wdiff draft-ietf-isis-mrt-00.txt draft-ietf-isis-mrt-01.txt

Network Working Group Z. Li
Internet-Draft N. Wu
Intended status: Standards Track Q. Zhao
Expires: August 13, 2015 April 21, 2016 Huawei Technologies
A. Atlas
C. Bowers
Juniper Networks
J. Tantsura
Ericsson
February 9,
October 19, 2015

Intermediate System to Intermediate System (IS-IS) Extensions for
Maximally Redundant Trees (MRT)
draft-ietf-isis-mrt-00
draft-ietf-isis-mrt-01

Abstract

This document describes necessary extensions to IS-IS to support the
distributed computation of Maximally Redundant Trees (MRT). Some
example Example
uses of the MRTs MRT include IP/LDP Fast-Reroute and global protection or
live-live for multicast traffic. The extensions indicate what MRT
profile(s) each router supports. Different MRT profiles can be
defined to support different uses and to allow transition of
capabilities. An extension is introduced to flood MRT-
Ineligible MRT-Ineligible
links, due to administrative policy. This document also defines the
Controlled Convergence sub-TLV, which is useful for MRT FRR as well
as other applications.

Status of This Memo

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provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on August 13, 2015. April 21, 2016.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Using MRT with Multi-Topology IGP Routing . . . . . . . . . . 4
5. Overview of IS-IS Signaling Signalling Extensions for MRT . . . . . . . 5
5.1. 4
4.1. Supporting MRT Profiles . . . . . . . . . . . . . . . . . 6
5.2. Electing 4
4.2. Selecting the GADAG Root . . . . . . . . . . . . . . . . . . . 6
5.3. 4
4.3. Advertising MRT-Ineligible Links for MRT . . . . . . . . 7
5.4. 5
4.4. Triggering an MRT Computation . . . . . . . . . . . . . . 7
6. 5
5. MRT Capability Advertisement . . . . . . . . . . . . . . . . 7
6.1. Advertising 5
5.1. MRT Capability Profile sub-TLV in the IS-IS LSP Router CAPABILITY TLV . 6
5.1.1. A note on the M-bit in OSPF . . . . . . . . 7
6.2. MRT Profile sub-TLV in IS-IS Router CAPABILITY TLV . . . 8
6.3. . . 7
5.2. MRT-Ineligible Links Link sub-TLV in IS-IS Router CAPABILITY the Extended IS
Reachability TLV . . . . . . . . . . . . . . . . . . . . 7
5.3. A Note on Multi-Topology Routing . . . . . . . 9
7. . . . . . 8
6. Controlled Convergence sub-TLV in IS-IS Router CAPABILITY TLV 10
8. 8
7. Handling MRT Capability Sending and Receiving Extensions . . . . . . . . 11
8.1. Advertising MRT extension . . . . . . . . . . . 10
7.1. Advertising MRT extensions . . . . . 12
8.2. Parsing MRT extension . . . . . . . . . . 10
7.2. Processing MRT extensions . . . . . . . . 12
9. Backwards . . . . . . . . 10
8. Backward Compatibility . . . . . . . . . . . . . . . . . . . 12
10. 10
9. Implementation Status . . . . . . . . . . . . . . . . . . . . 13
11. 11
10. Security Considerations . . . . . . . . . . . . . . . . . . . 13 11
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 11
12.1. MRT Profile and Controlled Convergence sub-TLVs . . . . 11
12.2. MRT-Ineligible Link sub-TLV . . . . . . . . . . . . . . 11
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 12
13.1. Normative References . . . . . . . . . . . . . . . . . . 13 12
13.2. Infomative References . . . . . . . . . . . . . . . . . 14 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 13

1. Introduction

The IS-IS protocol is specified in [ISO10589], with extensions for
supporting IPv4 and IPv6 specified in [RFC1195] and [RFC5308]. Each
Intermediate System (IS) (router) advertises one or more IS-IS Link
State Protocol Data Units (LSPs) with routing information. Each LSP
is composed of a fixed header and a number of tuples, each consisting
of a Type, a Length, and a Value. Such tuples are commonly known as
TLVs, and are a good way of encoding information in a flexible and
extensible format.

[I-D.ietf-rtgwg-mrt-frr-architecture] gives a complete solution for
IP/LDP fast-reroute using Maximally Redundant Trees (MRT) to provide
alternates. This document describes the necessary signaling signalling extensions for
supporting MRT-FRR used in an IS-IS routing domain.

2. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

3. Terminology

Redundant Trees (RT): A pair of trees where the path from any node X
to the root R along the first tree is node-disjoint with the path
from the same node X to the root R along the second tree. These can
be computed in 2-connected graphs.

Maximally Redundant Trees (MRT): A pair of trees where the path from
any node X to the root R along the first tree and the path from the
same node X to the root R along the second tree share the minimum
number of nodes and the minimum number of links. Each such shared
node is a cut-vertex. Any shared links are cut-links. Any RT is an
MRT but many MRTs are not RTs.

MRT Island: From the computing router, the set of routers that
support a particular MRT profile and are connected via MRT- eligible
links.

GADAG: Generalized Almost Directed Acyclic Graph - a graph which is
the combination of the ADAGs of all blocks. Transforming a network
graph into a GADAG is part of the MRT algorithm.

MRT-Red: MRT-Red is used to describe one of the two MRTs; it is used
to describe the associated forwarding topology and MT-ID.
Specifically, MRT-Red is the decreasing MRT where links in the GADAG
are taken in the direction from a higher topologically ordered node
to a lower one.

MRT-Blue: MRT-Blue is used to describe one of the two MRTs; it is
used to describe the associated forwarding topology and MT-ID.
Specifically, MRT-Blue is the increasing MRT where links in the GADAG
are taken in the direction from a lower topologically ordered node to
a higher one.

4. Using MRT with Multi-Topology IGP Routing

Both IS-IS and OSPF have support for multi-topology routing (see
[RFC5120] for ISIS and [RFC4915] for OSPF.) In addition to the
standard topology (identified by MT-ID=0), these extensions allow the
IGP to identify particular links and nodes as participating in
additional topologies (identified by MT-ID!=0). A given link can
belong to several topologies and be assigned different metrics in
each topology. The IGP runs an independent SPF computation for each
topology, finding independent shortest paths to prefixes in each
topology.

It is straightforward to extend the MRT computations to multi-
topology IGP routing. For each IGP topology identified by an IGP MT-
ID, we need to identify the node and links belonging to an MRT Island
for that IGP MT-ID. This process creates a graph for the MRT Island
for that specific IGP MT-ID, which can then be used to compute the
transit next-hops and alternate next-hops for MRT-Red and MRT-Blue
for that specific IGP MT-ID.

We expect that initial implementation and deployments of MRT will be
primarily concerned with computing MRT-Red and Blue trees for the
standard topology (IGP MT-ID=0). However, we have chosen to specify
the IS-IS MRT extensions to accommodate the computation of MRT-Red
and MRT-Blue in a multi-topology IS-IS environment. This comes at
the expense of 2-6 octets per TLV for MT-ID values, but it will allow
for standards-based multi-topology aware MRT implementations for ISIS
without any future standards work.

Using MRT in a multi-topology IGP environment does have one
complication which should be discussed. Forwarding LDP traffic over
MRT paths in the standard IGP topology requires the use of labels
bound to topology-scoped FECs to identify traffic on MRT-Red and Blue
trees. This is described in Section 6 of
[I-D.ietf-rtgwg-mrt-frr-architecture]. To facilitate this, an MRT
profile specifies IANA-assigned MRT-Red and MRT-Blue LDP MT-ID
values, which are then used by LDP to advertise labels for the MRT-
Red and Blue forwarding topologies. Note that the MRT-Red and MRT-
Blue LDP MT-ID values assigned by IANA for a given MRT profile
correspond to the MRT-Red and Blue forwarding trees associated with
the standard IGP topology with IGP MT-ID=0. For example, suppose
that a future MRT profile X is assigned (hypothetical) MRT-Red and
MRT-Blue LDP MT-ID values of 2001 and 2002. Then labels for shortest
path forwarding trees associated with the standard IGP topology will
be advertised using FECs with MT-ID=0, while the labels for the MRT-
Red and Blue forwarding trees for profile X will be advertised using
FECS with MT-ID=2001 and 2002, respectively. In the absence of
multi-topology IGP routing, all MT-IDs used by LDP for MRT are
assigned by IANA, so there are no potential conflicts in LDP MT-ID
usage.

