Internet DRAFT - draft-ietf-ospf-ttz
draft-ietf-ospf-ttz
Internet Engineering Task Force H. Chen
Internet-Draft R. Li
Intended status: Experimental Huawei Technologies
Expires: July 12, 2017 A. Retana
Cisco Systems, Inc.
Y. Yang
Sockrate
Z. Liu
China Mobile
January 8, 2017
OSPF Topology-Transparent Zone
draft-ietf-ospf-ttz-06.txt
Abstract
This document presents a topology-transparent zone (TTZ) in an OSPF
area. A topology-transparent zone comprises a group of routers and a
number of links connecting these routers. Any router outside of the
zone is not aware of the zone. A TTZ hides the internal topology of
the TTZ from the outside. It does not directly advertise any
internal information about the TTZ to a router outside of the TTZ.
The information about the links and routers such as a link down
inside the TTZ is not advertised to any router outside of the TTZ.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 12, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Conventions Used in This Document . . . . . . . . . . . . . . 5
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Topology-Transparent Zone . . . . . . . . . . . . . . . . . . 5
5.1. Overview of Topology-Transparent Zone . . . . . . . . . . 5
5.2. TTZ Example . . . . . . . . . . . . . . . . . . . . . . . 6
6. Extensions to OSPF Protocols . . . . . . . . . . . . . . . . . 8
6.1. General Format of TTZ LSA . . . . . . . . . . . . . . . . 8
6.2. TTZ ID TLV . . . . . . . . . . . . . . . . . . . . . . . . 9
6.3. TTZ Router TLV . . . . . . . . . . . . . . . . . . . . . . 9
6.4. TTZ Options TLV . . . . . . . . . . . . . . . . . . . . . 10
6.5. Link Scope TTZ LSA . . . . . . . . . . . . . . . . . . . . 11
7. Constructing LSAs for TTZ . . . . . . . . . . . . . . . . . . 12
7.1. TTZ Migration Process . . . . . . . . . . . . . . . . . . 13
8. Establishing Adjacencies . . . . . . . . . . . . . . . . . . . 14
8.1. Discovery of TTZ Neighbors . . . . . . . . . . . . . . . . 14
8.2. Adjacency between TTZ Edge and TTZ External Router . . . . 17
9. Advertisement of LSAs . . . . . . . . . . . . . . . . . . . . 17
9.1. Advertisement of LSAs within TTZ . . . . . . . . . . . . . 17
9.2. Advertisement of LSAs through TTZ . . . . . . . . . . . . 18
10. Computation of Routing Table . . . . . . . . . . . . . . . . . 18
11. Operations . . . . . . . . . . . . . . . . . . . . . . . . . . 18
11.1. Configuring TTZ . . . . . . . . . . . . . . . . . . . . . 18
11.2. Migration to TTZ . . . . . . . . . . . . . . . . . . . . . 19
11.3. Adding a Router into TTZ . . . . . . . . . . . . . . . . . 21
12. Manageability Considerations . . . . . . . . . . . . . . . . . 22
13. Security Considerations . . . . . . . . . . . . . . . . . . . 22
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
15. Contributors and Other Authors . . . . . . . . . . . . . . . . 23
16. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 24
17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
17.1. Normative References . . . . . . . . . . . . . . . . . . . 24
17.2. Informative References . . . . . . . . . . . . . . . . . . 25
Appendix A. Prototype Implementation . . . . . . . . . . . . . . 25
A.1. What are Implemented and Tested . . . . . . . . . . . . . 25
A.2. Implementation Experience . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27
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1. Introduction
Networks expand as business grows and traffic increases. For
scalability and manageability, a hierarchical network architecture is
usually deployed in OSPF networks by re-grouping routers into areas,
which is often challenging and causes service interruptions.
At first, reorganizing a network from one area into multiple areas or
from a number of existing areas into even more areas is a very
challenging and time consuming task since it involves significant
network architecture changes. Considering the one area case,
originally the network has only one area, which is the backbone.
This original backbone area will be reorganized into a new backbone
and a number of non-backbone areas. In general, each of the non-
backbone areas is connected to the new backbone area through the Area
Border Routers (ABRs) between the non-backbone and the backbone area
(refer to RFC 2328 section 3). It demands careful re-designing of
network topology in advance to guarantee backbone area continuity and
non-backbone area reachability, and requires significant
modifications of configurations on many routers to ensure consistent
routing.
Secondly, the services carried by the network may be interrupted
while the network is being reorganized from one area into multiple
areas or from a number of existing areas into even more areas since
every OSPF interface with an area change is going down with its old
area and then up with a new area.
This document presents a topology-transparent zone (TTZ) in an OSPF
area and describes extensions to OSPFv2 for supporting the topology-
transparent zone, which is scalable and resolves the issues above. A
TTZ hides the internal topology of the TTZ from the outside. It does
not directly advertise any internal information about the TTZ to a
router outside of the TTZ.
2. Terminology
TTZ link or TTZ internal link: A link whose ends are within a single
TTZ.
TTZ internal router: A router whose links are TTZ internal links
inside a single TTZ.
TTZ external router: A router outside of a TTZ that has no TTZ
internal links.
TTZ external link: A link not configured to be within a TTZ.
