Internet Engineering Task Force F. Brockners
Internet-Draft S. Bhandari
Intended status: Standards Track F. Maino
Expires: January 16, 2014 D. Lewis
Cisco
July 15, 2013
LISP Extensions for Segment Routing
draft-brockners-lisp-sr-00
Abstract
Segment Routing (SR) combines source routing and tunneling to steer
traffic through the transit network. The Locator/ID Separation
Protocol (LISP) separates IP addresses into Endpoint Identifiers
(EIDs) and Routing Locators (RLOCs) and also leverages tunneling
mechanisms. Mapping between EIDs and RLOCs is facilitated by the
LISP mapping system. Combining LISP and SR enables the LISP mapping
system to provide SR information to encapsulating routers so that
traffic can be steered in the transit network or the list of segments
a particular packet traverses is recorded in the packet header.
This document describes extensions required to the Locator/ID
Separation Protocol (LISP) to enable a LISP mapping system to
communicate list of segment identifiers or the request to record the
list of segments a particular packet traverses to the encapsulating
router.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 16, 2014.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Use cases that combine LISP and SR . . . . . . . . . . . . . 4
3.1. Traffic steering/traffic engineering . . . . . . . . . . 4
3.2. Traffic tracing . . . . . . . . . . . . . . . . . . . . . 4
4. LISP extensions to support SR . . . . . . . . . . . . . . . . 5
4.1. Example ELPs . . . . . . . . . . . . . . . . . . . . . . 7
4.1.1. Example: ELP with only SR used . . . . . . . . . . . 7
4.1.2. Example: ELP with SR and reencapsulating routers
combined . . . . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Manageability Considerations . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
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Segment Routing (SR) allows for a flexible definition of end-to-end
paths within network topologies by encoding paths as sequences of
topological sub-paths, called "segments" as described in
[I-D.filsfils-rtgwg-segment-routing]. Segment routing can be applied
to IPv6 with a new type of routing extension header. The Locator/ID
Separation Protocol [RFC6830] specifies an architecture and mechanism
for replacing the addresses currently used by IP with two separate
name spaces: Endpoint IDs (EIDs), used within sites; and Routing
Locators (RLOCs), used on the transit networks that make up the
Internet infrastructure. To achieve this separation, LISP defines
protocol mechanisms for mapping from EIDs to RLOCs. In addition,
LISP assumes the existence of a database to store and propagate those
mappings globally.
When LISP is combined with SR, the EID to RLOC mapping information
can be extended with segment routing information. This allows for a
closer correlation between the transit network, that is sometimes
also referred to as the underlay network, and the overlay network.
It is beyond the scope of this document to describe how the LISP
mapping system obtains a segment list for a particular EID-to-RLOC
mapping. This draft outlines use-cases for combining LISP and SR as
well as extensions to the LISP Canonical Address Format (LCAF) for
traffic engineering (LCAF type 10) [I-D.ietf-lisp-lcaf]. These
extensions are to be integrated into a future revision of
[I-D.ietf-lisp-lcaf].
2. Conventions
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].
This document uses the Terminology as defined in
[I-D.filsfils-rtgwg-segment-routing] and [I-D.ietf-lisp-lcaf].
Abbreviations used in this document:
AFI: Address Family Identifier
EID: Endpoint Identifier
ELP: Explicit Locator Path
ETR: Egress Tunnel Router
ITR: Ingress Tunnel Router
LCAF: LISP Canonical Address Format
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LISP: Locator/ID Separation Protocol
OAM: Operation Administration Maintenance
RLOC: Routing Locator
SR: Segment Routing
SID: Segment Identifier
Segment List: Ordered list of segment identifiers
3. Use cases that combine LISP and SR
Use-cases that combine LISP and SR include traffic steering/traffic
engineering as well as traffic tracing in the underlay network.
3.1. Traffic steering/traffic engineering
LISP combined with SR can be used to steer traffic in the underlay
network: The mapping system communicates a segment list to the LISP
ingress tunnel router (ITR) when resolving the EID-to-RLOC mapping as
part of a LISP Map-Reply. This extension allows the LISP mapping
system to provide a list of segment identifiers to encapsulating
routers so that traffic can be steered in the transit network. In a
typical setup the LISP ingress tunnel router would retrieve the
segment list from the mapping system along with the associated RLOC
using the EID as the lookup key. The ITR encapsulates the packet to
the RLOC, also including the segment list in the segment routing
extension header. The packet is forwarded to the ETR using segment
routing techniques. The ETR decapsulates the packet and delivers the
packet to the destination EID. Given that in SR with IPv6 transport
the entire segment list is available in the SR-specific extension
header of the outer IPv6 header, the LISP egress tunnel router, which
is the tunnel endpoint is also informed about the path a particular
packet took in the transport network.