When MRT is used together with multi-topology IGP routing, additional
LDP MT-IDs need to be specified for carrying traffic on the MRT-Red
and Blue forwarding trees associated with the additional IGP routing
topologies. Building on the previous example, suppose that a network
is configured with an additional IGP routing topology using MT-ID=20,
in addition to the standard topology with MT-ID=0. The router
advertises support for MRT with respect to MT-ID=20 with profile X,
as well as support for MRT with respect to MT-ID=0 with profile X.
The MRT-Red and Blue LDP MT-IDs for MT-ID=0 with profile X are still
inherited from profile X, as in the previous example. In order to
use LDP to create the MRT-Red and Blue forwarding trees for the IGP
topology with MT-ID=20, the router could, for example, advertise MRT-
Red and MRT-Blue LDP MT-ID values of 21 and 22 for IGP MT-ID=20 and
profile X. This overrides the (hypothetical) IANA-assigned values
MRT-Red and MRT-Blue LDP MT-ID values for profile X, but maintains
all other properties of profile X. Care must be taken to avoid
advertising LDP MT-ID values that conflict with implicitly advertised
IANA-assigned values LDP MT-ID.

The semantics of the IS-IS MRT extensions in this document are
designed to handle the most common case (MRT in the absence of multi-
topology IGP routing) in a simple manner. Setting the IGP MT-ID
field as well as the MRT-Blue and MRT-Red LDP MT-ID fields to 0 in
the TLV and sub-TLVs in this document results in the desired behavior
for the standard IGP topology.

5. Overview of IS-IS Signaling Signalling Extensions for MRT

As stated in [I-D.ietf-rtgwg-mrt-frr-algorithm], it is necessary for
each MRT-Capable router to compute MRT next hops in a consistent
fashion. This is achieved by using the same MRT profile and
selecting
the a common and unique GADAG root in a the MRT Island which is
connected by MRT-Eligible links. Each of these issues will be
discussed in the following sections separately.

5.1.

4.1. Supporting MRT Profiles

The contents and requirements of an MRT profile has been defined in
[I-D.ietf-rtgwg-mrt-frr-architecture]. The parameters and behavioral
rules contained in an MRT profile define one router's MRT
capabilities. Based on common capabilities, one unified MRT Island
is built.

The MRT-Capable router MUST advertise its corresponding MRT profiles
by IS-IS protocol extension within IS-IS routing domain. The
capabilities of the advertiser MUST completely conform to the profile
it claimed
completely, especially claimed, including the MT-IDs, the algorithm and the corresponding
forwarding mechanism. This advertisement MUST have level scope. One A
given router MAY support multiple MRT profiles and profiles. If so, it MUST
advertise each of these profiles in the corresponding IS-IS level.

The MT-
IDs used in one supported MRT Profile MUST NOT overlap with those MT-
IDs used in a different supported MRT Profile.

The default MRT Profile is defined in
[I-D.ietf-rtgwg-mrt-frr-architecture]. Its behavior is intended to
support IP/LDP unicast and multicast Fast-Reroute. MRT-Capable
routers SHOULD support the default MRT profile.

5.2. Electing

4.2. Selecting the GADAG Root

As per [I-D.ietf-rtgwg-mrt-frr-algorithm], a GADAG root MUST be
selected for one MRT Island. An unique GADAG root in common-sense common among
MRT Island routers is a necessity to do MRT computation. Since the
selection of the GADAG root can affect the alternates quality of paths for
traffic sent over MRT Red and Blue trees, the
traffic through it, GADAG Root Selection
Priority and the selection rules give GADAG Root Selection Policy gives a network operator a knob
to control the alternates and
the traffic inside the MRT Island.
Relevant discussion for ability to influence the relationship between GADAG root role and
MRT Island alternates is out selection of the scope of this document. GADAG root.

Each MRT-Capable router MUST advertise its priority for GADAG root
selection. One A router can only have one priority in the same a given MRT
Island. It can have multiple priorities for different MRT Islands it
supports. Routers that are marked as overloaded([RFC3787]) are not
qualified as candidate for root selection.

The GADAG Root Selection Policy (defined as part of an MRT profile)
may make use of the GADAG Root Selection Priority value advertised in
the MRT Profile in the IS-IS Router CAPABILITY TLV. For example, the
GADAG Root Selection Policy for the default MRT profile is the
following: Among the routers in the MRT Island and with the highest
priority advertised, an implementation MUST pick the router with the
highest Router ID to be the GADAG root.

When the current root is out of service or new router with higher
priority joined into the MRT Island, the GADAG root MUST be re-
selected. A new MRT computation will be triggered because of such a
topology change.