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TTZ edge router: A router is called TTZ edge router if some, but not
all, of its links are within a single TTZ.
TTZ router: A TTZ internal router or a TTZ edge router.
3. Conventions Used in This Document
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.
4. Requirements
A Topology-Transparent Zone may be deployed to resolve some critical
issues in existing networks and future networks. The requirements
for a TTZ are listed as follows:
o Routers outside a TTZ MUST NOT require any changes to operate with
the TTZ.
o A TTZ MUST be enclosed in a single area.
o A TTZ MUST hide the topology of the TTZ from any router outside of
the TTZ.
5. Topology-Transparent Zone
5.1. Overview of Topology-Transparent Zone
A Topology-Transparent Zone is identified by a TTZ identifier (ID),
and it consists of a group of routers and a number of links
connecting the routers. A TTZ MUST be contained within an OSPF area.
A TTZ ID is a 32-bit number that is unique for identifying a TTZ.
The TTZ ID SHOULD NOT be 0, to avoid confusion with Area 0. The same
TTZ ID MUST be configured on the routers and/or links that make up a
specific instance of a TTZ. All TTZ instances in an OSPF area MUST
be unique.
In addition to having similar functions of an OSPF area, an OSPF TTZ
makes some improvements on an OSPF area, which include:
o An OSPF TTZ represents a set of TTZ edge routers, connected by a
full mesh of virtual connections between them.
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o Non-TTZ link state information is handled as normal. TTZ Routers
receive the link state information about the topology outside of
the TTZ, store the information, and flood the information through
the TTZ to the routers outside of the TTZ.
5.2. TTZ Example
The figure below shows an area containing a TTZ: TTZ 600.
TTZ 600 ---- TTZ Internal Link
\ ==== Normal Link
Area X \ ^~^~^~^~^~^~^~^~^~^~^~^~
( )
===[R15]========(==[T61]----[T81]---[T63]==)======[R29]===
|| ( | \ / | ) ||
|| ( | \ / | ) ||
|| ( [T75] \ / | ) ||
|| ( | ___\ / | ) ||
|| ( | / [T71] [T79] ) ||
|| ( | [T73] / \ | ) ||
|| ( | / \ | ) ||
|| ( | / \ | ) ||
|| ( | / \ | ) ||
===[R17]========(==[T65]---[T77]----[T67]==)======[R31]===
\\ (// \\) //
|| //v~v~v~v~v~v~v~v~v~v~v~\\ ||
|| // \\ ||
|| // \\ ||
\\ // \\ //
======[R23]==============================[R25]=====
// \\
// \\
All the routers in the figure are in area X. Routers with T (i.e.,
T61, T63, T65, T67, T71, T73, T75, T77, T79 and T81) are also in TTZ
600, which contains the TTZ internal links connecting them. To
create a TTZ, we need configure it (refer to section 11).
There are two types of routers in a TTZ: TTZ internal and TTZ edge
routers. TTZ 600 has four TTZ edge routers T61, T63, T65 and T67.
Each of them has at least one adjacent router in TTZ 600 and one
adjacent router outside of TTZ 600. For instance, router T61 is a
TTZ edge router since it has an adjacent router R15 outside of TTZ
600 and three adjacent routers T75, T71 and T81 in TTZ 600.
In addition, TTZ 600 comprises six TTZ internal routers T71, T73,
T75, T77, T79 and T81. Each of them has all its adjacent routers in
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TTZ 600. For instance, router T71 is a TTZ internal router since its
adjacent routers T61, T63, T65, T67 and T73 are all in TTZ 600. It
should be noted that by definition, a TTZ internal router cannot also
be an ABR.
A TTZ hides the internal topology of the TTZ from the outside. It
does not directly advertise any internal information about the TTZ to
a router outside of the TTZ.
For instance, TTZ 600 does not send the information about TTZ
internal router T71 to any router outside of TTZ 600; it does not
send the information about the link between TTZ router T61 and T71 to
any router outside of TTZ 600.
The figure below illustrates area X from the point of view on a
router outside of TTZ 600 after TTZ 600 is created.
Area X ==== Normal Link
===[R15]===========[T61]=========[T63]=========[R29]===
|| || \\ // || ||
|| || \\ // || ||
|| || \\ // || ||
|| || \\// || ||
|| || //\ || ||
|| || // \\ || ||
|| || // \\ || ||
|| || // \\ || ||
|| || // \\ || ||
===[R17]===========[T65]=========[T67]=========[R31]===
\\ // \\ //
|| // \\ ||
|| // \\ ||
|| // \\ ||
\\ // \\ //
======[R23]============================[R25]=====
// \\
// \\
From a router outside of the TTZ, a TTZ is seen as the TTZ edge
routers connected each other. For instance, router R15 sees that
T61, T63, T65 and T67 are connected each other.
In addition, a router outside of the TTZ sees TTZ edge routers having
normal connections to the routers outside of the TTZ. For example,
router R15 sees that T61, T63, T65 and T67 have the normal
connections to R15, R29, R17 and R23, R25 and R31 respectively.
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6. Extensions to OSPF Protocols
The link state information about a TTZ includes router LSAs, which
can be contained and advertised in opaque LSAs [RFC5250] within the
TTZ. Some control information regarding a TTZ can also be contained
and advertised in opaque LSAs within the TTZ. These opaque LSAs are
called TTZ opaque LSAs or TTZ LSAs for short.
