LSR Working Group U. Chunduri
Internet-Draft Y. Qu
Intended status: Standards Track Futurewei
Expires: September 9, 2020 R. White
Juniper Networks
J. Tantsura
Apstra Inc.
L. Contreras
Telefonica
March 8, 2020
Preferred Path Routing (PPR) in OSPF
draft-chunduri-lsr-ospf-preferred-path-routing-04
Abstract
This document specifies a Preferred Path Routing (PPR), a routing
protocol 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
further extensions along the paths. Preferred path routing is
achieved through the addition of path descriptions to the 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],
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 September 9, 2020.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3
2. OSPFv2 PPR TLV . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. PPR-Flags . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. PPR-Prefix Sub-TLV . . . . . . . . . . . . . . . . . . . 6
2.3. PPR-ID Sub-TLV . . . . . . . . . . . . . . . . . . . . . 7
2.4. PPR-PDE Sub-TLV . . . . . . . . . . . . . . . . . . . . . 9
2.5. PPR-Attributes Sub-TLV . . . . . . . . . . . . . . . . . 11
3. OSPFv3 PPR TLV . . . . . . . . . . . . . . . . . . . . . . . 12
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 . . . . . . . . . . . . . . 19
4. Other Considerations . . . . . . . . . . . . . . . . . . . . 19
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
7. Security Considerations . . . . . . . . . . . . . . . . . . . 20
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
8.1. Normative References . . . . . . . . . . . . . . . . . . 20
8.2. Informative References . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
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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, 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.
Preferred path routing cab be described as a) enabling route
computation based on the specific path described along with the
prefix as opposed to shortest path towards the prefix and b)
forwarding based on the abstracted path identifier as opposed to the
individual segments on the packet. This also further described in
Section 2 of [I-D.chunduri-lsr-isis-preferred-path-routing].
Any prefix advertised with a path description from any node in the
network is called PPR. 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 computed
by a central controller, or by statically configuring the same on a
node in the network.
The issues caused by the large SID depth, and existing methods for
mitigation are introduced in
[I-D.chunduri-lsr-isis-preferred-path-routing] in Appendix A.1 and
A.2. To mitigate these issues and also to facilitate forwarding
plane extensibility, 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.
1.1. Acronyms
EL - Entropy Label
ELI - Entropy Label Indicator
MPLS - Multi Protocol Label Switching
MSD - Maximum SID Depth
MTU - Maximum Transferrable Unit
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PPR - Preferred Path Route
SID - Segment Identifier
SPF - Shortest Path First
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:
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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.
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.
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2.1. PPR-Flags
Flags: 2 octet field of PPR TLV has following flags defined:
PPR TLV Flags Format
0 1 2 3 4 5 6 7 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|IA|A | Reserved |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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
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.
Reserved: Reserved bits for future use. Reserved bits MUST be
reset on transmission and ignored on receive.
PPR path description for each OSPF area is computed and given to one
of the nodes in that area for dissemination. Similarly path
information when crossing the area boundaries MUST be relevant to the
destination area. If there is no path information available for the
destination area, PPR TLV MUST NOT be leaked regardless of the IA bit
status.
2.2. PPR-Prefix Sub-TLV
The structure of PPR-Prefix, for which path description is attached
to is as follows:
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MT-ID | Prefix Length | Mask Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// OSPFv2 Prefix (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-Prefix Sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: PPR-Prefix Sub-TLV Format
o Type - 1 (suggested value, IANA TBD) 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 OSPF prefix being encoded
in bytes.
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 have2 octet type, 2 octet length and value
field is defined per type.
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.
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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 //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// PPR-ID (cont., variable size) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: PPR-ID Sub-TLV Format
o Type - 2 (suggested value, IANA TBD) 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:
Type: 1 SR-MPLS SID/Label
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved - Reserved bits for future use. Reserved bits MUST be
reset on transmission and ignored on receive.
o PPR-ID Type - Data plane type of PPR-ID. Values are defined in
[I-D.chunduri-lsr-isis-preferred-path-routing]. Only Type 1 and
Type 2 are applicable here.
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.
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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 encoded as
SR-MPLS SID/Label. For Type 2 this is a 4 byte IPv4 address
encoded similar to PPR-Prefix.
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).
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 - 3 (TBD IANA, suggested value) from OSPFv2 PPR TLV Section 2
Sub-TLV registry.
o Length - Total length of the value field in bytes (variable).
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o PPR-PDE Type - This is 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. 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:
Type 0: This value MUST be set only when PPR-PDE Type is Non-
Topological. PDE-ID Len specified in bytes and encoded in NBO
in PDE-ID Value field which can represent a service/function.
This information is provisioned on the immediate topological PDE
preceding to this PDE based on the 'E' bit.
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.
Type 2: SR-MPLS Prefix SID. PDE-ID Len and PDE-ID Value are
same as Type 1.
Type 3: SR-MPLS Adjacency SID. PDE-ID Len and PDE-ID Value are
same as Type 1.
Type 4: IPv4 Node 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.
Type 5: IPv4 P2P interface 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.
Type 6: IPv4 LAN interface 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. This type MUST have OSPF
Neighbor ID sub-TLV in the PDE.
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:
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PPR-PDE Flags Format
0 1 2 3 4 5 6 7... 15
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L|D|E| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L: Loose Bit: This bit indicates the type of next "Topological
PDE-ID" in the path description. If set, the next PDE is Loose.
If this flag is unset, the next Topological PDE is Strict Type.
D: Destination Bit: 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.
