1. ODA000015 MPLS Basic Knowledge
1.0
This related to MPLS basics

2. Course Contents Chapter 1 MPLS Overview
Chapter 2 Label and Label Stack
Chapter 3 Label Forwarding and Allocation
Chapter 4 LDP and Configuration

3. MPLS MPLS——Multi-Protocol Label Switching Multi-Protocol
Support multiple Layer-3 protocols, such as IP, IPv6, IPX, SNA
Label Switching
Label packets, and replace IP forwarding with label switching

4. Origin: To Integrate IP with ATM
MPLS
ATM
Connectionless control plane
Connectionless control plane
Connection-oriented control plane
Connectionless forwarding plane
Connection-oriented forwarding plane
Connection-oriented forwarding plane

5. Connection-oriented Features1 2 S2 S6 S1 S3 S5 S8 VC S4 S7
connection-oriented: cell switching
VC = S1, S4, S7, S8
The data reach their destination in order along the same connection
Fixed time delay, easy to control
Connection types: PVC SVC
Connectionless: packet route
Path 1 = S1, S2, S6, S8
Path 2 = S1, S4, S7, S8
The data reach their destination out of order along different paths

6. Traditional IP Forwarding
Parse IP header
mapped to next hop
Parse IP header
mapped to next hop
Parse IP header
mapped to next hop
IP header is parse at each hop, resulting in low efficiency.
It is hard to deploy QoS and the efficiency is rather low.
All routers are expected to know all routes in the entire network.

7. Virtual Channel Connection (VCC) Virtual Path Connection(VPC)
ATM Switching Process
Virtual Channel Connection (VCC)
Virtual Path Connection(VPC)
UNI
UNI
NNI
NNI
VC switching
VP switching
VC switching
VPI = 1 VCI = 1
VPI = 2 VCI = 44
VPI = 26 VCI = 44
VPI = 20 VCI = 30
Connection-oriented
Routing depending on link layer, based on VPI/VCI or label
Ensure QoS and real-time service 37

8. Technology Combining the Advantages of ATM and IP+ = X R X
Router ATM switch MPLS
Router
Layer 3 routing – scalable and flexible
Layer 2 switching – High reliability and traffic engineering management
MPLS——multi-protocol label switching

9. MPLS Advantages
Replace IP header with short and fixed-length labels as forwarding basis to improve forwarding speed
Provide value-added service without prejudice to efficiency:
VPN
Traffic engineering
QOS

10. Basic Working Process of MPLS
Core LSR
Edge LSR
Edge LSR IP IP L1 IP L2 IP L3 IP
Traditional
IP forwarding
Traditional IP
forwarding
Label forwarding

11. Basic MPLS Concepts MPLS domain LSP LSR: Label Switch Router
LER
LSR
MPLS domain IP
MPLS
LSP
LSR: Label Switch Router
LER: Label Edge Router
LSP: Label Switch Path

12. Course Contents Chapter 1 MPLS Overview
Chapter 2 Label and Label Stack
Chapter 3 Label Forwarding and Allocation
Chapter 4 LDP and Configuration

13. MPLS Encapsulation Format and Label20 23 24 31
Label
EXP S
TTL
32 bits
Layer 2
header
MPLS header
IP header
Data
Two types of MPLS encapsulation for ATM and FR:
shim encapsulation: similar to other link layers
Cell mode: VC (VPI/VCI for ATM, DLCI for FR) is directly used as the label

14. Label Position in Packet
Ethernet
/SONET
/SDH packet
Ethernet header
/PPP header
Label
Layer-3 data
Cell mode
ATM packet
VPI/VCI
Layer-3 data

15. Label Stack
Layer2
header
MPLS
header
MPLS
header
IP header
Data
Theoretically, label stack enables limitless nesting to provide infinite service support. This is simply the greatest advantage of MPLS technology.

16. Course Contents Chapter 1 MPLS Overview
Chapter 2 Label and Label Stack
Chapter 3 Label Forwarding and Allocation
Chapter 4 LDP and Configuration

17. Basic Concepts of Label Forwarding
FEC (Forwarding Equivalence Class): Import the packets with identical characteristics into the same LSP
NHLFE (Next Hop Label Forwarding Entry): Describe label operations
next hop
label operation types: push/pop/swap
FTN (FEC to NHLFE): Map FEC to NHLFE
ILM (Incoming Label Map): Map MPLS label to NHLFE

