OSPF Topology-Transparent Zone
draft-chen-ospf-ttz-08
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
|
|
|---|---|---|---|
| Authors | Huaimo Chen , Richard Li , Gregory Cauchie , Alvaro Retana , Ning So , Vic Liu , Mehmet Toy , Lei Liu | ||
| Last updated | 2014-07-04 | ||
| Replaced by | draft-ietf-ospf-ttz, RFC 8099 | ||
| RFC stream | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-chen-ospf-ttz-08
Internet Engineering Task Force H. Chen
Internet-Draft R. Li
Intended status: Standards Track A. Kummar S N
Expires: January 5, 2015 Huawei Technologies
G. Cauchie
A. Retana
Cisco Systems, Inc.
N. So
Tata Communications
V. Liu
China Mobile
M. Toy
Comcast
L. Liu
UC Davis
July 4, 2014
OSPF Topology-Transparent Zone
draft-chen-ospf-ttz-08.txt
Abstract
This document presents a topology-transparent zone in a domain. 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. The information about the links and routers
inside the zone is not distributed to any router outside of the zone.
Any link state change such as a link down inside the zone is not seen
by 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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://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
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 January 5, 2015.
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Copyright Notice
Copyright (c) 2014 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
(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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 4
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Topology-Transparent Zone . . . . . . . . . . . . . . . . . . 4
4.1. Overview of Topology-Transparent Zone . . . . . . . . . . 4
4.2. An Example of TTZ . . . . . . . . . . . . . . . . . . . . 5
5. Changes to OSPF Protocols . . . . . . . . . . . . . . . . . . 6
5.1. Opaque LSAs for TTZ . . . . . . . . . . . . . . . . . . . 6
5.2. A TTZ Capability TLV in Router Information LSA . . . . . . 9
6. Constructing LSAs for TTZ . . . . . . . . . . . . . . . . . . 10
7. Establishing Adjacencies . . . . . . . . . . . . . . . . . . . 11
7.1. Discover TTZ Neighbor over Normal Adjacency . . . . . . . 11
7.2. Establishing TTZ Adjacencies . . . . . . . . . . . . . . . 11
7.3. Adjacency between TTZ Edge and Router outside . . . . . . 12
8. Distribution of LSAs . . . . . . . . . . . . . . . . . . . . . 12
8.1. Distribution of LSAs within TTZ . . . . . . . . . . . . . 13
8.2. Distribution of LSAs through TTZ . . . . . . . . . . . . . 13
9. Computation of Routing Table . . . . . . . . . . . . . . . . . 13
10. Operations . . . . . . . . . . . . . . . . . . . . . . . . . . 13
10.1. Configuring TTZ . . . . . . . . . . . . . . . . . . . . . 13
10.2. Smooth Migration to TTZ . . . . . . . . . . . . . . . . . 14
10.3. Adding a Router into TTZ . . . . . . . . . . . . . . . . . 15
11. Security Considerations . . . . . . . . . . . . . . . . . . . 16
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 16
14. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 17
15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
15.1. Normative References . . . . . . . . . . . . . . . . . . . 17
15.2. Informative References . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
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1. Introduction
The number of routers in a network becomes larger and larger as the
Internet traffic keeps growing. Through splitting the network into
multiple areas, we can extend the network further. However, there
are a number of issues when a network is split further into more
areas.
At first, 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. Considering the one area
case, originally the network has only one area, which is the
backbone. This original backbone area will be split 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 between the non backbone and the backbone area.
There is not any direct connection between any two non backbone
areas. Each area border router summarizes the topology of its
attached non backbone area for transmission on the backbone area, and
hence to all other area border routers.
Secondly, the services carried by the network may be interrupted
while the network is being split from one area into multiple areas or
from a number of existing areas into even more areas.
Furthermore, it is complex for a Multi-Protocol Label Switching
(MPLS) Traffic Engineering (TE) Label Switching Path (LSP) crossing
multiple areas to be setup. In one option, a TE path crossing
multiple areas is computed by using collaborating Path Computation
Elements (PCEs) [RFC5441] through the PCE Communication Protocol
(PCEP)[RFC5440], which is not easy to configure by operators since
the manual configuration of the sequence of domains is required.