6.1. General Format of TTZ LSA
The following is the general format of a TTZ LSA. It has an LS Type
= 10/9 and TTZ-LSA-Type, and contains a number of TLVs.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | LS Type = 10/9|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|TTZ-LSA-Type(9)| Instance ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
There are three TTZ LSAs of LS Type 10 defined:
o TTZ Router LSA: a TTZ LSA containing a TTZ ID TLV and a TTZ Router
TLV.
o TTZ Control LSA: a TTZ LSA containing a TTZ ID TLV and a TTZ
Options TLV.
o TTZ Indication LSA: a TTZ LSA containing a TTZ ID TLV with E = 0,
which indicates that the router originating this LSA is a TTZ
internal router.
There is one TTZ LSA of LS Type 9:
o TTZ Discovery LSA: a TTZ LSA containing a TTZ ID TLV and a
optional TTZ Options TLV.
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6.2. TTZ ID TLV
A TTZ ID TLV has the following format. It contains a TTZ ID (refer
to section 5.1) and some flags. It has the TLV-Length of 8 octets.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTZ-ID-TLV-Type (1) | TLV-Length (8) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTZ ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved (MUST be zero) |E|Z|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
E = 1: Indicating a router is a TTZ Edge router
Z = 1: Indicating a router has migrated to TTZ
When a TTZ router originates a TTZ LSA containing a TTZ ID TLV, it
MUST set flag E to 1 in the TTZ ID TLV if it is a TTZ edge router,
and to 0 if it is a TTZ internal router. It MUST set flag Z to 1
after it has migrated to TTZ, and to 0 before it migrates to TTZ or
after it rolls back from TTZ (refer to section 6.4).
6.3. TTZ Router TLV
The format of a TTZ Router TLV is as follows. It has the same
content as a standard OSPF Router LSA (RFC 2328) with the following
modifications.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTZ-RT-TLV-Type (2) | TLV-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |V|E|B| 0 | # links |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | # TOS | metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
For a router link, the existing eight bit Link Type field for a
router link is split into two fields as follows:
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0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| I | Type-1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
I bit flag:
1: Router link is a TTZ internal link.
0: Router link is a TTZ external link.
Type-1: The kind of the link. The values for Type-1 are the same
as those for Type defined in RFC 2328 section 12.4.1.
The Link Type field is 8 bits, the values 128-255 of the field are
reserved (refer to RFC 4940), which allows the reuse of the bottom 7
bits to indicate the type of a TTZ internal or external link.
6.4. TTZ Options TLV
The format of a TTZ Options TLV is as follows.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTZ-OP-TLV-Type (3) | TLV-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OP | Reserved (MUST be zero) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OP Value Meaning (Operation)
0x001 (T): Advertising TTZ Topology Information for Migration
0x010 (M): Migrating to TTZ
0x011 (N): Advertising Normal Topology Information for Rollback
0x100 (R): Rolling back from TTZ
A OP field of three bits is defined. It may have a value of 0x001
for T, 0x010 for M, 0x011 for N, or 0x100 for R, which indicates one
of the four operations above. When any of the other values is
received, it is ignored.
Advertising TTZ Topology Information for Migration (T): After a user
configures a TTZ router to advertise TTZ topology information,
advertising TTZ topology information for migration is triggered. The
TTZ router originates a TTZ Control LSA having a TTZ Options TLV with
OP for T. It also originates its other TTZ LSA such as a TTZ router
LSA or TTZ indication LSA. When another TTZ router receives the LSA
with OP for T, it originates its TTZ LSA as described in section 7.
Migrating to TTZ (M): After a user configures a TTZ router to migrate
to TTZ, migrating to TTZ is triggered. The TTZ router originates a
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TTZ Control LSA having a TTZ Options TLV with OP for M and migrates
to TTZ. When another TTZ router receives the LSA with OP for M, it
also migrates to TTZ. When a router migrates to TTZ, it computes
routes using the TTZ topology and the topology outside of the TTZ.
For a TTZ internal router, it also updates its TTZ indication LSA
with Z = 1. For a TTZ edge router, it updates its TTZ router LSA
with Z = 1 and its router LSA for virtualizing the TTZ. A TTZ router
determines whether it is internal or edge based on configurations
(refer to section 11.1).
Advertising Normal Topology Information for Rollback (N): After a
user configures a TTZ router to advertise normal topology
information, advertising Normal topology information for rollback is
triggered. The TTZ router originates a TTZ Control LSA having a TTZ
Options TLV with OP for N. It also advertises its normal LSAs such as
its normal router LSA and stops advertising its other TTZ LSAs. When
another TTZ router receives the LSA with OP for N, it forwards the
LSA, advertises its normal LSAs, and stops advertising its TTZ LSAs.
Rolling back from TTZ (R): After a user configures a TTZ router to
roll back from TTZ, rolling back from TTZ is triggered. The TTZ
router originates a TTZ Control LSA having a TTZ Options TLV with OP
for R and rolls back from TTZ. When another TTZ router receives the
LSA with OP for R, it also rolls back from TTZ.
