lesson 6-1 mpls basic - keio university€¦ · lesson 6-1 mpls basic objectives : mpls is...

1

Lesson 6-1 MPLS basic

Objectives :

MPLS is capsulated protocol for IP packet. MPLS is

connection oriented with 20 bit header. To understanding

MPLS protocol, we start from packet forwarding comparing

with label swapping.

2

Longest prefix matching method and Patricia tree

129.60.0.0/16 B140.252.13.0/24 A224.0.0.0/16 D

IP forwarding table

IP header

DA=129.60.32.1

128.5.0.0/16

129.60.225.0/24 E

C

129.60.83.0/24 D

Prefix NHR

129.0.0.0/16 E

127.32.0.0/16 B

This is an answer

224.0.0.0 |1110 0000| | | |

140.252.13.0 |1000 1100|1111 1100|0000 1101| |

129.60.0.0 |1000 0001|0011 1100| | |

129.60.83.0 |1000 0001|0011 1100|0101 0011| |

129.60.225.0 |1000 0001|0011 1100|1110 0001| |

129.0.0.0 |1000 0001|

128.5.0.0 |1000 0000|0011 0101| | |

127.32.0.0 |0111 1111|0000 0000|

1,2, 5, 8, 17,Reference bit position

(a) IP transmission table and the longest prefix matching

(b) Bit expansion of prefix

Fig. 5.1 (a) (b)

3

Longest prefix matching method and Patricia tree

8

0

129.60/16, B17

0 1

129/8,E

9

0

1

10

011

112

113

114

115

016

0

129.60. 32.1

127.32/16, B

224.0/16, D

140.252.13/24, A

128.5/16, C 129.60/16, B17

129.60.83/24, D 129.60. 225/24, E

8

0 1

0 1

0 1

0 1

129/8,E0 1

129.60.32.1 hits with 129.60/16, but does not hit with 129.60.83/24

1

2

5

Effective node

Intermediate node

(c) Patricia tree (d) Intermediate node in Patricia tree

Reference bit positionPrefix, NH

Fig. 5.1 (c) (d)

4Fig. 5.2 (a)

140.252.13.34

DA

DA Next hop

(a) Principle of IP datagram communication (Connectionless)

140.252.13.34

Route table

Connectionless communication by IP datagram and connection oriented communication by MPLS virtual connection

5Fig. 5.2 (b)

(b) Principle of connection oriented communication by virtual circuit

X

Y

Z

V

W

DA a

a b

Label push table

aDADA

140.252.13.34Label push

a

Label swap

Label pop

b cc

b

Connectionless communication by IP datagram and connection oriented communication by MPLS virtual connection

Virtual circuit

6

Comparison of requirements between IP address and MPLS label

Table 5.1

Role Uniqueness of value

IP address Recognize uniquely the destination hostRoute the IP packetsSearch IP route table

Must be unique all over the Internet.

MPLS label Recognize uniquely the virtual circuit (VC)Recognize uniquely FECForward the MPLS pacletsSearch the MPLS label table

May be unique just by link or by node.

7

Examples of FEC

SA DA SP DP PID

*192.168.32.6/24192.168.32.0/24

141.72.168.0/24141.72.168.0/24141.72.168.0/24

***

**

80

**

TCP

FEC1→FEC2→FEC3→

Fig.5.3

FEC : Forward Equivalent Class

FEC is not only SA/DA but also some connection type like port number.

8Fig.5.4

Shim header (MPLS header)

Label (20 bits) EXP(3 bits) S TTL

(8 bits)

1 bit

DataIPheader

PPPheader

Shimheader

POS (Packet over SONET)

DataIPheader

MACheader

Shimheader

Ethernet

Label(20 bit) Independent label by linkExp(3 bit) Reserved field for experimentS(1 bit) S=1 End label

S=0 Label is following TTL(8 bit) Decrements by 1 at every

time passing the router

MPLS label format

9Fig.5.5

NHLFE, FTN, ILM

NHLFELabel

NHLFEFEC NHLFE

ILM

FTN

ActionNHOP - Swap- Pop- Swap & push

Next Hop Label Forwarding Entry

Next Hop

FEC-to-NHLFE

Incoming Label mapping

10

Principle of packet transfer within MPLS network by label switching technique

R4

NHOP

L1Swap & PushH2

Label (out)ActionDA

R6NHOP

L2SwapL1Label (out)ActionLabel (in)

