Internet DRAFT - draft-chen-isis-ttz
draft-chen-isis-ttz
Internet Engineering Task Force H. Chen
Internet-Draft R. Li
Intended status: Standards Track Futurewei
Expires: February 19, 2021 Y. Yang
IBM
A. Kumar S N
RtBrick
Y. Fan
Casa Systems
N. So
V. Liu
M. Toy
Verizon
L. Liu
Fujitsu
K. Makhijani
Futurewei
August 18, 2020
IS-IS Topology-Transparent Zone
draft-chen-isis-ttz-12.txt
Abstract
This document presents a topology-transparent zone in an area. A
zone is a block/piece of an area, which comprises a group of routers
and a number of circuits connecting them. It is abstracted as a
virtual entity such as a single virtual node or zone edges mesh. Any
router outside of the zone is not aware of the zone. The information
about the circuits and routers inside the zone is not distributed to
any router outside of the zone.
Status of This Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 19, 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
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to this document.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Zone Abstraction . . . . . . . . . . . . . . . . . . . . . . 4
4. Topology-Transparent Zone . . . . . . . . . . . . . . . . . . 5
4.1. Zone as a Single Node . . . . . . . . . . . . . . . . . . 5
4.1.1. An Example of Zone as a Single Node . . . . . . . . . 5
4.1.2. Zone Leader Election . . . . . . . . . . . . . . . . 7
4.1.3. LS Generation for Zone as a Single Node . . . . . . . 8
4.1.4. Adjacency Establishment and Termination . . . . . . . 8
4.1.5. Computation of Routes . . . . . . . . . . . . . . . . 10
4.1.6. Extensions to Protocols . . . . . . . . . . . . . . . 11
4.2. Zone as Edges Full Mesh . . . . . . . . . . . . . . . . . 14
4.2.1. Extensions to IS-IS . . . . . . . . . . . . . . . . . 14
4.3. Advertisement of LSs . . . . . . . . . . . . . . . . . . 15
4.3.1. Advertisement of LSs within Zone . . . . . . . . . . 15
4.3.2. Advertisement of LSs through Zone . . . . . . . . . . 16
5. Seamless Migration . . . . . . . . . . . . . . . . . . . . . 16
5.1. Transfer Zone to a Single Node . . . . . . . . . . . . . 16
5.2. Roll Back from Zone as a Single Node . . . . . . . . . . 16
6. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 19
7. Security Considerations . . . . . . . . . . . . . . . . . . 19
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 20
10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 20
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
11.1. Normative References . . . . . . . . . . . . . . . . . . 20
11.2. Informative References . . . . . . . . . . . . . . . . . 21
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
[ISO10589] describes two levels of areas, which are level 1 and level
2 areas in IS-IS. There are scalability issues in using areas as the
number of routers in a network becomes larger and larger.
Through splitting the network into multiple areas, we may extend the
network further. However, dividing a network from one area into
multiple areas or from a number of existing areas to even more areas
is a very challenging and time consuming task since it is involved in
significant network architecture changes.
These issues can be resolved by using topology-transparent zone
(TTZ), which abstracts a zone (i.e., a block/piece of an area) as a
single virtual node or zone edges' mesh with minimum efforts and
minimum service interruption. Note that a zone can be an area (i.e.,
the entire piece of an area).
This document presents a topology-transparent zone and describes
extensions to IS-IS for supporting the topology-transparent zone.
1.1. 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 RFC 2119 [RFC2119].
1.2. Terminology
LSP: A Link State Protocol Data Unit (PDU) in IS-IS.
LS: A Link Sate, which is short for LSP in IS-IS.
TTZ: A Topology-Transparent Zone.
Zone: A block or piece of an area. In a special case, a zone is an
area (i.e., the entire piece of an area).
Zone External Node: A node outside of a zone.
Zone Internal Node: A node of a zone without any connection to a
node outside of the zone.
Zone Edge/Border: A node of a zone connecting to a node outside of
the zone.
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Zone Node: A zone internal node or a zone edge/border node (i.e., a
node of a zone).
Zone Link: A link connecting zone nodes (i.e., a link of a zone).