After a TTZ router originates a TTZ control LSA in response to a
configuration described above to control TTZ, it flushes the TTZ
control LSA if OP in the LSA is set for the configuration and the
configuration is removed.
6.5. Link Scope TTZ LSA
A TTZ LSA of LS Type 9 has the following format.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | LS Type = 9 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|TTZ-LSA-Type(9)| Instance ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ TTZ ID TLV ~
+---------------------------------------------------------------+
| |
~ (TTZ Options TLV) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
It contains a mandatory TTZ ID TLV, which may be followed by a
optional TTZ Options TLV. It is used to discover a TTZ neighbor.
7. Constructing LSAs for TTZ
For a TTZ, its topology is represented by the LSAs generated by its
TTZ routers for the link states in the TTZ, which include TTZ router
LSAs by TTZ edge routers, TTZ indication LSAs by TTZ internal
routers, normal router LSAs and network LSAs. The TTZ router LSAs
and TTZ indication LSAs MUST be generated after advertising TTZ
topology information for migration is triggered.
A TTZ edge router generates a TTZ router LSA that has a TTZ ID TLV
and a TTZ Router TLV. The former includes the ID of the TTZ to which
the router belongs and flag E set to 1, which indicates the
originator of the LSA is a TTZ Edge router. The TTZ router TLV
contains the TTZ external links to the routers outside of the TTZ and
the TTZ internal links to the routers inside the TTZ as described in
section 6. The TTZ router LSA containing this TLV is constructed and
advertised within the TTZ.
A TTZ internal router generates a TTZ indication LSA that has a TTZ
ID TLV containing the ID of the TTZ to which the router belongs and
flag E set to 0, which indicates the originator of the LSA is a TTZ
internal router. For a TTZ internal router, its regular Router LSA
is still generated. If a TTZ router is a Designated Router (DR), it
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originates its regular network LSA.
After receiving a trigger to migrate to TTZ such as a TTZ control LSA
with OP for M, a TTZ edge router MUST originate its normal router LSA
for virtualizing a TTZ, which comprises three groups of links in
general.
The first group are the router links connecting the TTZ external
routers. These router links are normal router links. There is a
router link for every adjacency between this TTZ edge router and a
TTZ external router.
The second group are the "virtual" router links connecting to the
other TTZ edge routers. For each of the other TTZ edge routers,
there is a corresponding point-to-point router link to it from this
TTZ edge router. The cost of the link is the cost of the shortest
path from this TTZ edge router to the other TTZ edge router within
the TTZ.
In addition, the LSA may contain a third group of links, which are
the stub links for the loopback addresses inside the TTZ to be
accessed by nodes outside of the TTZ.
7.1. TTZ Migration Process
After migration to TTZ is triggered, a TTZ router computes routes
using its TTZ topology (refer to section 10) and a TTZ edge router
originates its normal router LSA for virtualizing the TTZ in two
steps:
Step 1: The router updates its router LSA by adding a point-to-point
link to each of the other known edge routers in the TTZ, and also
by adding the stub links for the loopback addresses in the TTZ to
be accessed outside of the TTZ according to configuration policies
of operators.
Step 2: After MaxLSAGenAdvTime (0.3 s) or sr-time + MaxLSAAdvTime
(0.1 s), it removes the TTZ links from its router LSA, where sr-
time is the time from updating its router LSA to receiving the ack
for its router LSA and receiving the updated router LSAs
originated by the other TTZ edge routers. In other words, it
removes the TTZ links from its router LSA after sending its
updated router LSA and receiving the updated router LSAs
originated by the other TTZ edge routers for MaxLSAAdvTime or
after sending its updated router LSA for MaxLSAGenAdvTime.
MaxLSAAdvTime and MaxLSAGenAdvTime SHOULD be set to 100ms and
300ms respectively, but MAY be configurable. The former is the
maximum time for an LSA to be advertised to all the routers in an
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area. The latter is the maximum time for all TTZ router LSAs to
be generated by all TTZ edge routers and advertised to all the
routers in an area after a first TTZ router LSA is generated.
This is to avoid a possible short route down or change in a TTZ
external router while the TTZ is being virtualized. If each TTZ edge
router originates its router LSA by adding its point-to-point links
to the other TTZ edge routers and removing its TTZ links in one step,
a route taking a path through the TTZ in the TTZ external router may
be down or changed before all the router LSAs generated by the TTZ
edge routers reach the TTZ external router. When the TTZ external
router computes routes with some router LSAs originated by the TTZ
edge routers, bi-directional check for some of the point-to-point
links will fail. Thus the route taking the path through the shortest
path for the point-to-point link failing the bi-directional check
will be down or changed.
To roll back from a TTZ smoothly after receiving a trigger to roll
back from TTZ, a TTZ edge router MUST originate its normal router LSA
in the above two steps in a reverse way.
Step 1: Initially, it updates its normal router LSA by adding the
normal links for the links configured as TTZ links into the LSA.
Step 2: It then removes the point-to-point links to the other edge
routers of the TTZ for virtualizing the TTZ and the stub links for
the loopback addresses from its updated router LSA after sending
its updated router LSA and receiving the updated router LSAs
originated by the other TTZ edge routers for MaxLSAAdvTime or
after sending its updated router LSA for MaxLSAGenAdvTime.
