One document matched: draft-previdi-6man-segment-routing-header-00.txt
Network Working Group S. Previdi, Ed.
Internet-Draft C. Filsfils
Intended status: Standards Track Cisco Systems, Inc.
Expires: September 6, 2014 B. Field
Comcast
I. Leung
Rogers Communications
March 5, 2014
IPv6 Segment Routing Header (SRH)
draft-previdi-6man-segment-routing-header-00
Abstract
Segment Routing (SR) allows a node to steer a packet through a
controlled set of instructions, called segments, by prepending a SR
header to the packet. A segment can represent any instruction,
topological or service-based. SR allows to enforce a flow through
any path (topological, or application/service based) while
maintaining per-flow state only at the ingress node to the SR domain.
The Segment Routing architecture can be applied to the IPv6 data
plane with the addition of a new type of Routing Extension Header.
This draft describes the Segment Routing Extension Header Type and
how it is used by SR capable nodes.
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.
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 http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on September 6, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Structure of this document . . . . . . . . . . . . . . . . . . 4
2. Segment Routing Documents . . . . . . . . . . . . . . . . . . 4
3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Data Planes supporting Segment Routing . . . . . . . . . . 5
3.2. Illustrative Example . . . . . . . . . . . . . . . . . . . 5
4. IPv6 Instantiation of Segment Routing . . . . . . . . . . . . 6
4.1. Segment Routing Extension Header (SRH) . . . . . . . . . . 6
4.1.1. SRH and RFC2460 behavior . . . . . . . . . . . . . . . 9
4.1.2. SRH Optimization . . . . . . . . . . . . . . . . . . . 10
4.2. Segment Identifiers (SIDs) . . . . . . . . . . . . . . . . 10
4.2.1. Node-SID . . . . . . . . . . . . . . . . . . . . . . . 10
4.2.2. Adjacency-SID . . . . . . . . . . . . . . . . . . . . 11
5. SRH Procedures . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1. Segment Routing Operations . . . . . . . . . . . . . . . . 11
5.2. Segment Routing Node Functions . . . . . . . . . . . . . . 11
5.2.1. Ingress SR Node . . . . . . . . . . . . . . . . . . . 12
5.2.2. Transit Non-SR Capable Node . . . . . . . . . . . . . 13
5.2.3. SR Intra Segment Transit Node . . . . . . . . . . . . 13
5.2.4. SR Segment Endpoint Node . . . . . . . . . . . . . . . 14
5.3. FRR Flag Settings . . . . . . . . . . . . . . . . . . . . 14
6. SR-IPv6 Security . . . . . . . . . . . . . . . . . . . . . . . 14
6.1. Threat model . . . . . . . . . . . . . . . . . . . . . . . 15
6.2. Applicability of RFC 5095 to SRH . . . . . . . . . . . . . 15
6.3. Security fields in SRH . . . . . . . . . . . . . . . . . . 16
6.4. Nodes within the SR domain . . . . . . . . . . . . . . . . 17
6.5. Nodes outside of the SR domain . . . . . . . . . . . . . . 17
7. SR and Tunneling . . . . . . . . . . . . . . . . . . . . . . . 17
8. Example Use Case . . . . . . . . . . . . . . . . . . . . . . . 18
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
10. Manageability Considerations . . . . . . . . . . . . . . . . . 20
11. Security Considerations . . . . . . . . . . . . . . . . . . . 20
12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 20
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
14.1. Normative References . . . . . . . . . . . . . . . . . . . 20
14.2. Informative References . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
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1. Structure of this document
Section 3 gives an introduction on SR for IPv6 networks.
Section 4 defines the Segment Routing Header (SRH) allowing
instantiation of SR over IPv6 dataplane.
Section 5 details the procedures of the Segment Routing Header.
Section 6 describes the security aspect of SR-IPv6.
2. Segment Routing Documents
Segment Routing is described in [I-D.filsfils-rtgwg-segment-routing].
Segment Routing use cases are described in
[I-D.filsfils-rtgwg-segment-routing-use-cases].
Segment Routing IPv6 use cases are described in
[draft-martin-spring-segment-routing-ipv6-use-cases-00].
Segment Routing protocol extensions are defined in
[I-D.previdi-isis-segment-routing-extensions], and
[I-D.psenak-ospf-segment-routing-ospfv3-extension].
