LSR Working Group U. Chunduri
Internet-Draft R. Li
Intended status: Standards Track Huawei USA
Expires: December 18, 2018 R. White
LinkedIn
J. Tantsura
Nuage Networks
L. Contreras
Telefonica
Y. Qu
Huawei USA
June 16, 2018
Preferred Path Routing (PPR) in IS-IS
draft-chunduri-isis-preferred-path-routing-00
Abstract
This document specifies a Preferred Path Routing (PPR) mechanism to
simplify the path description of data plane traffic in Segment
Routing (SR) deployments. PPR aims to mitigate the MTU and data
plane processing issues that may result from SR packet overheads; and
also supports traffic measurement, accounting statistics and further
attribute extensions along the paths. Preferred Path Routing is
achieved through the addition of descriptions to 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/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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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 December 18, 2018.
Copyright Notice
Copyright (c) 2018 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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Challenges with Increased SID Depth . . . . . . . . . . . 4
1.3. Mitigation with MSD . . . . . . . . . . . . . . . . . . . 5
2. Preferred Path Routing (PPR) . . . . . . . . . . . . . . . . 6
2.1. PPR-ID and PPR Path Description . . . . . . . . . . . . . 6
3. PPR Related TLVs . . . . . . . . . . . . . . . . . . . . . . 7
3.1. PPR-Prefix Sub-TLV . . . . . . . . . . . . . . . . . . . 9
3.2. PPR-ID Sub-TLV . . . . . . . . . . . . . . . . . . . . . 9
3.3. PPR-PDE Sub-TLV . . . . . . . . . . . . . . . . . . . . . 11
3.4. PPR-Attributes Sub-TLV . . . . . . . . . . . . . . . . . 13
4. PPR Processing Procedure Example . . . . . . . . . . . . . . 14
4.1. PPR TLV Processing . . . . . . . . . . . . . . . . . . . 16
5. PPR Data Plane aspects . . . . . . . . . . . . . . . . . . . 17
5.1. SR-MPLS with PPR . . . . . . . . . . . . . . . . . . . . 17
5.2. SRv6 with PPR . . . . . . . . . . . . . . . . . . . . . . 17
5.3. PPR Native IP Data Planes . . . . . . . . . . . . . . . . 18
6. PPR Traffic Accounting . . . . . . . . . . . . . . . . . . . 18
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
9. Security Considerations . . . . . . . . . . . . . . . . . . . 20
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
10.1. Normative References . . . . . . . . . . . . . . . . . . 20
10.2. Informative References . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
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1. Introduction
In a network implementing Segment Routing (SR), packets are steered
through the network using Segment Identifiers (SIDs) carried in the
packet header. Each SID uniquely identifies a segment as defined in
[I-D.ietf-spring-segment-routing]. SR capabilities are defined for
MPLS and IPv6 data planes called SR-MPLS and SRv6 respectively.
In SR-MPLS, each segment is encoded as a label, and an ordered list
of segments are encoded as a stack of labels. This stack of labels
is carried as part of the packet header. In SRv6, a segment is
encoded as an IPv6 address, within a new type of IPv6 hop-by-hop
routing header/extension header (EH) called SRH
[I-D.ietf-6man-segment-routing-header]; an ordered list of IPv6
addresses/segments are encoded in SRH.
Section 1.2 and Section 1.3 describe performance, hardware
capabilities and various associated issues which may result in SR
deployments. These motivate the proposed solution, Preferred Path
Routing, which is specified in Section 2.
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
PPR - Preferred Path Routing/Route
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 headr
SRv6 - Segment Routing with Ipv6 data plane with SRH
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TE - Traffic Engineering
1.2. 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 A7 and B1
to B7 for illustration:
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) \ /
\ 10 10/ +-A10-+ \ \10 /10
\ / SID:100 \ \ /
SID:80 \A8-----A9/SID:90 \ 40 \ /
/ \ +---+ \ /
/10 B2x:125 \10 \ \/
B1--------B2============B3----B4--------B5-------B6----------B7
SID:110 SID:120 SID:130 SID:140 SID:150 SID:160 SID:170
Figure 1: SR-MPLS Network
Global ADJ SIDs are provisioned between A5-A6 and B2-B3. 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
(Section 1.3) 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 SR-IPv6 data plane, path size would be
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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.
