Internet DRAFT - draft-ietf-ccamp-gmpls-ason-routing-ospf
draft-ietf-ccamp-gmpls-ason-routing-ospf
Network Working Group Dimitri Papadimitriou
Internet Draft (Alcatel-Lucent)
Category: Experimental
Created: August 16, 2009
Expires: February 16, 2010
OSPFv2 Routing Protocols Extensions for ASON Routing
draft-ietf-ccamp-gmpls-ason-routing-ospf-09.txt
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Abstract
The ITU-T has defined an architecture and requirements for operating
an Automatically Switched Optical Network (ASON).
The Generalized Multiprotocol Label Switching (GMPLS) protocol suite
is designed to provide a control plane for a range of network
technologies including optical networks such as time division
multiplexing (TDM) networks including SONET/SDH and Optical Transport
Networks (OTNs), and lambda switching optical networks.
The requirements for GMPLS routing to satisfy the requirements of
ASON routing, and an evaluation of existing GMPLS routing protocols
are provided in other documents. This document defines extensions to
the OSPFv2 Link State Routing Protocol to meet the requirements for
routing in an ASON.
Note that this work is scoped to the requirements and evaluation
expressed in RFC 4258 and RFC 4652 and the ITU-T Recommendations
current when those documents were written. Future extensions of
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revisions of this work may be necessary if the ITU-T Recommendations
are revised or if new requirements are introduced into a revision of
RFC 4258.
Table of Contents
1. Introduction................................................. 3
1.1. Conventions Used In This Document.......................... 4
2. Routing Areas, OSPF Areas, and Protocol Instances............ 4
3. Reachability................................................. 5
3.1 Node IPv4 Local Prefix Sub-TLV.............................. 5
3.2 Node IPv6 Local Prefix Sub-TLV.............................. 6
4. Link Attribute............................................... 7
4.1 Local Adaptation............................................ 7
4.2 Bandwidth Accounting........................................ 8
5. Routing Information Scope.................................... 8
5.1 Terminology and Identification.............................. 8
5.2 Link Advertisement (Local and Remote TE Router ID Sub-TLV).. 9
5.3 Reachability Advertisement (Local TE Router ID Sub-TLV).... 10
6. Routing Information Dissemination........................... 11
6.1 Import/Export Rules........................................ 11
6.2 Discovery and Selection.................................... 12
6.2.1 Upward Discovery and Selection........................... 12
6.2.2 Downward Discovery and Selection......................... 13
6.2.3. Router Information Experimental Capabilities TLV........ 15
6.3 Loop Prevention............................................ 15
6.3.1 Associated RA ID......................................... 16
6.3.2 Processing............................................... 17
6.4 Resiliency................................................. 18
6.5 Neighbor Relationship and Routing Adjacency................ 19
6.6 Reconfiguration............................................ 19
7. OSPFv2 Scalability.......................................... 20
8. Security Considerations..................................... 20
9. IANA Considerations......................................... 20
10. Experimental Code Points................................... 21
10.1. Sub-TLVs of the Link TLV................................. 21
10.2. Sub-TLVs of the Node Attribute TLV....................... 21
10.3. Sub-TLVs of the Router Address TLV....................... 22
10.4. TLVs of the Router Information LSA....................... 22
11. References................................................. 23
11.1 Normative References...................................... 23
11.2 Informative References.................................... 24
12. Author's Address........................................... 25
Appendix 1: ASON Terminology................................... 26
Appendix 2: ASON Routing Terminology........................... 28
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1. Introduction
The Generalized Multiprotocol Label Switching (GMPLS) [RFC3945]
protocol suite is designed to provide a control plane for a range of
network technologies including optical networks such as time division
multiplexing (TDM) networks including SONET/SDH and Optical Transport
Networks (OTNs), and lambda switching optical networks.
The ITU-T defines the architecture of the Automatically Switched
Optical Network (ASON) in [G.8080].
[RFC4258] details the routing requirements for the GMPLS suite of
routing protocols to support the capabilities and functionality of
ASON control planes identified in [G.7715] and in [G.7715.1].
[RFC4652] evaluates the IETF Link State Routing Protocols against the
requirements identified in [RFC4258]. Section 7.1 of [RFC4652]
summarizes the capabilities to be provided by OSPFv2 [RFC2328] in
support of ASON routing. This document details the OSPFv2 specifics
for ASON routing.
Multi-layer transport networks are constructed from multiple networks
of different technologies operating in a client-server relationship.
The ASON routing model includes the definition of routing levels that
provide scaling and confidentiality benefits. In multi-level routing,
domains called routing areas (RAs) are arranged in a hierarchical
relationship. Note that as described in [RFC4652] there is no implied
relationship between multi-layer transport networks and multi-level
routing. The multi-level routing mechanisms described in this
document work for both single layer and multi-layer networks.
Implementations may support a hierarchical routing topology (multi-
level) for multiple transport network layers and/or a hierarchical
routing topology for a single transport network layer.
This document details the processing of the generic (technology-
independent) link attributes that are defined in [RFC3630],
[RFC4202], and [RFC4203] and that are extended in this document. As
detailed in Section 4.2, technology-specific traffic engineering
attributes (and their processing) may be defined in other documents
that complement this document.
Note that this work is scoped to the requirements and evaluation
expressed in [RFC4258] and [RFC4652] and the ITU-T Recommendations
current when those documents were written. Future extensions of
revisions of this work may be necessary if the ITU-T Recommendations
are revised or if new requirements are introduced into a revision of
[RFC4258].
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This document is classified as Experimental. Significant changes to
routing protocols are of concern to the stability of the Internet.