The terminology is used in this document has been defined in
[I-D.filsfils-rtgwg-segment-routing].
3. Introduction
Segment Routing (SR), defined in
[I-D.filsfils-rtgwg-segment-routing], allows a node to steer a packet
through a controlled set of instructions, called segments, by
prepending a SR header to the packet. A segment can represent any
instruction, topological or service-based. SR allows to enforce a
flow through any path (topological or service/application based)
while maintaining per-flow state only at the ingress node to the SR
domain. Segments can be derived from different components: IGP, BGP,
Services, Contexts, Locators, etc. The list of segment forming the
path is called the Segment List and is encoded in the packet header.
SR allows the use of strict and loose source based routing paradigms
without requiring any additional signaling protocols in the
infrastructure hence delivering an excellent scalability property.
The source based routing model described in
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[I-D.filsfils-rtgwg-segment-routing] is inherited from the ones
proposed by [RFC1940] and [RFC2460]. The source based routing model
offers the support for explicit routing capability.
3.1. Data Planes supporting Segment Routing
Segment Routing (SR), defined in
[I-D.filsfils-rtgwg-segment-routing], can be instantiated over MPLS
([I-D.filsfils-spring-segment-routing-mpls]) and IPv6. This document
defines its instantiation over the IPv6 data-plane.
Segment Routing for IPv6 (SR-IPv6) is required in networks where MPLS
data-plane is not used or, when combined with SR-MPLS, in networks
where MPLS is used in the core and IPv6 is used at the edge (home
networks, datacenters).
This document defines a new type of Routing Header (originally
defined in [RFC2460]) called the Segment Routing Header (SRH) in
order to convey the Segment List in the packet header as defined in
[I-D.filsfils-rtgwg-segment-routing]. Mechanisms through which
segment are known and advertised are outside the scope of this
document.
3.2. Illustrative Example
Typically, the domain ingress node obtains the path it has to use for
a given packet flow through either local configuration, local
computation or through an interaction with an external server such as
an SDN controller.
The output of the above is a segment list: a list of IPv6 addresses
(each representing a segment) that is encoded in the SRH. The
Segment List represents the path of the packet.
The ingress node encodes the first segment into the Destination
Address of the IPv6 header and the packet is forwarded towards the
first segment endpoint.
Each segment endpoint inspects the SRH, updates the DA (with the next
segment) and forwards the packet towards the next segment.
The SRH MAY be removed from the packet prior to send it to its
original destination.
When traveling within a segment, a packet may traverse non-SR-capable
nodes. These nodes will forward the packet based on its DA
regardless the content of the SRH that, in their case, will be
silently ignored as mandated by [RFC2460]. Therefore,
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interoperability between SR-capable and non-SR-capable nodes being
ensured, a gradual deployment of SR in existing networks is possible.
The details of the procedures of SR-IPv6 are described in Section 5.
4. IPv6 Instantiation of Segment Routing
When Segment Routing is applied to IPv6, segments are encoded as 128-
bit IPv6 addresses. This implies that, in the IPv6 instantiation of
SR, the SID values are in fact the prefixes advertised in the IPv6
control-plane. Hence there's no need to advertise any additional
specific identifier (other than IPv6 prefix) for the purpose of SR.
This simplifies the introduction of IPv6 Segment Routing in existing
protocols (i.e.: IS-IS, OSPF and BGP).
4.1. Segment Routing Extension Header (SRH)
A new type of the Routing Header (originally defined in [RFC2460]) is
defined: the Segment Routing Header (SRH) which has a new Routing
Type, to be assigned by IANA.
According to [I-D.filsfils-rtgwg-segment-routing], each segment is
represented by a Segment Identifier (SID). When SR is used over IPv6
networks, the SID is an IPv6 address (or prefix) as learned by IGP,
BGP or other protocols.
As an example, if an explicit path is to be constructed across a core
network running ISIS or OSPF, the segment list will contain SIDs
representing the nodes across the path (loose or strict) which,
usually, are the IPv6 loopback interface address of each node. If
the path is across service or application entities, the segment list
contains the IPv6 addresses of these services or application
instances.
The Segment Routing Header (SRH) is defined 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type | Next Segment |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Segment | Flags | HMAC Key ID | Policy List Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[0] (128 bits ipv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
...
