OSPF Topology-Transparent OSPF Topology-Transparent ZoneZone

Huaimo Chen, Renwei Li (Huawei)Gregory Cauchie (France Telecom)

Ning So (Verizon)

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ContentsContents

Why TTZ?Why TTZ?

What is TTZ?What is TTZ?

IntroductionIntroduction

How TTZ?How TTZ?

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Introduction

What happens if a network is bigger and bigger?

Scalability Issue, Slower convergence, etc.

Problems in Current Solution Using Area› Limitation on Scalability: at most two levels of hierarchies

› Very complex to provide end to end services

› Service interruptions when splitting ASes/Areas since Network Architecture i

s changed significantly

› Harder to operate & maintain network with more/multiple ASes & areas

› Not easy for applications/software to be aware of/drive/control networks with more/multiple ASes and areas in near future

› Harder for inter-cloud networking with more/multiple ASes and areas

TTZ may resolve these issues

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ContentsContents

Why TTZ?Why TTZ?

What is TTZ?What is TTZ?

IntroductionIntroduction

How TTZ?How TTZ?

Definition of TTZDefinition of TTZ

Configuring OSPF TTZConfiguring OSPF TTZ

TTZ vs AreaTTZ vs Area

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Definition of TTZ

A group of routers connected by links with TTZ ID which is virtualized as

• a group of TTZ edge routers fully connected or

• a single router

of which routers outside TTZ are NOT

aware

through which LSAs outside are distributed

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As a Group of Edge Routers Connected (Animated)

A group of routers connected by links with attribute TTZ ID.

Routers outside of TTZ are NOT aware of TTZ, just see the

edge routers of TTZ, which are connected.

Links, routers inside TTZ are NOT advertised to routers

outside of TTZ.

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TTZ

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TTZ as a Single Router (Animated)

Routers outside of TTZ are NOT aware of TTZ,

Just see TTZ as a Single Router.

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RT

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Configuring OSPF TTZ

Configurations on router R2:router ospf 1

Interface ethernet 1/0 ip address 10.10.120.1/24

Interface ethernet 2/0 ip address 192.168.20.1/24 ttz 192.168.100.100

Interface ethernet 3/0 ip address 192.168.30.1/24 ttz 192.168.100.100

Interface ethernet 4/0 ip address 192.168.40.1/24 ttz 192.168.100.100

No configuration changes on router outside TTZ

Configurations on router P1:

router ip ospf 1

Interface ethernet 0/0 ip address 10.10.120.1/24

Interface ethernet 1/0 ip address 10.10.220.1/24

San FranciscoR1

R2 R3

R4

P1 P2Eth0/0

Eth1/0

Eth1/0

Eth1/0

Eth2/0

Eth2/0

Eth3/0

Eth4/0

Eth4/0

Eth3/0Eth3/0

Eth4/0

Eth4/0Eth3/0

Eth1/0

Eth1/0

Eth0/0

Eth1/0

Eth2/0

Eth2/0

TTZ

OSPF

OSPF

OSPF

OSPF

OSPF OSPFOSPF

OSPF

OSPF OSPF

Configure TTZ ID on an interface in TTZ

TTZ vs Area

OSPF TTZ:

Virtualize TTZ as a router or a group of routers

Can see through a TTZ

2+ levels of hierarchies

Easy to set up TE LSP crossing TTZs

Minor network architecture changes when TTZ is used in a network

OSPF Area:

2 levels of hierarchies

Complex to set up TE LSP crossing areas

Significant network architecture changes when multiple areas are introduced to a network

TTZ has functions of Area & improves on Area

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ContentsContents

Why TTZ?Why TTZ?

What is TTZ?What is TTZ?

IntroductionIntroduction

How TTZ?How TTZ?

Improves Scalability 1 Order of MagnitudeImproves Scalability 1 Order of Magnitude

E2E Services Can Be Set Up Easily E2E Services Can Be Set Up Easily

Higher AvailabilityHigher Availability

Improves Scalability:1 Order of Magnitude (Animated)

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One more hierarchies

Area 0

Area 1

TTZ

TTZ TTZ

TTZ

TTZArea 0

Area 2

Area 3

Area 4

E2E TE LSP can be set up easily (Animated)

Path for LSP is computed easily in a normal way

LSP can be set up along the path computed

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TTZ

Source

Destination

Find path from R3 to R6 in a normal way

Find path from T4 to T10 in a normal way

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Higher Availability

• The routing tables on P1 and P2 are not re-calculated. • There will be no downloading from RIB to FIB.• When considering more complex POPs as TTZs, a

failure or crash of a router inside a POP will not affect anything outside of POP. And thus availability is higher.