Zone Neighbor: A node outside of a zone that is a neighbor of a
zone edge/border.
2. Requirements
Topology-Transparent Zone (TTZ) may be deployed for resolving some
critical issues such as scalability in existing networks and future
networks. The requirements for TTZ are listed as follows:
o TTZ MUST be backward compatible. When a TTZ is deployed on a set
of routers in a network, the routers outside of the TTZ in the
network do not need to know or support TTZ.
o TTZ MUST support at least one more levels of network hierarchies,
in addition to the hierarchies supported by existing routing
protocols.
o Abstracting a zone as a virtual entity, which is a single virtual
node or zone edges' mesh, SHOULD be smooth with minimum service
interruption.
o De-abstracting (or say rolling back) a virtual entity to a zone
SHOULD be smooth with minimum service interruption.
o Users SHOULD be able to easily set up an end to end service
crossing TTZs.
o The configuration for a TTZ in a network SHOULD be minimum.
o The changes on the existing protocols for supporting TTZ SHOULD be
minimum.
3. Zone Abstraction
A zone can be abstracted as a single virtual node or the zone edges'
full mesh.
When a zone is abstracted as a single virtual node, this single node
is connected to all the neighbors of the zone, and is in the same
area as the neighbors.
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When a zone is abstracted as its edges' full mesh, there is a full
mesh connections among the edges and each edge is also connected to
its neighbors outside of the zone.
4. Topology-Transparent Zone
A Topology-Transparent Zone (TTZ) comprises an Identifier (ID) and a
piece/block of an area such as a Level 2 area in IS-IS. It is
abstracted as a single virtual node or its edges' full mesh. TTZ and
zone will be used exchangably below.
4.1. Zone as a Single Node
After a zone is abstracted as a single virtual node having a virtual
node ID, every node outside of the zone sees a number of links
connected to this single node. Each of these links connects a zone
neighbor. The link states inside the zone are not advertised to any
node outside of the zone. The virtual node ID may be derived from
the zone ID.
4.1.1. An Example of Zone as a Single Node
The figure below shows an example of an area containing a TTZ: TTZ
600.
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TTZ 600
\
\ ^~^~^~^~^~^~^~^~^~^~^~^~
( )
===[R15]========(==[R61]------------[R63]==)======[R29]===
|| ( | \ / | ) ||
|| ( | \ / | ) ||
|| ( | \ / | ) ||
|| ( | ___\ / | ) ||
|| ( | / [R71] | ) ||
|| ( | [R73] / \ | ) ||
|| ( | / \ | ) ||
|| ( | / \ | ) ||
|| ( | / \ | ) ||
===[R17]========(==[R65]------------[R67]==)======[R31]===
\\ (// \\) //
|| //v~v~v~v~v~v~v~v~v~v~v~\\ ||
|| // \\ ||
|| // \\ ||
\\ // \\ //
======[R23]==============================[R25]=====
// \\
// \\
Figure 1: An Example of TTZ 600
The area comprises routers R15, R17, R23, R25, R29 and R31. It also
contains TTZ 600, which comprises routers R61, R63, R65, R67, R71 and
R73, and the circuits connecting them.
There are two types of routers in a TTZ: TTZ internal routers and TTZ
edge/border routers. A TTZ internal router is a router inside the
TTZ and its adjacent routers are inside the TTZ. A TTZ edge/border
router is a router inside the TTZ and has at least one adjacent
router that is outside of the TTZ.
The TTZ in the figure above comprises four TTZ edge/border routers
R61, R63, R65 and R67. Each TTZ edge/border router is connected to
at least one router outside of the TTZ. For instance, router R61 is
a TTZ edge/border router since it is connected to router R15, which
is outside of the TTZ.
In addition, the TTZ comprises two TTZ internal routers R71 and R73.
A TTZ internal router is not connected to any router outside of the
TTZ. For instance, router R71 is a TTZ internal router since it is
not connected to any router outside of the TTZ. It is just connected
to routers R61, R63, R65, R67 and R73 inside the TTZ.
