Internet DRAFT - draft-dhody-pce-bn-discovery-isis
draft-dhody-pce-bn-discovery-isis
PCE Working Group D. Dhody
Internet-Draft U. Palle
Intended status: Experimental Huawei Technologies India Pvt Ltd
Expires: March 19, 2015 September 15, 2014
ISIS Protocol Extensions for Boundary Node Discovery (BND)
draft-dhody-pce-bn-discovery-isis-09
Abstract
The Path Computation Element (PCE) may be used for computing multi-
domain (Area or AS) Multiprotocol Label Switching (MPLS) and
Generalized MPLS (GMPLS) Traffic Engineered (TE) Label Switch Path
(LSP).
In this circumstance, it is highly desirable to be able to
dynamically and automatically discover a set of Boundary Nodes (BN)
along with their domain information in a simple way. For that
purpose, this document defines extensions to the Intermediate System
to Intermediate System(IS-IS) routing protocol for the advertisement
of Boundary Node (BN)Discovery information within an IS-IS area or
within the entire IS-IS routing domain.
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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This Internet-Draft will expire on March 19, 2015.
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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Applications . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Existing Mechanisms . . . . . . . . . . . . . . . . . . . . . 6
4.1. ISIS . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Inter-AS TE Link . . . . . . . . . . . . . . . . . . . . 6
4.3. ISIS Area Topology . . . . . . . . . . . . . . . . . . . 6
5. Other Considerations . . . . . . . . . . . . . . . . . . . . 6
5.1. Static Configurations . . . . . . . . . . . . . . . . . . 6
5.2. Importance of Domain Information along with BNs . . . . . 6
5.3. Relationship to Domain-Sequence . . . . . . . . . . . . . 7
6. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Boundary Node (BN) Discovery Information . . . . . . . . 7
6.2. Flooding Scope . . . . . . . . . . . . . . . . . . . . . 7
7. The IS-IS BND Sub-TLV . . . . . . . . . . . . . . . . . . . . 7
7.1. BN-ADDRESS Sub-TLV . . . . . . . . . . . . . . . . . . . 8
7.2. BN-DOMAIN Sub-TLV . . . . . . . . . . . . . . . . . . . . 9
8. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 9
9. Backward Compatibility . . . . . . . . . . . . . . . . . . . 10
10. Impact on Network . . . . . . . . . . . . . . . . . . . . . . 10
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
12. Security Considerations . . . . . . . . . . . . . . . . . . . 11
13. Manageability Considerations . . . . . . . . . . . . . . . . 11
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
15.1. Normative References . . . . . . . . . . . . . . . . . . 11
15.2. Informative References . . . . . . . . . . . . . . . . . 12
1. Introduction
This document defines extensions to IS-IS [ISO10589] to allow a
boundary node in an IS-IS routing domain to advertise its location,
along with domain information.
Generic capability advertisement mechanisms for IS-IS are defined in
[RFC4971]. These allow a router to advertise its capabilities within
an IS-IS area or an entire IS-IS routing domain. This document
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leverages this generic capability advertisement mechanism to fully
satisfy the dynamic BN discovery.
This document defines a new sub-TLV (named the BN Discovery (BND))to
be carried within the IS-IS Router Capability TLV ([RFC4971]).
The BN information advertised is detailed in Section 6. Protocol
extensions and procedures are defined in Section 7 and Section 8.
A detailed description about the need for auto discovery of Boundary
Nodes (BN) and thier domains is also provided in this document.
The IS-IS extensions defined in this document allow for BN discovery
within an IS-IS routing domain. Boundary Node can be an Area Border
Router (ABR) or Autonomous System Border Router (ASBR).
This document defines a set of sub-TLVs that are nested within each
other. When the degree of nesting TLVs is 2 (a TLV is carried within
another TLV) the TLV carried within a TLV is called a sub-TLV.
Strictly speaking, when the degree of nesting is 3, a sub-sub-TLV is
carried within a sub-TLV that is itself carried within a TLV. For
the sake of terminology simplicity, a TLV carried within another TLV
is called a sub-TLV regardless of the degree of nesting.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Terminology
The following terminology is used in this document.
ABR: IS-IS Area Border Router. Routers used to connect two IGP
areas.
AS: Autonomous System.
ASBR: Autonomous System Border Router. Router used to connect
together ASes of the same or different service providers via one
or more inter-AS links
BN: A boundary node is either an ABR in the context of inter-area
Traffic Engineering or an ASBR in the context of inter-AS Traffic
Engineering.
