Internet DRAFT - draft-chunduri-ospf-lsr-preferred-path-routing
draft-chunduri-ospf-lsr-preferred-path-routing
LSR Working Group U. Chunduri
Internet-Draft Y. Qu
Intended status: Standards Track Huawei USA
Expires: December 20, 2018 R. White
LinkedIn
J. Tantsura
Nuage Networks
L. Contreras
Telefonica
June 18, 2018
Preferred Path Routing (PPR) in OSPF
draft-chunduri-ospf-lsr-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 with OSPFv2 and OSPFv3 protocols. 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 OSPF 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].
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."
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This Internet-Draft will expire on December 20, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3
2. OSPFv2 PPR TLV . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. PPR-Flags . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. PPR-Prefix sub-TLV . . . . . . . . . . . . . . . . . . . 6
2.3. PPR-ID sub-TLV . . . . . . . . . . . . . . . . . . . . . 7
2.4. PPR-PDE sub-TLV . . . . . . . . . . . . . . . . . . . . . 8
2.5. PPR-Attributes sub-TLV . . . . . . . . . . . . . . . . . 10
3. OSPFv3 PPR TLV . . . . . . . . . . . . . . . . . . . . . . . 11
3.1. OSPFv3 PPR-Prefix sub-TLV . . . . . . . . . . . . . . . . 13
3.2. OSPFv3 PPR-ID sub-TLVs . . . . . . . . . . . . . . . . . 14
3.3. OSPFv3 PPR-PDE sub-TLV . . . . . . . . . . . . . . . . . 16
3.4. OSPFv3 PPR-Attributes sub-TLV . . . . . . . . . . . . . . 18
4. Other Considerations . . . . . . . . . . . . . . . . . . . . 18
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
7. Security Considerations . . . . . . . . . . . . . . . . . . . 19
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.1. Normative References . . . . . . . . . . . . . . . . . . 19
8.2. Informative References . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
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.
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In SR-MPLS, a segment is encoded as a label and an ordered list of
segments is encoded as a stack of labels on the data packet. In
SRv6, a segment is encoded as an IPv6 address, with in a new type of
IPv6 hop-by-hop routing header/extension header (EH) called SRH
[I-D.ietf-6man-segment-routing-header], where an ordered list of IPv6
addresses/segments is encoded in SRH.
The issues caused by the large SID depth, and existing methods for
mitigation are introduced in [I.D. chunduri-lsr-isis-preferred-path-
routing] section 1.2 and 1.3. To mitigate these issues , and also to
facilitate forwarding plane a mechanism to identify the path with a
corresponding data plane identifier for accounting of traffic for SR
paths, this draft proposes a new OSPFv2 PPR TLV (Section 2), OSPFv3
PPR TLV (Section 3) to use the path with a corresponding data plane
identifier.
Preferred Path Routing means enabling route computation based on the
specific path described along with the prefix as opposed to shortest
path towards the prefix.
Any prefix advertised with a path description from any node in the
network is called Preferred Path Route. A PPR could be an SR path,
an explicitly provisioned Fast Re-Route (FRR) path or a service
chained path. A PPR can be signaled by any node, which receives the
SR path SR path computed by a central controller, or by operator by
statically configuring the same on a node in the network.
With corresponding data plane, Section 4 mechanism as in [I-
D.chunduri-isis-preferred-path-routing], reduces the SID stack in the
data plane with a single PPR ID.
1.1. Acronyms
EL - Entropy Label
ELI - Entropy Label Indicator
MPLS - Multi Protocol Label Switching
MSD - Maximum SID Depth
MTU - Maximum Transferrable Unit
NSP - Non Shortest Path
SID - Segment Identifier
SPF - Shortest Path First
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SR - Segment Routing
SRH - Segment Routing Header
SR-MPLS - Segment Routing with MPLS data plane
SRv6 - Segment Routing with Ipv6 data plane with SRH
SRH - IPv6 Segment Routing Header
TE - Traffic Engineering
2. OSPFv2 PPR TLV
Extended Prefix Opaque LSAs defined in [RFC7684] are used for
advertisements of PPRs. This section describes the encoding of PPR
TLV. This TLV can be seen as having 4 logical section viz., encoding
of the OSPFv2 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 OSPF PPR TLVs MAY be advertised in
each OSPF Extended Prefix Opaque LSA, but all TLVs included in a
single OSPF Extended Prefix Opaque LSA MUST have the same flooding
scope.