Although this issue can be addressed by using the Hierarchical PCE,
this solution may further increase the complexity of network design.
Especially, the current PCE standard method may not guarantee that
the path found is optimal.
This document presents a topology-transparent zone in an area and
describes extensions to OSPF for supporting the topology-transparent
zone, which is scalable and resolves the issues above.
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. The information about the links and routers
inside the zone is not distributed to any router outside of the zone.
Any link state change such as a link down inside the zone is not seen
by any router outside of the zone.
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2. 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.
3. Requirements
Topology-Transparent Zone (TTZ) may be deployed for resolving some
critical issues 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 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.
4. Topology-Transparent Zone
4.1. Overview of Topology-Transparent Zone
A Topology-Transparent Zone (TTZ) is identified by an Identifier
(ID), and it includes a group of routers and a number of links
connecting the routers. A TTZ is in an OSPF area.
The ID of a Topology-Transparent Zone (TTZ) or TTZ ID is a number
that is unique for identifying an entity such as a node in an OSPF
domain. It is not zero in general.
In addition to having the functions of an OSPF area, an OSPF TTZ
makes some improvements on an OSPF area, which include:
o An OSPF TTZ is virtualized as a group of TTZ edge routers
connected.
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o An OSPF TTZ receives the link state information about the topology
outside of the TTZ, stores the information in the TTZ and floods
the information through the TTZ to the routers outside of TTZ.
4.2. An Example of TTZ
The figure below illustrates an example of a routing area containing
a topology-transparent zone: TTZ 600.
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
The routing area comprises routers R15, R17, R23, R25, R29 and R31.
It also contains a topology-transparent zone TTZ 600. The TTZ 600
comprises routers R61, R63, R65, R67, R71 and R73, and the links
connecting them.
There are two types of routers in a TTZ: TTZ internal routers and TTZ
edge routers. A TTZ internal router is a router inside the TTZ and
every adjacent router of the TTZ internal router is a router inside
the TTZ. A TTZ edge 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 routers R61, R63,
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R65 and R67. Each TTZ edge router is connected to at least one
router outside of the TTZ. For instance, router R61 is a TTZ edge
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.
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 link between TTZ router R61 and R65 to any router outside of the
TTZ.
In order to create a TTZ, we MUST configure the same TTZ ID on the
edge routers and identify the TTZ internal links on them. In
addition, we SHOULD configure the TTZ ID on every TTZ internal router
which indicates that every link of the router is a TTZ internal link.
From a router outside of the TTZ, a TTZ is seen as a group of routers
fully connected. For instance, router R15 in the figure above, which
is outside of TTZ 600, sees TTZ 600 as a group of TTZ edge routers:
R61, R63, R65 and R67. These four TTZ edge routers are fully
connected.
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 four TTZ edge routers R61, R63, R65 and R67, which
have the normal connections to R15, R29, R17 and R23, R25 and R31
respectively.
5. Changes to OSPF Protocols
5.1. Opaque LSAs for TTZ
The link state information about a TTZ includes router LSAs and
network LSAs describing the TTZ topology. These LSAs can be
contained and distributed in opaque LSAs within the TTZ. Some
control information on a TTZ can also be contained and distributed in
opaque LSAs within the TTZ. These opaque LSAs are called TTZ opaque
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LSAs or TTZ LSAs for short.
The following is a general form of a TTZ LSA. It has an LS type = 10
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTZ-LSA-type | Opaque ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where TTZ-LSA-type may be TBD1 (TTZ-RT-LSA-type) for TTZ Router LSA,
TBD2 (TTZ-NW-LSA-type) for TTZ Network LSA, and TBD3 (TTZ-CT-LSA-
type) for TTZ Control LSA.
There are four types of TLVs: TTZ ID TLV, TTZ Router TLV, TTZ network
TLV and TTZ Options TLV. A TTZ ID TLV has the following format. It
contains a TTZ ID.