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[n] (128 bits ipv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Policy List[0] (128 bits ipv6 address) |
| (optional) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Policy List[1] (128 bits ipv6 address) |
| (optional) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Policy List[2] (128 bits ipv6 address) |
| (optional) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| |
| HMAC (256 bits) |
| (optional) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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where:
o Next Header: 8-bit selector. Identifies the type of header
immediately following the SRH.
o Hdr Ext Len: 8-bit unsigned integer, is the length of the SRH
header in 8-octet units, not including the first 8 octets.
o Routing Type: TBD, to be assigned by IANA.
o Next Segment (originally defined as "Segments Left" in [RFC2460]):
offset (in multiple of 8 octets not including the first 8 octets)
of the next active segment (according to terminology defined in
[I-D.filsfils-rtgwg-segment-routing]) in the SRH. Note that this
differs from the semantic defined in the Routing Header
specification ([RFC2460] defines it as "Segments Left").
Therefore, in the Segment Routing context, the "Segments Left"
field is renamed as "Next Segment".
o Last Segment: offset (in multiple of 8 octets not including the
first 8 octets) of the last segment of the path in the SRH.
o Flags: 4 bits of flags. Two flags are defined:
Bit-0: Clean-up Bit. Set when the SRH has to be removed from
the packet when packet reaches the last segment.
Bit-1: Protected Bit. Set when the packet has been rerouted
through FRR mechanism by a SR endpoint node. See Section 5.3
for more details.
o HMAC Key ID and HMAC field are defined in Section 6.
o Policy List flags. Define the type of the IPv6 addresses encoded
into the Policy List (see below). The following have been
defined:
Bits 0-2: determine the type of the first element after the
segment list.
Bits 3-5: determine the type of the second element.
Bits 6-8: determine the type of the third element.
Bits 9-1: determine the type of the fourth element.
The following values are used for the type:
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0x0: Not present. If value is set to 0x0, it means the element
represented by these bits is not present.
0x1: Ingress SR PE address.
0x2: Egress SR PE address.
0x3: Original Source Address.
o Segment List[n]: 128 bit IPv6 addresses representing the nth
segment of the path.
o Policy List. Optional addresses representing specific nodes in
the SR path such as:
Ingress SR PE: IPv6 address representing the SR node which has
imposed the SRH (SR domain ingress).
Egress SR PE: IPv6 address representing the egress SR domain
node.
Original Source Address: IPv6 address originally present in the
SA field of the packet.
The segments in the Policy List are encoded after the segment list
and they are optional. If none are in the SRH, all bits of the
Policy List Flags MUST be set to 0x0.
4.1.1. SRH and RFC2460 behavior
The SRH being a new type of the Routing Header, it also has the same
properties:
Can only appear once in the packet.
Only the router whose address is in the DA field of the packet
header MUST inspect the SRH.
Therefore, Segment Routing in IPv6 networks implies that the segment
identifier (i.e.: the IPv6 address of the segment) is moved into the
DA of the packet.
The DA of the packet changes at each segment termination/completion
and therefore the original DA of the packet MUST be encoded as the
last segment of the path.
As illustrated in Section 3.2, nodes that are within the path of a
segment will forward packets based on the DA of the packet without
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inspecting the SRH. This ensures full interoperability between SR-
capable and non-SR-capable nodes.
4.1.2. SRH Optimization
In order to optimize the way the SRH and, more precisely, the Segment
List is processed by SR nodes, it is desirable that most of the
necessary information of the SL is placed at the top of the list so
to avoid reading the whole content of the SRH prior to make
forwarding decisions.
With this in mind, when the SRH is created and the segment list is
inserted, the order of the segments in the segment list is as
follows:
o The Next Segment field points to the next segment to be examined
(offset within the SRH).
o The first segment being encoded in the DA by the ingress node, it
doesn't need to sit in the first position of the list.
o Hence, the first element of the segment list is the second segment
of the path so that, when the packet reaches the end of the first
segment, the node inspecting the SRH will find the second segment
at the beginning of the segment list.
o The other segments of the path are encoded sequentially after the
second segment.
o The last segment of the path is the original DA address.
o The last segment in the Segment List is used to encode the first
segment. This segment will never be inspected anyway (at least
not for forwarding purposes).
