Network Working Group C. Filsfils, Ed.
Internet-Draft S. Previdi, Ed.
Intended status: Standards Track Cisco Systems, Inc.
Expires: May 23, 2017 B. Decraene
S. Litkowski
Orange
R. Shakir
Google
November 19, 2016
Segment Routing Architecture
draft-ietf-spring-segment-routing-10
Abstract
Segment Routing (SR) leverages the source routing paradigm. A node
steers a packet through an ordered list of instructions, called
segments. A segment can represent any instruction, topological or
service-based. A segment can have a local semantic to an SR node or
global within an SR domain. SR allows to enforce a flow through any
topological path and service chain while maintaining per-flow state
only at the ingress node to the SR domain.
Segment Routing can be directly applied to the MPLS architecture with
no change on the forwarding plane. A segment is encoded as an MPLS
label. An ordered list of segments is encoded as a stack of labels.
The segment to process is on the top of the stack. Upon completion
of a segment, the related label is popped from the stack.
Segment Routing can be applied to the IPv6 architecture, with a new
type of routing header. A segment is encoded as an IPv6 address. An
ordered list of segments is encoded as an ordered list of IPv6
addresses in the routing header. The active segment is indicated by
the Destination Address of the packet. The next active segment is
indicated by a pointer in the new routing header.
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 RFC 2119 [RFC2119].
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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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Companion Documents . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Link-State IGP Segments . . . . . . . . . . . . . . . . . . . 7
3.1. IGP Segment, IGP SID . . . . . . . . . . . . . . . . . . 7
3.2. IGP-Prefix Segment, Prefix-SID . . . . . . . . . . . . . 7
3.2.1. Prefix-SID Algorithm . . . . . . . . . . . . . . . . 7
3.2.2. MPLS Dataplane . . . . . . . . . . . . . . . . . . . 9
3.2.3. IPv6 Dataplane . . . . . . . . . . . . . . . . . . . 10
3.3. IGP-Node Segment, Node-SID . . . . . . . . . . . . . . . 10
3.4. IGP-Anycast Segment, Anycast SID . . . . . . . . . . . . 11
3.5. IGP-Adjacency Segment, Adj-SID . . . . . . . . . . . . . 14
3.5.1. Parallel Adjacencies . . . . . . . . . . . . . . . . 15
3.5.2. LAN Adjacency Segments . . . . . . . . . . . . . . . 16
3.6. Binding Segment . . . . . . . . . . . . . . . . . . . . . 16
3.6.1. Mapping Server . . . . . . . . . . . . . . . . . . . 16
3.6.2. Tunnel Headend . . . . . . . . . . . . . . . . . . . 17
3.7. Inter-Area Considerations . . . . . . . . . . . . . . . . 17
4. BGP Peering Segments . . . . . . . . . . . . . . . . . . . . 18
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5. IGP Mirroring Context Segment . . . . . . . . . . . . . . . 19
6. Multicast . . . . . . . . . . . . . . . . . . . . . . . . . . 19
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
8. Security Considerations . . . . . . . . . . . . . . . . . . . 19
8.1. MPLS Data Plane . . . . . . . . . . . . . . . . . . . . . 20
8.2. IPv6 Data Plane . . . . . . . . . . . . . . . . . . . . . 21
9. Manageability Considerations . . . . . . . . . . . . . . . . 22
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 24
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
12.1. Normative References . . . . . . . . . . . . . . . . . . 25
12.2. Informative References . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction
With Segment Routing (SR), a node steers a packet through an ordered
list of instructions, called segments. A segment can represent any
instruction, topological or service-based. A segment can have a
local semantic to an SR node or global within an SR domain. SR
allows to enforce a flow through any path and service chain while
maintaining per-flow state only at the ingress node of the SR domain.
Segment Routing can be directly applied to the MPLS architecture
([RFC3031]) with no change on the forwarding plane. A segment is
encoded as an MPLS label. An ordered list of segments is encoded as
a stack of labels. The active segment is on the top of the stack. A
completed segment is popped off the stack. The addition of a segment
is performed with a push.
In the Segment Routing MPLS instantiation, a segment could be of
several types:
o an IGP segment,
o a BGP Peering segments,
o an LDP LSP segment,
o an RSVP-TE LSP segment,
o a BGP LSP segment.
The first two (IGP and BGP Peering segments) types of segments are
defined in this document. The use of the last three types of
segments is illustrated in [I-D.ietf-spring-segment-routing-mpls].
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Segment Routing can be applied to the IPv6 architecture ([RFC2460]),
with a new type of routing header. A segment is encoded as an IPv6
address. An ordered list of segments is encoded as an ordered list
of IPv6 addresses in the routing header. The active segment is
indicated by the Destination Address of the packet. Upon completion
of a segment, a pointer in the new routing header is incremented and
indicates the next segment.
Numerous use-cases illustrate the benefits of source routing either
for FRR, OAM or Traffic Engineering reasons.
This document defines a set of instructions (called segments) that
are required to fulfill the described use-cases. These segments can
either be used in isolation (one single segment defines the source
route of the packet) or in combination (these segments are part of an
ordered list of segments that define the source route of the packet).
1.1. Companion Documents
This document defines the SR architecture, its routing model, the
IGP-based segments, the BGP-based segments and the service segments.
Use cases are described in [RFC7855],
[I-D.ietf-spring-segment-routing-central-epe],
[I-D.ietf-spring-segment-routing-msdc],
[I-D.filsfils-spring-large-scale-interconnect],
[I-D.ietf-spring-ipv6-use-cases],
[I-D.ietf-spring-resiliency-use-cases], [I-D.ietf-spring-oam-usecase]
and [I-D.ietf-spring-sr-oam-requirement].
Segment Routing for MPLS dataplane is documented in
[I-D.ietf-spring-segment-routing-mpls].
Segment Routing for IPv6 dataplane is documented in
[I-D.ietf-6man-segment-routing-header].
IGP protocol extensions for Segment Routing are described in
[I-D.ietf-isis-segment-routing-extensions],
[I-D.ietf-ospf-segment-routing-extensions] and
[I-D.ietf-ospf-ospfv3-segment-routing-extensions] referred in this
document as "IGP SR extensions documents".
The FRR solution for SR is documented in
[I-D.francois-rtgwg-segment-routing-ti-lfa].
