Internet DRAFT - draft-chunduri-lsr-isis-preferred-path-routing
draft-chunduri-lsr-isis-preferred-path-routing
LSR Working Group U. Chunduri
Internet-Draft Intel Corporation
Intended status: Standards Track R. Li
Expires: January 12, 2023 Futurewei
R. White
Juniper Networks
L. Contreras
Telefonica
J. Tantsura
Microsoft
Y. Qu
Futurewei
July 11, 2022
Preferred Path Routing (PPR) in IS-IS
draft-chunduri-lsr-isis-preferred-path-routing-08
Abstract
This document specifies a Preferred Path Routing (PPR), a routing
protocol mechanism to simplify the path description using IS-IS
protocol. PPR builds on existing encapsulation to add the path
identity to the packet and supports further extensions along the
preferred paths. PPR aims to provide path steering, services and
support further extensions along the paths. Preferred path routing
is achieved through the addition of path descriptions to the IS-IS
advertised prefixes, and mapping those to a PPR data-plane
identifier.
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 RFC2119 [RFC2119],
RFC8174 [RFC8174] when, and only when they appear in all capitals, as
shown here.
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/.
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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 January 12, 2023.
Copyright Notice
Copyright (c) 2022 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3
2. PPR Details . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. PPR-ID and Data Plane Extensibility . . . . . . . . . . . 4
2.2. PPR Path Description . . . . . . . . . . . . . . . . . . 4
2.3. ECMP Considerations . . . . . . . . . . . . . . . . . . . 5
3. PPR Related TLVs . . . . . . . . . . . . . . . . . . . . . . 5
3.1. PPR-Prefix Sub-TLV . . . . . . . . . . . . . . . . . . . 7
3.2. PPR-ID Sub-TLV . . . . . . . . . . . . . . . . . . . . . 8
3.3. PPR-PDE Sub-TLV . . . . . . . . . . . . . . . . . . . . . 9
3.4. PPR-Attributes Sub-TLV . . . . . . . . . . . . . . . . . 12
4. PPR Processing Procedure Example . . . . . . . . . . . . . . 13
4.1. PPR TLV Processing . . . . . . . . . . . . . . . . . . . 14
4.2. Path Fragments . . . . . . . . . . . . . . . . . . . . . 15
5. PPR Data Plane aspects . . . . . . . . . . . . . . . . . . . 15
5.1. SR-MPLS with PPR . . . . . . . . . . . . . . . . . . . . 15
5.2. PPR Native IP Data Planes . . . . . . . . . . . . . . . . 16
5.3. SRv6 with PPR . . . . . . . . . . . . . . . . . . . . . . 16
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
7.1. PPR Sub-TLVs . . . . . . . . . . . . . . . . . . . . . . 17
7.2. IGP Parameters . . . . . . . . . . . . . . . . . . . . . 18
8. Security Considerations . . . . . . . . . . . . . . . . . . . 18
9. Contributing Authors . . . . . . . . . . . . . . . . . . . . 18
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10. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
10.1. Normative References . . . . . . . . . . . . . . . . . . 19
10.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Appendix . . . . . . . . . . . . . . . . . . . . . . 22
A.1. Challenges with Increased SID Depth . . . . . . . . . . . 22
A.2. Mitigation with MSD . . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction
PPR involves associating path descriptions to IS-IS advertised
prefixes, mapping those to a data-plane identifier and specifying a
mechanism to route packets with the abstracted identifier (PPR-ID),
as opposed to individual segments on the packet. This is specified
in detail in [I-D.chunduri-rtgwg-preferred-path-routing], along with
key use cases and deployment scenarios. PPR allows the traffic along
an engineered path through the network by replacing the label stack
with a path identifier, PPR-ID, in the packet. The PPR-ID can either
be a single label or a native destination address. To facilitate the
use of a single label to describe an entire path, a new TLV is added
to IS-IS, as described below in Section 3.
A PPR could be an SR path, a traffic engineered path computed based
on some constraints, an explicitly provisioned Fast Re-Route (FRR)
path or a service chained path. A PPR can be signaled by any node,
computed by a central controller, or manually configured by an
operator. PPR extends the source routing and path steering
capabilities to native IP (IPv4 and IPv6) data planes without
hardware upgrades; see Section 5.
1.1. Acronyms
EL - Entropy Label
ELI - Entropy Label Indicator
LSP - IS-IS Link State PDU
MPLS - Multi Protocol Label Switching
MSD - Maximum SID Depth
MTU - Maximum Transferrable Unit
NH - Next-Hop
PPR - Preferred Path Routing/Route
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PPR-ID - Preferred Path Route Identifier, a data plane identifier
SID - Segment Identifier
SPF - Shortest Path First
SR-MPLS - Segment Routing with MPLS data plane
SRH - Segment Routing Header - IPv6 routing Extension header
SRv6 - Segment Routing with IPv6 data plane with SRH
TE - Traffic Engineering
2. PPR Details
2.1. PPR-ID and Data Plane Extensibility
The PPR-ID describes a path through the network. A data plane type
and corresponding data plane identifier as specified in Section 3.2
is mapped to PPR-ID to allow data plane extensibility.
