One document matched: draft-dhody-pce-bn-discovery-ospf-02.txt
Differences from draft-dhody-pce-bn-discovery-ospf-01.txt
PCE Working Group D. Dhody
Internet-Draft U. Palle
Intended status: Informational Huawei Technologies India Pvt Ltd
Expires: September 29, 2011 March 28, 2011
OSPF Protocol Extensions for Boundary Node Discovery (BND)
draft-dhody-pce-bn-discovery-ospf-02
Abstract
There are various circumstances where it is highly desirable to be
able to dynamically and automatically discover a set of Boundary
Nodes (BN) along with their domain information. For that purpose,
this document defines extensions to the Open Shortest Path First
(OSPF) routing protocol for the advertisement of Boundary Node (BN)
Discovery information within an OSPF area or within the entire OSPF
routing domain.
Status of this Memo
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Copyright Notice
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This Internet-Draft will expire on September 29, 2011.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Boundary Node (BN) Discovery Information . . . . . . . . . 4
3.2. Flooding Scope . . . . . . . . . . . . . . . . . . . . . . 4
4. Applications . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Existing Mechanisms . . . . . . . . . . . . . . . . . . . . . 7
6. Static Configurations . . . . . . . . . . . . . . . . . . . . 7
7. Importance of Domain Information along with BNs . . . . . . . 7
8. Relationship to Domain-Sequence . . . . . . . . . . . . . . . 8
9. The OSPF BND TLV . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. BN-ADDRESS Sub-TLV . . . . . . . . . . . . . . . . . . . . 9
9.2. BN-DOMAIN Sub-TLV . . . . . . . . . . . . . . . . . . . . 10
10. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 10
11. Backward Compatibility . . . . . . . . . . . . . . . . . . . . 11
12. Impact on Network . . . . . . . . . . . . . . . . . . . . . . 11
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
13.1. OSPF TLV . . . . . . . . . . . . . . . . . . . . . . . . . 12
14. Security Considerations . . . . . . . . . . . . . . . . . . . 12
15. Manageability Considerations . . . . . . . . . . . . . . . . . 12
16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
17.1. Normative References . . . . . . . . . . . . . . . . . . . 12
17.2. Informative References . . . . . . . . . . . . . . . . . . 13
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1. Introduction
This document defines extensions to OSPFv2 [RFC2328] and OSPFv3
[RFC5340] to allow a boundary node in an OSPF routing domain to
advertise its location, along with domain information.
Generic capability advertisement mechanisms for OSPF are defined in
[RFC4970]. These allow a router to advertise its capabilities within
an OSPF area or an entire OSPF routing domain. This document
leverages this generic capability advertisement mechanism to fully
satisfy the dynamic BN discovery.
This document defines a new TLV (named the Boundary Node Discovery
TLV (BND TLV)) to be carried within the OSPF Router Information LSA
([RFC4970]).
The Boundary Node information advertised is detailed in Section 3.
Protocol extensions and procedures are defined in Sections 6 and 7.
The OSPF extensions defined in this document allow for Boundary Node
discovery within an OSPF routing domain. Boundary Node can be an ABR
or ASBR.
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: OSPF 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.
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BND: Boundary Node Discovery
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).
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.
OSPF: Open Shortest Path First.
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. Overview
3.1. 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.
3.2. Flooding Scope
The flooding scope for BN information advertised through OSPF can be
limited to OSPF area(s) the BN belongs to, or can be extended across
the entire OSPF routing domain.
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4. Applications
BRPC procedure as defined in [RFC5441], requires Path Computation
Element (PCE)[RFC4655] to be aware of the BNs for the inter-domain
path computation. As shown in the figure 1, Incase of OSPF Area0,
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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+--------------------+
| +-----+|
| Area 2 | PCE2||
| +-----+|
| |
| |
| BN4+----+ |
+--------+----+------+
+----------+----+---------+
| +----+ |
| |
| |
| |
+---------------+ | |+----------------+
| BN1 | | || BN5 |
| +-+-++ +++--+ |
| | | || ||| | |
| +-+-++ +++--+ |
| | | || |
| BN2 | | || BN6 |
| +-+-++ Area 0 +++--+ |
| Area 1 | | || ||| | Area 3 |
| +-+-++ +++--+ |
| | | || |
| BN3 | | +-----+ || BN7 |
|+-----+ +-+-++ | PCE5| +++--+ +-----+ |
|| PCE1| | | || +-----+ ||| | | PCE3| |
|+-----+ +-+-++ +++--+ +-----+ |
| | | || |
+---------------+ | |+----------------+
| |
| |
| +----+ |
+----------+----+---------+
+--------+----+------+
| BN8 +----+ |
| |
| |
| Area 4 +-----+|
| | PCE4||
| +-----+|
+--------------------+
Figure 1: OSPF Area Topology
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5. Existing Mechanisms
o E bit and B bit of Router LSA defined in [RFC2328] can help in
finding a router acting as ABR/ASBR but there is no way to find
out the domain information of this ABR/ASBR. As stated in section
4,Selection of correct BN is based on domain and thus it is
ineffective.