5.3.

4.3. Advertising MRT-Ineligible Links for MRT

For certain administrative or management reason, some links reasons, it may not be involved into desirable to
exclude some links from the MRT computation. In this scenario, MRT-Capable MRT-
Capable router MUST claim those MRT-Ineligible links are out of MRT
Island scope. If such claim splits current MRT Island then MRT
computation has to be done inside the modified MRT Island which the
computing router belongs to.

5.4.

4.4. Triggering an MRT Computation

A MRT Computation can be triggered through topology changes or MRT
capability changes of any router in the MRT Island. It is always
triggered for a given MRT Profile in the corresponding level. First,
the associated MRT Island is determined. Then, the GADAG Root is
selected. Finally, the actual MRT algorithm is run to compute the
transit MRT-Red and MRT-Blue topologies. Additionally, the router
MAY choose to compute MRT-FRR alternates or make other use of the MRT
computation results.

Prefixes can be attached and detached and have their associated MRT-
Red and MRT-Blue next-hops computed without requiring a new MRT
computation.

5. MRT Capability Advertisement

An MRT-Capable router MUST identify its MRT capabilities through IS-IS IS-
IS Link State Packet(LSP) Packets(LSPs) in level scope.

6.1. Advertising MRT Capability in IS-IS LSP

One new M-bit is introduced into TLV 229 to identify router is MRT-
Capable. Structure of TLV 229 is stated in [RFC5120] as pictured
below:

TYPE: 229

LENGTH: total length of the value field, it SHOULD be 2 times the
number of MT components.

VALUE: one or more 2-byte MT components, structured as follows:

No. of Octets
+--------------------------------+
|O |A |M |R | MT ID | 2
+--------------------------------+

Bit M identifies the originator is of MRT-Capable. The MRT-Blue and
the MRT-Red alternates will be calculated for the MT identified by
MT-ID.

This M-bit MUST be set and checked in LSP fragment 0. A MRT-Capable
router MUST advertise this TLV with M-bit set for corresponding MT.
For instance, if M-bit is set for MT-ID #0, MRT alternates will be
calculated for standard topology.

If only M-bit is advertised for MRT-Capabilities without any other
MRT information then the router is regarded as supporting default MRT
profile with default GADAG root selection priority.

6.2.

5.1. MRT Profile sub-TLV in the IS-IS Router CAPABILITY TLV

A new MRT Profile sub-TLV is introduced into the IS-IS Router
CAPABILITY
TLV[RFC4971] TLV (TLV #242 defined in [RFC4971]) to advertise MRT
capabilities. Since MRT is has per level scope, the S-bit and D-bit of
IS-IS Router CAPABILITY TLV MUST be set to zero. The structure of
the MRT Profile sub-TLV is pictured as shown below:

TYPE: TBA-MRT-ISIS-1 (To Be Allocated by IANA)

LENGTH: 8 4

VALUE:

MT ID

MT-ID (2 octet octets with 4 bits reserved)

MRT Profile ID (1 octet)

MRT-Red LDP MT-ID (2 octet)

MRT-Blue LDP MT-ID (2

GADAG Root Selection Priority (1 octet)
+--------------------------------+

Number of octets
+-------------------------------+
|R |R |R |R | MT ID MT-ID | 2
+----------------+---------------+
+-------------------------------+
| MRT Profile ID | 1
+----------------+
+-------------------------------+
| GADAG Root Selection Priority | 1
+----------------+---------------+
| MRT-Red LDP MT-ID | 2
+--------------------------------+
| MRT-Blue LDP
+-------------------------------+

MT-ID | 2
+--------------------------------+ is a 12-bit MT ID represents field containing the base MT topology which multi-topology ID. As
discussed in Section 5.3, this document specifies that the MT-ID
field MUST be set to zero.

The MRT computation is
based on. Profile ID represents the MRT profile this router supports
and supports.

The GADAG Root Selection Priority is the priority for root selection. selection as
GADAG root. A router advertising the MRT Profile sub-TLV MUST
specify a GADAG Root Selection Priority. The range of this priority
is [0, 255] with 128 as the 255]. The RECOMMENDED default value. value of the GADAG Root
Selection Priority is 128. The GADAG Root Selection Policy defined
as part of a given MRT profile determine determines how the GADAG Root
Selection Priority value is used.