For SR-MPLS, PPR-ID is mapped to an MPLS Label/SID and for SRv6, this
is mapped to an IPv6-SID. For native IP data planes, this is mapped
to either IPv4 or IPv6 address/prefix.
2.2. PPR Path Description
The path identified by the PPR-ID is described as a set of Path
Description Elements (PDEs), each of which represents a segment of
the path. Each node determines its location in the path as
described, and forwards to the next segment/hop or label of the path
description (see the Forwarding Procedure Example later in this
document).
These PPR-PDEs as defined in Section 3.3, like SR SIDs, can represent
topological elements like links/nodes, backup nodes, as well as non-
topological elements such as a service, function, or context on a
particular node.
A PPR path can be described as a Strict-PPR or a Loose-PPR. In a
Strict-PPR all nodes/links on the path are described with SR SIDs for
SR data planes or IPv4/IPv6 addresses for native IP data planes. In
a Loose-PPR only some of the nodes/links from source to destination
are described. More specifics and restrictions around Strict/Loose
PPRs are described in respective data planes in Section 5. Each PDE
is described as either an MPLS label towards the Next-Hop (NH) in
MPLS enabled networks, or as an IP NH, in the case of either
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"plain"/"native" IP or SRv6 enabled networks. A PPR path is related
to a set of PDEs using the TLVs as specified in Section 3.
2.3. ECMP Considerations
PPR inherently supports Equal Cost Multi Path (ECMP) for both strict
and loose paths. If a path is described using nodes, it would have
ECMP NHs established for PPR-ID along the path. However, one can
avoid ECMP on any segment of the path by pinning the path using a
link identifier to the next segment.
3. PPR Related TLVs
This section describes the encoding of PPR TLV. This TLV can be seen
as having 4 logical sections viz, encoding of the PPR-Prefix (IS-IS
Prefix), encoding of PPR-ID, encoding of path description with an
ordered PDE Sub-TLVs and a set of optional PPR attribute Sub-TLVs,
which can be used to describe one or more parameters of the path.
Multiple instances of this TLV MAY be advertised in IS-IS LSPs with
different PPR-ID Type (data plane) and with corresponding PDE Sub-
TLVS. The PPR TLV has Type TBD (suggested value xxx), and has the
following format:
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 | PPR-Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Fragment-ID | MT-ID | Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-Prefix Sub-TLV (variable size) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-ID Sub-TLV (variable size) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-PDE Sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-Attribute Sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: PPR TLV Format
o Type: 155 (Suggested Value, TBD IANA) from IS-IS top level TLV
registry.
o Length: Total length of the value field in bytes.
o PPR-Flags: 2 Octet bit-field of flags for this TLV; described
below.
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o Fragment-ID: This is an 8-bit Identifier value (0-255) of the TLV
fragment. If fragments are not needed to represent the complete
path, 'U' bit MUST be set and this value MUST be set to 0.
o MT-ID: The multi-topology identifier defined in [RFC5120]; the 4
most significant bits MUST be set to 0 on transmit and ignored on
receive. The remaining 12-bit field contains the MT-ID.
o Algorithm: 1 octet value represents the route computation
algorithm. Algorithm registry is as defined in [RFC8667].
Computation towards PPR-ID (Section 3.2) happens per MT-ID/
Algorithm pair.
o PPR-Prefix: A variable size Sub-TLV representing the destination
of the path being described. This is defined in Section 3.1.
o PPR-ID: A variable size Sub-TLV representing the data plane or
forwarding identifier of the PPR. Defined in Section 3.2.
o PPR-PDEs: Variable number of ordered PDE Sub-TLVs which represents
the path. This is defined in Section 3.3.
o PPR-Attributes: Variable number of PPR-Attribute Sub-TLVs which
represent the path attributes. These are defined in Section 3.4.
The Flags field has the following flag bits defined:
PPR TLV Flags Format
0 1 2 3 4 5 6 7 15
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|D|A|U|Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1. F: Flood bit. If set, the PPR TLV MUST be flooded across the
entire routing domain. If the F bit is not set, the PPR TLV MUST
NOT be leaked between IS-IS levels. This bit MUST NOT be altered
during the TLV leaking
2. D: Down Bit. When the PPR TLV is leaked from IS-IS level-2 to
level-1, the D bit MUST be set. Otherwise, this bit MUST be
clear. PPR TLVs with the D bit set MUST NOT be leaked from
level-1 to level-2. This is to prevent TLV looping across
levels.
3. A: Attach bit. The originator of the PPR TLV MUST set the A bit
in order to signal that the prefix and PPR-ID advertised in the
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PPR TLV are directly connected to the originators. If this bit
is not set, this allows any other node in the network to
advertise this TLV on behalf of the originating node of the PPR-
Prefix. If PPR TLV is leaked to other areas/levels the A-flag
MUST be cleared. In case if the originating node of the prefix
must be disambiguated for any reason including, if it is a Multi
Homed Prefix (MHP) or leaked to a different IS-IS level or
because [RFC7794] X-Flag is set, then PPR-Attribute Sub-TLV
Source Router ID SHOULD be included.
4. U: Ultimate fragment bit. bit MUST be set if a path has only one
fragment or if it is the last Fragment of the path. PPR-ID value
for all fragments of the same path MUST be the same.
5. Reserved: For future use; MUST be set to 0 on transmit and
ignored on receive.