The PCEP protocol extensions for Segment Routing are defined in
[I-D.ietf-pce-segment-routing].
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The interaction between SR/MPLS with other MPLS Signaling planes is
documented in [I-D.ietf-spring-segment-routing-ldp-interop].
2. Terminology
Segment: an instruction a node executes on the incoming packet (e.g.:
forward packet according to shortest path to destination, or, forward
packet through a specific interface, or, deliver the packet to a
given application/service instance).
SID: a Segment Identifier. Examples of SIDs are: a MPLS label, an
index value in a MPLS label space, an IPv6 address. Other types of
SIDs can be defined in the future.
Segment List: ordered list of SID's encoding the topological and
service source route of the packet. It is a stack of labels in the
MPLS architecture. It is an ordered list of IPv6 addresses in the
IPv6 architecture.
Segment Routing Domain (SR Domain): the set of nodes participating
into the source based routing model. These nodes may be connected to
the same physical infrastructure (e.g.: a Service Provider's network)
as well as nodes remotely connected to each other (e.g.: an
enterprise VPN or an overlay). Note that a SR domain may also be
confined within an IGP instance, in which case it is named SR-IGP
Domain.
Active segment: the segment that MUST be used by the receiving router
to process the packet. In the MPLS dataplane is the top label. In
the IPv6 dataplane is the destination address of a packet having the
Segment Routing Header as defined in
[I-D.ietf-6man-segment-routing-header].
PUSH: the insertion of a segment at the head of the Segment list.
NEXT: the active segment is completed, the next segment becomes
active.
CONTINUE: the active segment is not completed and hence remains
active. The CONTINUE instruction is implemented as the SWAP
instruction in the MPLS dataplane. In IPv6, this is the plain IPv6
forwarding action of a regular IPv6 packet according to its
Destination Address.
SR Global Block (SRGB): local property of an SR node. In the MPLS
architecture, SRGB is the set of local labels reserved for global
segments. Using the same SRGB on all nodes within the SR domain ease
operations and troubleshooting and is expected to be a deployment
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guideline. In the IPv6 architecture, the equivalent of the SRGB is
in fact the set of addresses used as global segments. Since there
are no restrictions on which IPv6 address can be used, the concept of
the SRGB includes all IPv6 global address space used within the SR
domain.
Global Segment: the related instruction is supported by all the SR-
capable nodes in the domain. In the MPLS architecture, a Global
Segment has a globally-unique index. The related local label at a
given node N is found by adding the globally-unique index to the SRGB
of node N. In the IPv6 architecture, a global segment is a globally-
unique IPv6 address.
Local Segment: the related instruction is supported only by the node
originating it. In the MPLS architecture, this is a local label
outside the SRGB. In the IPv6 architecture, this can be any IPv6
address whose reachability is not advertised in any routing protocol
(hence, the segment is known only by the local node).
IGP Segment: the generic name for a segment attached to a piece of
information advertised by a link-state IGP, e.g. an IGP prefix or an
IGP adjacency.
IGP-prefix Segment, Prefix-SID: an IGP-Prefix Segment is an IGP
segment attached to an IGP prefix. An IGP-Prefix Segment is global
(unless explicitly advertised otherwise) within the SR IGP instance/
topology and identifies an instruction to forward the packet along
the path computed using the routing algorithm specified in the
algorithm field, in the topology and the IGP instance where it is
advertised. The Prefix-SID is the SID of the IGP-Prefix Segment.
IGP-Anycast: an IGP-Anycast Segment is an IGP-prefix segment which
does not identify a specific router, but a set of routers. The terms
"Anycast Segment" or "Anycast-SID" are often used as an abbreviation.
IGP-Adjacency: an IGP-Adjacency Segment is an IGP segment attached to
an unidirectional adjacency or a set of unidirectional adjacencies.
By default, an IGP-Adjacency Segment is local (unless explicitly
advertised otherwise) to the node that advertises it.
IGP-Node: an IGP-Node Segment is an IGP-Prefix Segment which
identifies a specific router (e.g. a loopback). The terms "Node
Segment" or Node-SID" are often used as an abbreviation.
SR Tunnel: a list of segments to be pushed on the packets directed on
the tunnel. The list of segments can be specified explicitly or
implicitly via a set of abstract constraints (latency, affinity,
SRLG, ...). In the latter case, a constraint-based path computation
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is used to determine the list of segments associated with the tunnel.
The computation can be local or delegated to a PCE server. An SR
tunnel can be configured by the operator, provisioned via netconf or
provisioned via PCEP. An SR tunnel can be used for traffic-
engineering, OAM or FRR reasons.
Segment List Depth: the number of segments of an SR tunnel. The
entity instantiating an SR Tunnel at a node N should be able to
discover the depth insertion capability of the node N. The PCEP
discovery capability is described in [I-D.ietf-pce-segment-routing].
3. Link-State IGP Segments
Within a link-state IGP domain, an SR-capable IGP node advertises
segments for its attached prefixes and adjacencies. These segments
are called IGP segments or IGP SIDs. They play a key role in Segment
Routing and use-cases as they enable the expression of any
topological path throughout the IGP domain. Such a topological path
is either expressed as a single IGP segment or a list of multiple IGP
segments.
3.1. IGP Segment, IGP SID
The terms "IGP Segment" and "IGP SID" are the generic names for a
segment attached to a piece of information advertised by a link-state
IGP, e.g. an IGP prefix or an IGP adjacency.
3.2. IGP-Prefix Segment, Prefix-SID
An IGP-Prefix Segment is an IGP segment attached to an IGP prefix.
An IGP-Prefix Segment is global (unless explicitly advertised
otherwise) within the SR/IGP domain.
The required IGP protocol extensions are defined in IGP SR extensions
documents.
3.2.1. Prefix-SID Algorithm
The IGP protocol extensions for Segment Routing define the Prefix-SID
advertisement which includes a set of flags and the algorithm field.
The algorithm field has the purpose of associating a given Prefix-SID
to a routing algorithm.
In the context of an instance and a topology, multiple Prefix-SID's
MAY be allocated to the same IGP Prefix as long as the algorithm
value is different in each one.
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Multiple instances and topologies are defined in IS-IS and OSPF in:
[RFC5120], [RFC6822], [RFC6549] and [RFC4915].
