One document matched: draft-ietf-isis-mi-06.xml
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<rfc category="std" docName="draft-ietf-isis-mi-06.txt"
ipr="pre5378Trust200902">
<front>
<title abbrev="draft-ietf-isis-mi-06.txt">IS-IS Multi-Instance</title>
<author fullname="Stefano Previdi" initials="S" role="editor"
surname="Previdi">
<organization>Cisco Systems</organization>
<address>
<postal>
<street>Via Del Serafico 200</street>
<city>Rome</city>
<code>0144</code>
<country>Italy</country>
</postal>
<email>sprevidi@cisco.com</email>
</address>
</author>
<author fullname="Les Ginsberg" initials="L" surname="Ginsberg">
<organization>Cisco Systems</organization>
<address>
<postal>
<street>510 McCarthy Blvd.</street>
<city>Milpitas</city>
<code>95035</code>
<region>CA</region>
<country>USA</country>
</postal>
<email>ginsberg@cisco.com</email>
</address>
</author>
<author fullname="Mike Shand" initials="M" surname="Shand">
<address>
<email>imc.shand@googlemail.com</email>
</address>
</author>
<author fullname="Abhay Roy" initials="A" surname="Roy">
<organization>Cisco Systems</organization>
<address>
<postal>
<street>170 W. Tasman Dr.</street>
<city>San Jose</city>
<code>95134</code>
<region>CA</region>
<country>USA</country>
</postal>
<email>akr@cisco.com</email>
</address>
</author>
<author fullname="Dave Ward" initials="D" surname="Ward">
<organization>Cisco Systems</organization>
<address>
<postal>
<street>3700 Cisco Way</street>
<city>San Jose</city>
<code>95134</code>
<region>CA</region>
<country>USA</country>
</postal>
<email>wardd@cisco.com</email>
</address>
</author>
<date day="14" month="February" year="2012" />
<area>Routing Area</area>
<workgroup>Networking Working Group</workgroup>
<keyword>Sample</keyword>
<abstract>
<t>This draft describes a mechanism that allows a single router to share
one or more circuits among multiple Intermediate System To Intermediate
System (IS-IS) routing protocol instances.</t>
<t>Multiple instances allow the isolation of resources associated with
each instance. Routers will form instance specific adjacencies. Each
instance can support multiple topologies. Each topology has a unique
Link State Database (LSDB). Each Protocol Data Unit (PDU) will contain a
new Type Length Value (TLV) identifying the instance and the
topology(ies) to which the PDU belongs.</t>
</abstract>
<note title="Requirements Language">
<t>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].</t>
</note>
</front>
<middle>
<section title="Introduction">
<t>An existing limitation of the protocol defined by [IS-IS] is that
only one instance of the protocol can operate on a given circuit. This
document defines an extension to IS-IS to remove this restriction. The
extension is referred to as "Multi-instance IS-IS" (MI-IS-IS).</t>
<t>Routers which support this extension are referred to as
"Multi-instance capable routers" (MI-RTR).</t>
<t>The use of multiple instances enhances the ability to isolate the
resources associated with a given instance both within a router and
across the network. Instance specific prioritization for processing PDUs
and performing routing calculations within a router may be specified.
Instance specific flooding parameters may also be defined so as to allow
different instances to consume network wide resources at different
rates.</t>
<t>A given instance MAY support multiple topologies. Each topology is
associated with a unique LSDB and a topology specific IS-IS Update
Process. This differs from [RFC5120] where a single LSDB/single IS-IS
Update Process is used in support of all topologies.</t>
<t>MI-IS-IS might be used to support topology specific routing. When
used for this purpose it is an alternative to [RFC5120].</t>
<t>MI-IS-IS might also be used to support advertisement of information
on behalf of applications [I-D.ietf-isis-genapp]. The advertisement of
information not directly related to the operation of the IS-IS protocol
can therefore be done in a manner which minimizes its impact on the
operation of routing.</t>
<t>The above are examples of how MI-IS-IS might be used. The
specification of uses of MI-IS-IS is outside the scope of this
document.</t>
</section>
<section title="Elements Of Procedure">
<t>An Instance Identifier (IID) is introduced to uniquely identify an
IS-IS instance. The protocol extension includes a new TLV (IID-TLV) in
each IS-IS PDU originated by an MI-RTR except as noted in this document.