The extensions described in this document are intended for cautious
use in self-contained environments. The objective is to determine
whether these extensions are stable and functional, whether there is
a demand for implementation and deployment, and whether the
extensions have any impact on existing routing protocol deployments.
1.1. Conventions Used in This Document
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].
The reader is assumed to be familiar with the terminology and
requirements developed in [RFC4258] and the evaluation outcomes
detailed in [RFC4652].
General ASON terminology is provided in Appendix 1. ASON routing
terminology is described in Appendix 2.
2. Routing Areas, OSPF Areas, and Protocol Instances
An ASON routing area (RA) represents a partition of the data plane
and its identifier is used within the control plane as the
representation of this partition.
RAs are arranged in hierarchical levels such that any one RA may
contain multiple other RAs, and is wholly contained by a single RA.
Thus, an RA may contain smaller RAs inter-connected by links. The
limit of the subdivision results in an RA that contains just two
sub-networks interconnected by a single link.
An ASON RA can be mapped to an OSPF area, but the hierarchy of ASON
RA levels does not map to the hierarchy of OSPF routing areas.
Instead, successive hierarchical levels of RAs MUST be represented by
separate instances of the protocol. Thus, inter-level routing
information exchange (as described in Section 6) involves the export
and import of routing information between protocol instances.
An ASON RA may therefore be identified by the combination of its OSPF
instance identifier and its OSPF area identifier. With proper and
careful network-wide configuration, this can be achieved using just
the OSPF area identifier, and this process is RECOMMENDED in this
document. These concepts and the subsequent handling of network
reconfiguration is discussed in Section 6.
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3. Reachability
In order to advertise blocks of reachable address prefixes a
summarization mechanism is introduced that complements the
techniques described in [OSPF-NODE].
This extension takes the form of a network mask (a 32-bit number
indicating the range of IP addresses residing on a single IP
network/subnet). The set of local addresses are carried in an OSPFv2
TE LSA node attribute TLV (a specific sub-TLV is defined per address
family, i.e., IPv4 and IPv6, used as network-unique identifiers).
The proposed solution is to advertise the local address prefixes of
a router as new sub-TLVs of the (OSPFv2 TE LSA) Node Attribute top
level TLV. This document defines the following sub-TLVs:
- Node IPv4 Local Prefix sub-TLV: Length: variable
- Node IPv6 Local Prefix sub-TLV: Length: variable
3.1 Node IPv4 Local Prefix Sub-TLV
The Type field of the Node IPv4 Local Prefix sub-TLV is assigned a
value in the range 32768-32777 agreed by all participants in the
experiment. The Value field of this sub-TLV contains one or more
local IPv4 prefixes. The Length is measured in bytes and, as defined
in [RFC3630] reports the length in bytes of the Value part of the
sub-TLV. It is set to 8 x n, where n is the number of local IPv4
prefixes included in the sub-TLV.
The Node IPv4 Local Prefix sub-TLV has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length (8 x n) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Mask 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// ... //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Mask n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Network mask i: A 32-bit number indicating the IPv4 address mask
for the ith advertised destination prefix.
Each <Network mask, IPv4 Address> pair listed as part of this sub-
TLV represents a reachable destination prefix hosted by the
advertising Router ID.
The local addresses that can be learned from Opaque TE LSAs (that is,
the router address and TE interface addresses) SHOULD NOT be
advertised in the node IPv4 local prefix sub-TLV.
3.2 Node IPv6 Local Prefix Sub-TLV
The Type field of the Node IPv6 Local Prefix sub-TLV is assigned a
value in the range 32768-32777 agreed by all participants in the
experiment. The Value field of this sub-TLV contains one or more
local IPv6 prefixes. IPv6 Prefix representation uses [RFC5340]
Section A.4.1.
The Node IPv6 Local Prefix sub-TLV has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PrefixLength | PrefixOptions | (0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 Address Prefix 1 |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// ... //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PrefixLength | PrefixOptions | (0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 Address Prefix n |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Length reports the length of the Value part of the sub-TLV in
bytes. It is set to the sum over all of the local prefixes
included in the sub-TLV of
(4 + (number of 32-bit words in the prefix) * 4).
The encoding of each prefix potentially using fewer than four
32-bit words is described below.
PrefixLength: Length in bits of the prefix.
PrefixOptions: 8-bit field describing various capabilities
associated with the prefix (see [RFC5340] Section A.4.2).
IPv6 Address Prefix i: The ith IPv6 address prefix in the list.
Each prefix is encoded in an even multiple of 32-bit words using
the fewest pairs of 32-bit words necessary to include the entire
prefix. Thus, each prefix is encoded in either 64 or 128 bits
with trailing zero bit padding as necessary.
The local addresses that can be learned from TE LSAs, i.e., router
address and TE interface addresses, SHOULD NOT be advertised in the
node IPv6 local prefix sub-TLV.
4. Link Attribute
[RFC4652] provides a map between link attributes and characteristics
and their representation in sub-TLVs of the top level Link TLV of the
Opaque TE LSA [RFC3630] and [RFC4203], with the exception of the
Local Adaptation (see below). Advertisement of this information
SHOULD be supported on a per-layer basis, i.e., one Opaque TE LSA per
switching capability (and per bandwidth granularity, e.g., low-order
virtual container and high-order virtual container).
4.1 Local Adaptation
Local Adaptation is defined as a TE link attribute (i.e., sub-TLV)
that describes the cross/inter-layer relationships.