Initially, two "algorithms" have been defined:
o "Shortest Path": this algorithm is the default behavior. The
packet is forwarded along the well known ECMP-aware SPF algorithm
however it is explicitly allowed for a midpoint to implement
another forwarding based on local policy.. The "Shortest Path"
algorithm is in fact the default and current behavior of most of
the networks where local policies may override the SPF decision.
o "Strict Shortest Path": This algorithm mandates that the packet is
forwarded according to ECMP-aware SPF algorithm and instruct any
router in the path to ignore any possible local policy overriding
SPF decision. The SID advertised with "Strict Shortest Path"
algorithm ensures that the path the packet is going to take is the
expected, and not altered, SPF path.
An IGP-Prefix Segment identifies the path, to the related prefix,
along the path computed as per the algorithm field.
A packet injected anywhere within the SR/IGP domain with an active
Prefix-SID will be forwarded along path computed by the algorithm
expressed in the algorithm field.
The ingress node of an SR domain validates that the path to a prefix,
advertised with a given algorithm, includes nodes all supporting the
advertised algorithm. As a consequence, if a node on the path does
not support algorithm X, the IGP-Prefix segment will be interrupted
and will drop packet on that node. It's the responsibility of the
ingress node using a segment to check that all downstream nodes
support the algorithm of the segment.
A router MUST NOT forward any SR traffic associated with the SR
algorithm to the adjacent router, if the adjacent router has not
advertised support for such SR algorithm.
It has to be noted that Fast Reroute (FRR) mechanisms, such as the
one described in [I-D.francois-rtgwg-segment-routing-ti-lfa], that
are based on post-convergence SPF, are still compliant to the Strict-
SPF algorithm definition.
Details of the two defined algorithms are defined in
[I-D.ietf-isis-segment-routing-extensions],
[I-D.ietf-ospf-segment-routing-extensions] and
[I-D.ietf-ospf-ospfv3-segment-routing-extensions].
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3.2.2. MPLS Dataplane
When SR is used over the MPLS dataplane:
o the IGP signaling extension for IGP-Prefix segment includes the
P-Flag ([I-D.ietf-isis-segment-routing-extensions]) or the NP-Flag
([I-D.ietf-ospf-segment-routing-extensions]). A Node N
advertising a Prefix-SID SID-R for its attached prefix R unset the
P-Flag (or NP-Flag) in order to instruct its connected neighbors
to perform the NEXT operation while processing SID-R. This
behavior is equivalent to Penultimate Hop Popping in MPLS. When
the flag is unset, the neighbors of N MUST perform the NEXT
operation while processing SID-R. When the flag is set, the
neighbors of N MUST perform the CONTINUE operation while
processing SID-R.
o A Prefix-SID is allocated in the form of an index in the SRGB (or
as a local MPLS label) according to a process similar to IP
address allocation. Typically the Prefix-SID is allocated by
policy by the operator (or NMS) and the SID very rarely changes.
o While SR allows to attach a local segment to an IGP prefix (using
the L-Flag), we specifically assume that when the terms "IGP-
Prefix Segment" and "Prefix-SID" are used, the segment is global
(the SID is allocated from the SRGB or as an index). This is
consistent with all the described use-cases that require global
segments attached to IGP prefixes.
o The allocation process MUST NOT allocate the same Prefix-SID to
different IP prefixes.
o If a node learns a Prefix-SID having a value that falls outside
the locally configured SRGB range, then the node MUST NOT use the
Prefix-SID and SHOULD issue an error log warning for
misconfiguration.
o If a node N advertises Prefix-SID SID-R for a prefix R that is
attached to N, N MUST either clear the P-Flag in the advertisement
of SID-R, or else maintain the following FIB entry:
Incoming Active Segment: SID-R
Ingress Operation: NEXT
Egress interface: NULL
o A remote node M MUST maintain the following FIB entry for any
learned Prefix-SID SID-R attached to IP prefix R:
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Incoming Active Segment: SID-R
Ingress Operation:
If the next-hop of R is the originator of R
and instructed to remove the active segment: NEXT
Else: CONTINUE
Egress interface: the interface towards the next-hop along the
path computed using the algorithm advertised with
the SID toward prefix R.
3.2.3. IPv6 Dataplane
When SR is used over the IPv6 dataplane:
o The Prefix-SID is the prefix itself. No additional identifier is
needed for Segment Routing over IPv6.
o Any address belonging to any of the node's prefixes can be used as
Prefix-SIDs.
o An operator may want to explicitly indicate which of the node's
prefixes can be used as Prefix-SIDs through the setting of a flag
(e.g.: using the IGP prefix attribute defined in [RFC7794]) in the
routing protocol used for advertising the prefix.
o A global SID is instantiated through any globally advertised IPv6
address.
o A local SID is instantiated through a local IPv6 prefix not being
advertised and therefore known only by the local node.
A node N advertising an IPv6 address R usable as a segment identifier
MUST maintain the following FIB entry:
Incoming Active Segment: R
Ingress Operation: NEXT
Egress interface: NULL
Regardless Segment Routing, any remote IPv6 node will maintain a
plain IPv6 FIB entry for any prefix, no matter if they represent a
segment or not.
3.3. IGP-Node Segment, Node-SID
An IGP Node Segment is a an IGP Prefix Segment which identifies a
specific router (e.g. a loopback). The terms "Node Segment" or
"Node-SID" are often used as an abbreviation. The IGP SR extensions
define a flag that identifies Node-SIDs.
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A "Node Segment" or "Node-SID" is fundamental to SR. From anywhere
in the network, it enforces the ECMP-aware shortest-path forwarding
of the packet towards the related node.
An IGP Node-SID MUST NOT be associated with a prefix that is owned by
more than one router within the same routing domain.
3.4. IGP-Anycast Segment, Anycast SID
An IGP-Anycast Segment is an IGP-prefix segment which does not
identify a specific router, but a set of routers. The terms "Anycast
Segment" or "Anycast-SID" are often used as an abbreviation.
An "Anycast Segment" or "Anycast SID" enforces the ECMP-aware
shortest-path forwarding towards the closest node of the anycast set.
This is useful to express macro-engineering policies or protection
mechanisms.
An IGP-Anycast Segment MUST NOT reference a particular node.