o [RFC5392] 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 Any assumptions on area-id for the ABRs based on generic OSPF area
topology can be inaccurate; specially considering IBM
interpretation of ABR [RFC3509]
o Section 4 of [H-PCE] specifies each child PCE should know the
identity of the domains that neighbor its own domain and
advertises the same to the parent PCE. No method exist to find
the neighbor domain which need to be carried in NEIG-PCE-DOMAIN
Sub-TLV and BN discovery along with neighbor domain information
can help in generating NEIG-PCE-DOMAIN Sub-TLV.
6. 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 the BRPC procedure, we feel
this information should be dynamically learned and maintained.
7. 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
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].
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8. 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.
9. The OSPF BND TLV
The OSPF BN Discovery TLV (BND TLV) contains a non-ordered set of
sub-TLVs.
The format of the OSPF BND TLV and its sub-TLVs is identical to the
TLV format used by the Traffic Engineering Extensions to
OSPF[RFC3630]. That is, the TLV is composed of 2 octets for the
type, 2 octets specifying the TLV length, and a value field. The
Length field defines the length of the value portion in octets.
The OSPF BND TLV has the following format:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// sub-TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: To be assigned by IANA (suggested value 8)
Length: Variable
Value: This comprises of following sub-TLVs
Two sub-TLVs are defined:
Sub-TLV type Length Name
1 variable BN-ADDRESS sub-TLV
2 4 BN-DOMAIN sub-TLV
The BN-ADDRESS and BN-DOMAIN sub-TLVs MUST always be present within
the BND TLV.
Malformed BND TLVs or sub-TLVs not explicitly described in this
document MUST cause the LSA to be treated as malformed according to
the normal procedures of OSPF.
Any unrecognized sub-TLV MUST be silently ignored.
The BND TLV is carried within an OSPF Router Information LSA defined
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in [RFC4970].
The following sub-sections describe the sub-TLVs which are carried
within the BND TLV.
9.1. 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 that the BN is alive and reachable.
The BN-ADDRESS sub-TLV is mandatory; it MUST be present within the
BND 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 format of the BN-ADDRESS sub-TLV is as follows:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 1 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| address-type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// BN IP Address //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
BN-ADDRESS sub-TLV format
Type: 1
Length: 8 (IPv4) or 20 (IPv6)
Address-type:
1 IPv4
2 IPv6
Reserved: SHOULD be set to zero on transmission and MUST be ignored
on receipt.
BN IP Address: The IP address to be used to reach the BN.
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9.2. BN-DOMAIN Sub-TLV
The BN-DOMAIN sub-TLV specifies a BN-Domain (area 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 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:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 2 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Domain-type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Domain ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
BN-DOMAIN sub-TLV format
Type: 2
Length: 8
Two domain-type values are defined:
1 OSPF Area ID
2 AS Number
Domain ID: With the domain-type set to 1, this indicates the 32-bit
Area ID of an area where the BN (ABR) has connectivity. With domain-
type set to 2, this indicates an AS number of an AS where the BN
(ASBR) has connectivity. When the AS number is coded in two octets,
the AS Number field MUST have its first two octets set to 0.
10. Elements of Procedure
The BND TLV is advertised within OSPFv2 Router Information LSAs
(Opaque type of 4 and Opaque ID of 0) or OSPFv3 Router Information
LSAs (function code of 12), which are defined in [RFC4970]. As such,
elements of procedure are inherited from those defined in [RFC4970].
In OSPFv2, the flooding scope is controlled by the opaque LSA type(as
defined in [RFC5250]) and in OSPFv3, by the S1/S2 bits (as defined in
[RFC5340]). If the flooding scope is area local, then the BND TLV
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MUST be carried within an OSPFv2 type 10 router information LSA or an
OSPFV3 Router Information LSA with the S1 bit set and the S2 bit
clear. If the flooding scope is the entire IGP domain, then the BND
TLV MUST be carried within an OSPFv2 type 11 Router Information LSA
or OSPFv3 Router Information LSA with the S1 bit clear and the S2 bit
set.