The IID-TLV identifies the unique instance as well as the
topology/topologies to which the PDU applies. Each IS-IS PDU is
associated with only one IS-IS instance.</t>
<t>MI-RTRs form instance specific adjacencies. The IID-TLV included in
Intermediate System-Intermediate System Hellos (IIH) includes the IID
and the set of Instance Specific Topology Identifiers (ITID) that the
sending IS supports. When multiple instances share the same circuit each
instance will have a separate set of adjacencies.</t>
<t>MI-RTRs support the exchange of topology specific Link State PDUs for
the IID/ITID pairs that each neighbor supports. A unique IS-IS Update
process [see IS-IS] operates for each IID/ITID pair. This MAY also imply
IID/ITID specific routing calculations and IID/ITID specific routing and
forwarding tables. However, this aspect is outside the scope of this
specification.</t>
<t>The mechanisms used to implement support of the separation of IS-IS
instances and topology specific Update processes within a router are
outside the scope of this specification.</t>
<section title="Instance Identifier TLV">
<t>A new TLV is defined in order to convey the IID and ITIDs
supported. The IID-TLV associates PDUs with each IS-IS instance using
a unique 16-bit number. The IID-TLV is carried in all IS-IS PDUs
(Intermediate System to Intermediate System Hellos (IIH), Sequence
Number PDUs (SNP) and Link State PDUs (LSP)) which are associated with
a non-zero instance.</t>
<t>Multiple instances of IS-IS may co-exist on the same circuit and on
the same physical router. IIDs MUST be unique within the same routing
domain.</t>
<t>Instance identifier #0 is reserved for the standard instance
supported by legacy systems. IS-IS PDUs associated with the legacy
instance MUST NOT include an IID-TLV except where noted in this
document.</t>
<t>The IID-TLV MAY include one or more ITIDs. An ITID is a 16 bit
identifier where all values (0 - 65535) are valid.</t>
<t>The following format is used for the IID-TLV:</t>
<figure>
<artwork><![CDATA[ Type: 7
Length: 2 - 254
Value:
No. of octets
+-------------------------+
| IID (0 - 65535) | 2
+-------------------------+
| Supported ITID | 2
+-------------------------+
: :
+-------------------------+
| Supported ITID | 2
+-------------------------+
When the IID = 0, the list of supported ITIDs MUST NOT be present.
When the IID is non-zero and the TLV appears in an SNP or LSP,
exactly one ITID MUST be present indicating the topology with
which the PDU is associated. If no ITIDs or multiple ITIDs are
present then the PDU MUST be ignored.
When the IID is non-zero and the TLV appears in an IIH, the set
of ITIDs supported on the circuit over which the IIH is sent is
included. There MUST BE at least one ITID present.
Multiple IID-TLVs MAY appear in IIHs. If multiple IID-TLVs are
present and the IID value in all IID-TLVs is not the same then
the PDU MUST BE ignored.
]]></artwork>
</figure>
<t>A single IID-TLV will support advertisement of up to 126 ITIDs. If
multiple IID-TLVs are present in an IIH PDU the supported set of ITIDs
is the union of all ITIDs present in all IID-TLVs.</t>
<t>When an LSP purge is initiated, the IID-TLV MUST be retained but
the remainder of the body of the LSP SHOULD be removed. Purge
procedure is described in [RFC6233] and [RFC6232].</t>
<t>A PDU without an IID-TLV is assumed to belong to the standard
instance (#0).</t>
</section>
<section title="Instance Membership">
<t>Each MI-RTR is configured to be participating in one or more
instances of IS-IS. For each non-zero instance in which it
participates, an MI-RTR marks IS-IS PDUs (IIHs, LSPs or SNPs)
generated pertaining to that instance by including the IID-TLV with
the appropriate instance identifier.</t>
</section>
<section title="Use of Authentication">
<t>When authentication is in use, the IID, if present, is first used
to select the authentication configuration which is applicable. The
authentication check is then performed as normal. When multiple ITIDs
are supported, ITID specific authentication MAY be used in SNPs and
LSPs.</t>
</section>
<section title="Adjacency Establishment">
<t>In order to establish adjacencies, IS-IS routers exchange IIH PDUs.