Within an anycast group, all routers MUST advertise the same prefix
with the same SID value.
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+--------------+
| Group A |
|192.0.2.10/32 |
| SID:100 |
| |
+-----------A1---A3----------+
| | | \ / | | |
SID:10 | | | / | | | SID:30
203.0.113.1/32 | | | / \ | | | 203.0.113.3/32
PE1------R1----------A2---A4---------R3------PE3
\ /| | | |\ /
\ / | +--------------+ | \ /
\ / | | \ /
/ | | /
/ \ | | / \
/ \ | +--------------+ | / \
/ \| | | |/ \
PE2------R2----------B1---B3----+----R4------PE4
203.0.113.2/32 | | | \ / | | | 203.0.113.4/32
SID:20 | | | / | | | SID:40
| | | / \ | | |
+-----+-----B2---B4----+-----+
| |
| Group B |
| 192.0.2.1/32 |
| SID:200 |
+--------------+
Transit device groups
The figure above describes a network example with two groups of
transit devices. Group A consists of devices {A1, A2, A3 and A4}.
They are all provisioned with the anycast address 192.0.2.10/32 and
the anycast SID 100.
Similarly, group B consists of devices {B1, B2, B3 and B4} and are
all provisioned with the anycast address 192.0.2.1/32, anycast SID
200. In the above network topology, each PE device is connected to
two routers in each of the groups A and B.
PE1 can choose a particular transit device group when sending traffic
to PE3 or PE4. This will be done by pushing the anycast SID of the
group in the stack.
Processing the anycast, and subsequent segments, requires special
care.
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Obviously, the value of the SID following the anycast SID MUST be
understood by all nodes advertising the same anycast segment.
+-------------------------+
| Group A |
| 192.0.2.10/32 |
| SID:100 |
|-------------------------|
| |
| SRGB: SRGB: |
SID:10 |(1000-2000) (3000-4000)| SID:30
PE1---+ +-------A1-------------A3-------+ +---PE3
\ / | | \ / | | \ /
\ / | | +-----+ / | | \ /
SRGB: \ / | | \ / | | \ / SRGB:
(7000-8000) R1 | | \ | | R3 (6000-7000)
/ \ | | / \ | | / \
/ \ | | +-----+ \ | | / \
/ \ | | / \ | | / \
PE2---+ +-------A2-------------A4-------+ +---PE4
SID:20 | SRGB: SRGB: | SID:40
|(2000-3000) (4000-5000)|
| |
+-------------------------+
Transit paths via anycast group A
Considering a MPLS deployment, in the above topology, if device PE1
(or PE2) requires to send a packet to the device PE3 (or PE4) it
needs to encapsulate the packet in a MPLS payload with the following
stack of labels.
o Label allocated by R1 for anycast SID 100 (outer label).
o Label allocated by the nearest router in group A for SID 30 (for
destination PE3).
While the first label is easy to compute, in this case since there
are more than one topologically nearest devices (A1 and A2), unless
A1 and A2 allocated the same label value to the same prefix,
determining the second label is impossible. Devices A1 and A2 may be
devices from different hardware vendors. If both don't allocate the
same label value for SID 30, it is impossible to use the anycast
group "A" as a transit anycast group towards PE3. Hence, PE1 (or
PE2) cannot compute an appropriate label stack to steer the packet
exclusively through the group A devices. Same holds true for devices
PE3 and PE4 when trying to send a packet to PE1 or PE2.
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To ease the use of anycast segment in a short term, it is recommended
to configure the same SRGB on all nodes of a particular anycast
group. Using this method, as mentioned above, computation of the
label following the anycast segment is straightforward.
Using anycast segment without configuring the same SRGB on nodes
belonging to the same device group may lead to misrouting (in a MPLS
VPN deployment, some traffic may leak between VPNs).
3.5. IGP-Adjacency Segment, Adj-SID
An IGP-Adjacency Segment is an IGP segment attached to a
unidirectional adjacency or a set of unidirectional adjacencies. By
default, an IGP-Adjacency Segment is local to the node which
advertises it. However, an Adjacency Segment can be global if
advertised by the IGP as such. The SID of the IGP-Adjacency Segment
is called the Adj-SID.
The adjacency is formed by the local node (i.e., the node advertising
the adjacency in the IGP) and the remote node (i.e., the other end of
the adjacency). The local node MUST be an IGP node. The remote node
MAY be an adjacent IGP neighbor or a non-adjacent neighbor (e.g.: a
Forwarding Adjacency, [RFC4206]).
A packet injected anywhere within the SR domain with a segment list
{SN, SNL}, where SN is the Node-SID of node N and SNL is an Adj-SID
attached by node N to its adjacency over link L, will be forwarded
along the shortest-path to N and then be switched by N, without any
IP shortest-path consideration, towards link L. If the Adj-SID
identifies a set of adjacencies, then the node N load- balances the
traffic among the various members of the set.
Similarly, when using a global Adj-SID, a packet injected anywhere
within the SR domain with a segment list {SNL}, where SNL is a global
Adj-SID attached by node N to its adjacency over link L, will be
forwarded along the shortest-path to N and then be switched by N,
without any IP shortest-path consideration, towards link L. If the
Adj-SID identifies a set of adjacencies, then the node N load-
balances the traffic among the various members of the set. The use
of global Adj-SID allows to reduce the size of the segment list when
expressing a path at the cost of additional state (i.e.: the global
Adj-SID will be inserted by all routers within the area in their
forwarding table).
An "IGP Adjacency Segment" or "Adj-SID" enforces the switching of the
packet from a node towards a defined interface or set of interfaces.
This is key to theoretically prove that any path can be expressed as
a list of segments.
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The encodings of the Adj-SID include the B-flag. When set, the Adj-
SID refers to an adjacency that is eligible for protection (e.g.:
using IPFRR or MPLS-FRR).
The encodings of the Adj-SID include the L-flag. When set, the Adj-
SID has local significance. By default the L-flag is set.
A node SHOULD allocate one Adj-SIDs for each of its adjacencies.
A node MAY allocate multiple Adj-SIDs to the same adjacency. An
example is where the adjacency is established over a bundle
interface. Each bundle member MAY have its own Adj-SID.
A node MAY allocate the same Adj-SID to multiple adjacencies.
