as
SR-MPLS.
On the other hand, the size of IPv6 SID presents a scaling challenge
to use topological instructions that define strict explicit traffic-
engineered (TE) path or support network programming in combination
with service-based instructions. At the same time, that is where SR-
MPLS approach provides better results due to the smaller SID length.
It can be used to compress the SRv6 header size when a smaller
namespace of available SIDs is sufficient for addressing the
particular network.
SR-MPLS is broadly used in metro networks. With the gradual
deployment of SRv6 in the core networks, supporting interworking
between SR-MPLS and SRv6 becomes necessary for operators. It is
operationally more efficient and straightforward if SRv6 can use the
same size SIDs as in SR-MPLS. The SRH can be extended to define the
same, as in SR-MPLS, SID length to support the unified segment
identifier (U-SID). As a result, end-to-end SR tunnel may use U-SIDs
across SR-MPLS and SRv6 domains.
3. Unified SIDs in IPv6 Segment Routing Extension Header
SRH format has been defined in Section 3 of [RFC8754] as presented in
Figure 1
Weiqiang, et al. Expires 29 March 2022 [Page 4]
Internet-Draft Unified Identifier SRv6 September 2021
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type | Segments Left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Entry | Flags | Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[0] (128 bits IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
...
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[n] (128 bits IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
// Optional Type Length Value objects (variable) //
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: SRH format
This document defines a new field Size in the SRH Flags field as a
two-bits field, termed as UET (U-SID Encapsulation Type) flag, to
indicate which type of SIDs are encoded in SRH. The UET flag has the
following values:
0b00 - indicate a 128-bits SID, an IPv6 address, termed as UET-128
U-SID.
0b01 - indicate a 32-bits SID, termed as UET-32 U-SID. In some
environments, the context could be of IPv4 address, while in some
other cases, it could represent an index of list or range of IPv4/
IPv6 addresses. Another interpretation of 32-bits SID could be as
a complementary element of an IPv4/IPv6 prefix. Setting the
interpretation might be made through the control plane-based
signaling and is outside the scope of this document. If this SID
represents a complementary part of an IPv4/IPv6 prefix, the
original IP address can be re-constructed by using, for example,
Weiqiang, et al. Expires 29 March 2022 [Page 5]
Internet-Draft Unified Identifier SRv6 September 2021
mapping, stitching, shifting, or translating operation.
Specification of such a mechanism is outside the scope of this
document.
0b10 - indicate a 32-bits SID, termed as UET-MPLS U-SID, which
includes an MPLS label in the leftmost 20-bits as displayed in
Figure 2. Information in the Context field could be interpreted
as a flavor of a particular network programming behavior.
Specification of the network programming using this type of U-SID
is outside the scope of this document. [Ed.note. Replace with
reference to the U-SID network programming document.]
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS Label | Context |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Format of Unified SID with MPLS Label
0b11 - indicate a 16-bits SID, termed as UET-16 U-SID. It is
similar to 32bits SID and suitable for scenes with higher
compression efficiency
This document also introduces a compatible operation on Segment Left
field, also termed as SRH.SL. The relationship between the value of
SRH.UET and the interpretation of the SRH.SL is as follows:
* if SRH.UET Flag is UET-128, SRH.SL represents the count of
128bits-SID entries in SRH;
* if SRH.UET Flag is UET-32 or UET-MPLS, SRH.SL represents the count
of 32bits-SID entries in SRH;
* if SRH.UET Flag is UET-16, SRH.SL represents the count of 16bits-
SID entries in SRH.
4. Operations with Unified Segment Identifier
When SRH is used to include 32-bits long U-SIDs, the ingress and
transit nodes of an SR tunnel act as described in Section 5.1 and
Section 5.2 of [RFC8754] respectively.
Weiqiang, et al. Expires 29 March 2022 [Page 6]
Internet-Draft Unified Identifier SRv6 September 2021
4.1. Procedures of 32bits MPLS Label within SRH
This section describes how the UET-MPLS type of U-SID is used to
encode a compressed SRH. In this case, an ILM (Incoming Label Map)
entry can be used to map a U-SID to an IPv6 address. As a result, it
is not necessary to introduce a new type of index-based mapping
table. For the ILM entry of Adjacency-SID, the mapping result copied
to DA (Destination Address) is the remote interface IPv6 address.
For the ILM entry of Node-SID, the mapping result copied into DA is a
remote node loopback IPv6 address.
Operations on an MPLS label of U-SID type are the same as those
defined in [RFC8663]. However, SR-MPLS over SRH has the following
advantages compared with SR-MPLS over UDP:
* SRH is flexible to extend flags or sub-TLVs for service
requirements, but not in the case of SR-MPLS over UDP.
* Labels in SRH can meet 8 bytes alignment requirements as per
[RFC8200], but not in the case of SR-MPLS over UDP.
* The source address and the complete path information of the SR
policy are not discarded, but not in the case of SR-MPLS over UDP.
* The forwarding performance of SR-MPLS over SRH is better than the
UDP method because it only updates the destination address rather
than frequently removing and adding outer headers.
Procedures of SR-MPLS over IP of [RFC8663] described how to construct
an adjusted SR-MPLS FTN (FEC-to-NHLFE map) and ILM entry towards a
prefix-SID when next-hops are IP-only routers. The action of FTN and
ILM entry will steer the packet along an outer tunnel to the
destination node that has originated the FEC (Forwarding Equivalence
Class). UDP header is removed and put again at each segment
endpoint. However, for SR-MPLS over SRH in this document, the
proposed solution is not dependent on adjusted FIB (Forwarding
Information Base) entry. That is because no action is needed to get
from the FIB entry. A traditional ILM entry (maybe without out-label
because of IP-only next-hop) is enough to get the FEC information,
i.e., map a U-SID to an IPv6 address and copy to DA. Note that an
implementation can get FEC and next-hop/interface forwarding
information from the ILM entry, avoiding extra FIB lookup. An SRv6
policy chosen to encapsulate the U-SID list within SRH is determined
at the ingress node of this SRv6 policy. The SRH is preserved along
the SR to the egress. However, in the case of PSP (Penultimate
Segment Popping), the behavior is different from SR-MPLS over IP/UDP
method [RFC8663], so the source address (i.e., the ingress of the
SRv6 policy) is not discarded.