Two types of adjacencies exist in IS-IS: point-to-point and broadcast.
The following sub-sections describe the additional rules an MI-RTR
MUST follow when establishing adjacencies.</t>
<section title="Point-to-Point Adjacencies">
<t>MI-RTRs include the IID-TLV in the point-to-point hello PDUs they
originate. Upon reception of an IIH, an MI-RTR inspects the received
IID-TLV and if the IID matches any of the IIDs which the router
supports on that circuit, normal adjacency establishment procedures
are used to establish an instance specific adjacency. Note that the
absence of the IID TLV implies instance ID #0. For instances other
than IID #0, an adjacency SHOULD NOT be established unless there is
at least one ITID in common.</t>
<t>This extension allows an MI-RTR to establish multiple adjacencies
to the same physical neighbor over a point-to-point circuit.
However, as the instances are logically independent, the normal
expectation of at most one neighbor on a given point-to-point
circuit still applies.</t>
</section>
<section title="Multi-Access Adjacencies">
<t>Multi-Access (broadcast) circuits behave differently than
point-to-point in that PDUs sent by one router are visible to all
routers and all routers must agree on the election of a Designated
Intermediate System (DIS) independent of the set of ITIDs
supported.</t>
<t>MI-RTRs will establish adjacencies and elect a DIS per IS-IS
instance. Each MI-RTR will form adjacencies only with routers which
advertise support for the instances which the local router has been
configured to support on that circuit. Since an MI-RTR is not
required to support all possible instances on a LAN, it's possible
to elect a different DIS for different instances.</t>
</section>
</section>
<section title="Update Process Operation">
<t>For non-zero instances, a unique Update Process exists for each
supported ITID.</t>
<section title="Update Process Operation on Point-to-Point Circuits">
<t>On Point-to-Point circuits - including Point-to-Point Operation
over LAN [RFC5309] - the ITID specific Update Process only operates
on that circuit for those ITIDs which are supported by both ISs
operating on the circuit.</t>
</section>
<section title="Update Process Operation on Broadcast Circuits">
<t>On Broadcast circuits, a single DIS is elected for each supported
IID independent of the set of ITIDs advertised in LAN IIHs. This
requires that the DIS generate pseudo-node LSPs for all supported
ITIDs and that the Update Process for all supported ITIDs operate on
the Broadcast Circuit. In cases where the set of supported ITIDs for
a given non-zero IID is inconsistent among the MI-RTRs operating on
a broadcast circuit, connectivity for the topology(ies) associated
with ITIDs not supported by some MI-RTRs operating on the circuit
can be compromised.</t>
</section>
</section>
<section title="Interoperability Considerations">
<t>[IS-IS] requires that any TLV that is not understood is silently
ignored without compromising the processing of the whole IS-IS PDU
(IIH, LSP, SNP).</t>
<t>To a router not implementing this extension, all IS-IS PDUs
received will appear to be associated with the standard instance
regardless of whether an IID TLV is present in those PDUs. This can
cause interoperability issues unless the mechanisms and procedures
discussed below are followed.</t>
<section title="Interoperability Issues on Broadcast Circuits">
<t>In order for routers to correctly interoperate with routers not
implementing this extension and in order not to cause disruption, a
specific and dedicated Media Access Control (MAC) address is used
for multicasting IS-IS PDUs with any non-zero IID. Each level will
use a specific layer 2 multicast address. Such an address allows
MI-RTRs to exchange IS-IS PDUs with non-zero IIDs without these PDUs
being processed by legacy routers and therefore no disruption is
caused.</t>
<t>An MI-RTR will use the AllL1IS and AllL2IS ISIS MAC layer
addresses (as defined in [IS-IS]) when sending ISIS PDUs for the
standard instance (IID #0). An MI-RTR will use two new (TBD)
dedicated layer 2 multicast addresses (one for each level) when
sending IS-IS PDUs for any non-zero IID.</t>
<t>MI-RTRs MUST discard IS-IS PDUs received if either of the
following is true:</t>
<t><list style="symbols">
<t>The destination multicast address is AllL1IS or AllL2IS and
the PDU contains an IID-TLV</t>
</list><list style="symbols">
<t>The destination multicast address is one of the two new
addresses and the PDU contains an IID-TLV with a zero value for
the IID or has no IID-TLV.</t>
</list></t>
<t>NOTE: If the multicast addresses AllL1IS and/or AllL2IS are
improperly used to send IS-IS PDUs for non-zero IIDs, legacy systems
will interpret these PDUs as being associated with IID #0. This will
cause inconsistencies in the LSDB in those routers, may incorrectly
maintain adjacencies, and may lead to inconsistent DIS election.</t>