Swap & Push (L1)R4

ActionNHOPFTN NHLFE table

H2

NHLFEFEC

IP packet

L2

L3IP packetH1

Swap(L2)R6

ActionNHOPILM NHLFE table

L1

NHLFELabel

R7

NHOP

L3SwapL2

Label (out)ActionLabel (in)

Swap(L3)R7


L2

NHLFELabel

H2

NHOP

-POPL3

Label (out)ActionLabel (in)

POPH2


L3

NHLFELabel

IP packet H2R1

R2

R3

R4 R6

R8

R5

R7

Search L3 (IP) table and assign a label

Look at label and remove the label. Search L3 (IP) table.

Look at the label and swap

IP packetL1

IP packet

Fig.5.6

11

Processing the label stack processing（Exchange, Pop, Push）

L2

Swap outer labels

IP packet

IP packet L0

L0

IP packet L0

IP packet

L1 L3

Inner label is not changed

Two labels are attached by router 1. Outer label and Inner label are determined by R4, and R7, respectively.

R1

R2

R3

R4

R7

R8

R5

IP packet

H1

H2

R6

L3L0

POPPOP

R7H2

ILM NHLFE table

L2 SWAP (L3)R7

ILM NHLFE table

L1

NHLFELabel

SWAP (L2)R6

ActionNHOP

ILM NHLFE table

H2

NHLFEFEC

SWAP&PUSH (L0,L1)R4

ActionNHOP

ＦＴＮ NHLFE table

H3

ILM: In coming Label MappingFTN: FEC-to-NHLFENHLFE: Next Hop Label Forwarding EntryFig.5.7

12Fig.5.8

outer-LSP

inner-LSP

IP packet L0 L1

Hierarchical LSP network

13Fig.5.9

t1 t2

t1 t2 t3

R1 R2 R3 R4

PHP (Penultimate-HOP)

In R3, since it is known that the next hop is R4 by looking at t2, it is not required to attach L3 in this area.

PHP

IP searching only

PHP (Penultimate hop popping)

14Fig.5.10

Label L

Label L

Label L

Label merge

15Fig.5.12

Upstream Downstream Upstream Downstream

(b) Upstream type(a) Downstream type

Downstream notifies the label to upstream

Upstream notifies the label to downstream

Label assigning method(Signaling protocol)

16Fig.5.13

Upstream Downstream

Ｌａｂｅｌ Mapping (FEC,label)

Upstream Downstream

(1) Label request

(2)Ｌａｂｅｌ Mapping (FEC,label)

Upstream node obtains label automaticallyUpstream node requests for label

(a) On-demand type (b) Spontaneous type

Label distribution method

17

Conclusions for Lesson 6-1

Basic principles of MPLS are shown in this

lesson. Label swapping and Hierarchical LSP

is important techniques.

18

Lesson 6-2 Application of MPLS

Objectives :MPLS executes transmission of IP packets based on their

Labels. Traffic engineering or improving the routing efficiency

of external route is essential for MPLS application. It is

difficult to set up under IP date gram.

19Ｆｉｇ. 6.1

1.1.1.1 1.1.1.4 1.1.1.6

1.1.1.3 1.1.1.5

Congestion!

The shortest route is selected even if there is congestion.

1.1.1.2 1.1.1.1 1.1.1.4 1.1.1.6

1.1.1.3 1.1.1.5

Needs traffic regulation

1.1.1.2

(a) (b)

Problem of IGP

Shortest path routing courses congestion at hot-spot link.

20Fig.6.2

Concept of separating the routing from forwarding by MPLS (1)

x

DA

Next hop

BX

NHDA

A

B

C

E

D

x

DA: Unique in whole network

Routing table

XX

NHDA

DX

NHDA

(a) Packet transmission by IP datagram

Each router has a routing table based on DA.

Transmission of the packets (forwarding) and routing control (routing) have been combined in a single process.