(c). Some SR-MPLS deployments need accounting statistics for path
monitoring and traffic re-optimizations.
[I-D.hegde-spring-traffic-accounting-for-sr-paths] and
[I-D.cheng-spring-mpls-path-segment] propose solutions with various
forms of path segments (either with special labels or PATH segment
encoded at the bottom of the stack respectively). However, these
proposals further increases the depth of SID stack, when it is
compounded with MSD/RLDs of various nodes in the path.
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 needed
[I-D.ietf-isis-segment-routing-msd] 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
SRH data plane with the increased size of the SRH with 16 byte
SIDs.
c. MTU: Larger SID stacks on the data packet can cause potential
MTU/fragmentation issues.
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 (Section 5) and
Section 4), for Path-x in the example network Figure 1 above, SID
stack would be reduced from 8 SIDs to a single SID.
1.3. Mitigation with MSD
The number of SIDs in the stack a node can impose is referred as
Maximum SID Depth (MSD) capability
[I-D.ietf-isis-segment-routing-msd], which must be taken into
consideration when computing a path to transport a data packet in a
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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.
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.
2. Preferred Path Routing (PPR)
PPR mitigates the issues described in Section 1.2, while continuing
to allow the direction of traffic along an engineered path through
the network by replacing the label stack with a PPR-ID. 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.
2.1. PPR-ID and PPR Path Description
The PPR-ID describes a path through the network. For SR- MPLS this
is an MPLS Label/SID and for SRv6 this is an IPv6-SID. For native IP
data planes this is either IPv4 or IPv6 address/prefix.
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 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. PPR-PDE optionally, can also have more information
as described with in their Sub-TLVs.
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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 in MPLS
enabled networks, or as an IP next hop, in the case of either
"plain"/"native" IP or SRv6 enabled networks. A PPR path is related
to a set of PDEs using the following TLVs.
3. PPR Related TLVs
This section describes the encoding of PPR TLV. This TLV can be seen
as having 4 logical section 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 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-Prefix Sub-TLV (variable size) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-ID Sub-TLV (variable size) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-PDE Sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-Attribute Sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: PPR TLV Format
o Type: 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.
o PPR-Prefix: A variable size sub-TLV representing the destination
of the path being described. This is defined in Section 3.1.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|D|A| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1. S: If set, the PPR TLV MUST be flooded across the entire routing
domain. If the S flag 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: 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: The originator of the PPR TLV MUST set the A bit in order to
signal that the prefixes and PPR-IDs advertised in the PPR TLV
are directly connected to the originators. If this bit is not
set, this allows any other node in the network 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. Reserved: For future use; MUST be set to 0 on transmit and
ignored on receive.
The following sub-TLVs draw from a new registry for sub-TLV numbers;
this registry is to be created by IANA, and administered using the
first come first serve process.
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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 | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | Mask Length | IS-IS Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IS-IS Prefix (continued, variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-Prefix Sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: PPR-Prefix Sub-TLV Format
o Type: TBD (IANA to assign from sub-TLV registry described above).
o Length: Total length of the value field in bytes.
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 Prefix Length: The length of the prefix in bytes. For IPv4 it
MUST be 4 and IPv6 it MUST be 16 bytes.
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). Value of this field MUST be 4 octets for IPv4
Prefix and MUST be 16 octets for IPv6 Prefix. Encoding is similar
to TLV 135 [RFC5305] and TLV 236 [RFC5308] or MT-Capable [RFC5120]
IPv4 (TLV 235) and IPv6 Prefixes (TLV 237) respectively.
o PPR-Prefix Sub-TLVs - TBD. These have 1 octet type, 1 octet
length and value field is defined per the type field.
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 PPR-ID Type field. Both
PPR-Prefix and PPR-ID MUST belong to a same node in the network.
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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-ID Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-ID Type | PPR-ID Length |PPR-ID Mask Len| Algo |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// PPR-ID (variable size) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: PPR-ID Sub-TLV Format
o Type: TBD (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:
o
PPR-ID Flags Format
0 1 2 3 4 5 6 7.. 15
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L|A|Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o
1. L: If set, the PPR path is a Loose-PPR. If the this flag is
unset, then the PPR path is a Strict-PPR. A Strict-PPR lists
every single node or adjacency in the path description from
source to the destination.
