Network Working Group K. Kompella (Juniper Networks)
Internet Draft Y. Rekhter (Cisco Systems)
Expiration Date: May 2001 A. Banerjee (Calient Networks)
J. Drake (Calient Networks)
G. Bernstein (Ciena)
D. Fedyk (Nortel Networks)
E. Mannie (GTS Network)
D. Saha (Tellium)
V. Sharma (Tellabs)
OSPF Extensions in Support of Generalized MPLS
draft-kompella-ospf-gmpls-extensions-00.txt
1. Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as ``work in progress.''
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
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2. Abstract
This document specifies extensions to the OSPF routing protocol in
support of Generalized Multi-Protocol Label Switching (previously
known as Multi-Protocol Lambda Switching).
3. Introduction
This document specifies extensions to the OSPF routing protocol in
support of carrying link state information for Generalized Multi-
Protocol Label Switching (GMPLS, previously known as Multi-Protocol
Lambda Switching, MPL(ambda)S). For motivations and overall
architecture of MPL(ambda)S see [1]. The set of required
enhancements to OSPF are outlined in [2]. This document enhances the
routing extensions [3] required to support MPLS Traffic Engineering.
Some of these enhancements also need to be carried in the signaling
protocols [6].
The organization of the remainder of the document is as follows. In
Section 4, we describe the types of links that may be advertised in
OSPF TE LSAs. In Section 5, we define a new set of Type/Length/Value
(TLV) triplets, and describe their formats.
4. GMPLS TE Links
Traditionally, a TE link is advertised as an adjunct to a "regular"
OSPF link, i.e., an OSPF adjacency is brought up on the link, and
when the link is up, both the regular SPF properties of the link
(basically, the SPF metric) and the TE properties of the link are
then advertised.
However, GMPLS challenges this notion in three ways. First, links
that are not capable of sending and receiving on a packet-by-packet
basis may yet have TE properties; however, an OSPF adjacency cannot
be brought up on such links. Second, a Label Switched Path can be
advertised as a point-to-point TE link (see [LSP-HIER]); thus, an
advertised TE link need no longer be between two OSPF neighbors.
Finally, a number of links may be advertised as a single TE link
(perhaps for improved scalability), so again, there is no longer a
one-to-one association of a regular adjacency and a TE link.
Thus we have a more general notion of a TE link. A TE link is a
"logical" link that has TE properties, some of which may be
configured on the advertising Label Switching Router (LSR), others
which may be obtained from other LSRs by means of some protocol, and
yet others which may be deduced from the component(s) of the TE link.
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A TE link between a pair of LSRs doesn't imply the existence of an
OSPF adjacency between these LSRs. A TE link must also have some
means by which the advertising LSR can know of its liveness (this
means may be OSPF hellos, but is not limited to OSPF hellos). When
an LSR knows that a TE link is up, and can determine the TE link's TE
properties, the LSR may then advertise that link to its (regular)
OSPF neighbors using the TE TLVs. In this document, we call the
interfaces over which regular OSPF adjacencies are established
"control channels".
[3] defines the canonical TE properties, and says how to associate TE
properties to regular (packet-switched) links. This document extends
the set of TE properties, and also says how to associate TE
properties with non-packet-switched links such as links between
Optical Cross-Connects (OXCs). [5] says how to associate TE
properties with Label Switched Paths; [4] says how to associate TE
properties with a "bundle" of links.
4.1. Excluding data traffic from control channels
The control channels between nodes in a GMPLS network, such as OXCs
(see [1], [2]), SONET cross-connects and/or routers, are generally
meant for control and administrative traffic. These control channels
are advertised into OSPF as normal IS links as mentioned in the
previous section; this allows the routing of (for example) RSVP
messages and telnet sessions. However, if routers on the edge of the
optical domain attempt to forward data traffic over these channels,
the channel capacity will quickly be exhausted.
If one assumes that data traffic is sent to BGP destinations, and
control traffic to IGP destinations, then one can exclude data
traffic from the control plane by restricting BGP nexthop resolution.