Weiqiang, et al. Expires 29 March 2022 [Page 7]
Internet-Draft Unified Identifier SRv6 September 2021
4.1.1. Packet Forwarding Based on UET-MPLS U-SID
The packet forwarding based on UET-MPLS U-SID is similar to the
processing described in [RFC8663]. But it differs from that in FIB
action and segment list processing. For completeness, we repeat the
description of [RFC8663] with modification as follows.
+-----+ +-----+ +-----+ +-----+ +-----+
| A +-------+ B +-------+ C +--------+ D +--------+ H |
+-----+ +--+--+ +--+--+ +--+--+ +-----+
| | |
| | |
+--+--+ +--+--+ +--+--+
| E +-------+ F +--------+ G |
+-----+ +-----+ +-----+
+--------+ +--------+ +--------+
|IP(A->E)| |IP(A->G)| |IP(A->G)|
+--------+ +--------+ +--------+
|SRH | |SRH | |SRH |(or PSP)
| SL:2 | | SL:1 | | SL:0 |
| L(E) | | L(E) | | L(E) |
| L(G) | | L(G) | | L(G) |
| L(H) | | L(H) | | L(H) |
+--------+ +--------+ +--------+
| Packet | ---> | Packet | ---> | Packet |
+--------+ +--------+ +--------+
Figure 3: Packet Forwarding Example with UET-MPLS U-SID
In the example shown in Figure 3, assume that routers A, E, G, and H
are U-SID capable (i.e., both SR-MPLS and SRv6 capable) while the
remaining routers (B, C, D, and F) are only capable of forwarding IP
packets. Routers A, E, G, and H advertise their Segment Routing
related information via IS-IS or OSPF.
Now assume that router A (the Domain ingress) wants to send a packet
to router H (the Domain egress) via an SRv6 policy with the explicit
path {E->G->H}. Router A will impose an MPLS label stack within SRH
on the packet corresponding to the explicit path. Router A searches
ILM entry by the top label (that indicated router E), get the FEC
information and next-hop/interface forwarding information, a loopback
IPv6 address of E, and then copies to DA and sends the packet.
SRH.UET is set to UET-MPLS and the value of SRH.SL is 2.
Weiqiang, et al. Expires 29 March 2022 [Page 8]
Internet-Draft Unified Identifier SRv6 September 2021
When the IPv6 packet arrives at router E, router E picks the next
segment (label) within SRH based on the SRH.SL value of 2, searches
ILM entry by the next label, get the FEC information and next-hop/
interface forwarding information, a loopback IPv6 address of G, and
then copy to DA and sends the packet. SRH.UET is set to UET-MPLS,
and the value of SRH.SL is 1.
When the IPv6 packet arrives at router G, router G gets the next
segment (label) within SRH based on the SRH.SL value of 1, then looks
up ILM entry by the next label, gets the FEC information and next-
hop/interface forwarding information, a loopback IPv6 address of H,
and then copies it to IP DA and transmits the packet. Because the
value of SRH.SL is 0; the SRH can be removed if the behavior flavor
codepoint of the above next segment (label) is set to PSP.
4.2. Procedures of 32bits IP Address within SRH
This section describes how the UET-32 type of U-SID is used to encode
a compressed SRH.
[RFC6554] specifies the Source Routing Header (to avoid confusion
with Segment Routing Header, we call it SRH3 according to type 3) for
use strictly between RPL (Routing Protocol for Low-Power and Lossy
Networks) routers in the same RPL routing domain. It introduces
mechanisms to compact the source route entries when all entries share
the same prefix with the IPv6 Destination Address of a packet
carrying an SRH. For each entry in Address[1..n] within the Routing
header, the shared prefix octets are not carried, but only a shorter
truncated piece of the original 128bits. During packet forwarding,
the shorter entry gets one by one and restored to the original IPv6
address. The Segment Left field represents the number of segments
remaining, i.e., the number of explicitly listed intermediate nodes
still to be visited before reaching the final destination, not the
number of 128bits entries.
The described above mechanism, introduced in SRH3, could also be
brought to Segment Routing Header (SRH). However, unlike in SRH3,
using explicit fields within the Routing header to indicate the
number of prefix octets common with the IPv6 Destination Address,
this document introduces a new Flavor for Endpoint Behavior, defined
in [RFC8986], termed as UET Flavor, for SRv6 SIDs. The UET Flavor of
the current active SID indicates the next SID's compressed length
within SRH, thus preparing the next SID of the corresponding length.
The UET Flavor information of a SID can be stored in the local SID
entry of that SID.
Weiqiang, et al. Expires 29 March 2022 [Page 9]
Internet-Draft Unified Identifier SRv6 September 2021
This section defines the following two UET Flavors for Endpoint
Behavior:
UET-32 Flavor: a SID with UET-32 Flavor means in SRH that the next
SID is a 32bits IPv4 address or number.
UET-16 Flavor: a SID with UET-16 Flavor means in SRH that the next
SID is a 16bits address or number.
For the convenience of expression, we can use UET-128 Flavor for the
case when the next SID is a traditional 128bits IPv6 address. Note
that UET-128 Flavor is not defined in the document.
An SRv6 SID MUST NOT have multiple UET Flavors at the same time.
4.2.1. Packet Forwarding Based on UET-32 U-SID
This section describes the packet forwarding based on UET-32 U-SID.
For UET-16 U-SID, it is similar.