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A TTZ MUST hide the information inside the TTZ from the outside. It
MUST NOT directly distribute any internal information about the TTZ
to a router outside of the TTZ.
For instance, the TTZ in the figure above MUST NOT send the
information about TTZ internal router R71 to any router outside of
the TTZ in the routing domain; it MUST NOT send the information about
the circuit between TTZ router R61 and R65 to any router outside of
the TTZ.
From a router outside of the TTZ, a TTZ is seen as a single node
(refer to the Figure below). For instance, router R15, which is
outside of TTZ 600, sees TTZ 600 as a single node Rz, which has
normal connections to R15, R29, R17 and R23, R25 and R31.
TTZ 600
\
\ ^~^~^~^~^~^~^~^~^~^~^~^~
( )
===[R15]========( )======[R29]===
|| ( ) ||
|| ( ) ||
|| ( ) ||
|| ( ) ||
|| ( Rz ) ||
|| ( ) ||
|| ( ) ||
|| ( ) ||
|| ( ) ||
===[R17]========( )======[R31]===
\\ ( ) //
|| //v~v~v~v~v~v~v~v~v~v~v~\\ ||
|| // \\ ||
|| // \\ ||
\\ // \\ //
======[R23]==============================[R25]=====
// \\
// \\
Figure 2: TTZ 600 as Single Node Rz
4.1.2. Zone Leader Election
A node in a zone is elected as a leader for the zone, which is the
node with the highest priority (and the highest node ID when there
are more than one nodes having the same highest priority) in the
zone. The leader election mechanism described in
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[I-D.ietf-lsr-dynamic-flooding] may be used to elect the leader for
the zone.
4.1.3. LS Generation for Zone as a Single Node
The leader for the zone originates an LS (i.e., an LSP in IS-IS) for
the zone as a single virtual node and sends it to its neighbors.
The LS comprises all the links connecting the zone neighbors. The LS
ID is the ID of the virtual node for the zone. The Source ID or
Advertising Node/Router ID is the ID of the virtual node.
In addition, the LS may contain the stub links for the routes such as
the loopback addresses inside the zone to be accessed by zone
external nodes (i.e., nodes outside of the zone).
4.1.4. Adjacency Establishment and Termination
A zone edge node, acting as a single virtual node for the zone, forms
an adjacency with a node outside of the zone in a way described
below.
Case 1 for a new adjacency (i.e., no adjacency exists between the
edge and the node outside of the zone also called zone neighbor):
The edge node originates and sends the zone neighbor every protocol
packet such as Hello, which contains the virtual node ID as Source
ID.
When the edge node synchronizes its link state database (LSDB) with
the zone neighbor, it sends the zone neighbor the information about
all the link states except for the link states belonging to the zone
that are hidden from any node outside of the zone.
At the end of the LSDB synchronization, the LS for the zone as the
single virtual node is originated by the zone leader and distributed
to the zone neighbor. This LS contains the links connecting all the
zone neighbors, including this newly formed zone neighbor.
Case 2 for an existing adjacency (i.e., an adjacency already exists
between the zone edge and the zone neighbor):
At first, the edge acting as virtual node creates a new adjacency
between the virtual node for the zone and the zone external node in a
normal way. It sends Hellos and other packets containing the virtual
node ID as Source ID to the zone external node. The zone external
node establishes the adjacency with the virtual in the normal way.
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And then, the edge terminates the existing adjacency between the edge
and the external node after the zone has been transferred to the
virtual node. It stops sending Hellos for the adjacency to the zone
external node. Without receiving Hellos from the edge node for a
given time such as hold-timer interval, the zone external node
removes the adjacency to the edge node. Even though this adjacency
terminates, the edge node keeps the link to the external node in its
LS.
In another option, the zone edge sends Hellos to the zone neighbor
with additional information, including a flag T-bit set to one and a
TLV with the virtual node ID. This information requests the zone
neighbor to transfer the existing adjacency to the new adjacency
smoothly through working together with the zone edge in following
steps.