4.2. Segment Identifiers (SIDs)
The Segment Routing architecture described in
[I-D.filsfils-rtgwg-segment-routing], defines Node-SID and Adjacency-
SID. When SR is used over IPv6 data-plane the following applies.
4.2.1. Node-SID
The Node-SID identifies a node. With SR-IPv6 the Node-SID is an IPv6
prefix that the operator configured on the node and that is used as
the node identifier. Typically, in case of a router, this is the
IPv6 address of the node loopback interface. Therefore, SR-IPv6 does
not require any additional SID advertisement. The SID is in fact the
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IPv6 address of the node.
4.2.2. Adjacency-SID
The Adjacency-SID identifies a given interface. In the SR
architecture a node may advertise one or more Adj-SIDs allocated to a
given interface so to force the forwarding of the packet (when
received with that particular Adj-SID) into the interface, regardless
the routing entry for the packet destination. The same is defined
for SR-IPv6: a node may advertise a given IPv6 prefix which is
associated to the SR semantic of "send out the packet to the
interface this prefix is allocated to". Here also, the SID is in
fact the IPv6 prefix.
5. SRH Procedures
In this section we describe the different procedures on the SRH.
5.1. Segment Routing Operations
When Segment Routing is instantiated over the IPv6 data plane the
following applies:
o The segment list is encoded in the SRH.
o The active segment is in the destination address of the packet.
o The Segment Routing CONTINUE operation (as described in
[I-D.filsfils-rtgwg-segment-routing]) is implemented as a regular/
plain IPv6 operation consisting of DA based forwarding.
o The NEXT operation is implemented through the update of the DA
with the value represented by the Next Segment field in the SRH.
o The PUSH operation is implemented through the insertion of the SRH
or the insertion of additional segments in the SRH segment list.
5.2. Segment Routing Node Functions
SR packets are forwarded to segments endpoints (i.e.: nodes whose
address is in the DA field of the packet). The segment endpoint,
when receiving a SR packet destined to itself, does:
o Inspect the SRH.
o Determine the next segment.
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o Update the SRH (or, if requested, remove the SRH from the packet).
o Update the DA.
o Send the packet to the next segment.
The procedures applied to the SRH are related to the node function.
Following nodes functions are defined:
Ingress SR Node.
Transit Non-SR Node.
Transit SR Intra Segment Node.
SR Endpoint Node.
5.2.1. Ingress SR Node
Ingress Node can be a router at the edge of the SR domain or a SR-
capable host. The ingress SR node obtain the segment list by either:
Local path computation.
Interaction with an SDN controller delivering the path as a
complete SRH.
When creating the SRH (either at ingress node or in the SDN
controller) the following is done:
Next Header and Hdr Ext Len fields are set according to [RFC2460].
Routing Type field is set as TBD (SRH).
The DA of the packet is set with the address of the FIRST segment
of the path.
Next Segment field contains the offset of the SECOND segment of
the path which is encoded in the FIRST position of the segment
list. The segment list is encoded as follows:
The first element of the list contains the second segment (as
stated above).
All subsequent segments are encoded following the second
segment.
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The original DA of the packet is encoded as the last segment of
the path (which is NOT the last segment of the segment list).
The last segment of the segment list is the FIRST segment of
the path.
Last Segment field contains the offset of the last segment of the
path (i.e.: the original DA of the packet).
The packet is sent out to the first segment.
5.2.1.1. Security at Ingress
The procedures related to the Segment Routing security are detailed
in Section 6.
In the case where the SR domain boundaries are not under control of
the network operator (e.g.: when the SR domain edge is in a home
network), it is important to authenticate and validate the content of
any SRH being received by the network operator. In such case, the
security procedure described in Section 6 is to be used.
The ingress node (e.g.: the host in the home network) requests the
SRH to a control system (e.g.: an SDN controller) which delivers the
SRH with its HMAC signature on it.
Then, the home network host can send out SR packets (with an SRH on
it) that will be validated at the ingress of the network operator
infrastructure.
The ingress node of the network operator infrastructure, is
configured in order to validate the incoming SRH HMACs in order to
allow only packets having correct SRH according to their SA/DA
addresses.
5.2.2. Transit Non-SR Capable Node
SR is interoperable with plain IPv6 forwarding. Any non SR-capable
node will forward SR packets solely based on the DA. There's no SRH
inspection. This ensures full interoperability between SR and non-SR
nodes.