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 | AF | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-Prefix sub-TLV (variable size) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-ID sub-TLV (variable size) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-PDE sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-Attribute sub-TLVs(variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: OSPFV2 PPR TLV Format
o Type - TBD (IANA)from OSPF Extended Prefix Opaque LSA registry.
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o Length - Total length of the value field in bytes (variable).
o PPR-Flags - 2 Octet flags for this TLV are described below.
o AF - Address family for the prefix. Currently, the only supported
value is 0 for IPv4 unicast. The inclusion of address family in
this TLV allows for future extension.
o Reserved - 1 Octet reserved bits for future use. Reserved bits
MUST be reset on transmission and ignored on receive.
o PPR-Prefix - This is a variable size sub-TLV, which represents the
prefix for which path description is being attached to. This is
defined in Section 2.2.
o PPR-ID - This is a variable size sub-TLV, which represents the
data plane or forwarding identifier of the PPR. This is defined
in Section 2.3.
o PPR-PDEs - Variable number of ordered PDE sub-TLVs which
represents the path. This is defined in Section 2.4.
o PPR-Attributes - Variable number of PPR-Attribute sub-TLVs which
represent the path attributes. These are defined in Section 2.5.
2.1. PPR-Flags
Flags: 2 octet field of PPR TLV has following flags defined:
NSPF ID Flags Format
0 1 2 3 4 5 6 7 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|IA|A | Rsrvd. |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
w=Where:
IA-Flag: Inter-Area flag. If set, advertisement is of inter-area
type. An Area Boarder Router (ABR) that is advertising the OSPF
PPR TLV between areas MUST set this bit.
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 "OSPF Prefix". If PPR TLV
is propagated to other areas the A-flag MUST be cleared. In case
if the originating node of the prefix has to be disambiguated for
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any reason including, if it is a Multi Homed Prefix (MHP) or
propagated to a different OSPF area, then PPR-Attribute sub-TLV
Source Router ID SHOULD be included.
Rsrvd: reserved bits for future use. Reserved bits MUST be reset
on transmission and ignored on receive.
2.2. PPR-Prefix sub-TLV
The structure of PPR-Prefix, for which path description is attached
to is as follows:
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 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// OSPFv2 Prefix (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-Prefix sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: PPR-Prefix sub-TLV Format
o Type - TBD (See IANA for suggested value) from OSPFv2 PPR TLV
Section 2 sub-TLV registry.
o Length - Total length of the value field in bytes (variable).
o MT-ID - Multi-Topology ID (as defined in [RFC4915]).
o Prefix Len - contains the length of the prefix in bits. Only the
most significant octets of the Prefix are encoded.
o Mask Length - The length of the prefix in bits. Only the most
significant octets of the Prefix are encoded.
o OSPFv2 Prefix - represents the OSPFv2 prefix at the tail-end of
the advertised PPR. For the address family IPv4 unicast, the
prefix itself is encoded as a 32-bit value. The default route is
represented by a prefix of length 0.
o PPR-Prefix sub-TLVs - TBD. It has 2 octet type, 2 octet length
and value field is defined per type.
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2.3. PPR-ID sub-TLV
This represents the actual data plane identifier in the packet and
could be of any data plane as defined in PPR-ID-type field. Both
OSPF Prefix and PPR-ID MUST belong 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| Algo | PPR-ID //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// PPR-ID (cont., variable size) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: PPR-ID sub-TLV Format
o Type - TBD (See IANA for suggested value) from OSPFv2 PPR TLV
Section 2 sub-TLV registry.
o Length - Total length of the value field in bytes (variable).
o PPR-ID Type - Data plane type of PPR-ID. This is a new registry
(TBD IANA) for this sub-TLV and the defined types are as follows:
a. Type: 1 MPLS SID/Label
b. Type: 2 Native IPv4 Address/Prefix
o PPR-ID Flags - 2 Octet field for PPR-ID flags:
PPR-ID Flags Format
0 1 2 3 4 5 6 7 15
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L|A| Rsrvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1. L - If set, the PPR path is a Loose-PPR. If the flag is unset,
then the path described is a Strict-PPR. A Strict-PPR lists
every single node or adjacency in the path description from
source to the destination.
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2. A - If set, all non-PPR path nodes in the OSPF area 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 MUST be unset.
3. Reserved - Reserved bits for future use. Reserved bits MUST be
reset on transmission and ignored on receive.
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 Len - It is applicable for only for PPR-ID Type 2.
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 Prefix instead of 4 octet Address respectively.
o Algo - 1 octet value represents the SPF algorithm. Algorithm
registry is as defined in
[I-D.ietf-ospf-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.