The Interface Switching Capability Descriptor (ISCD) TE Attribute
[RFC4202] identifies the ability of the TE link to support cross-
connection to another link within the same layer, and the ability to
use a locally terminated connection that belongs to one layer as a
data link for another layer (adaptation capability). However, the
information associated to the ability to terminate connections
within that layer (referred to as the termination capability) is
embedded with the adaptation capability.
For instance, a link between two optical cross-connects will contain
at least one ISCD attribute describing the lambda switching capable
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(LSC) switching capability. Whereas a link between an optical cross-
connect and an IP/MPLS LSR will contain at least two ISCD attributes:
one for the description of the LSC termination capability and one for
the packet switching capable (PSC) adaptation capability.
In OSPFv2, the Interface Switching Capability Descriptor (ISCD) is a
sub-TLV (of type 15) of the top-level Link TLV (of type 2) [RFC4203].
The adaptation and termination capabilities are advertised using two
separate ISCD sub-TLVs within the same top-level link TLV.
Per [RFC4202] and [RFC4203], an interface MAY have more than one
ISCD sub-TLV. Hence, the corresponding advertisements should not
result in any compatibility issues.
Further refinement of the ISCD sub-TLV for multi-layer networks is
outside the scope of this document.
4.2 Bandwidth Accounting
GMPLS Routing defines an Interface Switching Capability Descriptor
(ISCD) that delivers, among other things, information about the
(maximum/minimum) bandwidth per priority that an LSP can make use of.
Per [RFC4202] and [RFC4203], one or more ISCD sub-TLVs can be
associated with an interface. This information, combined with the
Unreserved Bandwidth (sub-TLV defined in [RFC3630], Section 2.5.8),
provides the basis for bandwidth accounting.
In the ASON context, additional information may be included when the
representation and information in the other advertised fields are
not sufficient for a specific technology (e.g., SDH). The definition
of technology-specific information elements is beyond the scope of
this document. Some technologies will not require additional
information beyond what is already defined in [RFC3630], [RFC4202],
and [RFC4203].
5. Routing Information Scope
5.1. Terminology and Identification
The definition of short-hand terminology introduced in [RFC4652] is
repeated here for clarity.
- Pi is a physical (bearer/data/transport plane) node.
- Li is a logical control plane entity that is associated to a single
data plane (abstract) node. Each Li is identified by a unique TE
Router-ID. The latter is a control plane identifier, defined as the
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Router Address top level TLV of the Type 1 TE LSA [RFC3630].
Note: the Router Address top-level TLV definition, processing and
usage remain per [RFC3630]. This TLV specifies a stable IP address
of the advertising router (Ri) that is always reachable if there is
any IP connectivity to it (e.g. via the Data Communication
Network). Moreover, each advertising router advertises a unique,
reachable IP address for each Pi on behalf of which it makes
advertisements.
- Ri is a logical control plane entity that is associated to a
control plane "router". The latter is the source for topology
information that it generates and shares with other control plane
"routers". The Ri is identified by the (advertising) Router-ID
(32-bit) [RFC2328].
The Router-ID, which is represented by Ri and which corresponds to
the RC-ID [RFC4258], does not enter into the identification of the
logical entities representing the data plane resources such as
links. The Routing DataBase (RDB) is associated to the Ri.
Note: Aside from the Li/Pi mappings, these identifiers are not
assumed to be in a particular entity relationship except that the Ri
may have multiple Lis in its scope. The relationship between Ri and
Li is simple at any moment in time: an Li may be advertised by only
one Ri at any time. However, an Ri may advertise a set of one or
more Lis. Hence, the OSPFv2 routing protocol must support a single
Ri advertising on behalf of more than one Li.
5.2 Link Advertisement (Local and Remote TE Router ID sub-TLV)
A Router-ID (Ri) advertising on behalf multiple TE Router_IDs (Lis)
creates a 1:N relationship between the Router-ID and the TE
Router-ID. As the link local and link remote (unnumbered) ID
association is not unique per node (per Li unicity), the
advertisement needs to indicate the remote Lj value and rely on the
initial discovery process to retrieve the [Li;Lj] relationship. In
brief, as unnumbered links have their ID defined on per Li bases,
the remote Lj needs to be identified to scope the link remote ID to
the local Li. Therefore, the routing protocol MUST be able to
disambiguate the advertised TE links so that they can be associated
with the correct TE Router-ID.
For this purpose, a new sub-TLV of the (OSPFv2 TE LSA) top level
Link TLV is introduced that defines the local and the remote
TE Router-ID.
The Type field of the Local and Remote TE Router-ID sub-TLV is
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assigned a value in the range 32768-32777 agreed by all participants
in the experiment. The Length field takes the value 8. The Value
field of this sub-TLV contains 4 octets of Local TE Router Identifier
followed by 4 octets of Remote TE Router Identifier. The value of the
Local and the Remote TE Router Identifier SHOULD NOT be set to 0.
The format of the Local and Remote TE Router-ID sub-TLV is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length (8) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local TE Router Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote TE Router Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This sub-TLV is only required to be included as part of the top
level Link TLV if the Router-ID is advertising on behalf of more
than one TE Router-ID. In any other case, this sub-TLV SHOULD be
omitted except if operator plans to start of with 1 Li and
progressively add more Li's (under the same Ri) such as to maintain
consistency.
Note: The Link ID sub-TLV that identifies the other end of the link
(i.e., Router-ID of the neighbor for point-to-point links) MUST
appear exactly once per Link TLV. This sub-TLV MUST be processed as
defined in [RFC3630].
5.3 Reachability Advertisement (Local TE Router ID sub-TLV)
When the Router-ID is advertised on behalf of multiple TE Router-IDs
(Lis), the routing protocol MUST be able to associate the advertised
reachability information with the correct TE Router-ID.