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 | Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTZ ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format of a TTZ Router TLV is as follows. It contains the
contents of a normal router LSA. A TTZ router LSA includes a TTZ ID
TLV and a TTZ Router TLV.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTZ-RT-TLV-type | TLV-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|G| 0 |V|E|B| 0 | # links |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | # TOS | metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
Where G = 1/0 indicates that the router is an edge/internal router of
TTZ. For a router link, the existing eight bit Type field for a
router link may be split into two fields as follows:
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| I | Type-1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
I bit flag:
1: Router link is an internal link to a router inside TTZ.
0: This indicates that the router link is an external link.
Type-1: The kind of the link.
For a link inside a TTZ, I bit flag is set to one, indicating that
this link is an internal TTZ link. For a link connecting to a router
outside of a TTZ from a TTZ edge router, I bit flag is set to zero,
indicating that this link is an external TTZ link.
The value of Type-1 may be 1, 2, 3, or 4, which indicates that the
kind of a link being described is a point-to-point connection to
another router, a connection to a transit network, a connection to a
stub network, or a virtual link respectively.
A TTZ Network TLV has the following format. It contains the contents
of a normal network LSA. A TTZ network LSA includes a TTZ ID TLV and
a TTZ network TLV.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTZ-NW-TLV-type | TLV-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attached Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
Where Network ID is the interface address of the DR, which is
followed by the contents of a network LSA.
The format of TTZ Options TLV is as follows. A TTZ control LSA
contains a TTZ ID TLV and a TTZ Options TLV.
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 | Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|T|M|N|R| 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
T = 1: Distributing TTZ Topology Information for Migration
M = 1: Migrating to TTZ
N = 1: Distributing Normal Topology Information for Rollback
R = 1: Rolling back from TTZ
5.2. A TTZ Capability TLV in Router Information LSA
A new bit such as bit 6 for TTZ capability may be defined in the
Router Informational Capabilities TLV as follows:
Bit Capabilities
0 OSPF graceful restart capable [GRACE]
: ...
5 OSPF Experimental TE [EXP-TE]
6 OSPF TTZ capable [OSPF-TTZ]
7-31 Unassigned (Standards Action)
When the OSPF TTZ capable bit is set to one, a TTZ capability TLV
must follow the Router Informational Capabilities TLV to indicate a
link/router's TTZ capability and the TTZ to which the link/router
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belongs. It has the following format.
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-CAP-TLV-Type = 2 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTZ ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M| 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
It contains a TTZ ID and a number of TTZ bits. The following bits in
the TLV are assigned:
Bit Meaning
M Have Migrated to TTZ (i.e., works as TTZ)
1-31 Unassigned (Standards Action)
A link scope RI LSA with a OSPF TTZ capable bit set to one and a TTZ
Capability TLV will be used to discover a TTZ neighbor.
6. Constructing LSAs for TTZ
There are three types of LSAs for representing a TTZ: TTZ router LSA,
TTZ network LSA and Router LSA for virtualizing TTZ. The first two
is generated by any TTZ router, and the third by a TTZ edge router.
A TTZ router LSA generated by a TTZ router has a TTZ ID TLV and a TTZ
Router TLV. The former includes the ID of the TTZ to which the
router belongs. The latter contains the links to the router.
A TTZ network LSA for a broadcast link is generated by the DR for the
link. It contains a TTZ ID TLV and a TTZ network TLV. The former
has the ID of the TTZ to which the link belongs. The latter includes
the DR's address, the network mask, and the routers attached.
A router LSA for virtualizing a TTZ generated by an edge router of
the TTZ comprises two groups of links in general.
The first group are the router links connecting the routers outside
of the TTZ. These router links are normal router links. There is a
router link for every adjacency between this TTZ edge router and a
router outside of the TTZ.
The second group are the "virtual" router links. For each of the
other TTZ edge routers, there is a "virtual" router link to it. The
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cost of the router link may be the cost of the shortest path from
this TTZ edge router to it within the TTZ.