LISP with SR for traffic engineering adds to the LISP traffic
engineering use-cases described in [I-D.farinacci-lisp-te]. LISP
combined with SR offers traffic engineering without using
reencapsulating tunnels [RFC6830]. Reencapsulating tunnels and SR
with LISP are complementary traffic engineering techniques and could
be combined. SR could for example be used in an explicit locator
path (ELP) to further traffic engineer a path between two
reencapsulating routers.
3.2. Traffic tracing
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LISP combined with SR can be used to get more information about the
path a packet took in the underlay network without sending extra
probe traffic. When SR is applied to IPv6, the segment list
describing the path that a packet takes through the network can be
recorded in the SR-specific extension header of the outer IPv6 packet
header. This activity is referred to as segment tracing. Segment
tracing can be performed independently from steering traffic using SR
techniques. It can also be used in a transit network which performs
normal IPv6 routing. When tracing is enabled, the segment ID of
every segment that a packet traverses is recorded in the SR-specific
extension header. This means that the egress tunnel router receives
information about the path, represented by the segment list, a
particular packet has taken in the underlay network. Different from
OAM mechanisms which send active probe packets, tracing information
can be made available for production traffic. The egress tunnel
router can choose to provide the traced segment list back to the
mapping system, for example through a LISP Map-Register. This
information can be used to ensure path symmetry send/receive traffic
in the transit network, or can serve other OAM or statistical
purposes.
4. LISP extensions to support SR
Segment routing information can be contained within the LISP mapping
system. A segment identifier is a 32-bit identification either for a
topological instruction or a service instruction. See
[I-D.filsfils-rtgwg-segment-routing] for details.
An EID can be associated with one or multiple ordered lists of
segment identifiers, also referred to as "segment lists", encoding
the topological and service source route of a packet. The segment
list can serve either traffic engineering or operational purposes.
In case of traffic engineering purposes, the segment list describes
the set of segments a packet visits when traversing the transit
network. The segment list enables the ITR to steer traffic using
segment routing techniques. The ITR retrieves the segment list from
the mapping system along with the associated RLOC using the EID as
the lookup key. For operations and maintenance use, the segment list
documents the set of segments a packet visited on its way through the
transit network. It is beyond the scope of this document to describe
the detailed procedures how the LISP mapping system obtains a segment
list for a particular EID-to-RLOC mapping.
Segment routing extensions for LISP extend the Explicit Locator Path
(ELP) Canonical Address Format, which is LCAF type 10,
see[I-D.ietf-lisp-lcaf] for details. A new Address Family Identifier
(AFI) in LISP Canonical Address Format (LCAF) type
[I-D.ietf-lisp-lcaf] carries the 32-bit segment identifier. For a
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given EID lookup in the mapping database, the segment routing list in
ELP LCAF type can be returned to provide a segment list to each
locator in the Map-Reply locator set. The ELP LCAF type can also be
used to send the segment list that a particular packet traversed to
the LISP mapping system using a Map-Register message defined in
[RFC6833].
The segment identification AFI to be allocated is described below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI = TBD_SID | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
AFI=TBD_SID: TBD_SID is a value allocated from [AFI] for segment
identifiers.
Reserved: this 8-bit field reserved for future use and to carry
specific control bits. If used with the ELP LCAF, this field carries
several bits (see below).
SID: 4 byte segment identifier
The segment identification AFI is used within the ELP LCAF to
describe the list of segments a packet is to visit or has visited on
its way through the transit network. Further below examples are
shown how the segment identification AFI is used for the ELP LCAF
type. A new bit, the T-bit, is added to the LISP LCAF type 10
described in [I-D.ietf-lisp-lcaf]. This addition is to be integrated
into a future revision of [I-D.ietf-lisp-lcaf].
For the segment routing AFI, the T-bit is defined as follows:
T-Bit: An additional bit in the Rsvd3 field is to be allocated in
LCAF type 10. The T-bit (T=1) is used by the LISP mapping system to
indicate to an ITR that for particular EID-to-RLOC mapping the
segments traversed by packets SHOULD be recorded as a segment list in
the SR IPv6 extension header. This bit is ignored if present in a
Map-Register message. A Map-Register message could be used by the
ETR to inform the mapping system about the segments that a packet
visited in the transit network.