For this purpose, a new sub-TLV of the (OSPFv2 TE LSA) top level
Node Attribute TLV is introduced. This TLV associates the local
prefixes (see above) to a given TE Router-ID.
The Type field of the Local TE Router-ID sub-TLV is assigned a value
in the range 32768-32777 agreed by all participants in the
experiment. The Length field takes the value 4. The Value field of
this sub-TLV contains the Local TE Router Identifier [RFC3630]
encoded over 4 octets.
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The format of the Local TE Router-ID sub-TLV is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length (4) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local TE Router Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This sub-TLV is only required to be included be included as part of
the Node Attribute TLV if the Router-ID is advertising on behalf of
more than one TE Router-ID. In any other case, this sub-TLV SHOULD
be omitted.
6. Routing Information Dissemination
An ASON routing area (RA) represents a partition of the data plane
and its identifier is used within the control plane as the
representation of this partition. A RA may contain smaller RAs inter-
connected by links. The limit of the subdivision results is an RA
that contains two sub-networks interconnected by a single link. ASON
RA levels do not reflect routing protocol levels (such as OSPF
areas).
Successive hierarchical levels of RAs can be represented by separate
instances of the protocol.
Routing controllers (RCs) supporting RAs disseminate information
downward and upward in this hierarchy. The vertical routing
information dissemination mechanisms described in this section do not
introduce or imply a new OSPF routing area hierarchy. RCs supporting
RAs at multiple levels are structured as separate OSPF instances with
routing information exchanges between levels described by import and
export rules operating between OSPF instances.
The implication is that an RC that performs import/export of routing
information as described in this document does not implement an Area
Border Router (ABR) functionality.
6.1 Import/Export Rules
RCs supporting RAs disseminate information upward and downward in the
hierarchy by importing/exporting routing information as Opaque TE
LSAs (Opaque Type 1) of LS Type 10. The information that MAY be
exchanged between adjacent levels includes the Router-Address, Link,
and Node-Attribute top-level TLVs.
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The Opaque TE LSA import/export rules are governed as follows:
- If the export target interface is associated with the same RA as is
associated with the import interface, the Opaque LSA MUST NOT be
imported.
- If a match is found between the Advertising Router-ID in the
header of the received Opaque TE LSA and one of the Router-IDs
belonging to the RA of the export target interface, the Opaque LSA
MUST NOT be imported.
- If these two conditions are not met the Opaque TE LSA MAY be
imported according to local policy. If imported, the LSA MAY be
disseminated according to local policy. If disseminated, the normal
OSPF flooding rules MUST be followed and the Advertising Router-ID
MUST be set to the importing router's router-ID.
The imported/exported routing information content MAY be transformed,
e.g., filtered or aggregated, as long as the resulting routing
information is consistent. In particular, when more than one RC is
bound to adjacent levels and both are allowed to import/export
routing information, it is expected that these transformation are
performed in a consistent manner. Definition of these policy-based
mechanisms is outside the scope of this document.
In practice, and in order to avoid scalability and processing
overhead, routing information imported/exported downward/upward in
the hierarchy is expected to include reachability information (see
Section 3) and, upon strict policy control, link topology
information.
6.2 Discovery and Selection
6.2.1 Upward Discovery and Selection
In order to discover RCs that are capable of disseminating routing
information up the routing hierarchy, the following capability
descriptor bit is set in the OSPF Router Information Experimental
Capabilities TLV (see Section 6.2.3) carried in the Router
Information LSA ([RFC4970]).
- U bit: When set, this flag indicates that the RC is capable of
disseminating routing information upward to the adjacent level.
In the case that multiple RCs are advertized from the same RA with
their U bit set, the RC with the highest Router-ID, among those RCs
with the U bit set, SHOULD be selected as the RC for upward
dissemination of routing information. The other RCs MUST NOT
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participate in the upward dissemination of routing information as
long as the opaque LSA information corresponding to the highest
Router-ID RC does not reach MaxAge. This mechanism prevents more than
one RC advertizing routing information upward in the routing
hierarchy from the same RA.
Note that if the information to allow the selection of the RC that
will be used to disseminate routing information up the hierarchy from
a specific RA cannot be discovered automatically, it MUST be manually
configured.
Once an RC has been selected, it remains unmodified even if an RC
with a higher Router-ID is introduced and advertizes its capability
to disseminate routing information upward the adjacent level (i.e.,
U bit set). This hysteresis mechanism prevents from disturbing the
upward routing information dissemination process in case, e.g., of
flapping.
6.2.2 Downward Discovery and Selection
The same discovery mechanism is used for selecting the RC responsible
for dissemination of routing information downward in the hierarchy.
However, an additional restriction MUST be applied such that the RC
selection process takes into account that an upper level may be
adjacent to one or more lower (RA) levels. For this purpose a
specific TLV indexing the (lower) RA ID to which the RC's are capable
of disseminating routing information is needed.
The Downstream Associated RA ID TLV is carried in the OSPF Router
Information LSA [RFC4970]. The Type field of the Downstream
Associated RA ID TLV is assigned a value in the range 32768-32777
agreed by all participants in the experiment. The Length of this TLV
is n x 4 octets. The Value field of this sub-TLV contains the list of
Associated RA IDs. Each Associated RA ID value is encoded following
the OSPF area ID (32 bits) encoding rules defined in [RFC2328].