2. A: If set, all non-PPR path nodes in the IS-IS area/domain
MUST add a FIB entry for the PPR-ID with NH set to the
shortest path NH for the prefix being advertised. The use of
this is TBD. By default this flag MUST be unset.
3. Reserved: For future use; MUST be set to 0 on transmit and
ignored on receive.
o
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* 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:
o
A. Type: 1 MPLS SID/Label
B. Type: 2 Native IPv4 Address/Prefix
C. Type: 3 Native IPv6 Address/Prefix
D. 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. See PPR-ID below for the length of
this field and other considerations.
o PPR-ID Mask Length: It is applicable for 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 is an IPv4/IPv6 Prefix instead of 4/16 octet
Address respectively.
o Algo: 1 octet value represents the SPF algorithm. Algorithm
registry is as defined in
[I-D.ietf-isis-segment-routing-extensions].
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 and 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, it is a 16 byte IPv6 SID.
For PPR-ID Type 2, 3 or 4, if the PPR-ID Len is set to non-zero
value, then the PPR-ID MUST NOT be advertised as a routable prefix in
TLV 135, TLV 235, TLV 236 and TLV 237. Also PPR-ID MUST belong to
the node where Prefix is advertised from. PPR-ID Len = 0 case is a
special case and is discussed in Section 4.1.
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 set of contiguous
and ordered Sub-TLVs, where first Sub-TLV represents (the top of the
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stack in MPLS data plane or) first node/segment of the path. These
set of ordered Sub-TLVs can have both topological elements and non-
topological elements (e.g., service segments).
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 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PDE-ID Type | PDE-ID Len | PPR-PDE Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// PDE-ID Value (continued, variable size) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-PDE Sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: PPR-PDE Sub-TLV Format
o Type: TBD (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:
a. Type: 1 Topological
b. Type: 2 Non-Topological
o PDE-ID Type: 1 Octet PDE-forwarding IDentifier Type. A new
registry (TBD IANA) for this Sub-TLV and the defined types and
corresponding PDE-ID Len, PDE-ID Value are as follows:
a. Type 1: SID/Label type as defined in
[I-D.ietf-isis-segment-routing-extensions]. PDE-ID Len and PDE-
ID Value fields are per Section 2.3 of the referenced document.
b. Type 2: SR-MPLS Prefix SID. PDE-ID Len and PDE-ID Value are same
as Type 1.
c. Type 3: SR-MPLS Adjacency SID. PDE-ID Len and PDE-ID Value are
same as Type 1.
d. Type 4: IPv4 Address. PDE-ID Len is 4 bytes and PDE-ID Value is
4 bytes IPv4 address encoded similar to IPv4 Prefix described in
Section 3.1.
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e. Type 5: IPv6 Address. PDE-ID Len is 16 bytes and PDE-ID Value is
16 bytes IPv6 address encoded similar to IPv6 Prefix described in
Section 3.1.
f. Type 6: SRv6 Node SID as defined in
[I-D.bashandy-isis-srv6-extensions]. PDE-ID Len and PDE-ID Value
are as defined in SRv6 SID from the refrenced draft.
g. Type 7: SRv6 Adjacency-SID. PDE-ID Len 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|D|Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1. L: Loose Bit. Indicates the type of next "Topological PDE-ID" in
the path description and overrides the L bit in Section 3.2. If
set, the next PDE is Loose. If this flag is unset, the next
Topological PDE is Strict Type.
2. D: Destination 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 PPR-Prefix Section 3.1 belongs to, if
there is no sub-sub-TLV to override PPR-Prefix and PPR-ID values.
3. Reserved: 1 Octet reserved bits for future use. Reserved bits
MUST be reset on transmission and ignored on receive.
o PPR-PDE Sub-TLVs: TBD. These have 1 octet type, 1 octet length
and value field is defined per the type field.
3.4. PPR-Attributes Sub-TLV
PPR-Attribute Sub-TLVs describe the attributes of the path. The
following sub-TLVs draw from a new registry for sub-TLV numbers; this
registry is to be created by IANA, and administered using the first
come first serve process:
o Type 1 (Suggested Value - IANA TBD): Packet Traffic accounting
Sub-TLV. Length 0 and no value field. Specifies to create a
counter to count number of packets forwarded on this PPR-ID on
each node in the path description.