PPR path description for each IS-IS level is computed and given to
one of the nodes for L1 and L2 respectively. Similarly path
information when crossing the level boundaries MUST be relevant to
the destination level. If there is no path information available for
the destination level PPR TLV MUST NOT be leaked regardless of F and
D bits as defined above.
The following Sub-TLVs draw from a new registry for Sub-TLV numbers
as specified in Section 7.1 and Section 7.2.
3.1. PPR-Prefix Sub-TLV
The structure of PPR-Prefix is:
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 | Prefix Length | Mask Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IS-IS Prefix (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: PPR-Prefix Sub-TLV Format
o Type: 1 (IANA to assign from Sub-TLV registry described above).
o Length: Total length of the value field in bytes.
o Prefix Length: The length of the IS-IS Prefix being encoded in
bytes. For IPv4 it MUST be 4 and IPv6 it MUST be 16 bytes.
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o Mask Length: The length of the prefix in bits. Only the most
significant octets of the Prefix are encoded.
o IS-IS Prefix: The IS-IS prefix at the tail-end of the advertised
PPR. This corresponds to a routable prefix of the originating
node and it MAY have one of the [RFC7794] flags set (X-Flag/R-
Flag/N-Flag) in the IS-IS reachability TLVs. Length of this field
MUST be as per "Prefix Length". Encoding is same as TLV 135
[RFC5305] and TLV 236 [RFC5308] or MT-Capable [RFC5120] IPv4 (TLV
235) and IPv6 Prefixes (TLV 237) respectively.
3.2. PPR-ID Sub-TLV
This is the actual data plane identifier in the packet header and
could be of any data plane as defined in the PPR-ID Type field. Both
PPR-Prefix and PPR-ID belongs to a same node in the network.
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 |PPR-ID Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-ID Type | PPR-ID Length |PPR-ID Mask Len|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// PPR-ID (variable size) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: PPR-ID Sub-TLV Format
o Type: 2 (IANA to assign from Sub-TLV registry described above).
o Length: Total length of the value field in bytes.
o PPR-ID Flags: 2 Octet field for PPR-ID flags:
PPR-ID Flags Format
0 1 2 3 4 5 6 7.. 15
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved: For future use; MUST be set to 0 on transmit and
ignored on receive.
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o PPR-ID Type: Data plane type of PPR-ID. This is a new registry
(TBD IANA - Suggested values as below) for this Sub-TLV and the
defined types are as follows:
Type: 1 SR-MPLS SID/Label
Type: 2 Native IPv4 Address/Prefix
Type: 3 Native IPv6 Address/Prefix
Type: 4 IPv6 SID in SRv6 with SRH
o PPR-ID Length: Length of the PPR-ID field in octets and this
depends on the PPR-ID type.
o PPR-ID Mask Len: It is applicable only for PPR-ID Type 2, 3 and 4.
For Type 1 this value MUST be set to zero. It contains the length
of the PPR-ID Prefix in bits. Only the most significant octets of
the Prefix are encoded. This is needed, if PPR-ID followed by an
IPv4/IPv6 Prefix instead of 4/16 octet Address respectively.
o PPR-ID: This is the Preferred Path forwarding identifier that
would be on the data packet. The value of this field is variable
and it depends on the PPR-ID Type - for Type 1, this is encoded as
SR-MPLS SID/Label. For Type 2 this is a 4 byte IPv4 address. For
Type 3 this is a 16 byte IPv6 address. For Type 2 and Type 3
encoding is similar to "IS-IS Prefix" as specified in Section 3.1.
For Type 4, this is encoded as 16 byte SRv6 SID.
For PPR-ID Type 2, 3 or 4, PPR-ID MUST NOT be advertised as a
routable prefix in TLV 135, TLV 235, TLV 236 and TLV 237. PPR-ID
MUST belong to the node, from where the PPR-Prefix (Section 3.1) is
advertised.
3.3. PPR-PDE Sub-TLV
This Sub-TLV represents the PPR Path Description Element (PDE). PPR-
PDEs are used to describe the path in the form of a set of contiguous
and ordered Sub-TLVs, where first Sub-TLV represents (the top of the
stack in MPLS data plane or) first node/segment of the path. These
sets of ordered Sub-TLVs can have both topological elements and non-
topological elements (e.g., service segments).
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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 | PPR-PDE Type | PDE-ID Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PDE-ID Length | PPR-PDE Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// PDE-ID Value (variable size) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Sub-TLV Length | PPR-PDE Sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: PPR-PDE Sub-TLV Format
o Type: 3 (See IANA for suggested value) from IS-IS PPR TLV
Section 3 Sub-TLV registry.
o Length: Total length of the value field in bytes.
o PPR-PDE Type: A new registry (TBD IANA) for this Sub-TLV and the
defined types are as follows:
Type: 1 Topological
Type: 2 Non-Topological
o PDE-ID Type: 1 Octet PDE-forwarding IDentifier Type. A new
registry (Suggested Values as listed, IANA TBD) for this Sub-TLV
and the defined types and corresponding PDE-ID Length, PDE-ID
Value are as follows:
Type 0: This value MUST be set only when PPR-PDE Type is Non-
Topological. PDE-ID Length indicates the length of the PDE-ID
Value field in bytes. For this type, PDE-ID value represents a
service/function. This information is provisioned on the
immediate topological PDE preceding this PDE based on the 'E'
bit.