Zone Edge Zone Neighbor
(Transfer Zone
to Virtual Node) Hello(T=1, Virtual ID)
----------------------> OK for Transfer
Adjacency
Hello(T=1, Virtual ID)
Remote Ready for <----------------------
Transfer
Hello(Source=Virtual ID)
Start Transfer -----------------------> Transfer to New
Adjacency
Hello
Transfer to New <-----------------------
Adjacency . . .
Step 1: When "Transfer Zone to Virtual Node" is triggered, the zone
edge sends the zone neighbor a Hello containing additional
information T=1 and Virtual node ID.
Step 2: After receiving the Hello with T=1 and virtual node ID from
the zone edge, the zone neighbor sends the zone edge a Hello with
T=1 and virtual node ID, which means ok for transfer to the new
adjacency.
Step 3: The edge sends the zone neighbor a Hello containing the
virtual node ID as Source ID after receiving the Hello with T=1
and virtual node ID from the zone neighbor, which starts to
transfer to the new adjacency.
Step 4: The zone neighbor changes the existing adjacency to the new
adjacency after receiving the Hello containing the virtual node ID
as Source ID from the zone edge; and sends the zone edge a Hello
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without the additional information, which means that it
transferred to the new adjacency.
Step 5: The zone edge changes the existing adjacency to the new
adjacency after receiving the Hello without the additional
information from the zone neighbor; and continues to send the zone
neighbor a Hello containing the virtual node ID as Source ID. At
this point, the old adjacency is transferred to the new one.
For the zone neighbor, changing the existing adjacency to the new one
includes:
o Changing the existing adjacency ID from the edge node ID to the
virtual node ID through either removing the existing adjacency and
adding a new adjacency with the virtual node ID or just changing
the existing adjacency ID from the edge node ID to the virtual
node ID,
o Removing the link to the zone edge node from its LS and adding a
new link to the virtual node (or just changing the link to the
edge node to the link to the virtual node in its LS), and
o Continuing sending the zone edge Hellos without additional
information.
For the zone edge, changing the existing adjacency to the new one
includes:
o Keeping the link to the zone neighbor in its LS, and
o Continuing sending the zone neighbor Hellos containing the virtual
node ID as Source ID.
4.1.5. Computation of Routes
After a zone edge migrates to zone as a virtual node, it computes the
routes (i.e., shortest paths to the destinations) in the zone using
the zone topology (i.e., the topology of the zone without the virtual
node).
For the routes outside of the zone, it computes them using the zone
topology, the topology outside of the zone without the virtual node
and the connections between each zone edge and its zone neighbor.
After a zone internal node migrates to zone as a virtual node, it
computes the routes using the zone topology, the topology outside of
the zone without the virtual node and the connections between each
zone edge and its zone neighbor.
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4.1.6. Extensions to Protocols
The following TLVs are defined in IS-IS.
o Adjacent Node ID TLV: containing an adjacent node ID, to which an
adjacency is transferred or rolled back. In case of transfer, the
TLV contains the virtual node ID; in case of roll back, the TLV
contains the edge node ID.
o Zone TLV: containing a zone ID, a flags field and optional sub-
TLVs.
4.1.6.1. Adjacent Node ID TLV
The format of Adjacent Node ID TLV is illustrated 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD1) | Length (8) | Virtual/Edge Node ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Virtual/Edge Node ID (Continue) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |N|T|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type (1 byte): To be assigned by IANA.
Length (1 byte): Its value is 8.
Virtual/Edge Node ID (6 bytes): An adjacent node ID, to which an
adjacency is transferred or rolled back.
Flags field (16 bits): two new flag bits are defined as follows:
o T-bit: Short for Transfer Adjacency bit. The T-bit set to one
indicates a request for transferring to a new 'virtual' adjacency
from the existing adjacency and the new adjacency is identified by
the virtual node ID (or say abstract node ID).
o N-bit: Short for Roll Back to Normal Adjacency bit. The N-bit set
to one indicates a request for rolling back to a Normal adjacency
from the existing 'virtual' adjacency and the normal adjacency is
identified by the edge node ID.