8. Establishing Adjacencies
This section describes the TTZ adjacencies.
8.1. Discovery of TTZ Neighbors
For two routers A and B connected by a P2P link and having a normal
adjacency, they TTZ discover each other through a TTZ LSA of LS Type
9 with a TTZ ID TLV. We call this LSA D-LSA for short.
If two ends of the link have different TTZ IDs or only one end is
configured with TTZ ID, TTZ adjacency over the link MUST NOT be
"formed".
If two ends of the link have the same TTZ ID and Z flag value, A and
B are TTZ neighbors. The following is a sequence of events related
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to TTZ for this case.
A B
Configure TTZ Configure TTZ
D-LSA (TTZ-ID=100)
----------------------> Same TTZ ID and Z
A is B's TTZ Neighbor
D-LSA (TTZ-ID=100)
Same TTZ ID and Z <----------------------
B is A's TTZ Neighbor
A sends B a D-LSA with TTZ-ID after the TTZ is configured on it. B
sends A a D-LSA with TTZ-ID after the TTZ is configured on it.
When A receives the D-LSA from B and determines they have the same
TTZ ID and Z flag value, B is A's TTZ neighbor. A also sends B all
the TTZ LSAs it has and originates its TTZ LSA when one of the
following conditions is met.
o Z = 0 and there is a TTZ LSA with OP for T.
o Z = 1.
B is symmetric to A and acts similarly to A.
If two ends of the link have the same TTZ ID but Z flags are
different, a TTZ adjacency over the link MUST be "formed" in the
following steps. Suppose that A has migrated to TTZ and B has not
(i.e., flag Z in A's D-LSA is 1 and flag Z in B's D-LSA is 0).
A B
Configure TTZ Configure TTZ
D-LSA(TTZ-ID=100,Z=1)
----------------------> Same TTZ ID, but
different Z
A is B's TTZ Neighbor
D-LSA(TTZ-ID=100,Z=0)
Same TTZ ID, but <----------------------
different Z
B is A's TTZ Neighbor
TTZ LSAs
----------------------->
TTZ LSAs
<-----------------------
When A receives the D-LSA from B and determines they have the same
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TTZ ID but its Z = 1 and B's Z = 0, A sends B all the TTZ LSAs it has
and triggers B to migrate to TTZ. A updates and sends B its D-LSA by
adding an TTZ Options TLV with OP for M after sending B all the TTZ
LSAs.
D-LSA(TTZ-ID=100,OP=M)
Add TTZ Options -----------------------> Migrate to TTZ
TLV with OP for M
D-LSA(TTZ-ID=100,Z=1) Migrated to TTZ
<----------------------- Set Z=1
D-LSA(TTZ-ID=100,Z=1)
Remove ----------------------->
TTZ Options TLV
When B receives the D-LSA from A and determines they have the same
TTZ ID but its Z = 0 and A's Z = 1, B sends A all the TTZ LSAs it
has.
When B receives the D-LSA from A with OP for M, it starts to migrate
to TTZ. B updates and advertises its LSAs as needed.
After receiving B's D-LSA with Z = 1, A updates and sends B its D-LSA
by removing the TTZ Options TLV. It also updates and advertises its
LSAs as needed.
For a number of routers connected through a broadcast link and having
normal adjacencies among them, they also TTZ discover each other
through D-LSAs. The DR (Designated Router) for the link MUST "form"
TTZ adjacencies with the other routers if all the routers attached to
the link have the same TTZ ID configured on the connections to the
link. Otherwise, the DR MUST NOT "form" any TTZ adjacency with any
router attached to the link.
For a number of routers connected through a broadcast link and having
TTZ adjacencies among them, if a mis-configured router is introduced
on the broadcast link, the DR for the link MUST NOT "form" any TTZ
adjacency with this mis-configured router.
For routers connected via a link without any adjacency among them,
they TTZ discover each other through D-LSAs in the same way as
described above after they form a normal adjacency.
A TTZ adjacency over a link MUST be removed when one of the following
events happens.
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o TTZ ID on one end of the link is changed to a different one.
o TTZ ID on one end of the link is removed.
o The D-LSA is not received after the D-LSA-MAX-RETRANSMIT-TIME or
is explicitly flushed. The D-LSA-MAX-RETRANSMIT-TIME SHOULD be
set to 60 minutes, but MAY be configurable.
o Normal adjacency over the link is down.
When the TTZ ID on one end of the link is removed, the corresponding
D-LSA is flushed.
8.2. Adjacency between TTZ Edge and TTZ External Router
A TTZ edge router forms an adjacency with any TTZ external router to
which it is connected.
When the TTZ edge router synchronizes its link state database with
the TTZ external router, it sends the TTZ external router the
information about all the LSAs except for the LSAs belonging to the
TTZ that are hidden from any router outside of the TTZ.
At the end of the link state database synchronization, the TTZ edge
router originates its own router LSA for virtualizing the TTZ and
sends this LSA to its adjacent routers including the TTZ external
router.
9. Advertisement of LSAs
LSAs can be divided into a couple of classes according to their
Advertisements. The first class of LSAs is advertised within a TTZ.
The second is advertised through a TTZ.