In addition, the LSA may contain a third group of links, which are
stub links for other destinations inside the TTZ. They may be the
loopback addresses to be accessed by a node outside of the TTZ.
7. Establishing Adjacencies
This section describes the adjacencies in some different cases.
7.1. Discover TTZ Neighbor over Normal Adjacency
For two routers A and B connected by a P2P link and having a normal
adjacency, they discover TTZ each other through a link scope RI LSA
with an OSPF TTZ capable bit and a TTZ ID. We call this LSA D-LSA
for short. If two ends of the link have the same TTZ ID, A and B are
TTZ neighbors. The following is a sequence of events related to TTZ.
A B
Configure TTZ Configure TTZ
D-LSA (TTZ-ID=100)
---------------------------> Same TTZ ID
A is B's TTZ Neighbor
D-LSA (TTZ-ID=100)
Same TTZ ID <---------------------------
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,
B is A's TTZ neighbor. When B receives the D-LSA from A and
determines they have the same TTZ ID, A is B's TTZ neighbor.
For a number of routers connected through a broadcast link and having
normal adjacencies among them, they also discover TTZ each other
through D-LSAs. The DR for the link "forms" TTZ adjacency with each
of the other routers if all the routers attached to the link have the
same TTZ ID configured on the connections to the link.
7.2. Establishing TTZ Adjacencies
When a router (say A) is connected via a P2P link to another router
(say B) and there is not any adjacency between them over the link, a
user configures TTZ on two ends of the link to form a TTZ adjacency.
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While A and B are forming an adjacency, they start to discover TTZ
each other through D-LSAs in the same way as described above after
the normal adjacency is greater than ExStart. When the normal
adjacency is full and B becomes A's TTZ neighbor, A forms a TTZ
adjacency with B. Similarly, B forms a TTZ adjacency with A.
For a number of routers connected through a broadcast link and having
no adjacency among them, they start to form TTZ adjacencies after TTZ
is configured on the link. While forming adjacencies, they discover
TTZ each other through D-LSAs in the same way as described above
after the normal adjacency is greater than ExStart. The DR for the
link forms TTZ adjacency with each of 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 does not form any
adjacency with any router attached to the link.
An alternative way for forming an adjacency between two routers in a
TTZ is to extend hello protocol. Hello protocol is extended to
include TTZ ID in LLS of a hello packet. The procedure for handling
hellos is changed to consider TTZ ID. If two routers have the same
TTZ IDs in their hellos, an adjacency between these two routers is to
be formed; otherwise, no adjacency is formed.
7.3. Adjacency between TTZ Edge and Router outside
For an edge router in a TTZ, it forms an adjacency with any router
outside of the TTZ that has a connection with it.
When the edge router synchronizes its link state database with the
router outside of the TTZ, it sends the router outside of the TTZ 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 edge
router originates its own router LSA for virtualizing the TTZ and
sends this LSA to the router outside of the TTZ.
From the point of view of the router outside of the TTZ, it sees the
other end as a normal router and forms the adjacency in the same way
as a normal router. It is not aware of anything about its
neighboring TTZ. From the LSAs related to the TTZ edge router in the
other end, it knows that the TTZ edge router is connected to each of
the other TTZ edge routers and some routers outside of the TTZ.
8. Distribution of LSAs
LSAs can be divided into a couple of classes according to their
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distributions. The first class of LSAs is distributed within a TTZ.
The second is distributed through a TTZ.
8.1. Distribution of LSAs within TTZ
Any LSA about a link state in a TTZ is distributed within the TTZ.
It is not distributed to any router outside of the TTZ. For example,
a router LSA generated for a router in a TTZ is distributed within
the TTZ and not distributed to any router outside of the TTZ.
Any network LSA generated for a broadcast or NBMA network in a TTZ is
distributed in the TTZ and not sent to a router outside of the TTZ.
Any opaque LSA generated for a TTZ internal TE link is distributed
within the TTZ and not distributed to any router outside of the TTZ.