+-----+ +-----+ +-----+ +-----+ +-----+
| A +-------+ B +-------+ C +--------+ D +--------+ H |
+-----+ +--+--+ +--+--+ +--+--+ +-----+
| | |
| | |
+--+--+ +--+--+ +--+--+
| E +-------+ F +--------+ G |
+-----+ +-----+ +-----+
+--------+ +--------+ +--------+
|IP(A->E)| |IP(A->G)| |IP(A->G)|
+--------+ +--------+ +--------+
|SRH | |SRH | |SRH |
| SL:2 | | SL:1 | | SL:0 |
| 32-H | | 32-H | | 32-H |
| 32-G | | 32-G | | 32-G |
| 32-E | | 32-E | | 32-E |
+--------+ +--------+ +--------+
| Packet | ---> | Packet | ---> | Packet |
+--------+ +--------+ +--------+
Figure 4: Packet Forwarding Example with UET-32 U-SID
In the example shown in Figure 4, assume that routers A, E, G, and H
are U-SID capable while the remaining routers (B, C, D, and F) are
only capable of forwarding IP packets. Routers A, E, G, and H
Weiqiang, et al. Expires 29 March 2022 [Page 10]
Internet-Draft Unified Identifier SRv6 September 2021
advertise their Segment Routing related information via IS-IS or
OSPF, especially SRv6 SIDs with SID structure and UET-32 Flavor
information.
Suppose that router A allocates an END SID B:32-A::, router E
allocates an END SID B:32-E::, router G allocates an END SID
B:32-G::, and router H allocates an END SID B:32-H::. All these SIDs
have the same SID structure, i.e., share the same common prefix B
(also known as the SRv6 SID Locator Block), and the sum of the Node
Length, Function Length, Argument Length of each SID are the same.
Now assume that router A (the Domain ingress) wants to send a packet
to router H (the Domain egress) via an SRv6 policy with the explicit
path {E->;G->H}. Router A will impose a UET-32 U-SID stack within SRH
on the packet that corresponds to that explicit path. The U-SID
stack consists of three shorter 32bits UET-32 U-SIDs, which are 32-E,
32-G, 32-H. Router A gets the first U-SID 32-E from SRH and restores
it to the original IPv6 address B:32-E::, then copy it to DA and
sends the packet according to IPv6 FIB lookup. SRH.UET is initially
set to UET-32 and the value of SRH.SL is 2.
When the IPv6 packet arrives at router E, match the local SID entry
of B:32-E::. Router E get the next U-32 32-G within SRH based on the
SRH.SL value of 2, and restore it to the original IPv6 address
B:32-G::, then copy it to DA and sends the packet according to IPv6
FIB lookup. SRH.UET remains unchanged, and the value of SRH.SL is 1.
When the IPv6 packet arrives at router G, match the local SID entry
of B:32-G::. Router G gets the next U-32 32-H within SRH based on the
SRH.SL value of 1, and restore it to the original IPv6 address
B:32-H::, then copy it to DA and sends the packet according to IPv6
FIB lookup. SRH.UET remains unchanged, and the value of SRH.SL is 0.
The SRH can be removed if the local SID entry of B:32-G:: has PSP
Flavor.
When the IPv6 packet arrives at router H, match the local SID entry
of B:32-H:: and Proceed to process the next header in the packet.
5. The Use Case of Unified Segment Identifier
In addition to being used for compression, U-SID can also be used in
interworking between SR-MPLS and SRv6 domains. SR-MPLS is often used
in a metro network, for example, in the backhaul metro network of
CMCC. If the core network uses SRv6, for example, the core network
of the same operator, U-SID can be used in the SRv6 domain to
interwork with SR-MPLS in the metro network to form an end-to-end SR
policy or tunnel.
Weiqiang, et al. Expires 29 March 2022 [Page 11]
Internet-Draft Unified Identifier SRv6 September 2021
5.1. Nesting Interworking Between SR-MPLS and SRv6 Using Binding U-SID
SR-MPLS uses SR SIDs as MPLS labels in the MPLS stack, and the SIDs
are 32-bits long. SRv6 uses SR SIDs as IPv6 extension header in SRH,
and the SIDs are 128-bits long.
The type UET-MPLS of U-SID uses the same 32-bits long SIDs in the
MPLS stack and SRH. Thus, four 32-bits long U-SIDs can be placed in
the space of a single 128-bits long header. The encapsulation is
illustrated in Figure 5.
+---------+ +----------------------------------+
| | | IPv6 header |
| Ethernet| +----------------------------------+
| | | SRH |
+---------+ +----------------------------------+
| USID1 | | USID1 | USID2 | ... | USID4 |
+---------+ +----------------------------------+
| USID2 | | USID5 |... | USIDn | Null |
+---------+ +----------------------------------+
| ... | + Payload |
+---------+ +----------------------------------+
| USIDn |
+---------+
| Payload |
+---------+
Figure 5: 32-bits long U-SIDs Encapsulation
This document RECOMMENDS using Binding SID for interworking because
Binding SID allows hiding the difference between U-SID types of
different domains Additionally, a headend with only classical SRv6
SRH encapsulation capability, i.e., no capability to put multiple
short U-SIDs to a single 128bits entry, will not need to upgrade.
Although Binding SID that is allocated for the specific SR policy
instance will bring more states on some domain border nodes, the SR
policy instance itself maybe pre-exist due to other requirements.
The SR policy is created within each UET domain that can be upgraded
separately.
To interwork, an MPLS Binding SID could be allocated for an SRv6
policy, used to hide the details of the UET-128 domain (classical
SRv6) for a traditional MPLS Label stack. Similarly, an SRv6 Binding
SID could be allocated for an SR-MPLS policy, used to hide the UET-
MPLS domain's details for a conventional SRv6 SRH. An SRv6 Binding
SID allocated for an SRv6 policy that enables the UET-32 compression
Weiqiang, et al. Expires 29 March 2022 [Page 12]
Internet-Draft Unified Identifier SRv6 September 2021
style will hide the details of the UET-32 domain for a traditional
SRv6 SRH. There may be other combinations that are not discussed in
the document.