Adjacency suppression MUST NOT be performed by the IGP.
A node MUST install a FIB entry for any Adj-SID of value V attached
to data-link L:
Incoming Active Segment: V
Operation: NEXT
Egress Interface: L
The Adj-SID implies, from the router advertising it, the forwarding
of the packet through the adjacency identified by the Adj-SID,
regardless its IGP/SPF cost. In other words, the use of Adjacency
Segments overrides the routing decision made by SPF algorithm.
3.5.1. Parallel Adjacencies
Adj-SIDs can be used in order to represent a set of parallel
interfaces between two adjacent routers.
A node MUST install a FIB entry for any locally originated Adjacency
Segment (Adj-SID) of value W attached to a set of link B with:
Incoming Active Segment: W
Ingress Operation: NEXT
Egress interface: loadbalance between any data-link within set B
When parallel adjacencies are used and associated to the same Adj-
SID, and in order to optimize the load balancing function, a "weight"
factor can be associated to the Adj-SID advertised with each
adjacency. The weight tells the ingress (or a SDN/orchestration
system) about the loadbalancing factor over the parallel adjacencies.
As shown in Figure 1, A and B are connected through two parallel
adjacencies
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link-1
+--------+
| |
S---A B---C
| |
+--------+
link-2
Figure 1: Parallel Links and Adj-SIDs
Node A advertises following Adj-SIDs and weights:
o Link-1: Adj-SID 1000, weight: 1
o Link-2: Adj-SID 1000, weight: 2
Node S receives the advertisements of the parallel adjacencies and
understands that by using Adj-SID 1000 node A will loadbalance the
traffic across the parallel links (link-1 and link-2) according to a
1:2 ratio.
The weight value is advertised with the Adj-SID as defined in IGP SR
extensions documents.
3.5.2. LAN Adjacency Segments
In LAN subnetworks, link-state protocols define the concept of
Designated Router (DR, in OSPF) or Designated Intermediate System
(DIS, in IS-IS) that conduct flooding in broadcast subnetworks and
that describe the LAN topology in a special routing update (OSPF
Type2 LSA or IS-IS Pseudonode LSP).
The difficulty with LANs is that each router only advertises its
connectivity to the DR/DIS and not to each other individual nodes in
the LAN. Therefore, additional protocol mechanisms (IS-IS and OSPF)
are necessary in order for each router in the LAN to advertise an
Adj-SID associated to each neighbor in the LAN. These extensions are
defined in IGP SR extensions documents.
3.6. Binding Segment
3.6.1. Mapping Server
A Remote-Binding SID S advertised by the mapping server M for remote
prefix R attached to non-SR-capable node N signals the same
information as if N had advertised S as a Prefix-SID. Further
details are described in the SR/LDP interworking procedures
([I-D.ietf-spring-segment-routing-ldp-interop].
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The segment allocation and SRGB Maintenance rules are the same as
those defined for Prefix-SID.
3.6.2. Tunnel Headend
The segment allocation and SRGB Maintenance rules are the same as
those defined for Adj-SID. A tunnel attached to a head-end H acts as
an adjacency attached to H.
Note: an alternative consists of representing tunnels as forwarding-
adjacencies ( [RFC4206]). In such case, the tunnel is presented to
the routing area as a routing adjacency and is considered as such by
all area routers. The Remote-Binding SID is preferred as it allows
to advertise the presence of a tunnel without influencing the LSDB
and the SPF computation.
3.7. Inter-Area Considerations
In the following example diagram we assume an IGP deployed using
areas and where SR has been deployed.
! !
! !
B------C-----F----G-----K
/ | | |
S---A/ | | |
\ | | |
\D------I----------J-----L----Z (192.0.2.1/32, Node-SID: 150)
! !
Area-1 ! Backbone ! Area 2
! area !
Figure 2: Inter-Area Topology Example
In area 2, node Z allocates Node-SID 150 to his local prefix
192.0.2.1/32. ABRs G and J will propagate the prefix into the
backbone area by creating a new instance of the prefix according to
normal inter-area/level IGP propagation rules.
Nodes C and I will apply the same behavior when leaking prefixes from
the backbone area down to area 1. Therefore, node S will see prefix
192.0.2.1/32 with Prefix-SID 150 and advertised by nodes C and I.
It therefore results that a Prefix-SID remains attached to its
related IGP Prefix through the inter-area process.
When node S sends traffic to 192.0.2.1/32, it pushes Node-SID(150) as
active segment and forward it to A.
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When packet arrives at ABR I (or C), the ABR forwards the packet
according to the active segment (Node-SID(150)). Forwarding
continues across area borders, using the same Node-SID(150), until
the packet reaches its destination.
When an ABR propagates a prefix from one area to another it MUST set
the R-Flag.
4. BGP Peering Segments
In the context of BGP Egress Peer Engineering (EPE), as described in
[I-D.ietf-spring-segment-routing-central-epe], an EPE enabled Egress
PE node MAY advertise segments corresponding to its attached peers.
These segments are called BGP peering segments or BGP Peering SIDs.
They enable the expression of source-routed inter-domain paths.
An ingress border router of an AS may compose a list of segments to
steer a flow along a selected path within the AS, towards a selected
egress border router C of the AS and through a specific peer. At
minimum, a BGP Peering Engineering policy applied at an ingress PE
involves two segments: the Node SID of the chosen egress PE and then
the BGP Peering Segment for the chosen egress PE peer or peering
interface.
Hereafter, we will define three types of BGP peering segments/SID's:
PeerNodeSID, PeerAdjSID and PeerSetSID.
o PeerNode SID. A BGP PeerNode segment/SID is a local segment. At
the BGP node advertising it, its semantics is:
* SR header operation: NEXT.
* Next-Hop: the connected peering node to which the segment is
related.
o PeerAdj SID: A BGP PeerAdj segment/SID is a local segment. At the
BGP node advertising it, its semantics is:
* SR header operation: NEXT.
* Next-Hop: the peer connected through the interface to which the
segment is related.
o PeerSet SID. A BGP PeerSet segment/SID is a local segment. At
the BGP node advertising it, its semantics is:
* SR header operation: NEXT.
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* Next-Hop: loadbalance across any connected interface to any
peer in the related group.