If the MRT-Blue LDP MT-ID is 0, then the value specified in the
associated MRT Profile is assumed. If the MRT-Red LDP MT-ID is 0,
then the value specified in the associated MRT profile is assumed.
The MRT-Blue LDP MT-ID and MRT-Red LDP MT-ID MUST NOT be the reserved
values for LDP MT-IDs ([I-D.ietf-mpls-ldp-multi-topology] ). The
value for MRT-Blue LDP MT-ID and MRT-Red LDP MT-ID MUST be different
except for 0. As stated above, the MRT-Blue LDP MT-ID and MRT-Red
LDP MT-ID MUST NOT overlap among profiles if multiple MRT-Profile
sub-TLVs are advertised.

This sub-TLV can occur multiple times if this a router support supports multiple
MRT profiles. This can happen during transition or a network transition. Or it
can be used to support
multiple different uses of MRT within the same network
which prefer may perform better with different profiles.

6.3. MRT-Ineligible Links

A given router SHOULD NOT advertise multiple MRT Profile sub-TLVs
with the same MRT profile ID. If a router receives multiple MRT
Profile sub-TLVs with the same MRT profile ID from the same
originator, it MUST use one with the lowest value of GADAG Root
Selection Priority.

5.1.1. A note on the M-bit in OSPF

[I-D.ietf-ospf-mrt] defines MRT signalling extensions for OSPF. In
addition to the OSPF version of MRT Profile sub-TLV (which is carried
in the OSPF Router Information LSA), it also defines the M-bit (which
is carried in the OSPF Router-LSA.) As discussed in
[I-D.ietf-ospf-mrt], the M-bit in the Router-LSA ensures that all
routers in the area have up-to-date information if a router is
downgraded to a software version that does not support MRT and the
Router Information LSA.

The problematic scenario that requires the M-bit in the OSPF Router-
LSA does not occur in IS-IS. The presence or absence of an IS-IS
Router CAPABILITY TLV containing a given MRT Profile sub-TLV in the
IS-IS Link State PDU provides enough information for all routers to
determine which remote routers support MRT, even after a software
version downgrade of remote routers. Therefore, this document does
not define a corresponding M-bit for IS-IS.

5.2. MRT-Ineligible Link sub-TLV in the Extended IS Reachability TLV

As a matter of policy, an operator may choose to mark some links may not be available as
ineligible for the carrying MRT
computation, which can prevent alternates or traffic using these
links. traffic. For instance, policy can be
made to prevent fast-rerouted traffic from taking those links.

For a link to be excluded from marked as ineligible for use in the MRT computation, calculation,
it MUST be advertised as including the MRT-Ineligible Link sub-TLV in IS-IS Router CAPABILITY
the Extended IS Reachability TLV which is (TLV #22 defined in
level scope with S-bit and D-bit unset. [RFC5305] )
corresponding to the ineligible link. The MRT-Ineligible Link sub-
TLV is structured a zero-length sub-TLV as shown below:

TYPE: TBA-MRT-ISIS-2 (To Be Allocated by IANA)

LENGTH: from 9 to 255 octets 0

VALUE:

MT ID (2 octet with 4 bits reserved)

System ID and pseudo-node number (7 octet for each None

The presence of the zero-length MRT-Ineligible
Link)

No. Link sub-TLV in the
Extended IS Reachability TLV indicates that the associated link MUST
NOT be used in the MRT calculation for the default topology for all
profiles.

5.3. A Note on Multi-Topology Routing

[RFC5120] specifies how to support multi-topology routing in IS-IS.
The current document specifies how to signal support for MRT in the
default routing topology only. The format of Octets
+--------------------------------+
|R |R |R |R | MT ID | 2
+--------------------------------+
|System ID and pseudonode number | 7
+--------------------------------+
| Default metric | 3
+--------------------------------+
. .
. .
+--------------------------------+
|System ID the extensions in this
document allows the MRT Profile sub-TLV and pseudonode number | 7
+--------------------------------+
| Default metric | 3
+--------------------------------+

Each the MRT-Ineligible Link
sub-TLV to be scoped to topologies with non-zero MT-ID at some point
in future. However, this document restricts these extensions to
apply only to the default topology. The MRT Profile sub-TLV is
restricting by explicitly requiring the MT-ID field to be set to
zero. The MRT-Ineligible Link sub-TLV is identified restricted by neighbor's System ID and
pseudo-node number only allowing
it to be included in the Extended IS Reachability TLV (TLV#22) which
is scoped to the default topology, and Default metric, same as not allowing it to appear
TLV#222 (the topology-scoped version of the Extended IS Reachability TLV.
TLV).