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The format of the Downstream Associated RA ID TLV is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length (4 x n) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Associated RA ID 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// ... //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Associated RA ID n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
To discover RCs that are capable to disseminate routing information
downward the routing hierarchy, the following capability descriptor
bit is set in the OSPF Router Information Experimental Capabilities
TLV (see Section 6.2.3) carried in the Router Information LSA
([RFC4970]).
Note that the Downstream Associated RA ID TLV MUST be present when
the D bit is set.
- D bit: when set, this flag indicates that the RC is capable to
disseminate routing information downward the adjacent levels.
If multiple RCs are advertised for the same Associated RA ID, the RC
with the highest Router ID, among the RCs with the D bit set, MUST be
selected as the RC for downward dissemination of routing information.
The other RCs for the same Associated RA ID MUST NOT participate in
the downward dissemination of routing information as long as the
opaque LSA information corresponding to the highest Router ID RC does
not reach MaxAge. This mechanism prevents from having more than one
RC advertizing routing information downward the routing hierarchy.
Note that if the information to allow the selection of the RC that
will be used to disseminate routing information down the hierarchy to
a specific RA cannot be discovered automatically, it MUST be manually
configured.
The OSPF Router information Opaque LSA (Opaque type of 4, Opaque ID
of 0) and its content, in particular the Router Informational
Capabilities TLV [RFC4970] and TE Node Capability Descriptor TLV
[RFC5073], MUST NOT be re-originated.
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6.2.3. Router Information Experimental Capabilities TLV
A new TLV is defined for inclusion in the Router Information LSA to
carry experimental capabilities because the assignment policy for
bits in the Router Informational Capabilities TLV is "Standards
Action" [RFC5226] prohibiting its use from Experimental documents.
The format of the Router Information Experimental Capabilities TLV is
as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Experimental Capabilities |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type A value in the range 32768-32777 agreed by all
participants in the experiment.
Length A 16-bit field that indicates the length of the value
portion in octets and will be a multiple of 4 octets
dependent on the number of capabilities advertised.
Initially, the length will be 4, denoting 4 octets of
informational capability bits.
Value A variable length sequence of capability bits rounded
to a multiple of 4 octets padded with undefined bits.
The following experimental capability bits are assigned:
Bit Capabilities
0 The U bit (see Section 6.2.1)
1 The D bit (see Section 6.2.2)
6.3 Loop Prevention
When more than one RC is bound to an adjacent level of the hierarchy,
and is configured or selected to redistribute routing information
upward and downward, a specific mechanism is required to avoid
looping of routing information. Looping is the re-introduction of
routing information that has been advertized from the upper level
back to the upper level. This specific case occurs, for example, when
the RC advertizing routing information downward in the hierarchy is
not the same one that advertizes routing upward in the hierarchy.
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When these conditions are met, it is necessary to have a means by
which an RC receiving an Opaque TE LSA imported/exported downward by
an RC associated to the same RA, does not import/export the content
of this LSA back upward into the (same) upper level.
Note that configuration and operational simplification can be
obtained when both functionalities are configured on a single RC (per
pair of adjacent levels) fulfilling both roles. Figure 1 provides an
example where such simplification applies.
....................................................
. .
. RC_5 ------------ RC_6 .
. | | .
. | | RA_Y .
Upper . ********* ********* .
Layer ............* RC_1a *.........* RC_2a *.............
__________________* | *_________* | *__________________
............* RC_1b *... ...* RC 2b *.............
Lower . ********* . . ********* .
Layer . | . . | .
. RA_Z | . . | RA_X .
. RC_3 . . RC_4 .
. . . .
........................ .........................
Figure 1. Hierarchical Environment (Example)
In this case, the procedure described in this section MAY be
omitted, as long as these conditions are permanently guaranteed. In
all other cases, without exception, the procedure described in this
section MUST be applied.
6.3.1 Associated RA ID
We need some way of filtering the downward/upward re-originated
Opaque TE LSA. Per [RFC5250], the information contained in Opaque
LSAs may be used directly by OSPF. By adding the RA ID associated
with the incoming routing information the loop prevention problem can
be solved.
This additional information, referred to as the Associated RA ID, MAY
be carried in opaque LSAs that including any of the following top
level TLVs:
- the Router Address top level TLV
- the Link top level TLV
- the Node Attribute top level TLV.
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The Associated RA ID reflects the identifier of the area from which
the routing information is received. For example, for a multi-level
hierarchy, this identifier does not reflect the originating RA ID, it
will reflect the RA from which the routing information is imported.
The Type field of the Associated RA ID sub-TLV is assigned a value in
the range 32768-32777 agreed by all participants in the experiment.
The same value MUST be used for the Type regardless of which TLV the
sub-TLV appears in.
The Length of the Associated RA ID TLV is 4 octets. The Value field
of this sub-TLV contains the Associated RA ID. The Associated RA ID
value is encoded following the OSPF area ID (32 bits) encoding rules
defined in [RFC2328].
The format of the Associated RA ID TLV is defined as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length (4) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Associated RA ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.3.2 Processing
When fulfilling the rules detailed in Section 6.1 a given Opaque LSA
is imported/exported downward or upward the routing hierarchy, the
Associated RA ID TLV is added to the received opaque LSA list of TLVs
such as to identify the area from which this routing information has
been received.
When the RC adjacent to the lower or upper level routing level
receives this opaque LSA, the following rule is applied (in addition
the rule governing the import/export of opaque LSAs as detailed in
Section 6.1).
- If a match is found between the Associated RA ID of the received
Opaque TE LSA and the RA ID belonging to the area of the export
target interface, the Opaque TE LSA MUST NOT be imported.
- Otherwise, this opaque LSA MAY be imported and disseminated
downward or upward the routing hierarchy following the OSPF
flooding rules.