A peer set could be all the connected peers from the same AS or a
subset of these. A group could also span across AS. The group
definition is a policy set by the operator.
The BGP extensions necessary in order to signal these BGP peering
segments will be defined in a separate document.
5. IGP Mirroring Context Segment
It is beneficial for an IGP node to be able to advertise its ability
to process traffic originally destined to another IGP node, called
the Mirrored node and identified by an IP address or a Node-SID,
provided that a "Mirroring Context" segment be inserted in the
segment list prior to any service segment local to the mirrored node.
When a given node B wants to provide egress node A protection, it
advertises a segment identifying node's A context. Such segment is
called "Mirror Context Segment" and identified by the Mirror SID.
The Mirror SID is advertised using the Binding Segment defined in SR
IGP protocol extensions ( [I-D.ietf-isis-segment-routing-extensions],
[I-D.ietf-ospf-segment-routing-extensions] and
[I-D.ietf-ospf-ospfv3-segment-routing-extensions]).
In the event of a failure, a point of local repair (PLR) diverting
traffic from A to B does a PUSH of the Mirror SID on the protected
traffic. B, when receiving the traffic with the Mirror SID as the
active segment, uses that segment and process underlying segments in
the context of A.
6. Multicast
Segment Routing is defined for unicast. The application of the
source-route concept to Multicast is not in the scope of this
document.
7. IANA Considerations
This document does not require any action from IANA.
8. Security Considerations
Segment Routing is applicable to both MPLS and IPv6 data planes.
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Segment Routing adds some meta-data on the packet, with the list of
forwarding path elements (e.g.: nodes, links, services, etc.) that
the packet must traverse. It has to be noted that the complete
source routed path may be represented by a single segment. This is
the case of the Binding SID.
8.1. MPLS Data Plane
When applied to the MPLS data plane, Segment Routing does not
introduce any new behavior or any change in the way MPLS data plane
works. Therefore, from a security standpoint, this document does not
define any additional mechanism in the MPLS data plane.
SR allows the expression of a source routed path using a single
segment (the Binding SID). Compared to RSVP-TE which also provides
explicit routing capability, there are no fundamental differences in
term of information provided. Both RSVP-TE and Segment Routing may
express a source routed path using a single segment.
When a path is expressed using a single label, the syntax of the
meta-data is equivalent between RSVP-TE and SR.
When a source routed path is expressed with a list of segments
additional meta-data is added to the packet consisting of the source
routed path the packet must follow expressed as a segment list.
When a path is expressed using a label stack, if one has access to
the meaning (i.e.: the Forwarding Equivalence Class) of the labels,
one has the knowledge of the explicit path. For the MPLS data plane,
as no data plane modification is required, there is no fundamental
change of capability. Yet, the occurrence of label stacking will
increase.
From a network protection standpoint, there is an assumed trust model
such that any node imposing a label stack on a packet is assumed to
be allowed to do so. This is a significant change compared to plain
IP offering shortest path routing but not fundamentally different
compared to existing techniques providing explicit routing capability
such as RSVP-TE. By default, the explicit routing information MUST
NOT be leaked through the boundaries of the administered domain.
Segment Routing extensions that have been defined in various
protocols, leverage the security mechanisms of these protocols such
as encryption, authentication, filtering, etc.
In the general case, a segment routing capable router accepts and
install labels, only if these labels have been previously advertised
by a trusted source. The received information is validated using
existing control plane protocols providing authentication and
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security mechanisms. Segment routing does not define any additional
security mechanism in existing control plane protocols.
Segment Routing does not introduce signaling between the source and
the mid points of a source routed path. With SR, the source routed
path is computed using SIDs previously advertised in the IP control
plane. Therefore, in addition to filtering and controlled
advertisement of SIDs at the boundaries of the SR domain, filtering
in the data plane is also required. Filtering MUST be performed on
the forwarding plane at the boundaries of the SR domain and may
require looking at multiple labels/instruction.
For the MPLS data plane, there are no new requirement as the existing
MPLS architecture already allow such source routing by stacking
multiple labels. And for security protection, [RFC4381] section 2.4
and [RFC5920] section 8.2 already calls for the filtering of MPLS
packets on trust boundaries.
8.2. IPv6 Data Plane
When applied to the IPv6 data plane, Segment Routing does introduce
the Segment Routing Header (SRH,
[I-D.ietf-6man-segment-routing-header]) which is a type of Routing
Extension header as defined in [RFC2460].
The SRH adds some meta-data on the IPv6 packet, with the list of
forwarding path elements (e.g.: nodes, links, services, etc.) that
the packet must traverse and that are represented by IPv6 addresses.
A complete source routed path may be encoded in the packet using a
single segment (single IPv6 address).
From a network protection standpoint, there is an assumed trust model
such that any node adding an SRH to the packet is assumed to be
allowed to do so. Therefore, by default, the explicit routing
information MUST NOT be leaked through the boundaries of the
administered domain. Segment Routing extensions that have been
defined in various protocols, leverage the security mechanisms of
these protocols such as encryption, authentication, filtering, etc.
In the general case, an SR IPv6 router accepts and install segments
identifiers (in the form of IPv6 addresses), only if these SIDs are
advertised by a trusted source. The received information is
validated using existing control plane protocols providing
authentication and security mechanisms. Segment routing does not
define any additional security mechanism in existing control plane
protocols.
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In addition, SR domain boundary routers, by default, MUST apply data
plane filters so to only accept packets whose DA and SRH (if any)
contain addresses previously advertised as SIDs.
There are a number of security concerns with source routing at the
IPv6 data plane [RFC5095]. The new IPv6-based segment routing header
defined in [I-D.ietf-6man-segment-routing-header] and its associated
security measures address these concerns. The IPv6 Segment Routing
Header is defined in a way that blind attacks are never possible,
i.e., attackers will be unable to send source routed packets that get
successfully processed, without being part of the negations for
setting up the source routes or being able to eavesdrop legitimate
source routed packets. In some networks this base level security may
be complemented with other mechanisms, such as packet filtering,
cryptographic security, etc.
9. Manageability Considerations
In SR enabled networks, the path the packet takes is encoded in the
header. As the path is not signaled through a protocol, OAM
mechanisms are necessary in order for the network operator to
validate the effectiveness of a path as well as to check and monitor
its liveness and performance. However, it has to be noted that SR
allows to reduce substantially the number of states in transit nodes
and hence the number of elements that a transit node has to manage is
smaller.