Type 1: SID/Label type as defined in [RFC8667]. PDE-ID Length
and PDE-ID Value fields are per Section 2.3 of the referenced
document.
Type 2: SR-MPLS Prefix SID. PDE-ID Length and PDE-ID Value are
same as Type 1.
Type 3: SR-MPLS Adjacency SID. PDE-ID Length and PDE-ID Value
are same as Type 1.
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Type 4: IPv4 Node Loopback Address. PDE-ID Length 4 bytes and
PDE-ID Value is full 4 bytes IPv4 address encoded as specified
in "4-octet IPv4 address" of Sub-TLV 6/TLV 22 in [RFC5305].
Type 5: IPv4 Interface Address. PDE-ID Length is 4 bytes and
PDE-ID Value is full 4 bytes IPv4 address encoded as specified
in "4-octet IPv4 address" of Sub-TLV 6/TLV 22 in [RFC5305].
This PDE-ID in the path description represents the egress
interface of the path segment and corresponding adjacency is set
as nexthop for the PPR-ID.
Type 6: IPv6 Node Loopback Address. PDE-ID Length and PDE-ID
Value are encoded as specified in "Prefix Len" and "prefix"
portion of TLV 236 in [RFC5308] respectively.
Type 7: IPv6 Interface Address. PDE-ID Length is 16 bytes and
PDE-ID Value is full 16 bytes IPv6 address encoded as specified
in "Interface Address 1" portion of TLV 232 in [RFC5308]. This
PDE-ID in the path description represents the egress interface
of the path segment and corresponding adjacency is set as
nexthop for the PPR-ID.
Type 8: SRv6 Node SID as defined in
[I-D.ietf-lsr-isis-srv6-extensions]. PDE-ID Length and PDE-ID
Value are as defined in SRv6 SID from the referenced draft.
Type 9: SRv6 Adjacency-SID. PDE-ID Length and PDE-ID Values are
similar to SRv6 Node SID above.
o PPR-PDE Flags: 2 Octet bit-field of flags; described below:
PPR-PDE Flags Format
0 1 2 3 4 5 6 7 .. 15
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L|N|E| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L: Loose Bit. Indicates the type of next "Topological PDE-ID" in
the path description. This bit MUST be set for only Node/Prefix
PDE type. If this flag is unset, the next Topological PDE is
Strict Type.
N: Node Bit. By default this bit MUST be unset. This bit MUST
be set only for PPR-PDE Type is 1 i.e., Topological and this PDE
represents the node, where PPR-Prefix (Section 3.1) belongs to
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(if there is no further PDE specific Sub-TLVs to override PPR-
Prefix and PPR-ID values).
E: Egress Bit. By default this bit MUST be unset. This bit MUST
be set only for PPR-PDE Type is 2 i.e., Non-Topological and the
service needs to be applied on the egress side of the
topological PDE preceding this PDE.
Reserved: Reserved bits for future use. Reserved bits MUST be
reset on transmission and ignored on receive.
o Sub-TLV Length: 1 byte length of all Sub-TLVs followed. It MUST
be set to 0 if no further Sub-TLVs are present.
o PPR-PDE Sub-TLVs: These have 1 octet type, 1 octet length and
value field is defined per the type field. Types are as defined
in PPR-TLV Sub-TLVs (Section 7), encoded further as sub-sub-TLVs
of PPR-PDE and the length field represents the total length of the
value field in bytes.
IS-IS System-ID Sub-TLV: Type 4 (IANA TBD), Length Total length
of value field in bytes, Value: IS-IS System-ID of length "ID
Length" as defined in [ISO.10589.1992]. This Sub-TLV MUST NOT
be present, if the PPR-PDE Type is not Topological. Though the
type for this comes from the PPR Sub-TLV registry, here this is
a sub-sub-TLV and is part of PPR-ID/PPR-PDE Sub-TLV.
3.4. PPR-Attributes Sub-TLV
PPR-Attribute Sub-TLVs describe the attributes of the path. This
document defines the following optional PPR-Attribute Sub-TLVs:
o Type 5 (Suggested Value - IANA TBD): PPR-Prefix originating node's
IPv4 Router ID Sub-TLV. Length and Value fields are as specified
in [RFC7794].
o Type 6 (Suggested Value - IANA TBD): PPR-Prefix originating node's
IPv6 Router ID Sub-TLV. Length and Value fields are as specified
in [RFC7794].
o Type 7 (Suggested Value - IANA TBD): PPR-Metric Sub-TLV. Length 4
bytes, and Value is the metric of this path represented through
the PPR-ID. Different nodes can advertise the same PPR-ID for the
same Prefix with a different set of PPR-PDE Sub-TLVs and the
receiving node MUST consider the lowest metric value.