(It is assumed that OXCs are not BGP speakers.) Suppose that a
router R is attempting to install a route to a BGP destination D. R
looks up the BGP nexthop for D in its IGP's routing table. Say R
finds that the path to the nexthop is over interface I. R then
checks if it has an entry in its Link State database associated with
the interface I. If it does, and the link is not packet-switch
capable (see [5]), R installs a discard route for destination D.
Otherwise, R installs (as usual) a route for destination D with
nexthop I. Note that R need only do this check if it has packet-
switch incapable links; if all of its links are packet-switch
capable, then clearly this check is redundant.
Other techniques for excluding data traffic from control channels may
also be needed.
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5. OSPF Routing Enhancements
In this section we define the enhancements to the TE properties of
GMPLS TE links that can be announced in OSPF TE LSAs. The Traffic
Engineering (TE) LSA, which is an opaque LSA with area flooding scope
[3], has only one top-level Type/Length/Value (TLV) triplet and has
one or more nested TLVs for extensibility. The top-level TLV can
take one of two values (1) Router Address or (2) Link. In this
document, we enhance the sub-TLVs for the Link TLV in support of
GMPLS. Specifically, we add the following sub-TLVs:
1. Outgoing Interface Identifier,
2. Incoming Interface Identifier,
3. Link Protection Type,
4. Link Descriptor, and
5. Shared Risk Link Group.
This brings the list of sub-TLVs of the TE Link TLV to:
Sub-TLV Type Length Name
1 1 Link type
2 4 Link ID
3 4 Local interface IP address
4 4 Remote interface IP address
5 4 Traffic engineering metric
6 4 Maximum bandwidth
7 4 Maximum reservable bandwidth
8 32 Unreserved bandwidth
9 4 Resource class/color
10 4 Link Mux Capability
11 4 Outgoing Interface Identifier
12 4 Incoming Interface Identifier
13 32 Maximum LSP Bandwidth
14 4 Link Protection Type
15 variable Link Descriptor
16 variable Shared Risk Link Group
32768-32772 - Reserved for Cisco-specific
extensions
5.1. Outgoing Interface Identifier
A link from LSR A to LSR B may be assigned an "outgoing interface
identifier". This identifier is a non-zero 32-but number that is
assigned by LSR A. This identifier must be unique within the scope
of A. If such an identifier has been assigned, A can advertise it as
a sub-TLV of the Link TLV with type 11, length 4 and value equal to
the assigned identifier.
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5.2. Incoming Interface Identifier
Suppose there is a link L from A to B. Suppose further that the link
L' from B to A that corresponds to the same interface as L has been
assigned an outgoing interface identifier by B. The "incoming
interface identifier" for L (from A's point of view) is defined as
the outgoing interface identifier for L' (from B's point of view).
If A knows this value (by means beyond the scope of this document), A
can advertise it as a sub-TLV of the Link TLV with type 12, length 4
and value equal to L's incoming interface identifier.
5.3. Maximum LSP Bandwidth sub-TLV
The Maximum LSP Bandwidth takes the place of the Maximum Link
Bandwidth. However, while Maximum Link Bandwidth is a single fixed
value (usually simply the link capacity), Maximum LSP Bandwidth is
carried per priority, and may vary as LSPs are set up and torn down.
The Maximum LSP Bandwidth of a bundled link at priority p is defined
to be the maximum of the Maximum LSP Bandwidth at priority p of each
component link.
If a component link is a simple (unbundled) link, define its Maximum
LSP Bandwidth at priority p to be the smaller of its unreserved
bandwidth at priority p and its maximum link bandwidth.
The Maximum LSP Bandwidth TLV has type 13 and length 32 octets. The
value is a list of eight 4 octet fields in IEEE floating point format
of the Maximum LSP Bandwidth of the link, with priority 0 first and
priority 7 last.
Although Maximum Link Bandwidth is to be deprecated, for backward
compatibility, one MAY set the Maximum Link Bandwidth to the Maximum
LSP Bandwidth at priority 7 of the link.
5.4. Link Protection Type sub-TLV
The Link Protection Type sub-TLV represents the protection capability
that exists on a link. It is desirable to carry this information so
that it may be used by the path computation algorithm to set up LSPs
with appropriate protection characteristics.