Lifting these restrictions is for further study. Note that the MRT
signalling extensions in this document can co-exist with IS-IS multi-
topology routing, with the limitation that MRT Red and Blue
forwarding trees can only be built for the default topology.

The format of the Controlled Convergence sub-TLV (discussed below)
also contains an MT-ID field, allowing a Controlled Convergence sub-
TLV to be scoped to a particular topology. This document does not
place restrictions on the MT-ID field in the Controlled Convergence
sub-TLV. The Controlled Convergence sub-TLV MAY occur multiple times if multiple links has potential
applications that are
ineligible.

7. not limited to MRT, and a topology-scoped FIB
compute/install time makes sense on its own.

6. Controlled Convergence sub-TLV in IS-IS Router CAPABILITY TLV

Section 12.2 of [I-D.ietf-rtgwg-mrt-frr-architecture] describes the
need to wait for a configured or advertised period after a network
failure to insure that all routers are using their new SPTs. shortest path
trees. Similarly, avoiding micro-forwarding loops during convergence
[RFC5715] requires determining the maximum among all routers in the
area of the worst-case route computation and FIB installation time.
More details on the specific reasoning and need for flooding this
value are given in [I-D.atlas-bryant-shand-lf-timers].

A new Controlled Convergence sub-TLV is introduced into the IS-IS
Router CAPABILITY TLV [RFC4971] (TLV #242 defined in [RFC4971]) to advertise
the worst-case time for a router to compute and install all IS-IS
routes in the level after a change to a stable network. This
advertisement has per level scope, so the S-bit and D-bit of IS-IS
Router CAPABILITY TLV MUST be set to zero. The advertisement is
scoped by IGP MT-ID, allowing a router supporting multi-topology IGP routing
to advertise a different worst-
case compute and install worst-case FIB compute/install time for each IGP
topology. This make makes sense as the SPF computations and FIB
installations for each IGP topology are independent can potentially be done
independently of one another, and may have different worst-case
compute and install times.

The structure of the Controlled Convergence sub-TLV is shown below:

TYPE: TBA-MRT-ISIS-3 (To Be Allocated by IANA)

LENGTH: 3

VALUE:

MT ID

MT-ID (2 octet octets with 4 bits reserved)

FIB compute/install time (1 octet)

+--------------------------------+

Number of octets
+-------------------------------+
|R |R |R |R | MT ID MT-ID | 2
+----------------+---------------+
|FIB comp/in time|
+-------------------------------+
| FIB compute/install time | 1
+----------------+
+-------------------------------+

MT-ID is a 12-bit field containing the multi-topology ID.

The FIB compute/install time is the worst-case time the router may
take to compute and install all IS-IS routes in the level after a
change to a stable network. The value is an unsigned integer in
units of milliseconds.

The FIB compute/install time value sent by a router SHOULD be an
estimate taking into account network scale or real-time measurements,
or both. Advertisements SHOULD be dampened to avoid frequent
communication of small changes in the FIB compute/install time.

A router receiving the Controlled Convergence sub-TLV SHOULD estimate
the network convergence time as the maximum of the FIB compute/
install times advertised by the routers in a level, level for a given MT-ID,
including itself. In order to account for routers that do not
advertise the Controlled Convergence sub-TLV, a router MAY use a
locally configured minimum network convergence time as a lower bound
on the computed network convergence time. A router MAY use a locally
configured maximum network convergence time as an upper bound on the
computed network convergence time.

7. Handling MRT Capability Sending and Receiving

The M-bit which identifies router's MRT capability MUST be advertised
in LSP fragment 0. Those MRT related sub-TLVs SHOULD be ignored when
MRT Capability bit is unset. When changes in MRT capabilities are
received, a MRT computation SHOULD be triggered but MAY be delayed
for a while to allow reception of all MRT-related information.

8.1. Extensions

7.1. Advertising MRT extension extensions

MRT sub-TLVs are encapsulated in the Router Capability TLV and
advertised through LSP PDU for using the level-wide. LS-PDU with level-wide scope. MRT sub-TLVs are
optional. If one router does not support MRT, it MUST NOT advertise
those sub-TLVs.