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4.1.6.2. Zone TLV
The format of IS-IS Zone TLV is illustrated below. It may be added
into an LSP or a Hello PDU for a zone node. When a node in a zone
receives a CLI command triggering zone information distribution for
migration, it updates its LSP by adding an IS-IS Zone TLV with T set
to 1. When a node in a zone receives a CLI command activating
migration zone to an abstracted entity, it sets M to 1 in the Zone
TLV in its LSP.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD2) | Length | Zone ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Zone ID (Continue) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |E|Z|S| OP | Sub TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: IS-IS Zone TLV
Type (1 byte): To be assigned by IANA.
Length (1 byte): Its value is variable.
Zone ID (6 bytes): It is the identifier (ID) of a zone.
Flags field (16 bits): Three flag bits E, Z and S, and OP of 3 bits
are defined.
E = 1: Indicating a node is a zone edge node
Z = 1: Indicating a node has migrated to Zone as a virtual entity
S = 1: Indicating the virtual entity is a Single virtual node
When a zone node originates an LS containing a zone TLV, it MUST set
flag E to 1 if it is a zone edge node and to 0 if it is a zone-
internal node. It MUST set flag Z to 1 after it has migrated to zone
as a virtual entity and to 0 before it migrates zone to the virtual
entity or after it rolls back from zone as a virtual entity. When
the entity abstracted from a zone is a Single virtual node, flag S
MUST be set to 1.
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OP Value Meaning (Operation)
0x001 (T): Advertising Zone Topology Information for Migration
0x010 (M): Migrating Zone to a Virtual Entity
0x011 (N): Advertising Normal Topology Information for Rollback
0x100 (R): Rolling Back from the Virtual Entity
The value of OP indicates one of the four operations above. When any
of the other values is received, it is ignored.
When a node in a zone receives a CLI command triggering zone
information distribution for migration, it updates its LSP by adding
an IS-IS Zone TLV with T set to 1. When a node in a zone receives a
CLI command activating migration zone to a virtual entity, it sets M
to 1 in the Zone TLV in its LSP.
Two new sub-TLVs are defined, which may be added into an IS-IS Zone
TLV in an LSP. One is Zone IS Neighbor sub-TLV, or Zone ISN sub-TLV
for short. The other is Zone ES Neighbor sub-TLV, or Zone ESN sub-
TLV for short. A Zone ISN sub-TLV contains the information about a
number of IS neighbors in the zone connected to a zone edge router.
It has the format 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD) | Length |DefaultMetric(i| DelayMetric(i)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|ExpenseMetric(i| ErrorMetric(i)| Neighbor ID(i) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Zone ISN Sub TLV
A Zone ISN Sub TLV has 1 byte of Type, 1 byte of Length of
n*(IDLength + 4), which is followed by n tuples of Default Metric,
Delay Metric, Expense Metric, Error Metric and Neighbor ID.
A Zone ESN sub-TLV contains the information about a number of ES
neighbors in the zone connected to a zone edge node. It has the
format below.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD) | Length |Default Metric | DelayMetric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Expense Metric | Error Metric | Neighbor ID(i) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Zone ESN Sub TLV
4.2. Zone as Edges Full Mesh
OSPF Topology-Transparent Zone [RFC8099] describes the zone as edges'
full mesh and the extensions to OSPF for supporting zone as edges'
full mesh. Based on these extensions, IS-IS is extended by a few new
TLVs or Sub-TLVs.
4.2.1. Extensions to IS-IS
4.2.1.1. Updating LSPs for Zone
A zone internal node adds an IS-IS Zone TLV into its LSP after it
receives an LSP containing an IS-IS Zone TLV with T = 1 or a CLI
command triggering zone information distribution for migration. The
TLV has a zone ID set to the ID of the zone and E bit in Flags set to
0 indicating zone internal node. The node floods its LSP to its
neighbors in the zone.
When a node inside the zone receives an LSP containing an IS-IS Zone
TLV from a neighboring node in the zone, it stores the LSP and floods
the LSP to the other neighboring nodes in the zone.
For every zone edge node, it updates its LSP in three steps and
floods the LSP to all its neighbors.
At first, the zone edge node adds an IS-IS Zone TLV into its LSP
after it receives an LSP containing an IS-IS Zone TLV with T = 1 or a
CLI command triggering zone information distribution for migration.