8.2. Distribution of LSAs through TTZ
Any LSA about a link state outside of a TTZ received by an edge
router of the TTZ is distributed through the TTZ. 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 distributed in a domain.
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.
9. Computation of Routing Table
The computation of the routing table on a router is the same as that
described in RFC 2328, with one exception. A router in a TTZ MUST
ignore the router LSAs generated by the edge routers of the TTZ for
virtualizing the TTZ. It computes routes through using the TTZ
topology represented by TTZ LSAs and the topology outside of the TTZ.
10. Operations
10.1. 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
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link, the TTZ is determined. A router with some TTZ links and some
normal links is a TTZ edge router. A router with only TTZ links is a
TTZ internal router.
2. Configuring TTZ on Every Router in TTZ
We may configure a same TTZ ID on every router in the TTZ, and on
every 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 the above one.
10.2. Smooth 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 may take a few of steps or stages.
At first, users configure the TTZ feature on every router in the TTZ.
In this stage, a router does not originate its TTZ router LSA or TTZ
network LSAs. It will discover its TTZ neighbors.
Secondly, after configuring the TTZ, users may issue a CLI command on
one router in the TTZ, which triggers every router in the TTZ to
generate and distribute TTZ information among the routers in the TTZ.
When the router receives the command, it originates its TTZ router
LSA and TTZ network LSAs as needed, and distributes them to its TTZ
neighbors. It also originates a TTZ control LSA with T=1 (indicating
TTZ information generation and distribution for migration). When a
router in the TTZ receives the LSA with T=1, it originates its TTZ
router LSA and TTZ network LSAs as needed. 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 distribute TTZ information.
Thirdly, users SHOULD check whether every router in the TTZ is ready
for transferring to work as a TTZ router. A router in the TTZ is
ready after it has received all the necessary information from all
the routers in the TTZ. This information may be displayed on a
router through a CLI command.
And then users may activate the TTZ through using a CLI command such
as migrate to TTZ on one router in the TTZ. The router transfers to
work as a TTZ router, generates and distributes a TTZ control LSA
with M=1 (indicating Migrating to TTZ) after it receives the command.
After a router in the TTZ receives the TTZ control LSA with M=1, it
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also transfers to work as a TTZ router. Thus, activating the TTZ on
one TTZ router makes every router in the TTZ transfer to work as a
TTZ router, which flushes its normal router LSA and network LSAs,
computes routes through using the TTZ topology represented by TTZ
LSAs and the topology outside of the TTZ.
For an edge router of the TTZ, transferring to work as a TTZ router
comprises generating a router LSA to virtualize the TTZ and flooding
this LSA to all its neighboring routers.
10.3. Adding a Router into TTZ
When a non TTZ router (say R1) is connected via a P2P link to a TTZ
router (say T1) working as TTZ and there is a normal adjacency
between them over the link, a user can configure TTZ on two ends of
the link to add R1 into the TTZ to which T1 belongs. They discover
TTZ each other through D-LSAs in the same way as described above with
a bit addition. When T1 sends R1 a D-LSA, the D-LSA has a bit M=1
indicating that T1 works as TTZ. When R1 receives D-LSA with M=1, it
transfers to work as TTZ if it determines that T1 is its TTZ
neighbor. The following is a sequence of events related to TTZ.
T1 R1
Configure TTZ Configure TTZ
D-LSA(TTZ-ID=100,M=1)
---------------------------> Same TTZ ID
TTZ Neighbor, work as TTZ
D-LSA(TTZ-ID=100)
Same TTZ ID <---------------------------
TTZ Neighbor
After R1 receives the D-LSA with M=1 from T1, T1 becomes R1's TTZ
neighbor and R1 starts to work as TTZ. It originates its TTZ LSAs,
flushes old normal LSAs and computes routes using the TTZ topology
and the topology outside of the TTZ.
When T1 receives the D-LSA from R1, R1 is T1's TTZ neighbor, T1 re-
originates its TTZ LSAs and sends R1 all the TTZ LSAs.