2.4. PPR-PDE sub-TLV
This is a new sub-TLV type in PPR TLV Section 2 and is called as 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 stack in MPLS data plane or)
first node/segment of the path. These set of ordered sub-TLVs can
have both topological SIDs and non-topological SIDs (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 Len | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-PDE Flags | PDE-ID Value //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// PDE-ID Value (Contd., Variable size) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-PDE sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: PPR-PDE sub-TLV Format
o Type - TBD (See IANA for suggested value) from OSPFv2 PPR TLV
Section 2 sub-TLV registry.
o Length - Total length of the value field in bytes (variable).
o PPR-PDE Type - This is 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. This is 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 sub-TLV as defined in
[I-D.ietf-ospf-segment-routing-extensions]. PDE-ID Len and PDE-
ID Value fields are per Section 2.1 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 2.2.
o PDE-ID Len - 1 Octet. Length of PDE-ID field.
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o Reserved - 1 Octet reserved bits for future use. Reserved bits
MUST be reset on transmission and ignored on receive.
o PPR-PDE Flags - 2 Octet flags for this TLV are described below:
PPR-PDE Flags Format
0 1 2 3 4 5 6 7... 15
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L|D| Rsrvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1. L - This bit indicates the type of next "Topological PDE-ID" in
the path description and overrides the L bit in Section 2.3. If
set, the next PDE is Loose. If this flag is unset, the next
Topological PDE is Strict Type.
2. D - By default this bit MUST be unset. This bit MUST be set only
for PPR-PDE Type is Topological and this PDE represents the PDE-
ID corresponding to the PPR-Prefix Section 2.2.
3. Rsrvd - Reserved bits for future use. Reserved bits MUST be
reset on transmission and ignored on receive.
o PPR-PDE sub-TLVs - TBD. It has 2 octet type, 2 octet length and
value field is defined per type.
2.5. PPR-Attributes sub-TLV
PPR-Attribute sub-TLVs represent the attributes of the path
described. This is a new sub-TLV type (IANA TBD) in PPR TLV
Section 2. The following PPR-Attribute sub-TLVs (Type - IANA TBD)
are defined as follows:
o Type 4 (Suggested Value - IANA TBD): This is Packet Traffic
accounting sub-TLV. Length 0 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.
o Type 5 (Suggested Value - IANA TBD): This is Traffic statistics in
Bytes sub-TLV. Length 0 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.
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o Type 6 (Suggested Value - IANA TBD): This is PPR-Prefix
originating node's IPv4 Router ID sub-TLV. Length and Value field
are as specified in [RFC 7794] (TBD).
o Type 7 (Suggested Value - IANA TBD): This is PPR-Prefix
originating node's IPv6 Router ID sub-TLV. Length and Value field
are as specified in [RFC 7794] (TBD).
o Type 8 (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).
3. OSPFv3 PPR TLV
The OSPFv3 PPR TLV s a top level TLV of the following LSAs defined in
[I-D.ietf-ospf-ospfv3-lsa-extend].
E-Intra-Area-Prefix-LSA
E-Inter-Area-Prefix-LSA
E-AS-External-LSA
E-Type-7-LSA
Multiple OSPFv3 PPR TLVs MAY be advertised in each LSA mentioned
above. The OSPFv3 PPR TLV has the following format:
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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-Flags | AF | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OSPFv3 PPR-Prefix sub-TLV (variable size) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-ID sub-TLV (variable size) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-PDE sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-Attribute sub-TLVs(variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: OSPFv3 PPR TLV Format
o Type - TBD (IANA)from OSPF Extended Prefix Opaque LSA registry.
o Length - Total length of the value field in bytes (variable).
o PPR-Flags - 2 Octet flags for this TLV are described below.
o AF: Address family for the prefix.
o
AF: 0 - IPv4 unicast
AF: 1 - IPv6 unicast
o Reserved - 1 Octet reserved bits for future use. Reserved bits
MUST be reset on transmission and ignored on receive.
Flags: 2 octet field. The following flags are defined:
OSPFv3 PPR Flags Format
0 1 2 3 4 5 6 7 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|IA|A | Rsrvd |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
IA-Flag: Inter-Area flag. If set, advertisement is of inter-area
type. An ABR that is advertising the OSPF PPR TLV between areas
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MUST set this bit.
[I-D.ietf-ospf-ospfv3-segment-routing-extensions]
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 "OSPF Prefix". If PPR TLV
is propagated to other areas the A-flag MUST be cleared. In case
if the originating node of the prefix has to be disambiguated for
any reason including, if it is a Multi Homed Prefix (MHP) or
propagated to a different OSPF area, then PPR-Attribute sub-TLV
Source Router ID SHOULD be included.