SR OAM use cases and requirements for the MPLS data plane are defined
in [I-D.ietf-spring-oam-usecase] and
[I-D.ietf-spring-sr-oam-requirement]. OAM procedures for the MPLS
data plane are defined in [I-D.ietf-mpls-spring-lsp-ping].
SR routers receive advertisement of SIDs (index, label or IPv6
address) from the different routing protocols being extended for SR.
Each of these protocols have monitoring and troubleshooting
mechanisms so to provide operation and management functions for IP
addresses that MUST be extended in order to include troubleshooting
and monitoring functions of the SID.
SR architecture introduces the usage of global segments. Each global
segment must be bound to a globally-unique index or address. The
management of the allocation of such index or address by the operator
is critical for the network behavior to avoid situations like mis-
routing. In addition to the allocation policy/tooling that the
operator will have in place, an implementation SHOULD protect the
network in case of conflict detection by providing a deterministic
resolution approach.
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An operator may implement tools in order to audit the network and
ensure the good allocation of indexes, SIDs or IP addresses.
Conflict detection between SIDs, including Mapping Server binding
SIDs, and their resolution are addressed in
[I-D.ietf-spring-conflict-resolution].
SR with the MPLS data plane, can be gracefully introduced in an
existing LDP [RFC5036] network. This is described in
[I-D.ietf-spring-segment-routing-ldp-interop]. SR and LDP may also
inter-work. In this case, the introduction of mapping-server may
introduce some additional manageability considerations that are
discussed in [I-D.ietf-spring-segment-routing-ldp-interop].
When a path is expressed using a a label stack, the occurrence of
label stacking will increase. A node may want to signal in the
control plane it's ability in terms of size of the label stack it can
support.
A YANG data model [RFC6020] for segment routing configuration and
operations has been defined in [I-D.ietf-spring-sr-yang].
When Segment Routing is applied to the IPv6 data plane, segments are
identified through IPv6 addresses. The allocation, management and
troubleshooting of segment identifiers is no different than the
existing mechanisms applied to the allocation and management of IPv6
addresses.
In the SR over IPv6 data plane context, the allocation of SIDs
results into the allocation of IPv6 addresses. Therefore,
management, troubleshooting, monitoring functions are the same as the
one used for IPv6 addresses.
The control of a source routed path of an IPv6 packet having an SRH
SHOULD be implemented through the inspection of the packet header and
more precisely its DA and segment list (in the SRH). The DA of the
packet gives the active segment address. The segment list in the SRH
gives the entire path of the packet. The validation of the source
routed path is done through inspection of DA and SRH present in the
packet header matched to the equivalent routing table entries.
In the context of SR over the IPv6 data plane, the source routed path
is encoded in the SRH as described in
[I-D.ietf-6man-segment-routing-header]. The SR IPv6 source routed
path is instantiated into the SRH as a list of IPv6 address where the
active segment is in the Destination Address (DA) field of the IPv6
packet header. Typically, by inspecting in any node the packet
header, it is possible to derive the source routed path it belongs
to. Similar to the context of SR over MPLS data plane, an
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implementation may originate path control and monitoring packets
where the source routed path is inserted in the SRH and where each
segment of the path inserts in the packet the relevant data in order
to measure the end to end path and performance.
10. Contributors
The following people have substantially contributed to the definition
of the Segment Routing architecture and to the editing of this
document:
Ahmed Bashandy
Cisco Systems, Inc.
Email: bashandy@cisco.com
Martin Horneffer
Deutsche Telekom
Email: Martin.Horneffer@telekom.de
Wim Henderickx
Alcatel-Lucent
Email: wim.henderickx@alcatel-lucent.com
Jeff Tantsura
Ericsson
Email: Jeff.Tantsura@ericsson.com
Edward Crabbe
Individual
Email: edward.crabbe@gmail.com
Igor Milojevic
Email: milojevicigor@gmail.com
Saku Ytti
TDC
Email: saku@ytti.fi
11. Acknowledgements
We would like to thank Dave Ward, Dan Frost, Stewart Bryant, Pierre
Francois, Thomas Telkamp, Les Ginsberg, Ruediger Geib, Hannes
Gredler, Pushpasis Sarkar, Eric Rosen and Chris Bowers for their
comments and review of this document.
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12. References
12.1. 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,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <http://www.rfc-editor.org/info/rfc2460>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
<http://www.rfc-editor.org/info/rfc3031>.
[RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206,
DOI 10.17487/RFC4206, October 2005,
<http://www.rfc-editor.org/info/rfc4206>.
12.2. Informative References
[I-D.filsfils-spring-large-scale-interconnect]
Filsfils, C., Cai, D., Previdi, S., Henderickx, W.,
Cooper, D., Ferguson, F., Laberge, T., Lin, S., Decraene,
B., Jalil, L., jefftant@gmail.com, j., and R. Shakir,
"Interconnecting Millions Of Endpoints With Segment
Routing", draft-filsfils-spring-large-scale-
interconnect-04 (work in progress), October 2016.
[I-D.francois-rtgwg-segment-routing-ti-lfa]
Francois, P., Bashandy, A., and C. Filsfils, "Abstract",
draft-francois-rtgwg-segment-routing-ti-lfa-02 (work in
progress), November 2016.
[]
Previdi, S., Filsfils, C., Field, B., Leung, I., Linkova,
J., Aries, E., Kosugi, T., Vyncke, E., and D. Lebrun,
"IPv6 Segment Routing Header (SRH)", draft-ietf-6man-
segment-routing-header-02 (work in progress), September
2016.
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[I-D.ietf-isis-segment-routing-extensions]
Previdi, S., Filsfils, C., Bashandy, A., Gredler, H.,
Litkowski, S., Decraene, B., and j. jefftant@gmail.com,
"IS-IS Extensions for Segment Routing", draft-ietf-isis-
segment-routing-extensions-09 (work in progress), October
2016.
[I-D.ietf-mpls-spring-lsp-ping]
Kumar, N., Swallow, G., Pignataro, C., Akiya, N., Kini,
S., Gredler, H., and M. Chen, "Label Switched Path (LSP)
Ping/Trace for Segment Routing Networks Using MPLS
Dataplane", draft-ietf-mpls-spring-lsp-ping-01 (work in
progress), October 2016.