</section>
<section title="Interoperability using point-to-point circuits">
<t>In order for an MI-RTR to interoperate over a point-to-point
circuit with a router which does NOT support this extension, the
MI-RTR MUST NOT send IS-IS PDUs for instances other than IID #0 over
the point-to-point circuit as these PDUs may affect the state of IID
#0 in the neighbor.</t>
<t>The presence/absence of the IID-TLV in an IIH indicates that the
neighbor does/does not support this extension. Therefore, all IIHs
sent on a point-to-point circuit by an MI-RTR MUST include an
IID-TLV. This includes IIHs associated with IID #0. Once it is
determined that the neighbor does not support this extension, an
MI-RTR MUST NOT send PDUs (including IIHs) for instances other than
IID #0.</t>
<t>Until an IIH is received from a neighbor, an MI-RTR MAY send IIHs
for a non-zero instance. However, once an IIH with no IID TLV has
been received - indicating that the neighbor is not an MI-RTR - the
MI-RTR MUST NOT send IIHs for a non-zero instance. The temporary
relaxation of the restriction on sending IIHs for non-zero instances
allows a non-zero instance adjacency to be established on an
interface on which an MI-RTR does NOT support instance #0.</t>
<t>Point-to-point adjacency setup MUST be done through the use of
three-way handshaking procedure as defined in [RFC5303] in order to
prevent a non-MI capable neighbor from bringing up an adjacency
prematurely based on reception of an IIH w an IID-TLV for a non-zero
instance.</t>
</section>
</section>
</section>
<section title="Usage Guidelines">
<t>As discussed above, MI-IS-IS extends IS-IS to support multiple
instances on a given circuit. Each instance is uniquely identified by
the IID and forms instance specific adjacencies. Each instance supports
one or more topologies as represented by the ITIDs. All topologies
associated with a given instance share the instance specific
adjacencies. The set of topologies supported by a given IID MAY differ
from circuit to circuit. Each topology has its own set of LSPs and runs
a topology specific Update process. Flooding of topology specific LSPs
is only performed on circuits on which both the local router and the
neighbor(s) support a given topology (i.e. advertise the same ITID in
the set of supported ITIDs sent in the IID-TLV included in IIHs).</t>
<t>The following sub-sections provide some guidelines for usage of
instances and topologies within each instance. While this represents
examples based on the intent of the authors, implementors are not
constrained by the examples.</t>
<section title="One-One Mapping Between Topologies and Instances">
<t>When the set of information to be flooded in LSPs is intended to be
flooded to all MI-RTRs supporting a given IID a single topology MAY be
used. The information contained in the single LSDB MAY still contain
information associated with multiple applications as the GENINFO TLV
for each application has an application specific ID which identifies
the application to which the TLV applies [I-D.ietf-isis-genapp].</t>
</section>
<section title="Many-to-one Mapping Between Topologies and Instances">
<t>When the set of information to be flooded in LSPs includes subsets
which are of interest to a subset of the MI-RTRs supporting a given
IID, support of multiple ITIDs allows each subset to be flooded only
to those MI-RTRs which are interested in that subset. In the simplest
case, a one-one mapping between a given application and an ITID allows
the information associated with that application to be flooded only to
MI-RTRs which support that application - but a many-to-one mapping
between applications and a given ITID is also possible. When the set
of application specific information is large, the use of multiple
ITIDs provides significantly greater efficiencies as MI-RTRs only need
to maintain the LSDB for applications of interest and that information
only needs to be flooded over a topology defined by the MI-RTRs who
support a given ITID.</t>
<t>The use of multiple ITIDs also allows the dedication of a full LSP
set (256 LSPs at each level) for the use of a given (set of)
applications, thereby minimizing the possibility of exceeding the
carrying capacity of an LSP set which might arise if information for
all applications were to be included in a single LSP set.</t>
<t>Note that the topology associated with each ITID MUST be fully
connected in order for ITID specific LSPs to be successfully flooded
to all MI-RTRs who support that ITID.</t>
</section>
<section title="Considerations for the Number of Instances">
<t>The support of multiple topologies within the context of a single
instance provides better scalability in support of multiple
applications both in terms of the number of adjacencies which are
required and in the flooding of topology specific LSDB. In many cases
the use of a single non-zero instance would be sufficient and optimal.