Routing = Forwarding

21Fig.6.2

Concept of separating the routing from forwarding by MPLS (2)

Label: unique for each link

a

b

c

d

X

Y

Z

V

W

x

NHLabel

Label forwarding table

Pre-arrange the content of each label forwarding table for host x.

(b) Packet transmission by MPLS

Label is used instead of an address. Virtual circuit is pre-set-up before packet transmission.

22Ｆｉｇ.6.3

1.1.1.1 1.1.1.2 1.1.1.4 1.1.1.6

1.1.1.3 1.1.1.5

#1 #2#3

#1 #2#3

#1 #2#3

#1 #2#3

#1 #2#3 #1

#2 #3

Explicit route1.1.1.1->1.1.1.3->1.1.1.5->1.1.1.6

• Specifies the route at the source node

Source routing and route specifying （Explicit routing）

LSP : Label Switched Path

Source routing set up the LSP along the specified route in MPLS.

23Fig.6.4

1 2 30 4

5 6 7

(a) Strict specification

0-1(s)-2(s)-3(s)-4

1 2 30 4

5 6 7

(b) Ｌｏｏｓｅ specification

0-2(ｌ)-4

Both allowed Both allowed

Concept of Strict specification and Loose specification

(S) : Strict

(L) : Loose

24

NE node software structure

RSVP

CSPF

OSPF拡張

OSPF extension:Routing protocolCSPF: Restricted route calculationRSVP: RSVP signalling

Neighboring node

LSP attribute Route information

MPLS network

Destination node

LSP

Source node

Fig.6.5

Concept of CSPF that outputs the route from input information of traffic trunk attribution, resource attribute and topology database

CSPF (Constrain-based shortest path first)

25Fig.6.6

1.1.1.1 1.1.1.2 1.1.1.4 1.1.1.6

1.1.1.3 1.1.1.5

Remove

Concept of CSPF

ER-LSP Set-up by RSVP-TE

26

1.1.1.1 1.1.1.2 1.1.1.4 1.1.1.6

1.1.1.3 1.1.1.5

#1 #2

#3

#1 #2

#3

#1 #2

#3

#1 #2

#3

#1#2

#3 #1#2

#3Resv

Resv

Resv

Path->1.1.1.3->1.1.1.5->1.1.1.6

Path->1.1.1.5->1.1.1.6

Path->1.1.1.6

28

Table-6.2

Value Message Type1 Path2 Resv3 PathErr4 ResvErr5 PathTear6 ResvTear7 ResvConf

Message Type of RSVP

29

Format of ERO and RRO (See next OHP)

Class=20, C-Type=1ERO (Explicit route object)

0 1 2 30 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

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+|L| Type | Length | IPv4 address (4 bytes) |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| IPv4 address (continued) | Prefix Length | Resvd |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Class=20, C-Type=1RRO (Record route object)

0 1 2 30 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Type | Length | IPv4 address (4 bytes) |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| IPv4 address (continued) | Prefix Length | Flags |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type= 1 IPv42 IPv632 32 AS number

1: Local protection available2: Local protection in use

Fig.6.11

ERO : Explicit Route Object

PRO : Record Route Object

30

Ｆｉｇ.6.12

1 2 30 4

5 6 7

1(s)2(s)4(ｌ)

2(s)4(ｌ) 4(ｌ) 4(ｌ)

Popped after passing node 1

Popped after passing node 2

Not popped even after passing node 3

When the next pop is specified to Loose, node 3 selects route 2-3-4, because the cost of route 2-3-4 is lower than the route 2-6-7-4.

Processing the ERO and next hop

31Fig.6.13

1 2 30 4

5 6 7

It’s possible to know the upstream route of node 2 from RRO inside the Path message, and the downstream route of node 2 from RRO inside the Resv message.