• Suppose the Link R2-R3 Is Broken• Routers outside not aware of this

P1 P2Eth0/0

Eth1/0

Eth1/0

Eth1/0 Eth1/0

Eth1/0

Eth0/0

Eth1/0

San FranciscoR1

R2 R3

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Eth2/0

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Eth3/0

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Eth3/0Eth3/0

Eth4/0

Eth4/0Eth3/0

Eth2/0

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TTZ

Issues in a Bigger Network: Split to Areas (animated)

1. Significant changes on Network

Architecture and configuration when

split area, service may be interrupted

Area 1

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Area 4

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TTZ Avoids Splitting to Areas (Animated)

1. No need to split area (one area)

2. Smaller changes on Network Architecture

and configuration, network is more stable

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ContentsContents

Why TTZ?Why TTZ?

What is TTZ?What is TTZ?

IntroductionIntroduction

How TTZ?How TTZ?

OSPF Data Change — I bitOSPF Data Change — I bit

LSA Generation and FloodingLSA Generation and Flooding

Adjacency EstablishmentAdjacency Establishment

Routing Table ComputationRouting Table Computation

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OSPF Data Change — I bit

1 bit to identify if a link is in TTZ

0 1 2 7

I Link Type

I = 1: Link is in TTZ

I = 0: Link is not in TTZ

Meaning of “Link Type” of 7 bits is the same as that of “Link Type” of 8 bits.

0 1 2 7

Link Type

OptionsLS Age

Link State ID

LS Sequence Number

LS Checksum

Advertising Router

Length

Number of Links

I bit = 1 if link in TTZ

LS Type = 1

Router Link

Router Link

. . . . . .

Flags

Header

I bit = 1 if link in TTZ

Router LSA

LSA Generation and FloodingLSA Generation and Flooding• Every router in TTZ generates a router LSA containing all the router links,

each of which has I bit set to 1 if it is configured with TTZ ID. This LSA is flooded inside TTZ.

• TTZ virtualized as – A group of routers connected: TTZ edge router constructs a second router LSA

and sends it to all its neighbors. This LSA comprises two groups of links.

1. The router links connecting the routers outside of the TTZ from this TTZ edge router. 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.

2. The "virtual" router links. For each of the other TTZ edge routers, there is a "virtual" router link to it from this TTZ edge router. The cost of the router link from this TTZ router to one of the other TTZ edge routers is the cost of the shortest path from this TTZ edge router to it.

– A single router: DR of TTZ constructs a second router LSA and sends it to all its neighbors. This LSA comprises links between a TTZ edge router and a router outside of TTZ.

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HUAWEI TECHNOLOGIES CO., LTD. Page 19Huawei Confidential

Router LSA Generated by T1/T5 to inside TTZRouter LSA Generated by T1/T5 to inside TTZ

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OptionsLS Age

Link State ID (T1)

LS Sequence Number

LS Checksum

Advertising Router (T1)

Length

Number of LinksI=0 for Normal Link

LS Type = 1

Router Link: T1 to R2

Router Link: T1 to T5

Flags

Header

Router Link: T1 to T2

Router Link: T1 to T4

I=1 for TTZ link

I=1 for TTZ link

I=1 for TTZ link

OptionsLS Age

Link State ID (T5)

LS Sequence Number

LS Checksum

Advertising Router (T5)

Length

Number of LinksI=1 for TTZ Link

LS Type = 1

Router Link: T5 to T1

Router Link: T5 to T9

Flags

Header

Router Link: T5 to T4

Router Link: T5 to T6

I=1 for TTZ link

I=1 for TTZ link

I=1 for TTZ link

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Router LSA by T1 to outside TTZ Router LSA by T1 to outside TTZ as a Group of Nodes Connectedas a Group of Nodes Connected

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T1

OptionsLS Age

Link State ID (T1)

LS Sequence Number

LS Checksum

Advertising Router (T1)

Length

Number of LinksNormal Link

LS Type = 1

Router Link: T1 to R2

Router Link: T1 to T10

Flags

Header

Router Link: T1 to T3

Router Link: T1 to T4

Normal Link (“virtual”)

Normal Link (“virtual”)

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Router LSA Generated to outside TTZ Router LSA Generated to outside TTZ as a Single Nodeas a Single Node

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OptionsLS Age

Link State ID (RT)

LS Sequence Number

LS Checksum

Advertising Router (RT)

Length

Number of LinksNormal Link

LS Type = 1

Router Link: RT to R2

Router Link: RT to R11

Flags

Header

Router Link: RT to R3

Router Link: RT to R10

Normal Link

Normal Link

RT

. . .

Adjacency EstablishmentAdjacency Establishment• Between TTZ edge and non TTZ router, TTZ edge

– for TTZ as a group of routers connected• sends non TTZ router hellos in a normal way, and

• sends non TTZ router all the LSAs except for the LSAs belong to TTZ during LSDB synchronization.

– for TTZ as a single router RT• sends non TTZ router hellos in a normal way but with RT ID, and

• sends non TTZ router all the LSAs except for the LSAs belong to TTZ during LSDB synchronization.

• After adjacency is established, when TTZ edge router floods a LSA,

– it only floods the LSA that does not belong to TTZ to the non TTZ router through the adjacency between the TTZ edge router and the non TTZ router.

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Routing Table Computation

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Router in TTZ builds SPF tree using topology it sees

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