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4. PPR Processing Procedure Example
As specified in [I-D.chunduri-rtgwg-preferred-path-routing], a PPR
can be a TE path, locally provisioned by the operator or by a
controller. Consider the following IS-IS network to describe the
operation of PPR TLV as defined in Section 3:
1
_______
/ 1 \
+---R2-------R3---+
/ \_______/ \
/ 1 \
1 / \ 1
/ 1__R13__1 \
/ / \ \
R1------R6 R7-----------R4
\ 2 \__R14__/ 2 /\
\ 2 2 / \
3 \ / 3 \1
\ 4 / \
+----R8------R9-----R10------R12
\ 1 /
1 \ / 1
+----R11---+
Figure 5: IS-IS Network
In the (Figure 5), consider node R1 as an ingress node, or a head-end
node, and the node R4 may be an egress node or another head-end node.
The numbers shown on links between nodes indicate the bi-directional
IS-IS metric as provisioned. R1 may be configured to receive TE
source routed path information from a central entity (PCE [RFC5440],
Netconf [RFC6241] or a Controller) that comprises PPR information
which relates to sources that are attached to R1. It is also
possible to have a PPR provisioned locally by the operator for non-TE
needs (e.g. FRR or for chaining certain services).
The PPR TLV (as specified in Section 3) is encoded as an ordered list
of PPR-PDEs from source to a destination node in the network and is
represented with a PPR-ID (Section 3.2). The PPR TLV includes PPR-
PDE Sub-TLVs Section 3.3, which represent both topological and non-
topological elements and specifies the actual path towards a PPR-
Prefix at R4.
o The shortest path towards R4 from R1 are through the following
sequence of nodes: R1-R2-R3-R4 based on the provisioned metrics.
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o The central entity can define a few PPRs from R1 to R4 that
deviate from the shortest path based on other network
characteristic requirements as requested by an application or
service. For example, the network characteristics or performance
requirements may include bandwidth, jitter, latency, throughput,
error rate, etc.
o A first PPR may be identified by PPR-ID = 1 (value) and may
include the path of R1-R6-R7-R4 for a Prefix advertised by R4.
This is an example for a Loose-PPR and 'L' bit MUST be set
appropriately at Section 3.3.
o A second PPR may be identified by PPR-ID = 2 (value) and may
include the path of R1-R8-R9-R10-R4. This is an example for a
Strict-PPR and 'L' bit MUST be unset appropriately at Section 3.3.
Though this example shows PPR with all nodal SIDs, it is possible
to have a PPR with combination of node and adjacency SIDs (local
or global) or with PPR-PDE Type set to Non-Topological as defined
in Section 3.3 elements along with these.
4.1. PPR TLV Processing
The first topological sub-object or PDE (Section 3.3) relative to the
beginning of PPR Path contains the information about the first node
(e.g. in SR-MPLS it's the topmost label). The last topological sub-
object or PDE contains information about the last node (e.g. in SR-
MPLS it's the bottommost label).
Each receiving node determines whether an advertised PPR includes
information regarding the receiving node. Before processing any
further, validation MUST be done to see if any PPR topological PDE is
seen more than once (possible loop), if yes, this PPR TLV MUST be
ignored. Processing of PPR TLVs may be done, during the end of the
SPF computation (for MTID that is advertised in this TLV) and for
each prefix described through PPR TLV. For example, node R9 receives
the PPR information, and ignores the PPR-ID=1 (Section 4) because
this PPR TLV does not include node R9 in the path description/ordered
PPR-PDE list.
However, node R9 may determine that the second PPR identified by PPR-
ID = 2 does include the node R9 in its PDE list. Therefore, node R9
updates the local forwarding database to include an entry for the
destination address that R4 indicates, so that when a data packet
comprising a PPR-ID of 2 is received, forward the data packet to node
R10 instead of R11. This is done, even though from R9 the shortest
path to reach R4 via R11 (Cost 3: R9-R11-R12-R4) it chooses the NH to
R10 to reach R4 as specified in the PPR path description. Same
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process happens to all nodes or all topological PDEs as described in
the PPR TLV.
In summary, the receiving node checks first, if this node is on the
path by checking the node's topological elements (with PPR-PDE Type
set to Topological) in the path list. If yes, it adds/adjusts the
PPR-ID's shortest path NH towards the next topological PDE in the
PPR's Path.
4.2. Path Fragments
A complete PPR path may not fit into the maximum allowable size of
the IS-IS TLV. To overcome this a 7 bit Fragment-ID field is defined
in Section 3 . With this, a single PPR path is represented via one
or more fragmented PPR path TLVs, with all having the same PPR-ID.
Each fragment carries the PPR-ID as well as a numeric Fragment-ID
from 0 to (N-1), when N fragments are needed to describe the PPR
Graph (where N>1). In this case Fragment (N-1) MUST set the 'U' bit
(PPR-Flags) to indicate it is the last fragment. If Fragment-ID is
non-zero in the TLV, then it MUST not carry PPR-Prefix Sub-TLV. The
optional PPR Attribute Sub-TLVs which describe the path overall MUST
be included in the last fragment only (i.e., when the 'U' bit is
set).
5. PPR Data Plane aspects
Data plane for PPR-ID is selected by the entity (e.g., a controller,
locally provisioned by operator), which selects a particular PPR in
the network. Section 3.2 defines various data plane identifier types
and a corresponding data plane identifier is selected by the entity
which selects the PPR.