Note that in some cases, Binding SID will cause multiple SRH to be
inserted in the IPv6 header.
The SR-MPLS and SRv6 interworking is illustrated in Figure 6. An
end-to-end SR path from A to F crosses the SR-MPLS and SRv6 domains.
The SR-MPLS domain could be using the IPv4 or IPv6 address family.
The SRv6 border nodes (E/G) receive SR-MPLS packets and forward them
into the SRv6 domain using an SR-MPLS Binding SID [RFC8660].
+-----+ +-----+ +-----+ +-----+
| A +-----------+ B +-----------+ E +-----------+ F |
+-----+ +--+--+ +--+--+ +--+--+
| SR-MPLS | | SRv6 |
| | | |
+-----+ +--+--+ +--+--+ +--+--+
| C |-----------| D +-----------+ G +-----------+ H |
+-----+ +-----+ +-----+ +-----+
+--------------+
| Eth(E->G) |
+--------------+ +--------------+
| Eth(A->B) | |IPv6 DA:G.intf|
+--------------+ +--------------+ +--------------+
| USID(B) | | Eth(B->E) | |SRH |
+--------------+ +--------------+ |NH:MPLS SL:2|
| USID(E1) | | USID(E1) | |USID(ADJ E->G)|
+--------------+ +--------------+ |USID(ADJ G->H)|
| USID(E2) | | USID(E2) | |USID(ADJ H->F)|
+--------------+ +--------------+ +--------------+
|Label(service)| |Label(service)| |Label(service)|
+--------------+ +--------------+ +--------------+
| Payload | -> | Payload | -> | Payload |
+--------------+ +--------------+ +--------------+
Figure 6: SR-MPLS and SRv6 interworking
The SRv6 edge node E assigns two SIDs, e.g., E1 and E2, E1 is an SR-
MPLS Node-SID, E2 is an SR-MPLS Binding-SID, which represents an SRv6
policy (from E to F, via segment list E-G-H-F) with U-SID
encapsulation. At the headend A, the end-to-end segment list could
be B-E1-E2. Figure 3 demonstrates an example of the packet
forwarding, where U-SID is an MPLS label.
Weiqiang, et al. Expires 29 March 2022 [Page 13]
Internet-Draft Unified Identifier SRv6 September 2021
The reverse interworking is illustrated in Figure 7. An end-to-end
SR path from F to A crosses the SRv6 and SR-MPLS domains. The SRv6
border nodes (E/G) receive SRv6 packets and forward them into the SR-
MPLS domain using an SR-MPLS Binding SID or normal Prefix/Adjacency
SID.
+-----+ +-----+ +-----+ +-----+
| A +-----------+ B +-----------+ E +-----------+ F |
+-----+ +--+--+ +--+--+ +--+--+
| SR-MPLS | | SRv6 |
| | | |
+-----+ +--+--+ +--+--+ +--+--+
| C |-----------| D +-----------+ G +-----------+ H |
+-----+ +-----+ +-----+ +-----+
+--------------+
| Eth(F->H) |
+--------------+
|IPv6 DA:H.intf|
+--------------+
|SRH |
|NH:MPLS SL:2|
|USID(ADJ F->H)|
+--------------+ |USID(ADJ H->G)|
| Eth(E->B) | |USID(ADJ G->E)|
+--------------+ +--------------+ +--------------+
| Eth(B->A) | | USID(B) | | USID(B) |
+--------------+ +--------------+ +--------------+
| USID(A) | | USID(A) | | USID(A) |
+--------------+ +--------------+ +--------------+
|Label(service)| |Label(service)| |Label(service)|
+--------------+ +--------------+ +--------------+
| Payload | <- | Payload | <- | Payload |
+--------------+ +--------------+ +--------------+
Figure 7: SR-MPLS and SRv6 reverse interworking
The SRv6 edge node F assigns an SR-MPLS Binding-SID F2, which
represents an SRv6 policy (from F to E, via segment list F-H-G-E)
with U-SID encapsulation. At the headend F, the end-to-end segment
list could be F2-B-A.
Weiqiang, et al. Expires 29 March 2022 [Page 14]
Internet-Draft Unified Identifier SRv6 September 2021
5.2. Flat Interworking Between Different UET Domains Using Mixing U-SID
U-SRH can provide a different interworking scheme to support an end-
to-end SR tunnel or policy using a mixing type of U-SIDs if more
headend nodes have been upgraded to support encapsulating mixing
U-SID in SRH. For example, a SID list could contain some 128bits
classical SIDs, some 32bits U-SIDs (IP or Label), and some 16bits
U-SIDs at the same time. For this purpose, each U-SID in SRH must
meet the alignment requirement. For example, a UET-32 U-SID is
stored in a 4-byte alignment, and a UET-16 U-SID is stored in a
2-byte alignment.
The interworking of different UET domains is illustrated in Figure 8.
An end-to-end SR tunnel or policy from S to D with segment list <X,
ABR1, Y, ABR2, Z, D>, crosses the UET-128 domain, UET-32 domain and
UET-MPLS domain. Note that any order of UET domains is also possible
and is similar to the case displayed in Figure 8.
...................... .................... .....................
: : : : : :
+----+ +----+ +----+ +----+ +----+ +----+ +----+
| S +-----+ X +-----+ABR1+-----+ Y +-----+ABR2+-----+ Y +-----+ D |
+----+ +----+ +----+ +----+ +----+ +----+ +----+
: : : : : :
........UET-128....... .......UET-32....... .......UET-MPLS......