However, in cases where the set of topologies desired in support of a
set of applications is largely disjoint from the set of topologies
desired in support of a second set of applications, it could make
sense to use multiple instances.</t>
</section>
</section>
<section title="Relationship to M-ISIS">
<t>[RFC5120] defines support for Multi-Topology Routing. In that
document 12 bit Multi-topology IDs are defined to identify the
topologies which an IS-IS instance (a "standard instance" as defined by
this document) supports. There is no relationship between the
Multi-topology IDs defined in [RFC5120] and the ITIDs defined in this
document.</t>
<t>If an MI-RTR uses the extensions in support of the BFD Enabled TLV
[RFC6213] , the ITID SHOULD be used in place of the MTID in which case
all 16 bits of the identifier field are useable.</t>
<t>An MI-RTR MAY use the extensions defined in this document to support
multiple topologies in the context of an instance with a non-zero IID.
Each MI topology is associated with a unique LSDB identified by an ITID.
An ITID specific IS-IS Update Process operates on each topology. This
differs from [RFC5120] where a single LSDB/single IS-IS Update Process
is used in support of all topologies. Although it is possible for an
MI-RTR to use [RFC5120] multi-topology support within a non-zero
instance such usage is seen as unnecessary and is discouraged.</t>
</section>
<section title="Graceful Restart Interactions">
<t>[RFC5306] defines protocol extensions in support of graceful restart
of a routing instance. The extensions defined there apply to MI-RTRs
with the notable addition that as there are topology specific LSP
databases each of these must be synchronized following restart in order
for database synchronization to be complete. This involves the use of
additional T2 timers. See [RFC5306] for further details.</t>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>This document requires the definition of a new ISIS TLV that needs to
be reflected in the ISIS TLV code-point registry:</t>
<figure>
<artwork><![CDATA[
Type Description IIH LSP SNP Purge
---- --------------------- --- --- --- -----
7 Instance Identifier y y y y
]]></artwork>
</figure>
<t></t>
</section>
<section anchor="Security" title="Security Considerations">
<t>Security concerns for IS-IS are addressed in [IS-IS], [RFC5304], and
[RFC5310].</t>
<t>Use of the extensions defined here with authentication as defined in
[RFC5304] or [RFC5310] will result in the discarding of purges by legacy
systems which are in strict conformance with either of those RFCs. To
avoid this issue an MI-RTR MAY omit the IID-TLV in purges for the
standard instance (IID #0) until such time as all ISs in the network
have been upgraded to support [RFC6232].</t>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>The authors would like to acknowledge contributions made by Dino
Farinacci and Tony Li.</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
<?rfc include='reference.RFC.5304'?>
<?rfc include='reference.RFC.5120'?>
<?rfc include='reference.RFC.5303'?>
<?rfc include='reference.RFC.5306'?>
<?rfc include='reference.RFC.5310'?>
<?rfc include='reference.RFC.6213'?>
<?rfc include='reference.RFC.6232'?>
<?rfc include='reference.RFC.6233'?>
<?rfc include="reference.I-D.ietf-isis-genapp"?>
<?rfc ?>
<?rfc ?>
<?rfc ?>
<reference anchor="IS-IS">
<front>
<title>Intermediate system to Intermediate system intra-domain
routeing information exchange protocol for use in conjunction with
the protocol for providing the connectionless-mode Network Service
(ISO 8473), ISO/IEC 10589:2002, Second Edition.</title>
<author fullname="ISO "International Organization for Standardization""></author>
<date month="Nov" year="2002" />
</front>
</reference>
</references>
<references title="Informative References">
<?rfc include='reference.RFC.5309'?>
</references>
</back>
</rfc>
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