The TLV has a zone ID set to the ID of the zone, E bit in Flags set
to 1 indicating zone edge node and a Zone ISN Sub TLV. The Sub TLV
contains the information about the zone IS neighbors connected to the
zone edge node. In addition, the TLV may has a Zone ESN Sub TLV
comprising the information about the zone end systems connected to
the zone edge node.
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Secondly, it adds each of the other zone edge nodes as an IS neighbor
into the Intermediate System Neighbors TLV in the LSP after it
receives an LSP containing an IS-IS Zone TLV with M = 1 or a CLI
command activating migration zone to an abstracted entity. The
metric to the neighbor is the metric of the shortest path to the edge
node within the zone.
In addition, it adds a Prefix Neighbors TLV into its LSP. The TLV
contains a number of address prefixes in the zone to be reachable
from outside of the zone.
And then it removes the IS neighbors corresponding to the IS
neighbors in the Zone TLV (i.e., in the Zone ISN sub TLV) from
Intermediate System Neighbors TLV in the LSP, and the ES neighbors
corresponding to the ES neighbors in the Zone TLV (i.e., in the Zone
ESN sub TLV) from End System Neighbors TLV in the LSP. This SHOULD
be done after it receives the LSPs for virtualizing zone from the
other zone edges for a given time.
4.3. Advertisement of LSs
LSs can be divided into a couple of classes according to their
Advertisements. The first class of LSs is advertised within a zone.
The second is advertised through a zone.
4.3.1. Advertisement of LSs within Zone
Any LS about a link state in a zone is advertised only within the
zone. It is not advertised to any router outside of the zone. For
example, a router LS generated for a zone internal router is
advertised only within the zone.
Any network LS generated for a broadcast network in a zone is
advertised only within the zone. It is not advertised outside of the
zone.
After migrating to zone as a single virtual node or edges' full mesh,
every zone edge MUST NOT advertise any LS belonging to the zone or
any information in a LS belonging to the zone to any node outside of
the zone. The zone edge determines whether an LS is about a zone
internal link state by checking if the advertising router of the LS
is a zone internal router.
For any zone LS originated by a node within the zone, every zone edge
node MUST NOT advertise it to any node outside of the zone.
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4.3.2. Advertisement of LSs through Zone
Any LS about a link state outside of a zone received by a zone edge
is advertised using the zone as transit. For example, when a zone
edge node receives an LS from a node outside of the zone, it floods
the LS to its neighbors both inside and outside of the zone. This LS
may be any LS such as a router LSA that is advertised within an OSPF
area.
The nodes in the zone continue to flood the LS. When another zone
edge receives the LS, it floods the LS to its neighbors both inside
and outside of the zone.
5. Seamless Migration
This section presents the seamless migration between a zone and its
single virtual node. The seamless migration between a zone and its
edges' full mesh for IS-IS is similar to that described in OSPF
Topology-Transparent Zone [RFC8099] for OSPF.
5.1. Transfer Zone to a Single Node
After transfer a Zone to a Single Virtual Node is triggered, the zone
is abstracted as a single virtual node in two steps:
Step 1: Every zone edge node works together with each of its zone
neighbor nodes to create a new adjacency between the virtual node
and the neighbor node in the way described in Section 4.1.4 for
Adjacency Establishment and Termination procedure for case 2.
After creating the adjacency, each of the zone neighbor nodes
update its LS by adding the adjacency/link into its LS.
Step 2: The zone leader originates an LS for the virtual node after
receiving the updated LSes originated by all the zone neighbor
nodes, where the updated LSes contain all the zone neighbors.
Step 3: After receiving the LS for the virtual node, every zone edge
does not send any LS inside the zone to any zone neighbors. It
advertises its LS without any links inside the zone to the nodes
outside of the zone and terminates its adjacency to each of its
zone neighbors in the way described in Section 4.1.4 for Adjacency
Establishment and Termination procedure for case 2.
5.2. Roll Back from Zone as a Single Node
After roll back from Zone as a Signle Virtual Node is triggered,
rolling back is done in following steps:
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Step 1: Every zone edge creates an adjacency to each of its zone
neighbors in a normal way.