In the Traffic Engineering LSA, the Link Protection Type sub-TLV is a
sub-TLV of the Link TLV, with type 14, and length of four octets, the
first of which can take one of the following values:
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Value Link Protection Type
0 Unprotected
1 Shared
2 Dedicated 1:1
3 Dedicated 1+1
4 Enhanced
If the link is Unprotected, it means that there is no backup link for
traffic being carried on the link.
If the link has Shared protection, it means that for the N > 1
primary data-bearing channels, there are M disjoint backup data-
bearing channels reserved to carry the traffic. Additionally, the
protection data-bearing channel MAY carry low-priority preemptable
traffic. The bandwidth of backup data-bearing channels will be
announced in the unreserved bandwidth sub-TLV at the appropriate
priority.
If the link has Dedicated 1:1 protection, it means that for each
primary data-bearing channel, there is one disjoint backup data-
bearing channel reserved to carry the traffic. Additionally, the
protection data-bearing channel MAY carry low-priority preemptable
traffic. The bandwidth of backup data-bearing channels will be
announced in the unreserved bandwidth sub-TLV at the appropriate
priority.
If the link has Dedicated 1+1 protection, it means that a disjoint
backup data-bearing channel is reserved and dedicated for protecting
the primary data-bearing channel. This backup data-bearing channel
is not shared by any other connection, and traffic is duplicated and
carried simultaneously over both channels.
If the link has Enhanced protection, it indicates that the protection
scheme for the link is more reliable than the Dedicated 1+1, e.g., 4
fiber BLSR/MS-SPRING.
The second octet gives a priority value such that a new connection
with a higher priority (i.e., numerically lower than this value) is
guaranteed to be setup on a primary (or working) channel, and not on
a secondary (or protect) channel.
The format of the Link Protection Type sub-TLV is as shown below:
The Link Protection Type sub-TLV is optional and if an LSA does not
carry the TLV, then the Link Protection Type is unknown. The
protection capability of a link is typically pre-configured and does
not change dynamically over time. The working priority value is pre-
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 14 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Link Prot. Type| Working Pri | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
configured and does not depend on the traffic characteristics on the
primary data-bearing channel.
5.5. Link Descriptor sub-TLV
The Link Descriptor TLV represents the characteristics of the link,
in particular the link type and the bit transmission rate. These
characteristics represent one of the constraints on the type of LSPs
that could be carried over the link.
These characteristics should not be confused with the physical link
encoding or multiplex structure (if any). For example there are
systems where four OC-48s are switched and transported over a single
fiber via wavelength division multiplexing (WDM) technology. There
are systems where four OC-48s are transported in a transparent OC-192
time division multiplex (TDM) structure, i.e., all the overheads of
the OC-48's are persevered. In both these cases the essential
information from a routing perspective is that both of the links can
transport media of type OC-48.
In the Traffic Engineering LSA, the Link Descriptor sub-TLV is a sub-
TLV of the Link TLV, with type 15. The length is the length of the
list of Link Descriptors in octets. Each Link descriptor element
consists of the following fields: the first field is a one-octet
value which defines the link encoding type, the second field is a
one-octet value which defines the lowest priority at which that link
encoding type is available, the next two-octets are reserved, the
next field is four-octets and specifies the minimum reservable
bandwidth (in IEEE floating point format, the unit being bytes per
second) for this link encoding type, and the last four-octets
specifies the maximum reservable bandwidth (in IEEE floating point
format, the unit being bytes per second) for this link encoding type.
Link encoding type values are taken from the following list:
Value Link Encoding Type
1 Standard SONET
2 Arbitrary SONET
3 Standard SDH
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4 Arbitrary SDH
5 Clear
6 GigE
7 10GigE
The format of the Link Descriptors is shown in the next figure.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Type | Pri | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Minimum Reservable Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maximum Reservable Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A link having Standard SONET (or Standard SDH) link encoding type can
switch data at a minimum rate, which is given by the Minimum
Reservable Bandwidth on that link, and the maximum rate is given by
the Maximum Reservable Bandwidth on that link. Typical values of
these are enumerated in the GMPLS signaling draft [6]. In other
words, the Minimum and Maximum Reservable Bandwidth represents the
leaf and the root of one branch within the structure of the SONET (or
SDH) hierarchy. An LSP on that link may reserve any bit transmission
rate that is allowed by the SONET (or SDH) hierarchy between the
minimum and maximum reservable values (the spectrum is discrete).