BND: Boundary Node Discovery
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BRPC: Backward Recursive Path Computation
Domain: Any collection of network elements within a common sphere of
address management or path computational responsibility. Examples
of domains include Interior Gateway Protocol (IGP) areas and
Autonomous Systems (ASs).
H-PCE: Hierarchical PCE.
IGP: Interior Gateway Protocol. Either of the two routing
protocols, Open Shortest Path First (OSPF) or Intermediate System
to Intermediate System (IS-IS).
LSA: Link State Advertisement.
IS-IS: Intermediate System to Intermediate System.
PCE: Path Computation Element. An entity (component, application,
or network node) that is capable of computing a network path or
route based on a network graph and applying computational
constraints.
TLV: Type-Length-Variable data encoding.
3. Applications
Backward Recursive Path Computation (BRPC) procedure as defined in
[RFC5441], requires Path Computation Element (PCE) [RFC4655] to be
aware of the BNs for the inter-domain path computation. This
information would be either statically configured at PCE or learned
via some mechanism, as listed in Section 4.
In case of static configuration, as shown in the Figure 1, incase of
ISIS Backbone area(L2), configuration of BNs at PCE5 is extensive.
BRPC procedure guarantees a best path only if BNs are selected
correctly, any change in BNs at run time may lead to sub-optimal
path. Also Administrator need to configure ABR / ASBR ID in such a
way that it is reachable from all the domains, BND TLV can take care
of this automatically.
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+--------------------------+ +--------------------------+
| +------+| | +------+|
| Area1(L1) | PCE1 || | Area2(L1) | PCE2 ||
| +--+---+| | +--+---+|
| | | |
| +---------------------+----------+--------------------+ |
| | +------+ +------+| |+------+ +------+ | |
| | | BN1 | | BN2 || || BN3 | | BN4 | | |
| | +--+---+ +--+---+| |+--+---+ +---+--+ | |
+----+----|-----------+----+ +---+-----------+----+-----+
| | | | | |
| +-----------+-------+ +------+-----------+ |
| | | |
| | | |
| ++----++ |
| Backbone(L2) | PCE5 | |
| ++----++ |
| | | |
| | | |
| +-----------+-------+ +------+----------+ |
| | | | | |
| | | | | |
+----+----+-----------+----+ +---+----------+-----+-----+
| | +--+---+ +--+---+| |+--+---+ +--+---+ | |
| | | BN5 | | BN6 || || BN7 | | BN8 | | |
| | +------+ +------+| |+------+ +------+ | |
| +---------------------+----------+--------------------+ |
| | | |
| +------+| | +------+|
| Area3(L1) | PCE3 || | Area4(L1) | PCE4 ||
| +--+---+| | +--+---+|
+--------------------------+ +--------------------------+
Figure 1: ISIS Area Topology
The problems with existing mechanism to discover Boundary nodes are
listed in Section 4.
Hierarchal PCE (H-PCE) [RFC6805] mechanim MAY require a parent PCE to
be aware of child domain's boundary node, child PCE in any case
should be aware of all its boundary nodes and can use mechnims as
described in this document.
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4. Existing Mechanisms
4.1. ISIS
o As specified in [RFC1142] ABR/ASBR can be identified but not their
domain information. As stated in Section 5.2, Selection of
correct BN is based on domain and thus it is ineffective.
o Selection of ABR/ASBR based on ISIS Database is not a good idea,
first it requires PCE to look into ISIS core Database thus adding
to coupling, second it MAY require Border Gateway Protocol (BGP)
routes to be redistributed into ISIS which is also not a good
network design principle.
4.2. Inter-AS TE Link
o [RFC5316] specifies how to advertise TE properties of inter-AS
links; through which ASBR and remote AS can be discovered, but ABR
and their domain information cannot be discovered via above RFC.
o AS is made up of multiple Area, there maybe a need to clearly
identify a BN by combination of both AS number and Area-id. Refer
[DOMAIN-SEQ].
4.3. ISIS Area Topology
o To uniquely identify an ISIS L1 area, an unique area Id MUST be
assigned. There is no other way to learn this information. BND
can be used to advertise this information.
5. Other Considerations
5.1. Static Configurations
A simple solution would be to configure BNs (ABR and ASBR) at PCE(s)
along with their domain information. As this information is fairly
static this could work in simple situations. But as PCE are being
used in bigger and multiple domains, any sort of static
configurations would put extra effort on the system administrator.
Selection of correct BNs is the core of any inter-domain path
computation procedure, we feel this information should be dynamically
learned and maintained.
5.2. Importance of Domain Information along with BNs
There are methods to learn BNs dynamically from IGP, but the
knowledge of neighboring-domains is not possible to obtain. Without
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this the correct BN based on the domain-path can't be selected.