When the BN function is deactivated, the OSPF speaker MUST originate
a new Router Information LSA that no longer includes the
corresponding BND TLV, provided there are other TLVs in the LSA. If
there are no other TLVs in the LSA, it MUST either send an empty
Router Information LSA or purge it by prematurely aging it.
The BN address (i.e., the address indicated within the BN-ADDRESS
sub-TLV) SHOULD be reachable via some prefixes advertised by OSPF.
The BND TLV information regarding a specific BN is only considered
current and useable when the router advertising this information is
itself reachable via OSPF calculated paths in the same area of the
LSA in which the BND TLV appears.
A change in the state of a BN (activate, deactivate, domain change)
MUST result in a corresponding change in the BND TLV information
advertised by an OSPF router (inserted, removed, updated)in its LSA.
The way BNs determine the information they advertise, and how that
information is made available to OSPF, is out of the scope of this
document. Some information may be configured and other information
may be automatically determined by the OSPF.
A change in information in the BND TLV MUST NOT trigger any SPF
computation at a receiving router.
11. Backward Compatibility
The BND TLV defined in this document does not introduce any
interoperability issues.
A router not supporting the BND TLV will just silently ignore the TLV
as specified in [RFC4970].
12. Impact on Network
The routers acting as BNs will originate Opaque LSA with BND Tlv; As
there are only few BNs exist in the network, the performance impact
in flooding is very less.
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13. IANA Considerations
13.1. OSPF TLV
IANA has defined a registry for TLVs carried in the Router
Information LSA defined in [RFC4970].A number of IANA considerations
have been highlighted in previous sections of this document. IANA is
requested to make the following allocations.
Value TLV Name Reference
----- -------- ----------
To be BND (this document)
assigned
by IANA
14. Security Considerations
This document defines OSPF extensions for BN discovery within an
administrative domain. Hence the security of the BN discovery relies
on the security of OSPF.
Mechanisms defined to ensure authenticity and integrity of OSPF LSAs
[RFC2154], and their TLVs, can be used to secure the BN Discovery
information as well.
OSPF provides no encryption mechanism for protecting the privacy of
LSAs and, in particular, the privacy of the BN discovery information.
15. Manageability Considerations
TBD
16. Acknowledgments
We would like to thank Quintin Zhao, Daniel King, Adrian Ferral,
Suresh babu, Pradeep Shastry, Saravana Kumar and srinivasan for their
useful comments and suggestions.
17. References
17.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", March 1997.
[RFC2154] Murphy, S., Badger, M., and B. Wellington, "OSPF with
Digital Signatures", June 1997.
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[RFC2328] Moy, J., "OSPF Version 2", April 1998.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic
Engineering (TE) Extensions to OSPF Version 2",
September 2003.
[RFC4970] Lindem, A., Shen, N., Vasseur, JP., Aggarwal, R., and
S. Shaffer, "Extensions to OSPF for Advertising
Optional Router Capabilities", July 2007.
[RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
OSPF Opaque LSA Option", July 2008.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, Ed,
"OSPF for IPv6", July 2008.
17.2. Informative References
[DOMAIN-SEQ] Dhody, D. and U. Palle, "Standard Representation Of
Domain Sequence", March 2011.
[H-PCE] King, D. and A. Farrel , "The Application of the Path
Computation Element Architecture to the Determination
of a Sequence of Domains in MPLS & GMPLS",
December 2009.
[RFC3509] Zinin, A., Lindem, A., and D. Yeung, "Alternative
Implementations of OSPF Area Border Routers",
April 2003.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture",
August 2006.
[RFC5392] Chen, M., Zhang, R., and X. Duan, "OSPF Extensions in
Support of Inter-Autonomous System (AS)MPLS and GMPLS
Traffic Engineering", January 2009.
[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", April 2009.
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Authors' Addresses
Dhruv Dhody
Huawei Technologies India Pvt Ltd
Leela Palace
Bangalore, Karnataka 560008
INDIA
EMail: dhruvd@huawei.com
Udayasree Palle
Huawei Technologies India Pvt Ltd
Leela Palace
Bangalore, Karnataka 560008
INDIA
EMail: Udayasreepalle@huawei.com
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