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 PPR-PDE Sub-TLVs have 2 octet type, 2 octet length and value field
is defined per type.
o PPR-PDE Sub-TLV: Type 4 (IANA TBD), Length Total length of value
field in bytes, Value: The Router ID of the neighbor for which the
LAN interface is advertised. This Sub-TLV MUST NOT be present, if
the PPR-PDE Type is not equal to 1 i.e., Topological PDE and PDE-
ID Type 6.
2.5. 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): 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.
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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:
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.
AF: 0 - IPv4 unicast
AF: 1 - IPv6 unicast
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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 TLV Flags Format
0 1 2 3 4 5 6 7 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|IA|A | Reserved |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
IA-Flag: Inter-Area flag. If set, advertisement is of inter-area
type. An ABR that is advertising the OSPF PPR TLV between areas
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.
Reserved - reserved bits for future use. Reserved bits MUST be
reset on transmission and ignored on receive.
PPR path description for each OSPF area is computed and given to one
of the nodes in that area for dissemination. Similarly path
information when crossing the area boundaries MUST be relevant to the
destination area. If there is no path information available for the
destination area, PPR TLV MUST NOT be leaked regardless of the IA bit
status.
3.1. OSPFv3 PPR-Prefix Sub-TLV
The structure of OSPFv3 PPR-Prefix, for which path description is
attached to is as follows:
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | Mask Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// OSPFv3 Prefix (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPR-Prefix Sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: OSPFv3 PPR-Prefix Sub-TLV Format
o Type - 1 (suggested value, IANA TBD) 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.
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 have2 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.
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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 //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// PPR-ID (cont, variable size) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: OSPFv3 PPR-ID Sub-TLV Format
o Type - 2 (suggested value, IANA TBD) 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:
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 Flags - 2 Octet field for PPR-ID flags:
PPR-ID Flags Format
0 1 2 3 4 5 6 7 15
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L|A| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.
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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 encoded as
SR-MPLS SID/Label. For Type 2 this is encoded as 4 byte IPv4
address. For Type 3 this is encoded as 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, this is encoded as 16 byte IPv6 SID.
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 - 3 (suggested value, IANA TBD) from OSPFv3 PPR TLV Section 3
Sub-TLV registry.
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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:
Type: 1 Topological
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:
Type 0: This value MUST be set only when PPR-PDE Type is Non-
Topological. PDE-ID Len specified in bytes and encoded in NBO
in PDE-ID Value field which can represent a service/function.
This information is provisioned on the immediate topological PDE
preceding to this PDE based on the 'E' bit.
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.
Type 2: SR-MPLS Prefix SID. PDE-ID Len and PDE-ID Value are
same as Type 1.
Type 3: SR-MPLS Adjacency SID. PDE-ID Len and PDE-ID Value are
same as Type 1.
Type 4: IPv4 Node 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.
Type 5: IPv4 P2P interface 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.
Type 6: IPv4 LAN interface 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. This type MUST have OSPF
Neighbor ID Sub-TLV in the PDE.
Type 7: IPv6 Node 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.
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Type 8: IPv6 P2P interface 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.
Type 9: IPv6 LAN interface 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. This type MUST have OSPF
Neighbor ID Sub-TLV in the PDE.
Type 10: 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.
Type 11: 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|E| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L: Loose Bit. 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.
D: Destination Bit. 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.
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.
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o PPR-PDE Sub-TLVs have 2 octet type, 2 octet length and value field
is defined per type.
o PPR-PDE Sub-TLV: Type 4 (IANA TBD), Length Total length of value
field in bytes, Value: The Router ID of the neighbor for which the
LAN interface is advertised. This Sub-TLV MUST NOT be present, if
the PPR-PDE Type is not equal to 1 i.e., Topological PDE and PDE-
ID Type 6/9.
3.4. OSPFv3 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): 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.
4. Other Considerations
Please refer to [I-D.chunduri-isis-preferred-path-routing] section 4,
5, 6 and 7.
5. Acknowledgements
Thanks to Richard Li, Alex Clemm, Padma Pillay-Esnault, 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.
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 as specified in Section 2 Section 3
respectively .
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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 the extensions specified in this document. 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>.
[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>.
8.2. Informative References
[I-D.chunduri-lsr-isis-preferred-path-routing]
Chunduri, U., Li, R., White, R., Tantsura, J., Contreras,
L., and Y. Qu, "Preferred Path Routing (PPR) in IS-IS",
draft-chunduri-lsr-isis-preferred-path-routing-04 (work in
progress), July 2019.
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[]
Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", draft-ietf-6man-segment-routing-header-26 (work in
progress), October 2019.
[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. and S. Previdi, "OSPFv3 Extensions for Segment
Routing", draft-ietf-ospf-ospfv3-segment-routing-
extensions-23 (work in progress), January 2019.
[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-27 (work in progress), December 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-07 (work in progress), November
2019.
[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>.
[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>.
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Authors' Addresses
Uma Chunduri
Futurewei
2330 Central Expressway
Santa Clara, CA 95050
USA
Email: umac.ietf@gmail.com
Yingzhen Qu
Futurewei
2330 Central Expressway
Santa Clara, CA 95050
USA
Email: yingzhen.qu@futurewei.com
Russ White
Juniper Networks
Oak Island, NC 28465
USA
Email: russ@riw.us
Jeff Tantsura
Apstra Inc.
333 Middlefield Road
Menlo Park, CA 94025
USA
Email: jefftant.ietf@gmail.com
Luis M. Contreras
Telefonica
Sur-3 building, 3rd floor
Madrid 28050
Spain
Email: luismiguel.contrerasmurillo@telefonica.com
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