This mechanism ensures that no race condition occurs when the
conditions depicted in Figure 2 are met.
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RC_5 ------------- RC_6
| |
| | RA_Y
Upper ********* *********
Layer ............* RC_1a *.........* RC_2a *.............
__________________* | *_________* | *__________________
............* RC_1b *.........* RC 2b *.............
Lower ********* *********
Layer | |
| | RA_X
RC_3 --- . . . --- RC_4
Figure 2. Race Condition Prevention (Example)
Assume that RC_1b is configured for exporting routing information
upward toward RA_Y (upward the routing hierarchy) and that RC_2a is
configured for exporting routing information toward RA_X (downward
the routing hierarchy).
Assumes that routing information advertised by RC_3 would reach
RC_4 faster across RA_Y through hierarchy.
If RC_2b is not able to prevent from importing that information,
RC_4 may receive that information before the same advertisement
would propagate in RA_X (from RC_3) to RC_4. For this purpose RC_1a
inserts the Associated RA X to the imported routing information
from RA_X. Because RC_2b finds a match between the Associated RA
ID (X) of the received Opaque TE LSA and the ID (X) of the RA of the
export target interface, this LSA MUST NOT be imported.
6.4 Resiliency
OSPF creates adjacencies between neighboring routers for the purpose
of exchanging routing information. After a neighbor has been
discovered, bidirectional communication is ensured, and a routing
adjacency is formed between RCs, loss of communication may result in
partitioned OSPF areas and so in partitioned RAs.
Consider for instance (see Figure 2.) the case where RC_1a and RC_1b
is configured for exchanging routing information downward and upward
RA_Y, resp., and that RC_2a and RC_2b are not configured for
exchanging routing any routing information toward RA_X. If the
communication between RC_1a and RC_2a is broken (due, e.g., to RC_5 -
RC_6 communication failure), RA_Y could be partitioned.
In these conditions, it is RECOMMENDED that RC_2a be re-configurable
such as to allow for exchanging routing information downward to RA_X.
This reconfiguration MAY be performed manually or automatically. In
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the latter cases, automatic reconfiguration uses the mechanism
described in Section 6.2 (forcing MaxAge of the corresponding opaque
LSA information in case the originating RC becomes unreachable).
Manual reconfiguration MUST be supported.
6.5 Neighbor Relationship and Routing Adjacency
It is assumed that (point-to-point) IP control channels are
provisioned/configured between RCs belonging to the same routing
level. Provisioning/configuration techniques are outside the scope
of this document.
Once established, the OSPF Hello Protocol is responsible for
establishing and maintaining neighbor relationships. This protocol
also ensures that communication between neighbors is bidirectional.
Routing adjacency can subsequently be formed between RCs following
mechanisms defined in [RFC2328].
6.6 Reconfiguration
This section details the RA ID reconfiguration steps.
Reconfiguration of the RA ID occurs when the RA ID is modified
e.g. from value Z to value X or Y (see Figure 2.).
The process of reconfiguring the RA ID involves:
- Disable the import/export of routing information from the upper
and lower level (to prevent any LS information update).
- Change the RA ID of the local level RA from e.g. Z to X or Y.
Perform an LSDB checksum on all routers to verify that LSDB are
consistent.
- Enable import of upstream and downstream routing information such
as to re-synchronize local level LSDB from any LS information that
may have occurred in an upper or a lower routing level.
- Enable export of routing information downstream such as to re-sync
the downstream level with the newly reconfigured RA ID (as part of
the re-advertised Opaque TE LSA).
- Enable export of routing information upstream such as to re-sync
the upstream level with the newly reconfigured RA ID (as part of
the re-advertised Opaque TE LSA).
Note that the re-sync operation needs to be carried out only between
the directly adjacent upper and lower routing level.
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7. OSPFv2 Scalability
- Routing information exchange upward/downward in the hierarchy
between adjacent RAs SHOULD by default be limited to reachability
information. In addition, several transformations such as prefix
aggregation are RECOMMENDED when allowing decreasing the amount of
information imported/exported by a given RC without impacting
consistency.
- Routing information exchange upward/downward in the hierarchy
involving TE attributes MUST be under strict policy control. Pacing
and min/max thresholds for triggered updates are strongly
RECOMMENDED.
- The number of routing levels MUST be maintained under strict policy
control.
8. Security Considerations
This document specifies the contents and processing of Opaque LSAs
in OSPFv2 [RFC2328]. Opaque TE and RI LSAs defined in this document
are not used for SPF computation, and so have no direct effect on IP
routing. Additionally, ASON routing domains are delimited by the
usual administrative domain boundaries.
Any mechanisms used for securing the exchange of normal OSPF LSAs
can be applied equally to all Opaque TE and RI LSAs used in the ASON
context. Authentication of OSPFv2 LSA exchanges (such as OSPF
cryptographic authentication [RFC2328] and [OSPF-CA]) can be used to
secure against passive attacks and provide significant protection
against active attacks. [OSPF-CA] defines a mechanism for
authenticating OSPF packets by making use of the HMAC algorithm in
conjunction with the SHA family of cryptographic hash functions.
[RFC2154] adds i) digital signatures to authenticate OSPF LSA data,
ii) certification mechanism for distribution of routing information,
and iii) use a neighbor-to-neighbor authentication algorithm to
protect local OSPFv2 protocol exchanges.
9. IANA Considerations
This document makes no requests for IANA action.