5.2.3. SR Intra Segment Transit Node
Only the node whose address is in DA inspects and processes the SRH
(according to [RFC2460]). An intra segment transit node is not in
the DA and its forwarding is based on DA and its SR-IPv6 FIB.
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5.2.4. SR Segment Endpoint Node
The SR segment endpoint node is the node whose address is in the DA.
The segment endpoint node inspects the SRH and does:
1. IF DA = myself (segment endpoint)
2. IF Next Segment <> Last Segment THEN
update DA with Next Segment
increment Next Segment
3. ELSE IF Last Segment <> DA THEN
update DA with Next Segment
IF Clean-up bit is set THEN remove the SRH
4. ELSE give the packet to next PID (application)
End of processing.
5. Forward the packet out
5.3. FRR Flag Settings
A node supporting SR and doing Fast Reroute (as described in
[I-D.filsfils-rtgwg-segment-routing-use-cases], when rerouting
packets through FRR mechanisms, SHOULD inspect the rerouted packet
header and look for the SRH. If the SRH is present, the rerouting
node SHOULD set the Protected bit on all rerouted packets.
6. SR-IPv6 Security
This section analyses the security threat model as well as the
security issues and proposed solutions related to the new routing
header for segment routing (a.k.a. segment routing header SRH).
The segment routing header is simply another version of the routing
header as described in [RFC2460] and is:
o inserted when entering the segment routing domain which could be
done by a node or by a router;
o read and acted upon when reaching the destination of the IP
header.
Routers on the path that simply forward an IPv6 packet (i.e. the IPv6
destination address is not one of theirs) will never read and process
the SRH. Routers whose one interface IPv6 address equals the
destination address field of the SRH will have to parse the SRH and,
if supported and if the local configuration allows it, will act on
the SRH.
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6.1. Threat model
Using a routing extension header which is basically source routing
has some well-known security issues as described in [RFC4942] section
2.1.1 and [RFC5095]:
o amplification attacks: where a packet could be forged in such a
way to cause looping among a set of intermediate routers causing
unnecessary traffic, hence a denial of service against bandwidth;
o reflection attack: where a hacker could force an intermediate node
to appear as the immediate attacker, hence hiding the real
attacker from naive forensic;
o bypass attack: where an intermediate node could be used as a
stepping stone (for example in a DMZ) to attack another host (for
example in the datacenter or any back-end server.
These security issues did lead to obsoleting the routing header type
0 with [RFC5095] because:
o it was assumed to be acted upon by default by each and every
router on the Internet;
o it contained multiple segments in the payload.
Therefore, if intermediate nodes ONLY act on valid and authorized
SRH, then there is no security threat similar to RH-0. But as SR is
used for added value services, there is also a need to prevent non-
participating nodes to use those services; this is called 'service
stealing prevention'.
6.2. Applicability of RFC 5095 to SRH
In the segment routing architecture described in
[I-D.filsfils-rtgwg-segment-routing], there are basically two kinds
of nodes (routers and hosts):
o nodes within the segment routing domain, which is within one
single administrative domain, i.e., where all nodes are trusted
anyway else the damage caused by those nodes could be worse than
amplification attacks: traffic interception and man-in-the-middle
attacks, more server DoS by dropping packets, and so on.
o Nodes outside of the segment routing domain, which is outside of
the administrative segment routing domain hence they cannot be
trusted because there is no physical security for those nodes,
i.e., they can be replaced by hostile nodes or can be coerced in
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wrong behaviors.
6.3. Security fields in SRH
The security-related fields in SRH are:
o HMAC Key-id, 8bits wide, if HMAC key-id is null, then there is no
HMAC field;
o HMAC, 256 bits wide.
The HMAC field is the output of the hash of the concatenation of:
o the source IPv6 address;
o last segment, clean-up bit flag, HMAC key id, all addresses in the
Segment List;
o a pre-shared secret between SR nodes in the SR domain (routers,
controllers, ...).
The purpose of the HMAC field is to verify the validity and
authorization of the SRH itself. If an outsider of the SR domain
does not have access to the pre-shared secret, then it cannot compute
the right HMAC field and the first SR router on the path processing
the SRH and configure to check the validity of the HMAC will simply
reject the packet.