Step 2: After all the adjacencies between the zone edges and the
zone neighbors are created, the zone leader updates the LS for the
virtual node by changing every link metric to the maximum metric
in the LS.
Step 3: Every zone edge sends its LS with the links inside the zone
and all the LSes inside the zone to its zone neighbors. Every
zone edge acting as the virtual node terminates the adjacency
between the virtual node and each of its zone neighbors through
stopping Hellos to the neighbors.
In another option, rolling back is done as follows:
Step 1: Using the procedure described in the following, every zone
edge rolls back the existing virtual adjacency between the edge
node acting as the virtual node and the zone neighbor node to a
normal adjacency between the edge node and the neighbor.
Step 2: The zone leader may flush the LS for the virtual node.
Every zone edge sends Hello and other packets to its zone
neighbors, where the packets contain the edge node ID as Source
ID.
The procedure below smoothly rolls back the existing virtual
adjacency between the edge node acting as the virtual node and the
zone neighbor node to a normal adjacency between the edge node and
the neighbor node.
The edge node sends the neighbor node Hellos with additional
information, including a flag N-bit set to one and a TLV with the
edge node ID such as the Adjacent Node ID TLV with the edge node ID.
This information requests the neighbor node to roll back the existing
virtual adjacency to the normal adjacency smoothly through working
together with the edge node.
The following steps will roll back the existing virtual adjacency to
the normal one:
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zone Edge zone Neighbor
(Roll Back to
Normal Adjacency) Hello (N=1, Edge ID)
----------------------> OK to Roll Back to
Normal Adjacency
Hello (N=1, Edge ID)
Remote Ready for <----------------------
Rolling Back
Hello(Source=Edge ID)
Start Roll Back -----------------------> Roll Back to
Normal Adjacency
Hello
Roll Back to <-----------------------
Normal Adjacency . . .
Step 1: When "Roll Back from Zone as a Single Node" is triggered,
the edge node sends the neighbor node a Hello with the additional
information N=1 and Edge ID as normal adjacency ID in order to
roll back to the normal adjacency from the virtual adjacency.
Step 2: After receiving the Hello with the additional information
from the edge node, the neighbor node sends the edge node a Hello
with the additional information (i.e., N=1 and Edge ID as normal
adjacency ID), which means ok for rolling back to the normal
adjacency.
Step 3: The edge sends the neighbor a Hello containing the edge node
ID as Source ID after receiving the Hello with the additional
information from the neighbor, which starts to roll back to the
normal adjacency.
Step 4: The neighbor node changes the existing adjacency to the
normal adjacency after receiving the Hello containing the edge
node ID as Source ID from the edge node; and sends the edge node a
Hello without the additional information, which means that it
rolled back to the normal adjacency.
Step 5: The edge node changes the existing adjacency to the normal
adjacency after receiving the Hello without the additional
information from the neighbor node; and continues to send the
neighbor Hello containing the edge node ID as Source ID. At this
point, the virtual adjacency is rolled back to the normal
adjacency.
For the neighbor node, changing the existing virtual adjacency to the
normal one includes:
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o Changing the existing adjacency ID from the virtual node ID to the
edge node ID through either removing the existing adjacency and
adding a new adjacency with the edge node ID or just changing the
existing adjacency ID from the virtual node ID to the edge node
ID,
o Removing the link to the virtual node from its LS and adding a new
link to the edge node (or just changing the link to the virtual
node to the link to the edge node in its LS), and
o Continuing sending the edge node Hellos without additional
information.
For the edge node, changing the existing virtual adjacency to the
normal one includes:
o Sending its LS to the neighbor, and
o Continuing sending the neighbor node Hellos containing the edge
node ID as Source ID without additional information.
6. Operations
The Operations on TTZ described in OSPF Topology-Transparent Zone
[RFC8099] are for Zone as Edges Full Mesh in OSPF. They can be used
for Zone as Edges Full Mesh in IS-IS. They can also be used for Zone
as a Single Virtual Node in IS-IS.