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10. Experimental Code Points
This document is classified as Experimental. It defines new TLVs and
sub-TLVs for inclusion in OSPF LSAs. According to the assignment
policies for the registries of codepoints for these TLVs and sub-
TLVs, values must be assigned from the experimental ranges and must
not be recorded by IANA or mentioned in this document.
The following sections summarise the TLVs and sub-TLVs concerned.
10.1. Sub-TLVs of the Link TLV
This document defines the following sub-TLVs of the Link TLV carried
in the OSPF TE LSA:
- Local and Remote TE Router ID sub-TLV
- Associated RA ID sub-TLV
The defining text for code point assignment for sub-TLVs of the OSPF
TE Link TLV says ([RFC3630]):
o Types in the range 10-32767 are to be assigned via Standards
Action.
o Types in the range 32768-32777 are for experimental use; these
will not be registered with IANA, and MUST NOT be mentioned by
RFCs.
o Types in the range 32778-65535 are not to be assigned at this
time.
That means that the new sub-TLVs must be assigned type values from
the range 32768-32777. It is a matter for experimental
implementations to assign their own code points, and to agree with
cooperating implementations participating in the same experiments
what values to use.
Note that the same value for the Associated RA ID sub-TLV MUST be
used when it appears in the Link TLV, the Node Attribute TLV, and the
Router Address TLV.
10.2. Sub-TLVs of the Node Attribute TLV
This document defines the following sub-TLVs of the Node Attribute
TLV carried in the OSPF TE LSA.
- Node IPv4 Local Prefix sub-TLV
- Node IPv6 Local Prefix sub-TLV
- Local TE Router ID sub-TLV
- Associated RA ID sub-TLV
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The defining text for code point assignment for sub-TLVs of the OSPF
Node Attribute TLV says ([OSPF-NODE]):
o Types in the range 3-32767 are to be assigned via Standards
Action.
o Types in the range 32768-32777 are for experimental use; these
will not be registered with IANA, and MUST NOT be mentioned by
RFCs.
o Types in the range 32778-65535 are not to be assigned at this
time. Before any assignments can be made in this range, there
MUST be a Standards Track RFC that specifies IANA
Considerations that covers the range being assigned.
That means that the new sub-TLVs must be assigned type values from
the range 32768-32777. It is a matter for experimental
implementations to assign their own code points, and to agree with
cooperating implementations participating in the same experiments
what values to use.
Note that the same value for the Associated RA ID sub-TLV MUST be
used when it appears in the Link TLV, the Node Attribute TLV, and the
Router Address TLV.
10.3. Sub-TLVs of the Router Address TLV
The OSPF Router Address TLV is defined in [RFC3630]. No sub-TLVs are
defined in that document and there is no registry or allocation
policy for sub-TLVs of the Router Address TLV.
This document defines the following new sub-TLVs for inclusion in the
OSPF Router Address TLV:
- Associated RA ID sub-TLV
Note that the same value for the Associated RA ID sub-TLV MUST be
used when it appears in the Link TLV, the Node Attribute TLV, and the
Router Address TLV. This is consistent with potential for a future
definition of a registry with policies that match the other existing
registries.
10.4. TLVs of the Router Information LSA
This document defines two new TLVs to be carried in the Router
Information LSA.
- Downstream Associated RA ID TLV
- Router Information Experimental Capabilities TLV
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The defining text for code point assignment for TLVs of the OSPF
Router Information LSA says ([RFC4970]):
o 1-32767 Standards Action.
o Types in the range 32768-32777 are for experimental use; these
will not be registered with IANA and MUST NOT be mentioned by
RFCs.
o Types in the range 32778-65535 are reserved and are not to be
assigned at this time. Before any assignments can be made in
this range, there MUST be a Standards Track RFC that specifies
IANA Considerations that covers the range being assigned.
That means that the new TLVs must be assigned type values from the
range 32768-32777. It is a matter for experimental implementations to
assign their own code points, and to agree with cooperating
implementations participating in the same experiments what values to
use.
11. References
11.1 Normative References
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2154] Murphy, S., Badger, M. and B. Wellington, "OSPF with
Digital Signatures", RFC 2154, June 1997.
[RFC2328] J. Moy, "OSPF Version 2", RFC 2328, STD 54, April 1998.
[RFC3630] D. Katz et al. "Traffic Engineering (TE) Extensions to
OSPF Version 2", RFC 3630, September 2003.
[RFC3945] E.Mannie, Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945, October 2004.
[RFC4202] K. Kompella (Editor) et al., "Routing Extensions in
Support of Generalized MPLS," RFC 4202, October 2005.
[RFC4203] K. Kompella (Editor) et al., "OSPF Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)," RFC 4203, October 2005.
[RFC4970] A. Lindem et al., "Extensions to OSPF for Advertising
Optional Router Capabilities", RFC 4970, July 2007.
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[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
OSPF Opaque LSA Option", RFC 5250, July 2008.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.
[OSPF-NODE] R. Aggarwal and K. Kompella, "Advertising a Router's
Local Addresses in OSPF TE Extensions", draft-ietf-ospf-
te-node-addr, work in progress.
11.2 Informative References
[RFC4258] D.Brungard (Ed.) et al. "Requirements for Generalized
MPLS (GMPLS) Routing for Automatically Switched Optical
Network (ASON)," RFC 4258, November 2005.
[RFC4652] D.Papadimitriou (Ed.) et al. "Evaluation of existing
Routing Protocols against ASON Routing Requirements",
RFC 4652, October 2006.
[RFC5073] J.P.Vasseur et al., "Routing extensions for discovery of
Traffic Engineering Node Capabilities", RFC 5073,
December 2007.