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o Type 2 (Suggested Value - IANA TBD): Traffic statistics in Bytes
Sub-TLV. Length 0 and no value field. Specifies to create a
counter to count number of bytes forwarded on this PPR-ID
specified in the network header (e.g. IPv4, IPv6) on each node in
the path description.
o Type 3 (Suggested Value - IANA TBD): PPR-Prefix originating node's
IPv4 Router ID Sub-TLV. Length and Value field are as specified
in [RFC7794].
o Type 4 (Suggested Value - IANA TBD): PPR-Prefix originating node's
IPv6 Router ID Sub-TLV. Length and Value field are as specified
in [RFC7794].
o Type 5 (Suggested Value - IANA TBD): PPR-Metric Sub-TLV. Length 4
bytes, and Value is 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 (TBD more, on
what happens when metric is same for two different set of PPR-PDE
Sub-TLVs).
4. PPR Processing Procedure Example
As specified in Section 2, 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:
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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 6: IS-IS Network
In the (Figure 6) shown, 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 R1-R14 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 of
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 (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.
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.
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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 on
Section 3.2.
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 on Section 3.2. 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, determine 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 can be done, during the end of the
SPF computation (for MTID that is advertised in this TLV) and for the
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 of R4 indicates, 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 even though from R9 the shortest path to
reach R4 via R11 (Cost 3: R9-R11-R12-R4) it chooses the nexthop to
R10 to reach R4 as specified in the PPR path description. Same
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
shortest path nexthop computed towards PPR Prefix to the shortest
path nexthop towards the next topological PDE in the PPR's Path.
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For PPR-ID (Section 3.2) Type 2, 3 or 4, if the PPR-ID Len is set to
0, then Prefix would also become the PPR-ID (a special case). This
can be used for some situations, where certain optimizations are
required in the network. For this, path described in the PPR TLV
SHOULD be completely dis-joint from the shortest path route to the
prefix. If the disjoint-ness property is not maintained then the
traffic MAY not be using the PPR path, as and when it encounters any
node which is not in the path description.
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. Other data planes other than described below
can also use this TLV to describe the PPR. Further details TBD.
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 nexthop 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 also
programmed in the forwarding to enable specific function/service,
when the data packet hits with corresponding PPR-ID.
Based on '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
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 next topological PPR-PDE.
5.2. 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 nexthop 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
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setting the same as the destination IPv6 address and SL field in SRH
would be set to 0; however SRH [I-D.ietf-6man-segment-routing-header]
can contain any other TLVs and non-topological SIDs as needed.
5.3. 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. However this is applicable to only Strict-
PPR paths ('L' bit as specified in Section 3.2 MUST be unset).
Similarly for PPR-ID Type is 3, then source routing and packet
steering can be done in IPv6 data plane (PPR-IPv6), along the path as
described in PPR Path description. Whatever specified above for IPv4
applies here too, except that destination IP address of the data
packet is 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.
6. PPR Traffic Accounting
Section 3.4 defines few PPR-Attributes to indicate creation of
traffic accounting statistics in each node of the PPR path
description. Presence of "Packet Traffic Accounting" and "Traffic
Statistics" Sub-TLVs instruct to provision the hardware, to account
for the respective traffic statistics. Traffic accounting should
happen, when the actual data traffic hits for the PPR-ID in the
forwarding plane. This allows more granular and dynamic enablement
of traffic statistics for only certain PPRs as needed.
This approach, thus is more safe and secure than any mechanism that
involves creation of the state in the nodes with the data traffic
itself. This is because, creation and deletion of the traffic
accounting state for PPRs happen through IS-IS LSP processing and IS-
IS protocol control plane security Section 9 options are applicable
to this TLV.
How the traffic accounting is distributed to a central entity is out
of scope of this document. One can use any method (e.g. gRPC) to
extract the PPR-ID traffic stats from various nodes along the path.
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7. Acknowledgements
Thanks to Alex Clemm, Lin Han, Toerless Eckert 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 suggestions on this topic.
Earlier versions of draft-ietf-isis-segment-routing-extensions have a
mechanism to advertise EROs through Binding SID.
8. IANA Considerations
This document requests the following new TLV in IANA IS-IS TLV code-
point registry.