Figure 8: Interworking between different UET SID
5.2.1. UET Capability Advertisement
In an SRv6 network, each node can configure its U-SID Encapsulation
Capability (UEC), and advertise it to other nodes. A controller can
collect UEC information of all nodes. Typical UEC is:
UEC-128: Support classical 128bits SRv6 SID, which is the default
capability of an SRv6 node.
UEC-32: Support shorter 32bits IPv4 address or number.
UEC-MPLS: Support shorter 32bits MPLS label.
UEC-16: Support shorter 16bits number.
Each node can support one or more UECs. Refer to Figure 8, node S/X/
ABR1 can configure to support UEC-128 capability, node ABR1/Y/ABR2
can configure to support UEC-32 capability, and node ABR2/Y/D can
configure to support UEC-MPLS capability.
Weiqiang, et al. Expires 29 March 2022 [Page 15]
Internet-Draft Unified Identifier SRv6 September 2021
A UET domain is constructed by several connected SRv6 nodes with the
same UEC. For example, a UET-128 domain is constructed by the
connected nodes all with UEC-128.
5.2.2. SRv6 SID Allocated per UEC
An SRv6 SID is allocated per UEC. For example, an SRv6 Node can
allocate different END SIDs each for UEC-128, UEC-32, UEC-MPLS, etc.
The local SID entry of each SRv6 SID allocated per UEC will
explicitly have the specific UET Flavor attribute information.
In addition to the two UET Flavors, i.e., UET-32 and UET-16 Flavors
that is defined in Section 4.2, below is described a third UET Flavor
for SRv6 SID:
UET-MPLS Flavor: a SID with UET-MPLS Flavor means in SRH the next
SID is a 32bits MPLS label.
Each node allocates its SRv6 SID per UEC and advertises it to other
nodes with additional UET-Flavor. A controller can collect these
SIDs to be used for E2E SID List programming.
To save label resources, an MPLS label is not allocated per UEC.
Relevant UET-Flavor information can be directly inserted in the
context field of the label item in SRH. However, to meet the SRH
processing restrictions defined in [RFC8754], it is possible to
allocate MPLS labels for some of the topology-related SRv6 SIDs,
which will consume more label resources.
Refer to the scenario presented in Figure 8, where each node may
allocate the following SRv6 SID per UEC.
Node S: 128bits-END-SID-S for UEC-128.
Node X: 128bits-END-SID-X for UEC-128.
Node ABR1: 128bits-END-SID-ABR1 for UEC-128, and 128bits-END-SID-
ABR1' for UEC-32.
Node Y: 128bits-END-SID-Y for UEC-32.
Node ABR2: 128bits-END-SID-ABR2 for UEC-32, and 128bits-END-SID-
ABR2' for UEC-MPLS.
Node Z: 32bits-PREFIX-SID-Z. Note that MPLS Label allocation is
independent with UEC.
Weiqiang, et al. Expires 29 March 2022 [Page 16]
Internet-Draft Unified Identifier SRv6 September 2021
Node D: 32bits-PREFIX-SID-D. Note that MPLS Label allocation is
independent with UEC.
Note that the above SRv6 SID itself is always a 128bits IPv6 address,
with no relationship with its UET Flavor attribute. The UET Flavor
attribute indicates the next SID type, i.e., 128bits classical SID,
32bits IPv4 address, or 32bits MPLS Label, etc.
5.2.3. Packets Forwarding Procedures
Consider that the controller computes an E2E segment list <X, ABR1,
Y, ABR2, Z, D>.
For the above E2E segment list, the controller knows which UET domain
does each segment node belongs to, especially that ABR1 and ABR2 are
the border nodes between different UET domains. Controller will
select appropriate SID with specific UET Flavor attribute to indicate
the UET domain which the next SID belongs to, i.e., whether the next
SID is a classical IPv6 address or a shorter truncated value.
The SID list informed to headend could be:
FSU: First SID UET, which indicates the compression result of the
first SID, in this example, is set to UET-128.
No.1 SID: 128bits-END-SID-X (with BL|TL info of itself, and
UET-128 Flavor to indicate the compression result of the next SID)
No.2 SID: 128bits-END-SID-ABR1' (with BL|TL info of itself, and
UET-32 Flavor to indicate the compression result of the next SID)
No.3 SID: 128bits-END-SID-Y (with BL|TL info of itself, and UET-32
Flavor to indicate the compression result of the next SID)
No.4 SID: 128bits-END-SID-ABR2' (with BL|TL info of itself, and
UET-MPLS Flavor to indicate the compression result of the next
SID)
No.5 SID: 32bits-PREFIX-SID-Z, (with UET-MPLS Flavor to indicate
the compression result of the next SID)
No.6 SID: 32bits-PREFIX-SID-D, (with UET-128 Flavor to indicate
the compression result of the next SID)
Note:
Weiqiang, et al. Expires 29 March 2022 [Page 17]
Internet-Draft Unified Identifier SRv6 September 2021
FSU indicates the compression result of the first SRv6 SID itself,
while the UET Flavor attribute of the first SID just indicates the
compression result of the second SRv6 SID.
BL is the Block Length of SRv6 SID. TL is the Truncated Length of
SRv6 SID, i.e., the compression result.
The headend analysis of how to get the compressed SID List:
FSU is UET-128, so the first SID 128bits-END-SID-X uses 128 bits.
The No.1 SID, 128bits-END-SID-X, has UET-128 Flavor, which means the
next SID, 128bits-END-SID-ABR1', also needs to use 128 bits.
The No.2 SID, 128bits-END-SID-ABR1' has UET-32 Flavor, which means
the next SID, 128bits-END-SID-Y, needs to be compressed as 32 bits
IPv4 address.
The No.3 SID, 128bits-END-SID-Y, has UET-32 Flavor, which means the
next SID, 128bits-END-SID-ABR2', needs to be compressed as 32 bits
IPv4 address.