For example, consider a branch of SONET multiplexing tree : VT-1.5,
STS-1, STS-3c, STS-12c, STS-48c, STS-192c. If it is possible to
establish all these connections on a OC-192 link, it can be
advertised as follows: Minimum Reservable Bandwidth VT-1.5 and
Maximum Reservable Bandwidth STS-192.
A link having Arbitrary SONET (or Arbitrary SDH) link encoding type
can switch data at a minimum rate, which is given by the Minimum
Reservable Bandwidth on that link, and the maximum rate is given by
the Maximum Reservable Bandwidth on that link. Typical values of
these are enumerated in the GMPLS signaling draft [6]. An LSP on
that link may reserve any bit transmission rate that is a multiple of
the Minimum Reservable Bandwidth between the minimum and maximum
reservable values (the spectrum is discrete).
To handle the case where a link could support multiple branches of
the SONET (or SDH) multiplexing hierarchy, one could use multiple LSP
descriptors. For example, if a link supports VT-1.5 and VT-2 (which
are not part of same branch of SONET multiplexing tree), then it
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could advertise two LSP descriptors, one for each one.
For a link with Clear encoding, the minimum and maximum reservable
bandwidth will imply that the optical path is tuned to carry traffic
within those range of values. (Note that it should be possible to
carry OC-x as well as GigE or any other encoding format, as long as
the bit transmission rate of the data to be carried is within this
range.)
For other encoding types, the minimum and maximum reservable
bandwidth should be set to have the same values.
Link Descriptors present a new constraint for LSP path computation.
On a bundled link we assume that either the whole link is configured
with the Link Descriptor Types, or each of its component links are
configured with the Link Descriptor Types. In the latter case, the
Link Descriptor Type of the bundled link is set to the set union of
the Link Descriptor Types for all the component links.
It is possible that Link Descriptor TLV will change over time,
reflecting the allocation/deallocation of component links. In
general, creation/deletion of an LSP on a link doesn't necessarily
result in changing the Link Descriptor of that link. For example,
assume that STS-1, STS-3c, STS-12c, STS-48c and STS-192c LSPs can be
established on a OC-192 link whose Link Type is SONET. Thus,
initially in the Link Descriptor the minimum reservable bandwidth is
set to STS-1, and the maximum reservable bandwidth is set of STS-192.
As soon as an LSP of STS-1 size is established on the link, it is no
longer capable of STS-192c. Therefore, the node advertises a
modified Link Descriptor indicating that the maximum reservable
bandwidth is no longer STS-192, but STS-48. If subsequently there is
another STS-1 LSP, there is no change in the Link Descriptor. The
Link Descriptor remains the same until the node can no longer
establish a STS-48c LSP over the link (which means that at this point
more than 144 time slots are taken by LSPs on the link). Once this
happened, the Link Descriptor is modified again, and the modified
Link Descriptor is advertised to other nodes.
Note that changes to the Link Descriptor TLV will also affect the
Unreserved Bandwidth sub-TLV with respect to bandwidth available on
the link.
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5.6. Shared Risk Link Group TLV
A set of links may constitute a 'shared risk link group' (SRLG) if
they share a resource whose failure may affect all links in the set.
For example, two fibers in the same conduit would be in the same
SRLG. A link may belong to multiple SRLGs. Thus the SRLG TLV
describes a list of SRLGs that the link belongs to. An SRLG is
identified by a 32 bit number that is unique within an IGP domain.
The SRLG of a LSP is the union of the SRLGs of the links in the LSP.
The SRLG of a bundled link is the union of the SRLGs of all the
component links. The SRLG values are an unordered list of 4 octet
numbers that the link belongs to.