5.1. SR-MPLS with PPR
If PPR-ID Type is 1, then the PPR belongs to SR-MPLS data plane and
the complete PPR stack is represented with a unique SR SID/Label and
this gets programmed on the data plane of each node, with the
appropriate NH computed as specified in Section 4. PPR-ID here is a
label/index from the SRGB (like another node SID or global ADJ-SID).
PPR path description here is a set of ordered SIDs represented with
PPR-PDE (Section 3.2) Sub-TLVs. Non-Topological segments are also
programmed in the forwarding to enable specific function/service,
when the data packet hits with corresponding PPR-ID.
Based on the 'L' flag in PPR-ID Flags (Section 3.2), for SR-MPLS data
plane either 1 label or 2 labels need to be provisioned on individual
nodes on the path description. For the example network in Section 4,
for PPR-ID=1, which is a loose path, node R6 programs the bottom
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label as PPR-ID and the top label as the next topological PPR-PDE in
the path, which is a node SID of R7. The NH computed at R6 would be
the shortest path towards R7 i.e., the interface towards R13. If 'L'
flag is unset, only PPR-ID is programmed on the data plane with NH
set to the shortest path towards the next topological PPR-PDE.
5.2. PPR Native IP Data Planes
If PPR-ID Type is 2 then source routing and packet steering can be
done in IPv4 data plane (PPR-IPv4), along the path as described in
PPR Path description. This is achieved by setting the destination IP
address as PPR-ID, which is an IPv4 address in the data packet
(tunneled/encapsulated). There is no data plane change or upgrade
needed to support this.
Similarly for PPR-ID Type is 3, then source routing and packet
steering can be done in the IPv6 data plane (PPR-IPv6), along the
path as described in PPR Path description. Whatever specified above
for IPv4 applies here too, except that the destination IP address of
the data packet is an IPv6 Address (PPR-ID). This doesn't require
any IPv6 extension headers (EH), if there is no metadata/TLVs need to
be carried in the data packet.
Based on 'L' flag in PPR-ID Flags (Section 3.2), for PPR-ID Type 2 or
3 (Native IPv4 or IPv6 data planes respectively) the packet has to be
encapsulated using the capabilities (either dynamically signaled
through [I-D.ietf-isis-encapsulation-cap] or statically provisioned
on the nodes) of the next loose PDE in the path description.
For the example network in Section 4, for PPR-ID=1, which is a loose
path, node R6 programs to encapsulate the data packet towards the
next loose topological PPR-PDE in the path, which is R7. The NH
computed at R6 would be the shortest path towards R7 i.e., the
interface towards R13. If the 'L' flag is unset, only PPR-ID is
programmed on the data plane with NH set to the shortest path towards
the next topological PPR-PDE, with no further encapsulation of the
data packet.
5.3. SRv6 with PPR
If PPR-ID Type is 4, the PPR belongs to SRv6 with SRH data plane and
the complete PPR stack is represented with IPv6 SIDs and this gets
programmed on the data plane with the appropriate NH computed as
specified in Section 4. PPR-ID here is a SRv6 SID. PPR path
description here is a set of ordered SID TLVs similar to as specified
in Section 5.1. One way PPR-ID would be used in this case is by
setting it as the destination IPv6 address and SL field in SRH would
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be set to 0; however SRH [RFC8754] can contain any other TLVs and
non-topological SIDs as needed.
6. Acknowledgements
Thanks to Alex Clemm, Lin Han, Toerless Eckert, Asit Chakraborti,
Stewart Bryant and Kiran Makhijani for initial discussions on this
topic. Thanks to Kevin Smith and Stephen Johnson for various
deployment scenarios applicability from ETSI WGs perspective.
Authors also acknowledge Alexander Vainshtein for detailed
discussions and few suggestions on this topic.
Earlier versions of [RFC8667] have a mechanism to advertise EROs
through Binding SID.
7. IANA Considerations
This document requests the following new TLV in IANA IS-IS TLV code-
point registry.
TLV # Name
----- --------------
155 PPR TLV (Suggested Value, IANA TBD)
7.1. PPR Sub-TLVs
This document requests IANA to create a new Sub-TLV registry for PPR
TLV Section 3 with the following initial entries (suggested values).
Though these are defined as Sub-TLVs of PPR TLV, these can be part of
another Sub-TLV as a nested sub-sub-TLV (e.g. IS-IS System-ID).
Sub-TLV # Sub-TLV Name
--------- ---------------------------------------------------------
1 PPR-Prefix (Section 3.1)
2 PPR-ID (Section 3.2)
3 PPR-PDE (Section 3.3)
4 IS-IS System-ID (Section 3.3)
5 PPR-Prefix Source IPv4 Router ID (Section 3.4)
6 PPR-Prefix Source IPv6 Router ID (Section 3.4)
7 PPR-Metric (Section 3.4)
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7.2. IGP Parameters
This document requests additional IANA registries in an IANA managed
registry "Interior Gateway Protocol (IGP) Parameters" for various PPR
TLV parameters. The registration procedure is based on the "Expert
Review" as defined in [RFC8126]. The suggested registry names are:
o "PPR-Type" - Types are unsigned 8 bit numbers. Values are as
defined in Section 3 of this document.
o "PPR-Flags" - 1 Octet. Bits as described in Section 3 of this
document.
o "PPR-ID Type" - Types are unsigned 8 bit numbers. Values are as
defined in Section 3.2 of this document.
o "PPR-ID Flags" - 1 Octet. Bits as described in Section 3.2 of
this document.
o "PPR-PDE Type" - Types are unsigned 8 bit numbers. Values are as
defined in Section 3.3 of this document.
o "PPR-PDE Flags" - 1 Octet. Bits as described in Section 3.3 of
this document.
o "PDE-ID Type" - Types are unsigned 8 bit numbers. Values are as
defined in Section 3.3 of this document.