The No.4 SID, 128bits-END-SID-ABR2', has UET-MPLS Flavor, which means
the next SID, 32bits-PREFIX-SID-Z, needs to use 32 bits.
The No.5 SID, 32bits-PREFIX-SID-Z, has UET-MPLS Flavor, which means
the next SID, 32bits-PREFIX-SID-D, needs to use 32 bits.
The No.6 SID, 32bits-PREFIX-SID-D, has UET-128 Flavor, which means
the next SID, maybe a VPN service SRv6 SID, needs to use 128 bits.
Note that in some cases, an overlay VPN service SRv6 SID could be
compressed. At that time, the last SID within the underlay segment
list may select the UET-32 or UET-16 Flavor attribute.
Thus, the headend can get the following compressed SID List:
128 bits-END-SID-X with UET-128 Flavor
128 bits-END-SID-ABR1' with UET-32 Flavor
32 bits of 128 bits-END-SID-Y with UET-32 Flavor
32 bits of 128 bits-END-SID-ABR2' with UET-MPLS Flavor
32 bits-PREFIX-SID-Z (with UET-MPLS Flavor in context.field)
32 bits-PREFIX-SID-D (with UET-128 Flavor context.field)
Weiqiang, et al. Expires 29 March 2022 [Page 18]
Internet-Draft Unified Identifier SRv6 September 2021
At the However, to meet the SRH processing restrictions defined in
[RFC8754], it is possible to allocate MPLS labels for some of the
topology-related SRv6 SIDs, which will consume more label
resources.At the headend, the encapsulated SRH could be:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type | Segments Left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Entry | Flags |UET| | Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
~ 128bits VPN-SID ~ SN1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| 32bits-PREFIX-SID-D (with UET-128 in context.field) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 32bits-PREFIX-SID-Z (with UET-MPLS in context.field) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ SN2
| 32bits of 128bits-END-SID-ABR2' with UET-MPLS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 32bits of 128bits-END-SID-Y with UET-32 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
~ 128bits-END-SID-ABR1' with UET-32 ~ SN3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
~ 128bits-END-SID-X with UET-128 ~ SN4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
// //
// Optional Type Length Value objects (variable) //
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: SRH including different UET SID
The initial SRH.SL is set to 4: the number of 128bits based SIDs in
SRH, and the initial SRH.UET is set to UET-128, according to FSU,
which represents the first UET domain.
During the process of packets passing through multiple UET domains,
if SRH.UET change from UET-128 to UET-32 or UET-MPLS, SRH.SL will
quadruple, i.e., SRH.SL = SRH.SL * 4, which is the number of 32bits
based SIDs in SRH. When SRH.UET changed from UET-32 or UET-MPLS to
UET-128, SRH.SL will revert to its original size, i.e., SRH.SL =
SRH.SL / 4, which is the number of 128bits based SIDs in SRH.
Similarly, when SRH.UET changes from UET-128 to UET-16, SRH.SL =
SRH.SL * 8, from UET-32 to UET-16, SRH.SL = SRH.SL * 2, vice versa.
Weiqiang, et al. Expires 29 March 2022 [Page 19]
Internet-Draft Unified Identifier SRv6 September 2021
Refer to Figure 8, next we will describe the process of packets
passing through each UET domain.
Before transmitting packets to segment node 1 (SN1) X, the headend S
decrements SRH.SL by one and gets the first 128bits SID from
SRH.List[], 128bits-END-SID-X with UET-128. Then copies to DA, and
then the lookups up FIB to where send the packet. Now, the SRH.SL
value is 3 and SRH.UET is UET-128.
At the SN1 X, the local SID matches the DA and has the UET-128 Flavor
attribute. Hence, SRH.UET has not changed. It decrements SRH.SL by
one, gets the next 128bits SID from SRH.List[], 128bits-END-SID-ABR1'
with UET-32, copies the value to DA, and then looks up FIB to where
to send the packet. At this time, SRH.SL is 2 and SRH.UET is UET-
128.
At the SN2 ABR1, the local SID matches the DA has UET-32 Flavor
attribute. Hence, SRH.UET has changed from UET-128 to UET-32. Tne
node will firstly calculate SRH.SL * 4, then decrement SRH.SL by 1,
get the next 32bits SID from SRH.List[], 32bits of 128bits-END-SID-Y
with UET-32, convert it to a complete IPv6 SID, copy to DA, and
lookup FIB to send packets. At this time, SRH.SL is 7 and SRH.UET is
UET-32.
At the SN3 Y, the local SID matches the DA has UET-32 Flavor
attribute. Thus, SRH.UET has not changed. The node will decrement
SRH.SL by 1, get the next 32bits SID from SRH.List[], 32bits of
128bits-END-SID-ABR2' with UET-MPLS, convert it to a complete IPv6
SID, copy to DA, and lookup FIB to send packets. At this time,
SRH.SL is 6, SRH.UET is UET-32.
At the SN4 ABR2, the local SID matches the DA has UET-MPLS Flavor
attribute. Hence, SRH.UET has changed from UET-32 to UET-MPLS.
Because the size of SID has not changed, the node will decrement
SRH.SL by 1, get the next 32bits SID from SRH.List[], 32bits-PREFIX-
SID-Z (with UET-MPLS in context.field), map it to a complete IPv6
prefix FEC by ILM entry, copy to DA, and lookup FIB (or directly get
forwarding information from ILM entry) to send packets. Note that
the UET information in the context.field needs to be compared with
the value in SRH.UET. Since values are equal no change and no
additional processing. At this time, SRH.SL is 5, SRH.UET is 0b02.
At the SN5 Z, the address route entry matches the DA and has no UET
Flavor attribute. As a result, SRH.UET has not changed. The node
decrements SRH.SL by 1, will get the next 32bits SID from SRH.List[],
32bits-PREFIX-SID-D (with UET-128 in context.field), map it to a
complete IPv6 prefix FEC by ILM entry, copy to DA, and lookup FIB (or
directly get forwarding information from ILM entry) to send packets.