[RFC5441] mentions:
"Note that PCE(i) only considers the entry BNs of domain(i), i.e.,
only the BNs that provide connectivity from domain(i-1). In other
words, the set BN-en(k,i) is only made of those BNs that provide
connectivity from domain (i-1) to domain(i). "
This selection of correct BNs providing connectivity between correct
domains cannot be made by the information obtained from IGP. Without
the correct selection we would not be following [RFC5441].
5.3. Relationship to Domain-Sequence
[DOMAIN-SEQ] provides a standard representation of Domain Sequence in
all deployment scenarios. The Domain Information carried in the BN-
DOMAIN sub-tlv is same as the sub-objects inside the domain sequence.
6. Overview
6.1. Boundary Node (BN) Discovery Information
The BN discovery information is composed of:
o The BN location: an IPv4 and/or IPv6 address that is used to reach
the BN. It is RECOMMENDED to use an address that is always
reachable from all connected domains;
o The set of two or more Domain(s) into which the BN has
connectivity;
Changes in BN discovery information may occur as a result of BN
configuration update or domain status change.
6.2. Flooding Scope
The flooding scope for BN information advertised through IS-IS can be
a single L1 area, an L1 area and the L2 sub-domain, or the entire IS-
IS routing domain.
7. The IS-IS BND Sub-TLV
The IS-IS BND sub-TLV contains a non-ordered set of sub-TLVs.
The format of the IS-IS BND sub-TLV and its sub-TLVs is identical to
the TLV format used by the Traffic Engineering Extensions to IS-IS
[RFC5305]. That is, the TLV is comprised of 1 octet for the type, 1
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octet specifying the TLV length, and a value field. The Length field
defines the length of the value portion in octets.
The IS-IS BND sub-TLV has the following format:
TYPE: To be assigned by IANA (suggested value 6)
LENGTH: Variable
VALUE: Set of sub-TLVs
Two sub-TLVs are defined:
Sub-TLV type Length Name
1 variable BN-ADDRESS sub-TLV
2 variable BN-DOMAIN sub-TLV
The BN-ADDRESS and BN-DOMAIN sub-TLVs MUST always be present within
the BND sub-TLV.
Any unrecognized sub-TLV MUST be silently ignored.
The BND sub-TLV is carried within an IS-IS CAPABILITY TLV defined in
[RFC4971].
The following sub-sections describe the sub-TLVs.
7.1. BN-ADDRESS Sub-TLV
The BN-ADDRESS sub-TLV specifies an IP address that can be used to
reach the BN. It is RECOMMENDED to make use of an address that is
always reachable, provided the BN is alive and reachable.
The BN-ADDRESS sub-TLV is mandatory; it MUST be present within the
BND sub-TLV. It MAY appear twice, when the BN has both an IPv4 and
IPv6 address. It MUST NOT appear more than once for the same address
type. If it appears more than once for the same address type, only
the first occurrence is processed and any others MUST be ignored.
The BN-ADDRESS sub-TLV has the following format:
TYPE: 1
LENGTH: 5 for an IPv4 address or 17 for an IPv6 address.
VALUE: This comprises one octet indicating the address
-type and 4 or 16 octets encoding the IPv4 or
IPv6 address to be used to reach the BN.
Address-type:
1 IPv4
2 IPv6
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7.2. BN-DOMAIN Sub-TLV
The BN-DOMAIN sub-TLV specifies a BN-Domain (area and/or AS) where
the BN has topology connectivity.
The BN-DOMAIN sub-TLV is mandatory; it MUST be present within the BND
TLV.
A BND sub-TLV MUST include two or more BN-DOMAIN sub-TLVs as the BN
has connectivity into multiple BN-Domains.
The BN-DOMAIN sub-TLV has the following format:
TYPE: 2
LENGTH: Variable
VALUE: This is composed of one octet indicating the
domain-type (area ID or AS Number) and a
variable length IS-IS area ID or a 32-bit AS
number, identifying a BN-Domain where the BN
has visibility and can compute paths.
Two domain types are defined:
1 Area ID
2 AS Number
The Area ID is the area address as defined in [ISO10589].
When the AS number is coded in two octets, the AS Number field MUST
have its first two octets set to 0.
8. Elements of Procedure
The BND sub-TLV is advertised within an IS-IS Router Capability TLV
defined in [RFC4971]. As such, elements of procedures are inherited
from those defined in [RFC4971].
The flooding scope is controlled by the S flag in the IS-IS Router
Capability TLV (see [RFC4971]). When the scope of the BND sub-TLV is
area local, it MUST be carried within an IS-IS Router Capability TLV
having the S bit cleared. When the scope of the BND sub-TLV is the
entire IS-IS routing domain, it MUST be carried within an IS-IS
Router Capability TLV having the S bit set.