Rsrvd - reserved bits for future use. Reserved bits MUST be reset
on transmission and ignored on receive.
3.1. OSPFv3 PPR-Prefix sub-TLV
The structure of OSPFv3 PPR-Prefix, for which path description is
attached to is as follows:
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 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// OSPFv3 Prefix (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-Prefix sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: OSPFv3 PPR-Prefix sub-TLV Format
o Type - TBD (See IANA for suggested value) from OSPFv3 PPR TLV
Section 3 sub-TLV registry.
o Length - Total length of the value field in bytes (variable).
o Prefix Len - contains the length of the prefix in bits. Only the
most significant octets of the Prefix are encoded.
o Mask Length - The length of the prefix in bits. Only the most
significant octets of the Prefix are encoded.
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o OSPFv3 Prefix - represents the OSPFv3 prefix at the tail-end of
the advertised PPR. For the address family IPv4 unicast, the
prefix itself is encoded as a 32-bit value. The default route is
represented by a prefix of length 0. For the address family (AF
in OSPFv3 PPR TLV) in IPv6 unicast, the prefix, encoded as an even
multiple of 32-bit words, padded with zeroed bits as necessary.
This encoding consumes ((PrefixLength + 31) / 32) 32-bit words.
o PPR-Prefix sub-TLVs - TBD. It has 2 octet type, 2 octet length
and value field is defined per type.
3.2. OSPFv3 PPR-ID sub-TLVs
This represents the actual data plane identifier in the packet and
could be of any data plane as defined in PPR-ID-type field. Both
OSPF Prefix and PPR-ID MUST belong 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| Algo | PPR-ID //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// PPR-ID (cont, variable size) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: OSPFv3 PPR-ID sub-TLV Format
o Type - TBD (See IANA for suggested value) from OSPFv3 PPR TLV
Section 3 sub-TLV registry.
o Length - Total length of the value field in bytes (variable).
o PPR-ID Type - Data plane type of PPR-ID. This is a new registry
(TBD IANA) for this sub-TLV and the defined types are as follows:
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 Flags - 2 Octet field for PPR-ID flags:
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PPR-ID Flags Format
0 1 2 3 4 5 6 7 15
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L|A| Rsrvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1. L - If set, the PPR path is a Loose-PPR. If the flag is unset,
then the path described 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 OSPF area 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 MUST be unset.
3. Reserved - Reserved bits for future use. Reserved bits MUST be
reset on transmission and ignored on receive.
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 Len - 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-ospf-ospfv3-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 OSPF Prefix as specified in Section 2.2. For Type 4,
it is a 16 byte IPv6 SID.
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3.3. OSPFv3 PPR-PDE sub-TLV
This is a new sub-TLV type in PPR TLV Section 3 and is called as 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 stack in MPLS data plane or)
first node/segment of the path. These set of ordered sub-TLVs can
have both topological SIDs and non-topological SIDs (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 | PDE-ID Type | PDE-ID Len | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-PDE Flags | PDE-ID Value //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// PDE-ID Value (Contd., Variable size) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-PDE sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: OSPFv3 PPR-PDE sub-TLV Format
o Type - TBD (See IANA for suggested value) from OSPFv3 PPR TLV
Section 3 sub-TLV registry.
o Length - Total length of the value field in bytes (variable).
o PPR-PDE Type - This is 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. This is 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 sub-TLV as defined in
[I-D.ietf-ospf-segment-routing-extensions]. PED-ID Len and PDE-
ID Value fields are per Section 2.1 of the referenced document.
b. Type 2: SR-MPLS Prefix SID. PDE-ID Len and PDE-ID Value are same
as Type 1.
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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 2.2.
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 2.2.
f. Type 6: SRv6 Node SID as defined in
[I-D.li-ospf-ospfv3-srv6-extensions]. PDE-ID Len and PDE-ID
Value are as defined in SRv6 SID.
g. Type 7: SRv6 Adjacency-SID. PDE-ID Len and PDE-ID Value are as
defined in Type 6.
o PDE-ID Len - 1 Octet. Length of PDE-ID field.
o Reserved - 1 Octet reserved bits for future use. Reserved bits
MUST be reset on transmission and ignored on receive.
o PPR-PDE Flags - 2 Octet flags for this TLV are described below:
PPR-PDE Flags Format
0 1 2 3 4 5 6 7... 15
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L|D| Rsrvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1. L - This 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 - By default this bit MUST be unset. This bit MUST be set only
for PPR-PDE Type is Topological and this PDE represents the PDE-
ID corresponding to the PPR-Prefix Section 3.1.