9.1. Advertisement of LSAs within TTZ
Any LSA about a link state in a TTZ is advertised only within the
TTZ. It is not advertised to any router outside of the TTZ. For
example, a router LSA generated for a TTZ internal router is
advertised only within the TTZ.
Any network LSA generated for a broadcast or NBMA network in a TTZ is
advertised only within the TTZ. It is not advertised outside of the
TTZ.
Any opaque LSA generated for a TTZ internal TE link is advertised
only within the TTZ.
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After migrating to TTZ, every edge router of a TTZ MUST NOT advertise
any LSA about a link state in the TTZ to any router outside of the
TTZ. The TTZ edge router determines whether an LSA is about a TTZ
internal link state by checking if the advertising router of the LSA
is a TTZ internal router (i.e., there is a TTZ indication LSA
generated by the TTZ internal router and having the same advertising
router).
For any TTZ LSA originated by a router within the TTZ, every edge
router of the TTZ MUST NOT advertise it to any router outside of the
TTZ.
9.2. Advertisement of LSAs through TTZ
Any LSA about a link state outside of a TTZ received by an edge
router of the TTZ is advertised using the TTZ as transit. For
example, when an edge router of a TTZ receives an LSA from a router
outside of the TTZ, it floods it to its neighboring routers both
inside the TTZ and outside of the TTZ. This LSA may be any LSA such
as a router LSA that is advertised within an OSPF area.
The routers in the TTZ continue to flood the LSA. When another edge
router of the TTZ receives the LSA, it floods the LSA to its
neighboring routers both outside of the TTZ and inside the TTZ.
10. Computation of Routing Table
After a router migrates to TTZ, the computation of the routing table
on the router is the same as that described in RFC 2328 section 16
with one exception. The router in a TTZ ignores the router LSAs
generated by the TTZ edge routers for virtualizing the TTZ. It
computes routes using the TTZ router LSAs and the regular LSAs,
excluding the router LSAs for virtualizing the TTZ. That is that it
computes routes using the TTZ topology and the topology outside of
the TTZ, excluding the links for virtualizing the TTZ.
11. Operations
11.1. Configuring TTZ
This section proposes some options for configuring a TTZ.
1. Configuring TTZ on Every Link in TTZ
If every link in a TTZ is configured with a same TTZ ID as a TTZ
link, the TTZ is determined. A router with some links in a TTZ and
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some links not in this TTZ is a TTZ edge router. A router with all
its links in a TTZ is a TTZ internal router.
2. Configuring TTZ on Routers in TTZ
A same TTZ ID is configured on every TTZ internal router in a TTZ,
and on every TTZ edge router's links connecting to the routers in the
TTZ.
A router configured with the TTZ ID on some of its links is a TTZ
edge router. A router configured with the TTZ ID only is a TTZ
internal router. All the links on a TTZ internal router are TTZ
links. This option is simpler than option 1 above.
For a TTZ edge router X with different TTZ IDs on its different
links, router X connects two or more different TTZs. In this case,
router X originates its router LSA for virtualizing the TTZs. This
LSA includes the normal links connecting to routers outside of these
TTZs and the virtual links to the other edge routers of each of these
TTZs. Router X also originates its TTZ router LSA for each of TTZs.
The TTZ router LSA for TTZ N includes the links to routers outside of
these TTZs, the virtual links to the other edge routers of the other
TTZs, and the TTZ links to the routers in TTZ N.
11.2. Migration to TTZ
For a group of routers and a number of links connecting the routers
in an area, making them transfer to work as a TTZ without any service
interruption takes a few of steps or stages.
At first, a user configures the TTZ feature on every router in the
TTZ. In this stage, a router does not originate or advertise its TTZ
topology information. It will discover its TTZ neighbors.
Secondly, after configuring the TTZ, a user issues a configuration on
one router in the TTZ, which triggers every router in the TTZ to
generate and advertise TTZ information among the routers in the TTZ.
When the router receives the configuration, it originates a TTZ
control LSA with OP for T (indicating TTZ information generation and
advertisement for migration). It also originates its TTZ LSA such as
TTZ router LSA or TTZ indication LSA, and advertises the LSA to its
TTZ neighbors. When another router in the TTZ receives the LSA with
OP for T, it originates its TTZ LSA. In this stage, every router in
the TTZ has dual roles. One is to function as a normal router. The
other is to generate and advertise TTZ information.
Thirdly, a user checks whether a router in the TTZ is ready for
migration to TTZ. A router in the TTZ is ready after it has received
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all the TTZ LSAs including TTZ router LSAs from TTZ edge routers and
TTZ indication LSAs from TTZ internal routers. This information may
be displayed on a router through a configuration.
And then a user activates the TTZ through using a configuration such
as migrate to TTZ on one router in the TTZ. The router migrates to
TTZ, generates and advertises a TTZ control LSA with OP for M
(indicating Migrating to TTZ) after it receives the configuration.
After another router in the TTZ receives the TTZ control LSA with OP
for M, it also migrates to TTZ. Thus, activating the TTZ on one TTZ
router propagates to every router in the TTZ, which migrates to TTZ.
For an edge router of the TTZ, migrating to work as a TTZ router
comprises generating a router LSA to virtualize the TTZ and flooding
this LSA to all its neighboring routers in two steps as described in
section 7.