Note that an L1L2 node may include a BND TLV in a Router Capability
TLV with the S bit cleared in both in its L1 and L2 LSPs. This
allows the flooding scope to be restricted to the L1 area and the L2
sub-domain.
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When the BN function is deactivated, the IS-IS speaker MUST originate
a new IS-IS LSP that no longer includes the corresponding BND TLV.
The BN address (i.e., the address indicated within the BN-ADDRESS
sub-TLV) SHOULD be reachable via some prefixes advertised by IS-IS.
The BND sub-TLV information regarding a specific BN is only
considered current and useable when the router advertising this
information is itself reachable via IS-IS calculated paths at the
level of the LSP in which the BND sub-TLV appears.
A change in the state of a BN (activate, deactivate, domain change)
MUST result in a corresponding change in the BND sub-TLV information
advertised by an IS-IS router (inserted, removed, updated) in its
LSP. The way BNs determine the information they advertise, and how
that information is made available to IS-IS, is out of the scope of
this document. Some information may be configured and other
information may be automatically determined by ISIS.
A change in information in the BND sub-TLV MUST NOT trigger any SPF
computation at a receiving router.
9. Backward Compatibility
The BND TLV defined in this document does not introduce any
interoperability issues.
An IS-IS router not supporting the BND sub-TLV will just silently
ignore the sub-TLV as specified in [RFC4971].
10. Impact on Network
The routers acting as BNs will originate LSP with BND Tlv; As there
are only few BNs exist in the network, the performance impact in
flooding is very less.
11. IANA Considerations
IANA has defined a registry for the sub-TLVs carried in the IS-IS
Router Capability TLV defined in [RFC4971]. IANA has assigned a new
sub-TLV codepoint for the BND sub-TLV carried within the Router
Capability TLV.
Value Sub-TLV References
----- -------- ----------
To be BND sub-TLV (this document)
assigned
by IANA
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12. Security Considerations
This document defines IS-IS extensions for BN discovery within an
administrative domain. Hence the security of the BN discovery relies
on the security of IS-IS.
Mechanisms defined to ensure authenticity and integrity of IS-IS LSPs
[RFC5304] and their TLVs, can be used to secure the BND sub-TLV as
well.
IS-IS provides no encryption mechanism for protecting the privacy of
LSPs and, in particular, the privacy of the BN discovery information.
13. Manageability Considerations
TBD
14. Acknowledgments
We would like to thank Quintin Zhao, Daniel King, Adrian Ferral,
Suresh babu, Pradeep Shastry, Saravana Kumar, Srinivasan and
Venugopal reddy k for their useful comments and suggestions.
15. References
15.1. Normative References
[RFC1142] Oran, D., "OSI IS-IS Intra-domain Routing Protocol", RFC
1142, February 1990.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4971] Vasseur, JP., Shen, N., and R. Aggarwal, "Intermediate
System to Intermediate System (IS-IS) Extensions for
Advertising Router Information", RFC 4971, July 2007.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, October 2008.
[RFC5316] Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in
Support of Inter-Autonomous System (AS) MPLS and GMPLS
Traffic Engineering", RFC 5316, December 2008.
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[ISO10589]
ISO, "Intermediate system to Intermediate system routeing
information exchange protocol for use in conjunction with
the Protocol for providing the Connectionless-mode Network
Service (ISO 8473)", ISO/IEC 10589:2002, Nov 2002.
15.2. Informative References
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, October 2008.
[RFC5441] Vasseur, JP., Zhang, R., Bitar, N., and JL. Le Roux, "A
Backward-Recursive PCE-Based Computation (BRPC) Procedure
to Compute Shortest Constrained Inter-Domain Traffic
Engineering Label Switched Paths", RFC 5441, April 2009.
[RFC6805] King, D. and A. Farrel, "The Application of the Path
Computation Element Architecture to the Determination of a
Sequence of Domains in MPLS and GMPLS", RFC 6805, November
2012.
[DOMAIN-SEQ]
Dhody, D., Palle, U., and R. Casellas, "Standard
Representation Of Domain Sequence (draft-ietf-pce-pcep-
domain-sequence-05)", July 2014.
Authors' Addresses
Dhruv Dhody
Huawei Technologies India Pvt Ltd
Leela Palace
Bangalore, Karnataka 560008
India
EMail: dhruv.ietf@gmail.com
Udayasree Palle
Huawei Technologies India Pvt Ltd
Leela Palace
Bangalore, Karnataka 560008
India
EMail: udayasree.palle@huawei.com
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