3. Rsrvd - Reserved bits for future use. Reserved bits MUST be
reset on transmission and ignored on receive.
o PPR-PDE sub-TLVs - TBD. It has 2 octet type, 2 octet length and
value field is defined per type.
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3.4. OSPFv3 PPR-Attributes sub-TLV
PPR-Attribute sub-TLVs represent the attributes of the path
described. This is a new sub-TLV type (IANA TBD) in PPR TLV
Section 3. The following PPR-Attribute sub-TLVs (Type - IANA TBD)
are defined as follows:
o Type 4 (Suggested Value - IANA TBD): This is Packet Traffic
accounting sub-TLV. Length 0 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.
o Type 5 (Suggested Value - IANA TBD): This is Traffic statistics in
Bytes sub-TLV. Length 0 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 6 (Suggested Value - IANA TBD): This is PPR-Prefix
originating node's IPv4 Router ID sub-TLV. Length and Value field
are as specified in [RFC 7794] (TBD).
o Type 7 (Suggested Value - IANA TBD): This is PPR-Prefix
originating node's IPv6 Router ID sub-TLV. Length and Value field
are as specified in [RFC 7794] (TBD).
o Type 8 (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. Other Considerations
Please refer to [I-D.chunduri-isis-preferred-path-routing] section 3,
4 and 5.
5. Acknowledgements
Thanks to Richard Li, Alex Clemm, Toerless Eckert, Kiran Makhijani
and Lin Han 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.
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Earlier versions of draft-ietf-ospf-segment-routing-extensions have a
mechanism to advertise EROs through Binding SID.
6. IANA Considerations
This document requests the following new TLV in IANA OSPFv2 and
OSPFv3 TLV code-point registry.
TLV # Name
----- --------------
TBD PPR TLV
This document also requests IANA to create new registries for PPR TLV
Flags field, PPR Flags, and PPR sub-TLVs in PPR TLV as described in
Section 2 and Section 3.
7. Security Considerations
Existing security extensions as described in [RFC2328] and [RFC7684]
apply to these segment routing extensions. While OSPF is under a
single administrative domain, there can be deployments where
potential attackers have access to one or more networks in the OSPF
routing domain. In these deployments, stronger authentication
mechanisms such as those specified in [RFC7474] SHOULD be used.
Advertisement of the additional information defined in this document
introduces no new security concerns in OSPF 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.
8. References
8.1. Normative References
[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>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
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8.2. Informative References
[I-D.ietf-6man-segment-routing-header]
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-ospf-ospfv3-lsa-extend]
Lindem, A., Roy, A., Goethals, D., Vallem, V., and F.
Baker, "OSPFv3 LSA Extendibility", draft-ietf-ospf-ospfv3-
lsa-extend-23 (work in progress), January 2018.
[I-D.ietf-ospf-ospfv3-segment-routing-extensions]
Psenak, P., Filsfils, C., Previdi, S., Gredler, H.,
Shakir, R., Henderickx, W., and J. Tantsura, "OSPFv3
Extensions for Segment Routing", draft-ietf-ospf-ospfv3-
segment-routing-extensions-13 (work in progress), May
2018.
[I-D.ietf-ospf-segment-routing-extensions]
Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", draft-ietf-ospf-segment-
routing-extensions-25 (work in progress), April 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.
[I-D.li-ospf-ospfv3-srv6-extensions]
Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak,
"OSPFv3 Extensions for SRv6", draft-li-ospf-
ospfv3-srv6-extensions-01 (work in progress), March 2018.
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, DOI 10.17487/RFC4915, June 2007,
<https://www.rfc-editor.org/info/rfc4915>.
[RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
"Security Extension for OSPFv2 When Using Manual Key
Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,
<https://www.rfc-editor.org/info/rfc7474>.
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[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <https://www.rfc-editor.org/info/rfc7684>.
Authors' Addresses
Uma Chunduri
Huawei USA
2330 Central Expressway
Santa Clara, CA 95050
USA
Email: uma.chunduri@huawei.com
Yingzhen Qu
Huawei USA
2330 Central Expressway
Santa Clara, CA 95050
USA
Email: yingzhen.qu@huawei.com
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
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Luis M. Contreras
Telefonica
Sur-3 building, 3rd floor
Madrid 28050
Spain
Email: luismiguel.contrerasmurillo@telefonica.com
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