Since the advertisement scope of the MRT sub-TLV is level-wide, the
D-Bit and S-Bit of the Router Capability TLV MUST be set as 0 when it
is advertised. If other sub-TLVs in the Router Capability TLV need
different values for those two bits, there then the router MUST be an independent originate
multiple Router Capability TLV for MRT sub-TLVs. TLVs with different bit values.

When MRT related MRT-related information is changed for the router or existing
IS-IS LSP mechanisms are triggered for refreshing or updating, MRT
sub-TLVs MUST be advertised if the router is MRT-Capable.

For

Based on administrative policies or reasons, policy, it may be desirable to exclude
certain links from the MRT computation. The MRT-Ineligible sub-
TLV sub-TLV
is used to advertise which links should be excluded. Note that an
interface advertised as MRT-Ineligigle MRT-Ineligible by a router is ineligible with
respect to all profiles advertised by that router.

8.2. Parsing

7.2. Processing MRT extension extensions

The processing associated with MRT extension MUST extensions SHOULD NOT affect the peer setup
significantly degrade IS-IS adjacency formation and maintenance or
the routing calculation of the standard topology. for normal shortest path routes.

MRT sub-TLVs SHOULD be validated like other sub-TLVs when received.
MRT sub-TLVs SHOULD also be taken into account for the checksum calculation
calculations and authentication.

If MT-ID conflict is found for MRT-Red or MRT-blue from multiple sub-
TLVs then those associated sub-TLVs MUST be ignored.

Links advertised in as MRT-ineligible using the MRT-Ineligible sub-TLV
MUST be precluded excluded from the MRT
Computation. computation. The removal of those individual
links may change from the computing
router's MRT Island significantly.

9. Backwards Compatibility

The M-bit for can partition an MRT Island or it can
significantly modify the construction of the GADAG and the result MRT capability,
Red and Blue trees. Therefore, all routers must perform the same
computation using the same set of links.

8. Backward Compatibility

The MRT Profile sub-TLV and sub-TLV, the MRT-
Ineligible MRT-Ineligible Link sub-TLV, and the
Controlled Convergence sub-TLV defined in this document SHOULD NOT introduce
any interoperability issues. are
compatible with existing implementations of IS-IS. Routers that do
not support these MRT extensions SHOULD are expected to silently ignore them. Alternates or traffic MUST
NOT be affected

Router that do support these extensions have mechanisms to recognize
routers that don't support these extensions (or are not configured to
participate in current IS-IS routing domain.

10. MRT) and behave accordingly.

9. Implementation Status

[RFC Editor: please remove this section prior to publication.]

Please see [I-D.ietf-rtgwg-mrt-frr-architecture] for details on
implementation status.

11.

10. Security Considerations

This

The IS-IS extension is extensions in this document do not believed to introduce new security
concerns.

11. Acknowledgements

The authors would like to thank Shraddha Hegde for her useful
suggestions.

12. IANA Considerations

Please

12.1. MRT Profile and Controlled Convergence sub-TLVs

IANA is requested to allocate values for the following sub-TLVs types
in the IS-IS Router CAPABILITY TLV
Types defined in [RFC4971]: the MRT
Profile sub-TLV (TBA-MRT-ISIS-1), MRT-Ineligible
Link sub-TLV (TBA-MRT-ISIS-2), (TBA-MRT-ISIS-1) and Controlled Convergence sub-TLV
(TBA-MRT-ISIS-3). The IANA registry for these sub-TLV types is
displayed as "sub-TLVs for TLV 242" (http://www.iana.org/assignments/
isis-tlv-codepoints/isis-tlv-codepoints.xhtml#isis-tlv-codepoints-
242). The new entries in this registry are shown below.

Value Description Reference
-------------- ------------------------------ ------------
TBA-MRT-ISIS-1 MRT Profile sub-TLV [This draft]
TBA-MRT-ISIS-3 Controlled Convergence sub-TLV [This draft]

12.2. MRT-Ineligible Link sub-TLV

IANA is requested to allocate a value for the following sub-TLVs type
in the Extended IS Reachability TLV defined in [RFC5305]: MRT-
Ineligible Link sub-TLV (TBA-MRT-ISIS-2). The IANA registry for
these sub-TLV types is displayed as "Sub-TLVs for TLVs 22, 23, 141,
222, and 223" (http://www.iana.org/assignments/isis-tlv-codepoints/
isis-tlv-codepoints.xhtml#isis-tlv-codepoints-22-23-141-222-223).
The new entry in this registry is shown below.