[OSPF-CA] Bhatia, M., Manral, V., White, R., and M., Barnes, "OSPF
HMAC-SHA Cryptographic Authentication", draft-ietf-ospf-
hmac-sha, work in progress.
For information on the availability of ITU Documents, please see
http://www.itu.int
[G.7715] ITU-T Rec. G.7715/Y.1306, "Architecture and
Requirements for the Automatically Switched Optical
Network (ASON)," June 2002.
[G.7715.1] ITU-T Draft Rec. G.7715.1/Y.1706.1, "ASON Routing
Architecture and Requirements for Link State Protocols,"
November 2003.
[G.8080] ITU-T Rec. G.8080/Y.1304, "Architecture for the
Automatically Switched Optical Network (ASON),"
November 2001 (and Revision, January 2003).
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12. Author's Address
Dimitri Papadimitriou
Alcatel-Lucent Bell
Copernicuslaan 50
B-2018 Antwerpen
Belgium
Phone: +32 3 2408491
EMail: dimitri.papadimitriou@alcatel-lucent.be
Acknowledgements
The authors would like to thank Dean Cheng, Acee Lindem, Pandian
Vijay, Alan Davey, Adrian Farrel, Deborah Brungard, and Ben Campbell
for their useful comments and suggestions.
Lisa Dusseault and Jari Arkko provided useful comments during IESG
review.
Question 14 of Study Group 15 of the ITU-T provided useful and
constructive input.
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Appendix 1: ASON Terminology
This document makes use of the following terms:
Administrative domain: (see Recommendation G.805) for the purposes of
[G7715.1] an administrative domain represents the extent of resources
which belong to a single player such as a network operator, a service
provider, or an end-user. Administrative domains of different players
do not overlap amongst themselves.
Control plane: performs the call control and connection control
functions. Through signaling, the control plane sets up and releases
connections, and may restore a connection in case of a failure.
(Control) Domain: represents a collection of (control) entities that
are grouped for a particular purpose. The control plane is subdivided
into domains matching administrative domains. Within an
administrative domain, further subdivisions of the control plane are
recursively applied. A routing control domain is an abstract entity
that hides the details of the RC distribution.
External NNI (E-NNI): interfaces are located between protocol
controllers between control domains.
Internal NNI (I-NNI): interfaces are located between protocol
controllers within control domains.
Link: (see Recommendation G.805) a "topological component" which
describes a fixed relationship between a "subnetwork" or "access
group" and another "subnetwork" or "access group". Links are not
limited to being provided by a single server trail.
Management plane: performs management functions for the Transport
Plane, the control plane and the system as a whole. It also provides
coordination between all the planes. The following management
functional areas are performed in the management plane: performance,
fault, configuration, accounting and security management
Management domain: (see Recommendation G.805) a management domain
defines a collection of managed objects which are grouped to meet
organizational requirements according to geography, technology,
policy or other structure, and for a number of functional areas such
as configuration, security, (FCAPS), for the purpose of providing
control in a consistent manner. Management domains can be disjoint,
contained or overlapping. As such the resources within an
administrative domain can be distributed into several possible
overlapping management domains. The same resource can therefore
belong to several management domains simultaneously, but a management
domain shall not cross the border of an administrative domain.
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Subnetwork Point (SNP): The SNP is a control plane abstraction that
represents an actual or potential transport plane resource. SNPs (in
different subnetwork partitions) may represent the same transport
resource. A one-to-one correspondence should not be assumed.
Subnetwork Point Pool (SNPP): A set of SNPs that are grouped together
for the purposes of routing.
Termination Connection Point (TCP): A TCP represents the output of a
Trail Termination function or the input to a Trail Termination Sink
function.
Transport plane: provides bi-directional or unidirectional transfer
of user information, from one location to another. It can also
provide transfer of some control and network management information.
The Transport Plane is layered; it is equivalent to the Transport
Network defined in G.805 Recommendation.
User Network Interface (UNI): interfaces are located between protocol
controllers between a user and a control domain. Note: there is no
routing function associated with a UNI reference point.
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Appendix 2: ASON Routing Terminology
This document makes use of the following terms:
Routing Area (RA): a RA represents a partition of the data plane and
its identifier is used within the control plane as the representation
of this partition. Per [G.8080] a RA is defined by a set of sub-
networks, the links that interconnect them, and the interfaces
representing the ends of the links exiting that RA. A RA may contain
smaller RAs inter-connected by links. The limit of subdivision
results in a RA that contains two sub-networks interconnected by a
single link.
Routing Database (RDB): repository for the local topology, network
topology, reachability, and other routing information that is updated
as part of the routing information exchange and may additionally
contain information that is configured. The RDB may contain routing
information for more than one Routing Area (RA).
Routing Components: ASON routing architecture functions. These
functions can be classified as protocol independent (Link Resource
Manager or LRM, Routing Controller or RC) and protocol specific
(Protocol Controller or PC).
Routing Controller (RC): handles (abstract) information needed for
routing and the routing information exchange with peering RCs by
operating on the RDB. The RC has access to a view of the RDB. The RC
is protocol independent.
Note: Since the RDB may contain routing information pertaining to
multiple RAs (and possibly to multiple layer networks), the RCs
accessing the RDB may share the routing information.
Link Resource Manager (LRM): supplies all the relevant component and
TE link information to the RC. It informs the RC about any state
changes of the link resources it controls.
Protocol Controller (PC): handles protocol specific message exchanges
according to the reference point over which the information is
exchanged (e.g. E-NNI, I-NNI), and internal exchanges with the RC.
The PC function is protocol dependent.
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Full Copyright Statement
Copyright (c) 2009 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 in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
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