If an LSR is required to have multiple diversely routed LSPs to
another LSR, the path computation should attempt to route the paths
so that they do not have any links in common, and such that the path
SRLGs are disjoint.
The SRLG sub-TLV is a sub-TLV of the Link TLV with type 16. The
length is the length of the list in octets. The value is an
unordered list of 32 bit numbers that are the SRLGs that the link
belongs to. The format is as shown below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 16 | 4 * No. of SRLGs in link |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Shared Risk Link Group Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ............ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Shared Risk Link Group Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The SRLG TLV starts with a configured value and does not change over
time, unless manually reconfigured. The SRLG TLV is optional and if
an LSA doesn't carry the SRLG TLV, then it means that SRLG of that
link is unknown.
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6. Security Considerations
The sub-TLVs proposed in this document does not raise any new
security concerns.
7. Acknowledgements
The authors would like to thank Suresh Katukam, Jonathan Lang and
Quaizar Vohra for their comments on the draft.
8. References
[1] Awduche, D., Rekhter, Y., Drake, J., Coltun, R., "Multi-
Protocol Lambda Switching: Combining MPLS Traffic Engineering
Control With Optical Crossconnects",
draft-awduche-mpls-te-optical-02.txt (work in progress)
[2] Basak, D., Awduche, D., Drake, J., Rekhter, Y., "Multi-
protocol Lambda Switching: Issues in Combining MPLS Traffic
Engineering Control With Optical Crossconnects",
draft-basak-mpls-oxc-issues-01.txt (work in progress)
[3] Katz, D., Yeung, D., "Traffic Engineering Extensions to OSPF",
draft-katz-yeung-ospf-traffic-02.txt (work in progress)
[4] Kompella, K., Rekhter, Y., Berger, L., "Link Bundling in MPLS
Traffic Engineering", draft-kompella-mpls-bundle-04.txt (work
in progress)
[5] Kompella, K., Rekhter, Y., "LSP Hierarchy with MPLS TE",
draft-ietf-mpls-lsp-hierarchy-00.txt (work in progress)
[6] Generalized MPLS Group, "Generalized MPLS - Signaling Functional
Description", draft-ietf-mpls-generalized-signaling-01.txt (work
in progress)
[7] Lang J., Mitra K., Drake J., Kompella K., Rekhter Y., Berger L.,
Saha, D., Sandick, H., and Basak D., "Link Management Protocol",
draft-ietf-mpls-lmp-01.txt (work in progress)
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9. Authors' Information
Kireeti Kompella
Juniper Networks, Inc.
1194 N. Mathilda Ave
Sunnyvale, CA 94089
Email: kireeti@juniper.net
Yakov Rekhter
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
Email: yakov@cisco.com
Ayan Banerjee
Calient Networks
5853 Rue Ferrari
San Jose, CA 95138
Phone: +1.408.972.3645
Email: abanerjee@calient.net
John Drake
Calient Networks
5853 Rue Ferrari
San Jose, CA 95138
Phone: (408) 972-3720
Email: jdrake@calient.net
Greg Bernstein
Ciena Corporation
10480 Ridgeview Court
Cupertino, CA 94014
Phone: (408) 366-4713
Email: greg@ciena.com
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Don Fedyk
Nortel Networks Corp.
600 Technology Park Drive
Billerica, MA 01821
Phone: +1-978-288-4506
Email: dwfedyk@nortelnetworks.com
Eric Mannie
GTS Network Services
RDI Department, Core Network Technology Group
Terhulpsesteenweg, 6A
1560 Hoeilaart, Belgium
Phone: +32-2-658.56.52
E-mail: eric.mannie@gtsgroup.com
Debanjan Saha
Tellium Optical Systems
2 Crescent Place
P.O. Box 901
Ocean Port, NJ 07757
Phone: (732) 923-4264
Email: dsaha@tellium.com
Vishal Sharma
Tellabs Research Center
One Kendall Square
Bldg. 100, Ste. 121
Cambridge, MA 02139-1562
Phone: (617) 577-8760
Email: Vishal.Sharma@tellabs.com
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