In normal operations for migration to TTZ and rollback from TTZ, a
user issues a series of configurations according to certain
procedures. In an abnormal case, for example two conflicting
configurations are issued on two TTZ routers in a TTZ at the same
time, a TTZ router issues an error and logs the error when it detects
a conflict.
A conflicting configuration may be detected on a router on which the
configuration is issued. Thus some abnormal cases may be prevented.
When a configuration for migration/rollback is issued on a router,
the router checks whether it is in a correct sequence of
configurations for migration/rollback through using the information
it has. For migrating a part of an area to a TTZ, the correct
sequence of configurations is as follows in general:
1) configure TTZ on every router in the part of the area to be
migrated to TTZ;
2) configure on one router in the TTZ to trigger every router in the
TTZ to generate and advertise TTZ information for migration; and
3) configure on one router in the TTZ to trigger every router in the
TTZ to migrate to TTZ.
After receiving a configuration on a router to migrate to TTZ, which
is for 3), the router checks whether 2) is performed through checking
if it has received/originated TTZ LSAs. If it has not, it issues an
error to an operator (generation and advertisement of TTZ information
for migration to TTZ is not done yet) and rejects the configuration
at this time.
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After a router receives a TTZ LSA with OP for M for 3) from another
router, it checks whether 2) is performed through checking if it has
received/originated TTZ LSAs. If it has not, it issues an error and
logs the error, and does not migrate to TTZ. In this case, it does
not originate its router LSA for virtualizing the TTZ if it is a TTZ
edge router.
After receiving a configuration on a router to generate and advertise
TTZ information, which is for 2), the router checks whether 1) is
performed through checking if TTZ is configured on it. If it is not,
it issues an error to an operator (TTZ is not configured on it yet)
and rejects the configuration at this time.
For rolling back from TTZ, the correct sequence of configurations is
below.
1) configure on one router in the TTZ to trigger every router in the
TTZ to advertise normal LSAs and stop advertising TTZ LSAs;
2) configure on one router in the TTZ to trigger every router in the
TTZ to roll back from TTZ.
After receiving a configuration on a router to roll back from TTZ,
which is for 2), the router checks whether 1) is performed through
checking if it has received TTZ LSA with OP for N. If it has not, it
issues an error to an operator (advertise normal LSAs and stop
advertising TTZ LSAs for rolling back from TTZ is not done yet) and
rejects the configuration at this time.
After a router receives a TTZ LSA with OP for R for 2) from another
router, it checks whether 1) is performed through checking if it has
received TTZ LSA with OP for N. If it has not, it issues an error and
logs the error, and does not roll back from TTZ.
After receiving a configuration on a router to advertise normal LSAs
and stop advertising TTZ LSAs for rolling back from TTZ, which is for
1), the router checks whether it has any TTZ LSAs. If it does not,
it issues an error to an operator (no TTZ to be rolled back) and
rejects the configuration at this time.
11.3. Adding a Router into TTZ
When a non TTZ router (say R1) is connected via a P2P link to a
migrated TTZ router (say T1), and there is a normal adjacency between
them over the link, a user can configure TTZ on both ends of the link
to add R1 into the TTZ to which T1 belongs. They TTZ discover each
other as described in section 8.
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When a number of non TTZ routers are connected via a broadcast or
NBMA link to a migrated TTZ router (say T1), and there are normal
adjacencies among them, a user configures TTZ on the connection to
the link on every router to add the non TTZ routers into the TTZ to
which T1 belongs. The DR for the link "forms" TTZ adjacencies with
the other routers connected to the link if they all have the same TTZ
ID configured for the link. This is determined through the TTZ
discovery process described in section 8.
12. Manageability Considerations
Section 11 (Operations) outlines the configuration process and
deployment scenarios for a TTZ. The configurable item is enabling a
TTZ on a router and/or an interface on a router. The TTZ function
may be controlled by a policy module and assigned a suitable user
privilege level to enable. A suitable model may be required to
verify the TTZ status on routers participating in the TTZ, including
their role as internal or edge TTZ router. The mechanisms defined in
this document do not imply any new liveness detection and monitoring
requirements in addition to those indicated in [RFC2328].
13. Security Considerations
A notable beneficial security aspect of TTZ is that the TTZ is
enclosed in a single area, and TTZ could be used to mask the internal
topology. External routers that are not participating in the TTZ
will not be aware of the internal TTZ topology. It should be noted
that a malicious node could inject TTZ LSAs with the OP Field set to
M or R, which could trigger the migration into/from a TTZ and may
result in the isolation of some routers in the network. Good
security practice might reuse the OSPF authentication and other
security mechanisms described in [RFC2328] and [RFC7474], to mitigate
this type of risk.
14. IANA Considerations
Under Registry Name: Opaque Link-State Advertisements (LSA) Option
Types [RFC5250], IANA is requested to assign a new Opaque type
registry value for Topology-Transparent Zone (TTZ) LSA as follows:
+====================+===============+=======================+
| Registry Value | Opaque Type | reference |
+====================+===============+=======================+
| IANA TBD | TTZ LSA | This document |
| (9 Suggested) | | |
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+--------------------+---------------+-----------------------+
IANA is to create and maintain a new registry:
o OSPFv2 TTZ LSA TLVs
Initial values for the registry are given below. The future
assignments are to be made through IETF Review.