7. Security Considerations
The mechanism described in this document does not raise any new
security issues for the IS-IS protocols.
8. IANA Considerations
Under the registry name "IS-IS TLV Codepoints", IANA is requested to
assign new registry types for Adjacent Node ID, Zone ID and Zone
Options as follows:
+==============+===================+=====================+
| TLV Type | TLV Name | reference |
+==============+===================+=====================+
| 26(suggested)| Adjacent Node ID | This document |
+--------------+-------------------+---------------------+
| 27(suggested)| Zone | This document |
+--------------+-------------------+---------------------+
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9. Contributors
Alvaro Retana
Futurewei
Raleigh, NC
USA
Email: alvaro.retana@futurewei.com
10. Acknowledgement
The authors would like to thank Acee Lindem, Abhay Roy, Christian
Hopps, Dean Cheng, Russ White, Tony Przygienda, Wenhu Lu, Lin Han,
Kiran Makhijani, Padmadevi Pillay Esnault, and Yang Yu for their
valuable comments on TTZ.
11. References
11.1. Normative References
[I-D.ietf-lsr-dynamic-flooding]
Li, T., Psenak, P., Ginsberg, L., Chen, H., Przygienda,
T., Cooper, D., Jalil, L., Dontula, S., and G. Mishra,
"Dynamic Flooding on Dense Graphs", draft-ietf-lsr-
dynamic-flooding-07 (work in progress), June 2020.
[I-D.ietf-spring-segment-routing]
Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing
Architecture", draft-ietf-spring-segment-routing-15 (work
in progress), January 2018.
[ISO10589]
International Organization for Standardization,
"Intermediate System to Intermediate System Intra-Domain
Routing Exchange Protocol for use in Conjunction with the
Protocol for Providing the Connectionless-mode Network
Service (ISO 8473)", ISO/IEC 10589:2002, Nov. 2002.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, DOI 10.17487/RFC1195,
December 1990, <https://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,
<https://www.rfc-editor.org/info/rfc2119>.
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[RFC5029] Vasseur, JP. and S. Previdi, "Definition of an IS-IS Link
Attribute Sub-TLV", RFC 5029, DOI 10.17487/RFC5029,
September 2007, <https://www.rfc-editor.org/info/rfc5029>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC7142] Shand, M. and L. Ginsberg, "Reclassification of RFC 1142
to Historic", RFC 7142, DOI 10.17487/RFC7142, February
2014, <https://www.rfc-editor.org/info/rfc7142>.
[RFC8099] Chen, H., Li, R., Retana, A., Yang, Y., and Z. Liu, "OSPF
Topology-Transparent Zone", RFC 8099,
DOI 10.17487/RFC8099, February 2017,
<https://www.rfc-editor.org/info/rfc8099>.
11.2. Informative References
[Clos] Clos, C., "A Study of Non-Blocking Switching Networks",
The Bell System Technical Journal Vol. 32(2), DOI
10.1002/j.1538-7305.1953.tb01433.x, March 1953,
<http://dx.doi.org/10.1002/j.1538-7305.1953.tb01433.x>.
[RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008,
<https://www.rfc-editor.org/info/rfc5307>.
Authors' Addresses
Huaimo Chen
Futurewei
Boston, MA
USA
Email: huaimo.chen@futurewei.com
Richard Li
Futurewei
2330 Central expressway
Santa Clara, CA
USA
Email: richard.li@futurewei.com
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Yi Yang
IBM
Cary, NC
United States of America
Email: yyietf@gmail.com
Anil Kumar S N
RtBrick
Bangalore
India
Email: anil.ietf@gmail.com
Yanhe Fan
Casa Systems
USA
Email: yfan@casa-systems.com
Ning So
Plano, TX 75082
USA
Email: ningso01@gmail.com
Vic Liu
USA
Email: liu.cmri@gmail.com
Mehmet Toy
Verizon
USA
Email: mehmet.toy@verizon.com
Lei Liu
Fujitsu
USA
Email: liulei.kddi@gmail.com
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Kiran Makhijani
Futurewei
USA
Email: kiranm@futurewei.com
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