Weiqiang, et al. Expires 29 March 2022 [Page 20]
Internet-Draft Unified Identifier SRv6 September 2021
Note that the UET information in context.field needs to be compared
to SRH.UET. Because it is changed from UET-MPLS to UET-128, the
SRH.SL will be reverted to its original size, i.e., let SRH.SL / 4.
At this time, SRH.SL is 1, SRH.UET is UET-128.
At the SN6 D, the address route entry matched by DA has no associated
UET Flavor attribute. Hence, SRH.UET has not changed. The node
decrements SRH.SL by 1, will get the next 128bits SID from
SRH.List[], 128bits VPN-SID, and follow the rest process described in
[RFC8986].
6. Control Plane in Support of Unified SID
The introduction of the Unified Identifier may rely on the existing
SR extensions to the routing protocols. But some enhancements in the
control plane are still required. This section analyzes control
plane protocols and identifies necessary extensions.
Each node in the SRv6 domain needs to advertise its U-SID
Encapsulation Capability, this information can be carried within
SRv6-Capabilities sub-TLV defined in
[I-D.ietf-lsr-isis-srv6-extensions] and SRv6 Capabilities TLV defined
in [I-D.ietf-lsr-ospfv3-srv6-extensions]. It need also allocate SRv6
SID (Topology type and Service Function type) per UEC and advertise
to other nodes, the advertisement of SRv6 END SID, END.X SID, LAN
END.X SID defined in [I-D.ietf-lsr-isis-srv6-extensions] and
[I-D.ietf-lsr-ospfv3-srv6-extensions] need to be extended to carry
UET-Flavor information. This information can be collected and sent
to the central controller through BGP-LS. The controller then can
send the computed segment list to the headend through BGP or PCEP,
and each segment will include explicit UET Flavor information. The
detailed procedures are outside the scope of this document.
The SR-MPLS extensions to Interior Gateway Protocols (IGP), IS-IS
[RFC8667], OSPF [RFC8665], and OSPFv3 [RFC8666], defined how 20-bits
and 32-bits SIDs advertised and bound to SR objects and/or
instructions. Extensions to BGP Link-state address family [RFC9085]
enabled propagation of segment information of variable length via
BGP. Already defined SR-MPLS extensions can be used to get MPLS
U-SID mapping FIB entry, and it can coexist with SRv6 extensions to
the same IGP/BGP-LS instance. For simplicity, this document suggests
using the existing mature SR-MPLS control plane and FIB entry for the
MPLS U-SID advertisement and mapping entry. However, it is possible
to base it on SRv6 related TLVs/sub-TLVs to advertise the MPLS U-SID.
It is outside the scope of this specification and will be discussed
in another document.
Weiqiang, et al. Expires 29 March 2022 [Page 21]
Internet-Draft Unified Identifier SRv6 September 2021
7. SRH with U-SID Pseudo-code
Processing of SRH with U-SID is demonstrated in the following pseudo-
code:
Headend sending packet:
S01. set initial SRH.UET, respond to the FSU, i.e.,
the compressed result of the first SID;
S02. set initial SRH.SL, it is the count of 128bits-based SIDs;
S03. if (SRH.UET == UET-128) {
S04. SRH.SL --;
S05. Get SRH.List[SRH.SL], 128bits, copy to IPv6 Header DA; Or,
headend know the first SID before SRH encapsulation,
just copy it to DA.
S06. FIB lookup according to DA, and forward packet;
S07. }
S08. else if (SRH.UET == UET-32) {
S09. SRH.SL = SRH.SL * 4;
S10. SRH.SL --;
S11. Get SRH.List[SRH.SL], 32bits, convert to 128bits SRv6 SID, copy
to IPv6 Header DA; Or, headend know the first SID before SRH
encapsulation, just copy it to DA;
S12. FIB lookup according to DA, and forward packet;
S13. }
S14. else if (SRH.UET == UET-MPLS) {
S15. SRH.SL = SRH.SL * 4;
S16. SRH.SL --;
S17. Get SRH.List[SRH.SL], 32bits, lookup ILM entry and map it to 128
IPv6 address, copy it to IPv6 Header DA; Or, headend know
the first SID before SRH encapsulation, just copy it to DA;
S18. FIB lookup according to DA, or directly get forwarding
information from ILM entry and forward packet;
S19. }
S20. else if (SRH.UET == UET-16) {
S21. SRH.SL = SRH.SL * 8;
S22. SRH.SL --;
S23. Get SRH.List[SRH.SL], 16bits, convert to 128bits SRv6 SID, copy
to IPv6 Header DA; Or, headend know the first SID before SRH
encapsulation, just copy it to DA;
S24. FIB lookup based on DA and forward packet;
S25. }
Transit/Egress receive packets:
Weiqiang, et al. Expires 29 March 2022 [Page 22]
Internet-Draft Unified Identifier SRv6 September 2021
S01. If DA matched local SID entry, copy the UET attr of local SID entry
to SRH.UET, check when SRH.UET changed from UET-128 to UET-32 or
UET-MPLS, SRH.SL*4, when from UET-32 or UET-MPLS to UET-128,
SRH.SL / 4, similar treatment of UET-16 related SRH.SL update;
Else If DA matched normal address route entry,
SRH.UET no update;
S02. if (SRH.SL == 0) {
S03. process the inner payload;
S04. }
S05. else {
S06. if (SRH.UET == UET-128) {
S07. SRH.SL -- ;
S08. Get SRH.List[SRH.SL], 128bits, copy it to IPv6 Header DA;
S09. FIB lookup based on DA and forward packet;
S10. }
S11. else if (SRH.UET == UET-32) {
S12. SRH.SL -- ;
S13. Get SRH.List[SRH.SL], 32bits, convert to 128bits SRv6 SID, copy
to IPv6 Header DA;
S14. FIB lookup based on DA and forward packet;
S15. }
S16. else if (SRH.UET == UET-MPLS) {
S17. SRH.SL --
S18. Get SRH.List[SRH.SL], 32bits, lookup ILM entry, map it to
128bits IPv6 address, copy it to IPv6 Header DA;
S19. Get UET info from SRH.List[SRH.SL] Context Field, copy it to
SRH.UET. Check if SRH.UET changed from UET-MPLS to UET-128,
SRH.SL/4;
S20. FIB lookup according to DA, or, directly get forwarding
information from ILM entry, and forward packet;
S21. }
S22. else if (SRH.UET == UET-16) {
S23. SRH.SL -- ;
S24. Get SRH.List[SRH.SL], 16bits, convert to 128bits SRv6 SID, copy
to IPv6 Header DA;
S25. FIB lookup based on DA and forward packet;
S26. }
S27. }
8. U-SID supporting SRv6 programming
U-SID can support SRv6 programming defined by [RFC8986]. The details
will be described in another document.