[I-D.ietf-ospf-ospfv3-segment-routing-extensions]
Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
Shakir, R., Henderickx, W., and J. Tantsura, "OSPFv3
Extensions for Segment Routing", draft-ietf-ospf-ospfv3-
segment-routing-extensions-07 (work in progress), October
2016.
[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-10 (work in progress), October 2016.
[I-D.ietf-pce-segment-routing]
Sivabalan, S., Medved, J., Filsfils, C., Crabbe, E.,
Raszuk, R., Lopez, V., Tantsura, J., Henderickx, W., and
J. Hardwick, "PCEP Extensions for Segment Routing", draft-
ietf-pce-segment-routing-08 (work in progress), October
2016.
[I-D.ietf-spring-conflict-resolution]
Ginsberg, L., Psenak, P., Previdi, S., and M. Pilka,
"Segment Routing Conflict Resolution", draft-ietf-spring-
conflict-resolution-02 (work in progress), October 2016.
[I-D.ietf-spring-ipv6-use-cases]
Brzozowski, J., Leddy, J., Townsley, W., Filsfils, C., and
R. Maglione, "IPv6 SPRING Use Cases", draft-ietf-spring-
ipv6-use-cases-07 (work in progress), July 2016.
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[I-D.ietf-spring-oam-usecase]
Geib, R., Filsfils, C., Pignataro, C., and N. Kumar, "A
Scalable and Topology-Aware MPLS Dataplane Monitoring
System", draft-ietf-spring-oam-usecase-04 (work in
progress), October 2016.
[I-D.ietf-spring-resiliency-use-cases]
Filsfils, C., Previdi, S., Decraene, B., and R. Shakir,
"Resiliency use cases in SPRING networks", draft-ietf-
spring-resiliency-use-cases-08 (work in progress), October
2016.
[I-D.ietf-spring-segment-routing-central-epe]
Filsfils, C., Previdi, S., Aries, E., Ginsburg, D., and D.
Afanasiev, "Segment Routing Centralized BGP Peer
Engineering", draft-ietf-spring-segment-routing-central-
epe-02 (work in progress), September 2016.
[I-D.ietf-spring-segment-routing-ldp-interop]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., and
S. Litkowski, "Segment Routing interworking with LDP",
draft-ietf-spring-segment-routing-ldp-interop-04 (work in
progress), July 2016.
[I-D.ietf-spring-segment-routing-mpls]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., Horneffer, M., Shakir, R.,
jefftant@gmail.com, j., and E. Crabbe, "Segment Routing
with MPLS data plane", draft-ietf-spring-segment-routing-
mpls-05 (work in progress), July 2016.
[I-D.ietf-spring-segment-routing-msdc]
Filsfils, C., Previdi, S., Mitchell, J., Aries, E., and P.
Lapukhov, "BGP-Prefix Segment in large-scale data
centers", draft-ietf-spring-segment-routing-msdc-02 (work
in progress), October 2016.
[I-D.ietf-spring-sr-oam-requirement]
Kumar, N., Pignataro, C., Akiya, N., Geib, R., Mirsky, G.,
and S. Litkowski, "OAM Requirements for Segment Routing
Network", draft-ietf-spring-sr-oam-requirement-02 (work in
progress), July 2016.
[I-D.ietf-spring-sr-yang]
Litkowski, S., Qu, Y., Sarkar, P., and J. Tantsura, "YANG
Data Model for Segment Routing", draft-ietf-spring-sr-
yang-05 (work in progress), October 2016.
Filsfils, et al. Expires May 23, 2017 [Page 27]
Internet-Draft Segment Routing November 2016
[RFC4381] Behringer, M., "Analysis of the Security of BGP/MPLS IP
Virtual Private Networks (VPNs)", RFC 4381,
DOI 10.17487/RFC4381, February 2006,
<http://www.rfc-editor.org/info/rfc4381>.
[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,
<http://www.rfc-editor.org/info/rfc4915>.
[RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
"LDP Specification", RFC 5036, DOI 10.17487/RFC5036,
October 2007, <http://www.rfc-editor.org/info/rfc5036>.
[RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
of Type 0 Routing Headers in IPv6", RFC 5095,
DOI 10.17487/RFC5095, December 2007,
<http://www.rfc-editor.org/info/rfc5095>.
[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,
<http://www.rfc-editor.org/info/rfc5120>.
[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
<http://www.rfc-editor.org/info/rfc5920>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<http://www.rfc-editor.org/info/rfc6020>.
[RFC6549] Lindem, A., Roy, A., and S. Mirtorabi, "OSPFv2 Multi-
Instance Extensions", RFC 6549, DOI 10.17487/RFC6549,
March 2012, <http://www.rfc-editor.org/info/rfc6549>.
[RFC6822] Previdi, S., Ed., Ginsberg, L., Shand, M., Roy, A., and D.
Ward, "IS-IS Multi-Instance", RFC 6822,
DOI 10.17487/RFC6822, December 2012,
<http://www.rfc-editor.org/info/rfc6822>.
[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, <http://www.rfc-editor.org/info/rfc7794>.
Filsfils, et al. Expires May 23, 2017 [Page 28]
Internet-Draft Segment Routing November 2016
[RFC7855] Previdi, S., Ed., Filsfils, C., Ed., Decraene, B.,
Litkowski, S., Horneffer, M., and R. Shakir, "Source
Packet Routing in Networking (SPRING) Problem Statement
and Requirements", RFC 7855, DOI 10.17487/RFC7855, May
2016, <http://www.rfc-editor.org/info/rfc7855>.
Authors' Addresses
Clarence Filsfils (editor)
Cisco Systems, Inc.
Brussels
BE
Email: cfilsfil@cisco.com
Stefano Previdi (editor)
Cisco Systems, Inc.
Via Del Serafico, 200
Rome 00142
Italy
Email: sprevidi@cisco.com
Bruno Decraene
Orange
FR
Email: bruno.decraene@orange.com
Stephane Litkowski
Orange
FR
Email: stephane.litkowski@orange.com
Rob Shakir
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
Email: robjs@google.com
Filsfils, et al. Expires May 23, 2017 [Page 29]