When a number of non TTZ routers are connected via a broadcast link
to a TTZ router (say T1) working as TTZ 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 adjacency with
each of the other routers if all the routers have the same TTZ ID
configured on the connections to the link.
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When a router (say R1) is connected via a P2P link to a TTZ router
(say T1) and there is not any adjacency between them over the link, a
user can configure TTZ on two ends of the link to add R1 into the TTZ
to which T1 belongs.
While R1 and T1 are forming an adjacency, they start to discover TTZ
each other through D-LSAs in the same way as described above after
the adjacency is greater than ExStart. When the adjacency is full
and T1 becomes R1's TTZ neighbor, R1 works as TTZ if T1 works as TTZ.
When a router (say R1) is connected via a broadcast link to a group
of TTZ routers on the link and there is not any adjacency between R1
and any over the link, a user can configure TTZ on the connection to
the link on R1 to add R1 into the TTZ to which the TTZ routers
belong. R1 starts to form an adjacency with the DR for the link
after the configuration.
While R1 and the DR are forming an adjacency, they start to discover
TTZ each other through D-LSAs in the same way as described above
after the adjacency is greater than ExStart. When the adjacency is
full and the DR becomes R1's TTZ neighbor, R1 works as TTZ if the DR
works as TTZ. If R1 and the DR can not "form" any TTZ adjacency
because TTZ is not configured or is mis-configured on R1, DR will not
bring the normal adjacency between DR and R1 to Full, but bring the
adjacency to ExStart until TTZ is correctly configured on R1.
11. Security Considerations
The mechanism described in this document does not raise any new
security issues for the OSPF protocols.
12. IANA Considerations
TBD
13. Contributors
Veerendranatha Reddy Vallem
Huawei Technologies
Banglore
India
Email: veerendranatharv@huawei.com
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14. Acknowledgement
The author would like to thank Acee Lindem, Abhay Roy, Dean Cheng,
Russ White, William McCall, Tony Przygienda, Lin Han and Yang Yu for
their valuable comments on this draft.
15. References
15.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC4970] Lindem, A., Shen, N., Vasseur, JP., Aggarwal, R., and S.
Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 4970, July 2007.
[RFC2370] Coltun, R., "The OSPF Opaque LSA Option", RFC 2370,
July 1998.
[RFC5613] Zinin, A., Roy, A., Nguyen, L., Friedman, B., and D.
Yeung, "OSPF Link-Local Signaling", RFC 5613, August 2009.
15.2. Informative References
[RFC5441] Vasseur, JP., Zhang, R., Bitar, N., and JL. Le Roux, "A
Backward-Recursive PCE-Based Computation (BRPC) Procedure
to Compute Shortest Constrained Inter-Domain Traffic
Engineering Label Switched Paths", RFC 5441, April 2009.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element
(PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009.
Authors' Addresses
Huaimo Chen
Huawei Technologies
Boston, MA
USA
Email: huaimo.chen@huawei.com
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Renwei Li
Huawei Technologies
2330 Central expressway
Santa Clara, CA
USA
Email: renwei.li@huawei.com
Anil Kumar S N
Huawei Technologies
Banglore
India
Email: anil.sn@huawei.com
Gregory Cauchie
FRANCE
Email: greg.cauchie@gmail.com
Alvaro Retana
Cisco Systems, Inc.
7025 Kit Creek Rd.
Raleigh, NC 27709
USA
Email: aretana@cisco.com
Ning So
Tata Communications
2613 Fairbourne Cir.
Plano, TX 75082
USA
Email: ningso01@gmail.com
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Vic Liu
China Mobile
No.32 Xuanwumen West Street, Xicheng District
Beijing, 100053
China
Email: liuzhiheng@chinamobile.com
Mehmet Toy
Comcast
1800 Bishops Gate Blvd.
Mount Laurel, NJ 08054
USA
Email: mehmet_toy@cable.comcast.com
Lei Liu
UC Davis
CA
USA
Email: liulei.kddi@gmail.com
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