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4.1. Example ELPs
4.1.1. Example: ELP with only SR used
This example shows the Explicit Locator Path (ELP) Canonical Address
Format in a setup where segment routing is used in the transit
network between ITR and ETR. Traffic engineering using
reencapsulating routers is not used.
The reply to an EID-to-RLOC lookup contains the SIDs to be visited in
the underlay network to reach the RLOC address returned in AFI=x. In
the example below SID_1,...,SID_p are to be used for segment routing
towards the "Address" RLOC. SID_p is the identifier of the last
segment which takes the packet to the "Address" RLOC.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI = 16387 | Rsvd1 | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 10 | Rsvd2 | n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI = TBD_SID | Rsvd3 |T|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID_1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI = TBD_SID | Rsvd3 |T|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID_p |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI = x | Rsvd3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4.1.2. Example: ELP with SR and reencapsulating routers combined
This example shows the Explicit Locator Path (ELP) Canonical Address
Format when using SR combined with reencapsulation routers.
Segment routing and traffic engineering using reencapsulating routers
can be combined. In the example below, segment routing is used to
steer traffic in the underlay between reencapsulating routers "f" and
"g". There is no segment routing used between any of the other
reencapsulating router hops.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI = 16387 | Rsvd1 | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 10 | Rsvd2 | n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI = x | Rsvd3 |L|P|S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reencap Hop 1 ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI = x | Rsvd3 |L|P|S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reencap Hop f ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI = TBD_SID | Rsvd3 |T|L|P|S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID_1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI = TBD_SID | Rsvd3 |T|L|P|S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID_p |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI = x | Rsvd3 |L|P|S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reencap Hop g ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI = x | Rsvd3 |L|P|S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reencap Hop k ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5. IANA Considerations
A new AFI for segment identifiers is to be allocated by IANA (see
[AFI] for a list of currently allocated AFIs).
6. Manageability Considerations
Manageability considerations will be addressed in a later version of
this document..
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7. Security Considerations
Security considerations will be addressed in a later version of this
document.
8. Acknowledgements
The authors would like to thank Dino Farinacci for his input on this
document.
9. References
9.1. Normative References
[AFI] , "IANA, Address Family Identifier (AFIs), http://
www.iana.org/assignments/address-family-numbers/address-
family-numbers.xhtml", July 2013.
[I-D.filsfils-rtgwg-segment-routing]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe,
"Segment Routing Architecture", draft-filsfils-rtgwg-
segment-routing-00 (work in progress), June 2013.
[I-D.ietf-lisp-lcaf]
Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical
Address Format (LCAF)", draft-ietf-lisp-lcaf-02 (work in
progress), March 2013.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9.2. Informative References
[I-D.farinacci-lisp-te]
Farinacci, D., Lahiri, P., and M. Kowal, "LISP Traffic
Engineering Use-Cases", draft-farinacci-lisp-te-03 (work
in progress), July 2013.
[I-D.filsfils-rtgwg-segment-routing-use-cases]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe,
"Segment Routing Use Cases", draft-filsfils-rtgwg-segment-
routing-use-cases-00 (work in progress), June 2013.
[I-D.sivabalan-pce-segment-routing]
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Sivabalan, S., Filsfils, C., Medved, J., Crabbe, E., and
R. Raszuk, "PCE-Initiated Traffic Engineering Path Setup
in Segment Routed Networks", draft-sivabalan-pce-segment-
routing-00 (work in progress), June 2013.
[RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
Locator/ID Separation Protocol (LISP)", RFC 6830, January
2013.
[RFC6833] Fuller, V. and D. Farinacci, "Locator/ID Separation
Protocol (LISP) Map-Server Interface", RFC 6833, January
2013.
Authors' Addresses
Frank Brockners
Cisco
Hansaallee 249, 3rd Floor
DUESSELDORF, NORDRHEIN-WESTFALEN 40549
Germany
Email: fbrockne@cisco.com
Shwetha Bhandari
Cisco
Cessna Business Park, Sarjapura Marathalli Outer Ring Road
Bangalore, KARNATAKA 560 087
India
Email: shwethab@cisco.com
Fabio Maino
Cisco
San Jose
USA
Email: fmaino@cisco.com
Darrel Lewis
Cisco
San Jose
USA
Email: darlewis@cisco.com
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