8. Security Considerations
Security concerns for IS-IS are addressed in [RFC5304] and [RFC5310].
Further security analysis for the IS-IS protocol is done in [RFC7645]
with detailed analysis of various security threats and why [RFC5304]
should not be used in the deployments. Advertisement of the
additional information defined in this document introduces no new
security concerns in IS-IS protocol. However, for extensions related
ro SR-MPLS and SRH data planes, those particular data plane security
considerations do apply here.
9. Contributing Authors
The following people contributed substantially to the content of this
document and should be considered co-authors.
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Yingzhen Qu
Futurewei
2330 Central Expressway
Santa Clara
CA 95050
USA
Email: yingzhen.qu@futurewei.com
10. References
10.1. Normative References
[I-D.chunduri-rtgwg-preferred-path-routing]
Bryant, S., Chunduri, U., and A. Clemm, "Preferred Path
Routing Framework", draft-chunduri-rtgwg-preferred-path-
routing-02 (work in progress), May 2022.
[ISO.10589.1992]
International Organization for Standardization,
"Intermediate system to intermediate system intra-domain-
routing routine information exchange protocol for use in
conjunction with the protocol for providing the
connectionless-mode Network Service (ISO 8473)",
ISO Standard 10589, 1992.
[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>.
[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>.
10.2. Informative References
[I-D.bryant-rtgwg-plfa]
Bryant, S., Chunduri, U., and T. Eckert, "Preferred Path
Loop-Free Alternate (pLFA)", draft-bryant-rtgwg-plfa-04
(work in progress), May 2022.
[I-D.chunduri-dmm-5g-mobility-with-ppr]
Chunduri, U., Contreras, L. M., Bhaskaran, S., Tantsura,
J., and P. Muley, "Transport aware 5G mobility with PPR",
draft-chunduri-dmm-5g-mobility-with-ppr-00 (work in
progress), November 2020.
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[I-D.ietf-dmm-tn-aware-mobility]
Chunduri, U., Kaippallimalil, J., Bhaskaran, S., Tantsura,
J., and P. Muley, "Mobility aware Transport Network
Slicing for 5G", draft-ietf-dmm-tn-aware-mobility-03 (work
in progress), March 2022.
[I-D.ietf-isis-encapsulation-cap]
Xu, X., Decraene, B., Raszuk, R., Chunduri, U., Contreras,
L. M., and L. Jalil, "Advertising Tunnelling Capability in
IS-IS", draft-ietf-isis-encapsulation-cap-01 (work in
progress), April 2017.
[I-D.ietf-isis-mpls-elc]
Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
and M. Bocci, "Signaling Entropy Label Capability and
Entropy Readable Label Depth Using IS-IS", draft-ietf-
isis-mpls-elc-13 (work in progress), May 2020.
[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", draft-ietf-lsr-isis-srv6-extensions-18
(work in progress), October 2021.
[I-D.ietf-mpls-sfc]
Farrel, A., Bryant, S., and J. Drake, "An MPLS-Based
Forwarding Plane for Service Function Chaining", draft-
ietf-mpls-sfc-07 (work in progress), March 2019.
[I-D.ietf-teas-enhanced-vpn]
Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
Framework for Enhanced Virtual Private Network (VPN+)
Services", draft-ietf-teas-enhanced-vpn-10 (work in
progress), March 2022.
[I-D.xuclad-spring-sr-service-chaining]
Clad, F., Xu, X., Filsfils, C., Bernier, D., Li, C.,
Decraene, B., Ma, S., Yadlapalli, C., Henderickx, W., and
S. Salsano, "Segment Routing for Service Chaining", draft-
xuclad-spring-sr-service-chaining-01 (work in progress),
March 2018.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120,
DOI 10.17487/RFC5120, February 2008,
<https://www.rfc-editor.org/info/rfc5120>.
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[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, DOI 10.17487/RFC5304, October
2008, <https://www.rfc-editor.org/info/rfc5304>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
DOI 10.17487/RFC5308, October 2008,
<https://www.rfc-editor.org/info/rfc5308>.
[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, DOI 10.17487/RFC5310, February
2009, <https://www.rfc-editor.org/info/rfc5310>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.
[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>.
[RFC7645] Chunduri, U., Tian, A., and W. Lu, "The Keying and
Authentication for Routing Protocol (KARP) IS-IS Security
Analysis", RFC 7645, DOI 10.17487/RFC7645, September 2015,
<https://www.rfc-editor.org/info/rfc7645>.
[RFC7794] Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and
U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4
and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794,
March 2016, <https://www.rfc-editor.org/info/rfc7794>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
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[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>.
[RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
"Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
DOI 10.17487/RFC8491, November 2018,
<https://www.rfc-editor.org/info/rfc8491>.
[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>.