PathRRO=(0,1)

Path

RRO=0 RRO=0

PathRRO=(0,1,2)

PathRRO=(0,1,2,3)

Resv(4,3,2,1)

Resv(4,3,2)

Resv(4,3)

Resv(4)

Session Attribute Obj.- Label Recording flag set

Option

Processing the RRO

32Ｆｉｇ.6.15

0 4

0 4

0 4

Tunnel ID=1 LSP-ID=10


Tunnel ID=1 LSP-ID=20（New）


BW=10 Mb/s

BW=25 Mb/s

BW=25 Mb/s

ID=20, closed after newsetup is completed

Bandwidth changing procedure of traffic trunk with RSVP-TE

33Fig.6.16

Tunnel-ID=1, LSP-ID=10

Tunnel-ID=1, LSP-ID=20

（LSP to be closed）

（New LSP）

Share the bandwidth

Shared Explicit style

34Ｆｉｇ.6.18

0 4

0 4

0 4

0 4

LSP-ID=10

Copy to LSP-ID=10 and 20LSP-ID=10

LSP-ID=20

LSP-ID=10

LSP-ID=20

LSP-ID=20

Select only LSP-ID=20

Select only LSP-ID=10

Switching by “make-before-break”

35

ISP-A

ISP-B

ISP-C

ISP-D

NW-a

Ｆｉｇ.6.19

Exchanging of route information by BGP-4 protocol

36Fig.6.20

IP header

Prefix NHR

IP header

IP forwarding table

IP forwarding at 1.1.1.1 router

1.1.1.21.1.1.31.1.1.41.1.1.51.1.1.6

1.1.1.21.1.1.31.1.1.21.1.1.31.1.1.2

IX

ISP-A ISP-B

1.1.1.3 1.1.1.5

External route 10.1.1.1

1.1.1.1 1.1.1.2 1.1.1.4

10.1.1.1 1.1.1.6

1.1.1.6

How about core routers?

BGP router

Non-BGP routerIBGP BGP router

How this router know that the NH of BGP-4 levelof 10.1.1.1 is ISP-b?

Notification of route information of BGP-4 within AS

This is not NHR of 1.1.1.1.

37Fig.6.21

デフォルトルート

94 95 96 97 98 99 00

Ｘ1000

http://www.telstra.net/ops/bgptable.html

10

20

30

40

50

60

70

80

90

0

Nu

mb

er o

f ex

tern

al r

ou

tes

(nu

mb

er o

f P

refi

xes)

Year

Increasing trend of number of entries into the routing table.

38Fig.6.22

IX

AS2AS3

IP packet

LSP full-mesh in between border routers

Transit traffic

B

C D

Border router A

AS1

Realization of transit service by LSP tunneling

39Fig.6.23

PE

PE

P

P

Site1CE

Site2CE

Site5CE

PE

Site4CE

Site3CE

VPN#1

VPN#2

P: providerPE: provider edgeCE: customer edge

VPN architecture

40Fig.6.24


PE

PE

P

P

Site1CE

Site2CE

Site5CE

PE

Site4CE

Site3CE

VPN#2

VPN#1

Overlay model

41Fig.6.25

PE

PE

P

P

Site1CE

Site2CE

Site5CE

PE

Site4CE

Site3CE

VPN#1

VPN#2


Peer model （RFC2547 specification)

42Fig.6.26

TokyoNew York

ParisLondon

Bank

Automobile

Intranet Extranet

TokyoNew York

ParisLondon

Bank

Automobile

Example of VPN （Intranet and Extranet）

43Fig.6.27

P

Site2 CE2

Site1 CE1

VRF#1

VRF#2VRF#3=VRF#1+#2

Site3 CE3

VPN-A (Automobile)

VPN-B (Bank)PE3

PE1

PE2

Flexible service by VRFVRF : Virtual Routing and Forwarding

PE : Provider Edge

CE : Customer Edge

Both VPN-A,B VRF

Only VPN-A VRF

Only VPN-B VRF

44Fig.6.30

P

Site2 CE

Site1 CE

VRF#1

VRF#2VRF#3= VRF#1+#2

Site3 CE

VPN-A (Automobile)

PE

PE

PEIP packet L0 L1

IP packet L0 L2

IP packetIP packet

VPN-B (Bank)

Label stack （Outer label and inner label）

Inner label for CE

Outer label for forwarding

45

Conclusions for Lesson 6-2

Traffic engineering is key technique for MPLS.

Explicit routing can control traffic flows in the

network.

lesson 6-1 mpls basic - keio university€¦ · lesson 6-1 mpls basic objectives : mpls is...

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