The HMAC field is located at the end of the SRH simply because only
the router on the ingress of the SR domain needs to process, then all
other SR nodes can ignore it (based on local policy). This is to
speed up forwarding operations because some hardware platforms can
only parse in hardware so many bytes.
The HMAC Key-id field allows for the simultaneous existence of
several hash algorithms (SHA-128, SHA-256, ... or future ones) as
well as pre-shared keys. This allows for pre-shared key roll-over
when two pre-shared keys are supported for a while when all SR nodes
converged to a fresher pre-shared key. The HMAC key-id is opaque,
i.e., it has no syntax except as an index to the right combination of
pre-shared key and hash algorithm. It also allows for interoperation
among different SR domains if allowed by local policy.
How HMAC key-id and pre-shared secret are synchronized between
participating nodes in the SR domain is outside of the scope of this
document ([RFC6407] GDOI could be a basis).
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6.4. Nodes within the SR domain
Those nodes can be trusted to generate and to process SRH received on
interfaces that are part of the SR domain (AS or set of ASs under
common administration where SR is enabled). These nodes MUST drop
all packets received on an interface that is not part of the SR
domain and containing a SRH whose HMAC field cannot be validated by
local policies. This includes obviously packet with a SRH generated
by a non-cooperative SR domain.
If the validation fails, then these packets MUST be dropped, ICMP
error messages (parameter problem) SHOULD be generated (but rate
limited) and SHOULD be logged.
6.5. Nodes outside of the SR domain
Nodes outside of the SR domain cannot be trusted for physical
security; hence, they need to request by some means (outside of the
scope of this document) a complete SRH for each new connection. The
SRH MUST include a HMAC key-id and HMAC field which is computed
correctly (see Section 6.3).
When an outside node sends a packet with an SRH and towards a SR
ingress node, the packet MUST contain the HMAC field and the SR
ingress node MUST be in the segment list of the SRH.
The ingress SR router, i.e., the router with an interface address
equals to the destination address, MUST verify the HMAC field.
If the validation is successful, then the packet is simply forwarded
as usual for a SR packet. As long as the packet travels within the
SR domain, no further HMAC check is done. Subsequent routers in the
SR domain MAY verify the HMAC field.
If the validation fails, then this packet MUST be dropped, an ICMP
error message (parameter problem) SHOULD be generated (but rate
limited) and SHOULD be logged.
7. SR and Tunneling
Encapsulation can be realized in two different ways with SR-IPv6:
Outer encapsulation.
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SRH with SA/DA original addresses.
Outer encapsulation tunneling is the traditional method where an
additional IPv6 header is prepended to the packet. The original IPv6
header being encapsulated, everything is preserved and the packet is
switched/routed according to the outer header (that could contain a
SRH).
SRH allows encoding both original SA and DA and therefore, hence an
operator may decide to change the SA/DA at ingress and restore them
at egress. This can be achieved without outer encapsulation, by
changing SA/DA and encoding the original values in the Segment List
(the last segment of the path being the original DA) and in the
Policy List (original SA).
8. Example Use Case
A more detailed description of use cases are available in
[draft-martin-spring-segment-routing-ipv6-use-cases-00]. In this
section, a simple SR-IPv6 example is illustrated.
In the topology described in Figure 2 it is assumed an end-to-end SR
deployment. Therefore SR is supported by all nodes from A to J.
Home Network | Backbone | Datacenter
| |
| +---+ +---+ +---+ | +---+ |
+---|---| C |---| D |---| E |---|---| I |---|
| | +---+ +---+ +---+ | +---+ |
| | | | | | | | +---+
+---+ +---+ | | | | | | |--| X |
| A |---| B | | +---+ +---+ +---+ | +---+ | +---+
+---+ +---+ | | F |---| G |---| H |---|---| J |---|
| +---+ +---+ +---+ | +---+ |
| |
| +-----------+
| SDN |
| Orch/Ctlr |
+-----------+
Figure 2: Sample SR topology
The following workflow applies to packets sent by host A and destined
to server X.
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. Host A sends a request for a path to server X to the SDN
controller or orchestration system.
. The SDN controller/orchestrator builds a SRH with:
. Segment List: C, F, J, X
. HMAC
that satisfies the requirements expressed in the request
by host A and based on policies applicable to host A.
. Host A receives the SRH and insert it into the packet.