Value OSPFv2 TTZ LSA TLV Name Definition
----- ----------------------- ----------
0 Reserved
1 TTZ ID TLV see section 6.2
2 TTZ Router TLV see section 6.3
3 TTZ Options TLV see section 6.4
4-32767 Unassigned
32768-65535 Reserved
15. Contributors and Other Authors
1. Other Authors
Mehmet Toy
USA
Email: mehmet.toy@verizon.com
Gregory Cauchie
FRANCE
Email: greg.cauchie@gmail.com
Anil Kumar S N
India
Email: anil.sn@huawei.com
Ning So
USA
Email: ningso01@gmail.com
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Lei Liu
USA
Email: lliu@us.fujitsu.com
2. Contributors
Veerendranatha Reddy Vallem
India
Email: veerendranatharv@huawei.com
William McCall
USA
will.mccall@rightside.co
16. 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 this draft.
17. References
17.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, DOI 10.17487/
RFC2328, April 1998,
<http://www.rfc-editor.org/info/rfc2328>.
[RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
OSPF Opaque LSA Option", RFC 5250, DOI 10.17487/RFC5250,
July 2008, <http://www.rfc-editor.org/info/rfc5250>.
[RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
"Security Extension for OSPFv2 When Using Manual Key
Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,
<http://www.rfc-editor.org/info/rfc7474>.
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[RFC4940] Kompella, K. and B. Fenner, "IANA Considerations for
OSPF", BCP 130, RFC 4940, DOI 10.17487/RFC4940, July 2007,
<http://www.rfc-editor.org/info/rfc4940>.
17.2. Informative References
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
DOI 10.17487/RFC3630, September 2003,
<http://www.rfc-editor.org/info/rfc3630>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<http://www.rfc-editor.org/info/rfc5440>.
Appendix A. Prototype Implementation
A.1. What are Implemented and Tested
1. CLI Commands for TTZ
The CLIs implemented and tested include:
o the CLIs of the simpler option for configuring TTZ, and
o the CLIs for controlling migration to TTZ.
2. Extensions to OSPF Protocols for TTZ
All the extensions defined in section "Extensions to OSPF Protocols"
are implemented and tested except for rolling back from TTZ. The
testing results illustrate:
o A TTZ is virtualized to outside as its edge routers connected each
other. Any router outside of the TTZ sees the edge routers (as
normal routers) connecting each other and to some other routers.
o The link state information about the routers and links inside the
TTZ is contained within the TTZ. It is not advertised to any
router outside of the TTZ.
o TTZ is transparent. From a router inside a TTZ, it sees the
topology (link state) outside of the TTZ. From a router outside
of the TTZ, it sees the topology beyond the TTZ. The link state
information outside of the TTZ is advertised through the TTZ.
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o TTZ is backward compatible. Any router outside of a TTZ does not
need to support or know TTZ.
3. Smooth Migration to TTZ
The procedures and related protocol extensions for smooth migration
to TTZ are implemented and tested. The testing results show:
o A part of an OSPF area is smoothly migrated to a TTZ without any
routing disruptions. The routes on every router are stable while
the part of the area is being migrated to the TTZ.
o Migration to TTZ is very easy to operate.
4. Add a Router to TTZ
Adding a router into TTZ is implemented and tested. The testing
results illustrate:
o A router can be easily added into a TTZ and becomes a TTZ router.
o The router added into the TTZ is not seen on any router outside of
the TTZ, but it is a part of the TTZ.
5. Leak TTZ Loopbacks Outside
Leaking loopback addresses in a TTZ to routers outside of the TTZ is
implemented and tested. The testing results illustrate:
o The loopback addresses inside the TTZ are advertised to the
routers outside of the TTZ.
o The loopback addresses are accessible from a router outside of the
TTZ.
A.2. Implementation Experience
The implementation of TTZ re-uses the existing OSPF code along with
additional simple logic. A couple of engineers started to work on
implementing the TTZ from the middle of June, 2014 and finished
coding it just before the end of July, 2014. After some testing and
bug fixes, it works as expected.
In our implementation, the link state information in a TTZ opaque LSA
is stored in the same link state database as the link state
information in a normal LSA. For each TTZ link in the TTZ opaque
LSA, there is an additional flag, which is used to differentiate
between a TTZ link and a Normal link.
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Before migration to TTZ, every router in the TTZ computes its routing
table using the normal links. After migration to TTZ, every router
in the TTZ computes its routing table using the TTZ links and normal
links. In the case where both the TTZ link and the normal link
exist, the TTZ link is used.
Authors' Addresses
Huaimo Chen
Huawei Technologies
Boston, MA
USA
Email: huaimo.chen@huawei.com
Renwei Li
Huawei Technologies
2330 Central expressway
Santa Clara, CA
USA
Email: renwei.li@huawei.com
Alvaro Retana
Cisco Systems, Inc.
7025 Kit Creek Rd.
Raleigh, NC 27709
USA
Email: aretana@cisco.com
Yi Yang
Sockrate
USA
Email: yyang1998@gmail.com
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Zhiheng Liu
China Mobile
No.32 Xuanwumen West Street, Xicheng District
Beijing, 100053
China
Email: liu.cmri@gmail.com
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