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Network Working Group                     K. Kompella (Juniper Networks)
Internet Draft                            Y. Rekhter  (Cisco Systems)
Expiration Date: March 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)

            IS-IS Extensions in Support of Generalized MPLS


                draft-ietf-isis-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 IS-IS 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 IS-IS 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 IS-IS 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
   IS-IS TE LSAs (we call Link State PDUs LSAs to avoid confusion with
   Label Switched Paths).  In Section 5, we define a new set of
   Type/Length/Value (TLV) triplets, as well as extend a proposed TLV,
   and describe their formats.


4. GMPLS Links

   In this section we describe the various types of links that can be
   announced in IS-IS TE LSAs, namely, normal links, non-packet links,
   and forwarding adjacencies.


4.1. Normal links

   If the nodes on both ends of a link can send and receive on a packet-
   by-packet basis, this link is a normal link.  Control packets (IS-IS
   protocol packets and signaling packets) and data packets can be sent
   over the link, so nothing special needs to be done.


4.2. Non-packet links

   If either node on the end of a bi-directional link cannot
   multiplex/demultiplex individual packets on that link (see [5]) then
   that link cannot be used for sending IS-IS hellos and LSAs.  In this
   case, a proxy control channel is needed for sending and receiving



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   control packets.  From IS-IS's point of view, the combination of the
   data link (in the context of this document, a non-packet link is also
   called a bearer channel) and the control channel is a single link;
   the TE attributes associated with this link are those of the bearer
   channel, but are sent over the control channel.

   The association of a bearer channel with a control channel is by
   configuration.  Note that for a bearer channel D to be associated
   with a control channel C, D and C should have the same end points,
   and that the same association must be made at both ends.  The means
   by which it is verified that the two ends have the same associations
   is outside the scope of this document, however, see [7].

   If there are several non-packet links between the same pair of nodes,
   the associated control channels may be logical interfaces over the
   same physical control link.


4.2.1. Excluding data traffic from control channels

   The control channels between nodes in a GMPLS network, such as
   optical cross-connects (OXCs) (see [1], [2]), SONET cross-connects
   and/or routers, are generally meant for control and administrative
   traffic.  These control channels are advertised into IS-IS 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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4.3. Forwarding Adjacency

   An LSR uses MPLS TE procedures to create and maintain an LSP.  The
   LSR then may (under its local configuration control) to announce this
   LSP as a link into IS-IS.  When this link is advertised into the same
   instance of IS-IS as the one that determines the route taken by the
   LSP, we call such a link a "forwarding adjacency" (FA).  For details
   about FAs (for example, their TE properties, the methodology for
   their use in constrained SPF path computation, etc) see [5].


4.4. Link Bundling

   For each type of link just described, it is possible to "bundle"
   several links together, i.e., treat them as a single link from IS-
   IS's point of view.  For example, several normal links can be
   advertised as a single normal link.

   The mechanisms for bundling, including the restrictions on when links
   can be bundled and the TE attributes of the bundle are described in
   [4].


5. IS-IS Routing Enhancements

   In this section we define the routing enhancements on the various
   types of links that can be announced in IS-IS TE LSAs, namely, normal
   links, non-packet links, and forwarding adjacencies.  In this
   document, we enhance the sub-TLVs for the extended IS reachability
   TLV (see [3]) in support of GMPLS.  Specifically, we add the
   following sub-TLV:

        Sub-TLV Type    Length    Name
                  20         1    Link Protection Type

   We further add two new TLVs.

         TLV Type       Length    Name
         136 (TBD)    variable    Link Descriptor
         138 (TBD)    variable    Shared Risk Link Group











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5.1. 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.  This is a sub-TLV (of
   type 20) of the extended IS reachability TLV (type 22) as defined in
   [3].

   If the link has 1+1 protection, it means that a disjoint backup
   bearer channel is reserved and dedicated for protecting the primary
   bearer channel.  This backup bearer channel is not shared by any
   other connection, and traffic is duplicated and carried
   simultaneously over both channels.

   If the link has 1:N protection, it means that for N primary bearer
   channels, there is one disjoint backup bearer channel reserved to
   carry the traffic.  Additionally, the protection bearer channel MAY
   carry low-priority preemptable traffic.  The bandwidth of backup
   bearer channels will be announced in the unreserved bandwidth sub-TLV
   at the appropriate priority.

   If the link has ring protection, it means that the primary bearer
   channel is protected by the presence of an alternate link possibly
   using other links and nodes in the network.

   The Link Protection Type sub-TLV has a length of two octets, the
   first of which can take one of the following values:

      Value        Link Protection Type
          0        Reserved (see signaling draft [6])
          1        None
          2        1+1
          3        1:N
          4        Ring

   The second octet gives a priority value, such that a new connection
   with a priority value higher than this value is guaranteed to be
   setup on a primary (or working) channel, and not on a secondary (or
   protect) channel.

   The Link Protection Type sub-TLV is optional and if an LSA does not
   carry the TLV, then the Link Protection Type is unknown.








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5.2. Link Descriptor 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 a 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.

   The proposed Link Descriptor TLV (of type 136 TBD) contains a new
   data structure consisting of:
       7 octets of System ID and Pseudonode Number
       4 octets of IPv4 interface address
       4 octets of IPv4 neighbor address
   and a list of Link Descriptors, where each element in the list has 10
   octets.  The length of the TLV is thus 15+10*n octets, where n is the
   number of elements in the list.

   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 third
   field is four-octets and specifies the minimum reservable bandwidth
   (in IEEE floating point format, the units being bytes per second) for
   this link encoding type, and the last field is four-octets and
   specifies the maximum reservable bandwidth (in IEEE floating point
   format, the units 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
          4        Arbitrary SDH
          5        Clear
          6        GigE
          7        10GigE

   A link having Standard SONET (or Standard SDH) link encoding type can
   switch data at a minimum rate, which is given by the Minimum



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   Reservable Bandwidth on that link, and the maximum rate is given by
   the Maximum Reservable Bandwidth on that link.  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.  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
   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



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   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.


5.3. 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 proposed SRLG (of type 138 TBD) contains a new data structure
   consisting of:
       7 octets of System ID and Pseudonode Number
       4 octets of IPv4 interface address
       4 octets of IPv4 neighbor address
   and a list of SRLG values, where each element in the list has 4
   octets.  The length of the TLV is thus 15+4*n octets, where n is the
   number of elements in the list.



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   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.


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] Smit, H., Li, T., "IS-IS Extensions for Traffic Engineering",
       draft-ietf-isis-traffic-02.txt (work in progress)

   [4] Kompella, K., Rekhter, Y., Berger, L., "Link Bundling in MPLS
       Traffic Engineering", draft-kompella-mpls-bundle-02.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] Optical MPLS Group, "MPLS Optical/Switching Signaling Functional
       Description" (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-lang-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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