The packet has now:
. SA: A
. DA: C
. SRH with
. SL: F,J,X,C
. PL: C (ingress), J (egress)
Note that X is the last segment and C is the
first segment (encoded at the end of the SL).
. When packet arrives in C (first segment), C does:
. Validate the HMAC of the SRH.
. Update the DA with the next segment (found in SRH):
DA is set to F.
. Forward the packet to F.
. Packet arrives in F which inspects the SRH and find the
next segment:
. DA is set to J.
. Packet travels across G and H nodes which do plain
IPv6 forwarding based on DA. No inspection of SRH needs
to be done in these nodes. However, any SR capable node
is allowed to set the Protected bit in case of FRR
protection.
. Packet arrives in J where two options are available
depending on the settings of the cleanup bit set in the
SRH:
. If the cleanup bit is set, then node J will strip out
the SRH from the packet, set the DA as X and send
the packet out.
. If the clean-up bit is not set, the DA is set to X
and the packet is sent out with the SRH.
The packet arrives in the server that may or may not support SR. The
return traffic, from server to host, may be sent using the same
procedures.
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9. IANA Considerations
TBD
10. Manageability Considerations
TBD
11. Security Considerations
Security mechanisms applied to Segment Routing over IPv6 networks are
detailed in Section 6.
12. Contributors
Eric Vynke contributed to this document through the writings of
Section 6.
13. Acknowledgements
The authors would like to thank John Leddy, John Brzozowski, Mark
Townsley, Christian Martin, Roberta Maglione and James Connolly for
their contribution to this document.
14. References
14.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
of Type 0 Routing Headers in IPv6", RFC 5095,
December 2007.
[RFC6407] Weis, B., Rowles, S., and T. Hardjono, "The Group Domain
of Interpretation", RFC 6407, October 2011.
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14.2. Informative References
[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-01 (work in
progress), October 2013.
[I-D.filsfils-rtgwg-segment-routing-use-cases]
Filsfils, C., Francois, P., Previdi, S., Decraene, B.,
Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
Ytti, S., Henderickx, W., Tantsura, J., Kini, S., and E.
Crabbe, "Segment Routing Use Cases",
draft-filsfils-rtgwg-segment-routing-use-cases-02 (work in
progress), October 2013.
[I-D.filsfils-spring-segment-routing-mpls]
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 with MPLS data plane",
draft-filsfils-spring-segment-routing-mpls-00 (work in
progress), October 2013.
[I-D.previdi-isis-segment-routing-extensions]
Previdi, S., Filsfils, C., Bashandy, A., Gredler, H.,
Litkowski, S., and J. Tantsura, "IS-IS Extensions for
Segment Routing",
draft-previdi-isis-segment-routing-extensions-05 (work in
progress), February 2014.
[I-D.psenak-ospf-segment-routing-ospfv3-extension]
Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
Shakir, R., and W. Henderickx, "OSPFv3 Extensions for
Segment Routing",
draft-psenak-ospf-segment-routing-ospfv3-extension-01
(work in progress), February 2014.
[RFC1940] Estrin, D., Li, T., Rekhter, Y., Varadhan, K., and D.
Zappala, "Source Demand Routing: Packet Format and
Forwarding Specification (Version 1)", RFC 1940, May 1996.
[RFC4942] Davies, E., Krishnan, S., and P. Savola, "IPv6 Transition/
Co-existence Security Considerations", RFC 4942,
September 2007.
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[draft-martin-spring-segment-routing-ipv6-use-cases-00]
Brzozowski, J., Leddy, J., Leung, I., Previdi, S.,
Townsley, M., Martin, C., Filsfils, C., and R. Maglione,
"IPv6 Segment Routing Use Cases", March 2014.
Authors' Addresses
Stefano Previdi (editor)
Cisco Systems, Inc.
Via Del Serafico, 200
Rome 00142
Italy
Email: sprevidi@cisco.com
Clarence Filsfils
Cisco Systems, Inc.
Brussels,
BE
Email: cfilsfil@cisco.com
Brian Field
Comcast
4100 East Dry Creek Road
Centennial, CO 80122
US
Email: Brian_Field@cable.comcast.com
Ida Leung
Rogers Communications
8200 Dixie Road
Brampton, ON L6T 0C1
CA
Email: Ida.Leung@rci.rogers.com
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