Type Description 22 23 141 222 223 Ref.
-------------- --------------------------- -- -- --- --- --- --------
TBA-MRT-ISIS-2 MRT-Ineligible Link sub-TLV y y n n n [This
draft]

13. References

13.1. Normative References

[I-D.ietf-mpls-ldp-multi-topology]
Zhao, Q., Raza, K., Zhou, C., Fang, L., Li, L., and D.
King, "LDP Extensions for Multi Topology", draft-ietf-
mpls-ldp-multi-topology-12 (work in progress), April 2014.

[I-D.ietf-rtgwg-mrt-frr-algorithm]
Enyedi,
Envedi, G., Csaszar, A., Atlas, A., Bowers, C., and A.
Gopalan, "Algorithms for computing Maximally Redundant
Trees for IP/LDP Fast-Reroute", draft-rtgwg-mrt-frr-
algorithm-01 Fast- Reroute", draft-ietf-rtgwg-mrt-frr-
algorithm-06 (work in progress), July 2014. October 2015.

[I-D.ietf-rtgwg-mrt-frr-architecture]
Atlas, A., Kebler, R., Bowers, C., Enyedi, Envedi, G., Csaszar,
A., Tantsura, J., Konstantynowicz, M., and R. White, "An Architecture for IP/LDP IP/
LDP Fast-Reroute Using Maximally Redundant Trees", draft-rtgwg-mrt-frr-architecture-04 draft-
ietf-rtgwg-mrt-frr-architecture-07 (work in progress), July 2014.

[RFC3137] Retana, A., Nguyen, L., White, R., Zinin, A., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 3137,
June 2001.
October 2015.

[RFC3787] Parker, J., Ed., "Recommendations for Interoperable IP
Networks using Intermediate System to Intermediate System
(IS-IS)", RFC 3787, DOI 10.17487/RFC3787, May 2004. 2004,
<http://www.rfc-editor.org/info/rfc3787>.

[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <http://www.rfc-editor.org/info/rfc5305>.

13.2. Infomative References

[I-D.atlas-bryant-shand-lf-timers]
K, A. and S. Bryant, "Synchronisation of Loop Free Timer
Values", draft-atlas-bryant-shand-lf-timers-04 (work in
progress), February 2008.

[I-D.ietf-ospf-mrt]
Atlas, A., Hegde, S., Bowers, C., Tantsura, J., and Z. Li,
"OSPF Extensions to Support Maximally Redundant Trees",
draft-ietf-ospf-mrt-01 (work in progress), October 2015.

[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, DOI 10.17487/RFC1195,
December 1990. 1990, <http://www.rfc-editor.org/info/rfc1195>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997. 1997,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, DOI 10.17487/RFC4915, June 2007. 2007,
<http://www.rfc-editor.org/info/rfc4915>.

[RFC4971] Vasseur, JP., Ed., Shen, N., Ed., and R. Aggarwal, Ed.,
"Intermediate System to Intermediate System (IS-IS)
Extensions for Advertising Router Information", RFC 4971,
DOI 10.17487/RFC4971, July 2007. 2007,
<http://www.rfc-editor.org/info/rfc4971>.

[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120,
DOI 10.17487/RFC5120, February 2008. 2008,
<http://www.rfc-editor.org/info/rfc5120>.

[RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
DOI 10.17487/RFC5308, October
2008. 2008,
<http://www.rfc-editor.org/info/rfc5308>.

[RFC5715] Shand, M. and S. Bryant, "A Framework for Loop-Free
Convergence", RFC 5715, DOI 10.17487/RFC5715, January 2010.
2010, <http://www.rfc-editor.org/info/rfc5715>.

Authors' Addresses

Zhenbin Li
Huawei Technologies
Huawei Bld., No.156 Beiqing Rd.
Beijing 100095
China

Email: lizhenbin@huawei.com

Nan Wu
Huawei Technologies
Huawei Bld., No.156 Beiqing Rd.
Beijing 100095
China

Email: eric.wu@huawei.com
Quintin Zhao
Huawei Technologies
125 Nagog Technology Park
Acton, MA 01719
USA

Alia Atlas
Juniper Networks
10 Technology Park Drive
Westford, MA 01886
USA

Email: akatlas@juniper.net

Chris Bowers
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
USA

Email: cbowers@juniper.net

Jeff Tantsura
Ericsson
300 Holger Way
San Jose, CA 95134
USA

Email: jeff.tantsura@ericsson.com