Weiqiang, et al. Expires 29 March 2022 [Page 23]
Internet-Draft Unified Identifier SRv6 September 2021
9. Benefits
To be discussed in the next version.
10. Implementation Considerations
The Unified SID solution has been already implemented and tested by
two companies:
* Centec has conducted its PoC, and the report is available at
https://cloud.tencent.com/developer/article/1540023.
* Broadcom, in its lab, also conducted PoC testing of the U-SID
solution.
11. IANA Considerations
IANA is requested to allocate the two-bits long field from the
Segment Routing Header Flags registry referred to as Size.
12. Security Considerations
This specification inherits all security considerations of [RFC8402]
and [RFC8754].
13. Contributors
Weiqiang, et al. Expires 29 March 2022 [Page 24]
Internet-Draft Unified Identifier SRv6 September 2021
Wan Xiaolan
New H3C Technologies Co. Ltd
No.8, Yongjia Road, Haidian District
Beijing
China
Email: wxlan@h3c.com
Cheng Wei
Centec
Building B, No.5 Xing Han Street, Suzhou Industrial Park
Suzhou
China
Email: Chengw@centecnetworks.com
S.Zadok
Broadcom
Israel
Email: shay.zadok@broadcom.com
14. Acknowledgements
TBD
15. Normative References
[I-D.ietf-lsr-isis-srv6-extensions]
Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
Z. Hu, "IS-IS Extensions to Support Segment Routing over
IPv6 Dataplane", Work in Progress, Internet-Draft, draft-
ietf-lsr-isis-srv6-extensions-17, 18 June 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-lsr-
isis-srv6-extensions-17>.
[I-D.ietf-lsr-ospfv3-srv6-extensions]
Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak,
"OSPFv3 Extensions for SRv6", Work in Progress, Internet-
Draft, draft-ietf-lsr-ospfv3-srv6-extensions-02, 15
February 2021, <https://datatracker.ietf.org/doc/html/
draft-ietf-lsr-ospfv3-srv6-extensions-02>.
Weiqiang, et al. Expires 29 March 2022 [Page 25]
Internet-Draft Unified Identifier SRv6 September 2021
[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>.
[RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6
Routing Header for Source Routes with the Routing Protocol
for Low-Power and Lossy Networks (RPL)", RFC 6554,
DOI 10.17487/RFC6554, March 2012,
<https://www.rfc-editor.org/info/rfc6554>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[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>.
[RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing with the MPLS Data Plane", RFC 8660,
DOI 10.17487/RFC8660, December 2019,
<https://www.rfc-editor.org/info/rfc8660>.
[RFC8663] Xu, X., Bryant, S., Farrel, A., Hassan, S., Henderickx,
W., and Z. Li, "MPLS Segment Routing over IP", RFC 8663,
DOI 10.17487/RFC8663, December 2019,
<https://www.rfc-editor.org/info/rfc8663>.
[RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler,
H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", RFC 8665,
DOI 10.17487/RFC8665, December 2019,
<https://www.rfc-editor.org/info/rfc8665>.
[RFC8666] Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions
for Segment Routing", RFC 8666, DOI 10.17487/RFC8666,
December 2019, <https://www.rfc-editor.org/info/rfc8666>.
Weiqiang, et al. Expires 29 March 2022 [Page 26]
Internet-Draft Unified Identifier SRv6 September 2021
[RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C.,
Bashandy, A., Gredler, H., and B. Decraene, "IS-IS
Extensions for Segment Routing", RFC 8667,
DOI 10.17487/RFC8667, December 2019,
<https://www.rfc-editor.org/info/rfc8667>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
[RFC9085] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Gredler,
H., and M. Chen, "Border Gateway Protocol - Link State
(BGP-LS) Extensions for Segment Routing", RFC 9085,
DOI 10.17487/RFC9085, August 2021,
<https://www.rfc-editor.org/info/rfc9085>.
Authors' Addresses
Cheng Weiqiang
China Mobile
Beijing,
China
Email: chengweiqiang@chinamobile.com
Greg Mirsky
Ericsson
Email: gregimirsky@gmail.com
Peng Shaofu
ZTE Corporation
No.50 Software Avenue, Yuhuatai District
Nanjing,
China
Email: peng.shaofu@zte.com.cn
Weiqiang, et al. Expires 29 March 2022 [Page 27]
Internet-Draft Unified Identifier SRv6 September 2021
Liu Aihua
ZTE Corporation
Zhongxing Industrial Park, Nanshan District
Shenzhen,
China
Email: liu.aihua@zte.com.cn
Gyan S. Mishra
Verizon Inc.
13101 Columbia Pike
Silver Spring, MD 20904
United States of America
Phone: 301 502-1347
Email: gyan.s.mishra@verizon.com
Weiqiang, et al. Expires 29 March 2022 [Page 28]