TLV # Name
----- --------------
TBD PPR TLV
This document requests IANA to create a new Sub-TLV registry for PPR
TLV Section 3 with the following initial entries (suggested values):
Sub-TLV # Sub-TLV Name
--------- ---------------------------------------------------------
1 PPR-Prefix (Section 3.1)
2 PPR-ID (Section 3.2)
3 PPR-PDE (Section 3.3)
This document also requests IANA to create a new Sub-TLV registry for
PPR Path attributes with the following initial entries (suggested
values):
Sub-TLV # Sub-TLV Name
--------- ---------------------------------------------------------
1 Packet Traffic Accounting (Section 3.4)
2 Traffic Statistics (Section 3.4)
3 PPR-Prefix Source IPv4 Router ID (Section 3.4)
4 PPR-Prefix Source IPv6 Router ID (Section 3.4)
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5 PPR-Metric (Section 3.4)
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 an 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 an 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 an 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 an unsigned 8 bit numbers. Values are
as defined in Section 3.3 of this document.
9. Security Considerations
Security concerns for IS-IS are addressed in [RFC5304] and [RFC5310].
Further security analysis for 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 as this extension is
related to SR-MPLS and SRH data planes as defined in
[I-D.ietf-spring-segment-routing], those particular data plane
security considerations does apply here.
10. References
10.1. Normative References
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[I-D.ietf-isis-segment-routing-msd]
Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
"Signaling MSD (Maximum SID Depth) using IS-IS", draft-
ietf-isis-segment-routing-msd-12 (work in progress), May
2018.
[I-D.ietf-spring-segment-routing]
Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing
Architecture", draft-ietf-spring-segment-routing-15 (work
in progress), January 2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
10.2. Informative References
[I-D.bashandy-isis-srv6-extensions]
Ginsberg, L., Bashandy, A., Filsfils, C., Decraene, B.,
and Z. Hu, "IS-IS Extensions to Support Routing over IPv6
Dataplane", draft-bashandy-isis-srv6-extensions-02 (work
in progress), March 2018.
[I-D.cheng-spring-mpls-path-segment]
Cheng, W., Wang, L., Li, H., Chen, M., Zigler, R., and S.
Zhan, "Path Segment in MPLS Based Sement Routing Network",
draft-cheng-spring-mpls-path-segment-01 (work in
progress), March 2018.
[I-D.hegde-spring-traffic-accounting-for-sr-paths]
Hegde, S., "Traffic Accounting for MPLS Segment Routing
Paths", draft-hegde-spring-traffic-accounting-for-sr-
paths-01 (work in progress), October 2017.
[]
Previdi, S., Filsfils, C., Leddy, J., Matsushima, S., and
d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header
(SRH)", draft-ietf-6man-segment-routing-header-13 (work in
progress), May 2018.
[I-D.ietf-isis-mpls-elc]
Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
Litkowski, "Signaling Entropy Label Capability and
Readable Label-stack Depth Using IS-IS", draft-ietf-isis-
mpls-elc-03 (work in progress), January 2018.
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[I-D.ietf-isis-segment-routing-extensions]
Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A.,
Gredler, H., Litkowski, S., Decraene, B., and J. Tantsura,
"IS-IS Extensions for Segment Routing", draft-ietf-isis-
segment-routing-extensions-17 (work in progress), June
2018.
[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-01 (work in progress), May 2018.
[I-D.xuclad-spring-sr-service-chaining]
Clad, F., Xu, X., Filsfils, C., daniel.bernier@bell.ca,
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>.
[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>.
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[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>.
[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>.
Authors' Addresses
Uma Chunduri
Huawei USA
2330 Central Expressway
Santa Clara, CA 95050
USA
Email: uma.chunduri@huawei.com
Richard Li
Huawei USA
2330 Central Expressway
Santa Clara, CA 95050
USA
Email: richard.li@huawei.com
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Russ White
LinkedIn
Oak Island, NC 28465
USA
Email: russ@riw.us
Jeff Tantsura
Nuage Networks
755 Ravendale Drive
Mountain View, CA 94043
USA
Email: jefftant.ietf@gmail.com
Luis M. Contreras
Telefonica
Sur-3 building, 3rd floor
Madrid 28050
Spain
Email: luismiguel.contrerasmurillo@telefonica.com
Yingzhen Qu
Huawei USA
2330 Central Expressway
Santa Clara, CA 95050
USA
Email: yingzhen.qu@huawei.com
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