Appendix A. Appendix
A.1. Challenges with Increased SID Depth
SR label stacks carried in the packet header create challenges in the
design and deployment of networks and networking equipment.
Following examples illustrates the need for increased SID depth in
various use cases:
(a). Consider the following network where SR-MPLS data plane is in
use and with same SRGB (5000-6000) on all nodes i.e., A1 to A11 and
B1 to B7 for illustration:
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SID:10 SID:20 SID:30 SID:40 SID:50 SID:300(Ax) SID:60 SID:70
A1--------A2-------A3-------A4-------A5===============A6-- ----------A7
| \ / \5 5/ \ SID:310(Ay) \ /
| 5 \ 10 10/ +-A10-+ \ \10 10/
| \ SID:80 / |SID:100 \ \ /
A11 SID:111 \A8-----A9/ | \ 40 \ /
| / SID:90 \ +-----+ +---+ \ /
| 5 /10 \10 5 \ \ \ /
| /SID:125(B2x) \ \ \ \/
B1-------B2==============B3----B4------B5-------=B6----------B7
SID:127(B2y)
SID:110 SID:120 SID:130 SID:140 SID:150 SID:160 SID:170
=== = Path with Parallel Adjacencies and ADJ-SIDs
--- = Shortest Path Nodal SID
Figure 6: SR-MPLS Network
Global ADJ-SIDs are provisioned between A5-A6 and B2-B3 (with
parallel adjecencies). All other SIDs shown are nodal SID
indices.
All metrics of the links are set to 1, unless marked otherwise.
Shortest Path from A1 to A7: A2-A3-A4-A5-A6-A7
Path-x: From A1 to A7 - A2-A8-B2-B2x-A9-A10-Ax-A7; Pushed Label
Stack @A1: 5020:5080:5120:5125:5090:5100:5300:5070 (where B2x is a
local ADJ-SID and Ax is a global ADJ-SID).
In this example, the traffic engineered path is represented with a
combination of Adjacency and Node SIDs with a stack of 8 labels.
However, this value can be larger, if the use of entropy label
[RFC6790] is desired and based on the Readable Label Depth
(Appendix A.2) capabilities of each node and additional labels
required to insert ELI/EL at appropriate places.
Though above network is shown with SR-MPLS data plane, if the
network were to use SRv6 data plane, path size would be increased
even more because of the size of the IPv6 SID (16 bytes) in SRH.
(b). Apart from the TE case above, when deploying
[I-D.ietf-mpls-sfc] or [I-D.xuclad-spring-sr-service-chaining], with
the inclusion of services, or non-topological segments on the label
stack, can also make the size of the stack much larger.
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Overall the additional path overhead in various SR deployments may
cause the following issues:
a. HW Capabilities: Not all nodes in the path can support the
ability to push or read label stack (with additional non-
topological and special labels) needed to satisfy user/operator
requirements. Alternate paths, which meet these user/operator
requirements may not be available.
b. Line Rate: Potential performance issues in deployments, which use
data plane with extension header as both size of the SIDs in the
extension header and the fixed extension header size itself needs
to be factored by the hardware.
c. MTU: Larger SID stacks on the data packet can cause potential
MTU/fragmentation issues (SRH).
d. Header Tax: Some deployments, such as 5G, require minimal packet
overhead in order to conserve network resources. Carrying 40 or
50 octets of data in a packet with hundreds of octet of header
would be an unacceptable use of available bandwidth.
With the solution proposed in this document, for Path-x in Figure 6
above, SID stack would be reduced from 8 SIDs to a single SID witout
any additional overhead.
A.2. Mitigation with MSD
The number of SIDs in the stack a node can impose is referred as
Maximum SID Depth (MSD) capability [RFC8491], which must be taken
into consideration when computing a path to transport a data packet
in a network implementing segment routing. [I-D.ietf-isis-mpls-elc]
defines another MSD type, Readable Label Depth (RLD) that is used by
a head-end to insert Entropy Label pair (ELI/EL) at appropriate
depth, so it could be read by transit nodes. There are situations
where the source routed path can be excessive as path represented by
SR SIDs need to describe all the nodes and ELI/EL based on the
readability of the nodes in that path. Registries setforth in
[RFC8491] applicable for MPLS data plane and for IPv6 data plane with
SRH.
MSDs (and RLD type) capabilities advertisement help mitigate the
problem for a central entity to create the right source routed path
per application/operator requirements. However the availability of
actual paths meeting these requirements are still limited by the
underlying hardware and their MSD capabilities in the data path.
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Authors' Addresses
Uma Chunduri
Intel Corporation
Email: umac.ietf@gmail.com
Richard Li
Futurewei
2330 Central Expressway
Santa Clara, CA 95050
USA
Email: richard.li@futurewei.com
Russ White
Juniper Networks
Oak Island, NC 28465
USA
Email: russ@riw.us
Luis M. Contreras
Telefonica
Sur-3 building, 3rd floor
Madrid 28050
Spain
Email: luismiguel.contrerasmurillo@telefonica.com
Jeff Tantsura
Microsoft
Email: jefftanti.ietf@gmail.com
Yingzhen Qu
Futurewei
2330 Central Expressway
Santa Clara, CA 95050
USA
Email: yingzhen.qu@futurewei.com
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