18. Label Forwarding A B C D label operation: pop Label operation: push
Label operation: swap
ILM->NHLFE
Parse IP header
distribute FEC
mapped to next hop
Label operation: swap
Parse IP header
FEC bound with LSP
FTN->NHLFE
ILM->NHLFE
ILM->NHLFE A B C D
Ingress LER
LSR
LSR
Egress LER
The traditional routing protocol and Label Distribution Protocol (LDP) serve to create routing table and label mapping table (FEC-Label mapping) in each LSR for FECs with service requirement, i.e. create LSP successfully.
Ingress LER receives a packet, determines the FEC that the packet belongs to, and label the packet
In MPLS domain, packets are forwarded in accordance with labels and label forwarding table via the forwarding unit
Egress LER removes the label and continues forwarding the packet

19. Transmitting interface Transmitting interface
NHLFE A:
FEC
NHLFE
next hop
Transmitting interface
Label operation
Others
/24 B E1
Add label L1 …
B,C:
Ingress label
NHLFE
Next hop
Transmitting
interface
label operation
Others L1 C E1
Remove the previous label and add L2 … D:
Ingress label
NHLFE
Next hop
Transmitting interface
Label operation
Others L2 D
Remove label …

20. PHP ILM->NHLFE ILM->NHLFE Ingress LER LSR LSR Egress LER
Label operation: push
Label operation: swap
Parse IP header
Distribute FEC
Mapped to next hop
Label operation: pop
Parse IP header
FEC bound with LSP
FTN->NHLFE
ILM->NHLFE
ILM->NHLFE
Ingress LER
LSR
LSR
Egress LER
The label at the outmost layer does not make any sense to the last hop. Thus, it is advisable to pop the label at the last hop but one to ease the burden of the last hop.
If there is only one layer of label, the last hop will perform IP forwarding directly; otherwise, it will perform the internal label forwarding.

21. Creating LSP LSP drive modes:
Driven by stream: incoming packets drive LSP creation
Driven by topology: topology information (route) drives LSP creation
Driven by application: application (like QoS) drives LSP creation
Signaling protocol is used to distribute labels between LSRs and establish LSP:
LDP
CR-LDP (Constraint-based Routing LDP)
RSVP-TE (Resource Reservation Protocol)
MP-BGP
PIM

22. Several Issues Concerning Label Distribution
Label allocation mode
DoD : downstream-on-demand
DU: downstream unsolicited
Label control mode
Ordered
Independent
Label hold mode
Conservative retention mode : upon receiving a label, if there is no route destined for the corresponding FEC, hold the label for later use
Liberal mode: upon receiving a label, if there is no route destined for corresponding FEC, discard the label

23. Label Allocation Mode: DoD
Label 18 is allocated to /24
Route triggering
分配到
/24
Label 20 is allocated
to /24
分配到
/24
的标签为 18
的标签为 20
/24
/24
LSR LSR LSR3
Upstream
Downstream
Requesting labels destined for /24
请求到目的地址
Requesting labels
destined for /24
/24
的标签
的标签
The upstream LSR sends a label request (containing FEC description information) to the downstream LSR.
The downstream LSR allocates a label to this FEC and feeds back the bound label to the upstream LSR via the label mapping message.

24. Label Allocation Mode: DU
Route triggering
Label 18 can be used
to reach /24 到
/24 到
/24
Label 20 can be used
to reach /24
Downstream
Upstream
可以使用标签 18
可以使用标签 20
/24
/24
Once the LDP session is set up successfully, the downstream LSR will initiatively advertise the label mapping message to its upstream LSR.
The upstream router will save the label in the label mapping table.

25. Label Control Mode: Ordered
Upstream
Downstream
Not until it receives a label mapping message from its downstream LSP will it send the message upstream

26. Label Control Mode: Independent
Downstream
Upstream
Whether it receives a label mapping message from its downstream LSR, it will send upstream a label mapping message immediately.

27. Common Collocation 1: DoD + Ordered + Liberal
Downstream
Upstream
It is relatively easy to control the use of labels and the creation of LSPs

28. Common Collocation 2: DU + Ordered + Conservative
Upstream
Downstream
A waste of label resources
Useless LSPs would be created
LSPs can be set up quickly

29. LSP Loop Detection
Path looping shall be avoided even in setting up LSP within the MPLS domain.
LSP path looping can be avoided in two ways:
Maximum hop number;
Path vector

30. Course Contents Chapter 1 MPLS Overview
Chapter 2 Label and Label Stack
Chapter 3 Label Forwarding and Allocation
Chapter 4 LDP and Configuration

31. Basic Concepts of LDP LDP is a MPLS control and signaling protocol
Main functions:
Release Label-FEC mapping
Create and maintain label switching path
LDP serves to distribute and maintain label mapping messages between peers in the form of message.
LDP uses the TCP transmission service.

32. LDP Message Types
Discovery message: Used to discover LDP adjacencies in the network
Session message: Used to set up, maintain and terminate a session between LDP peers
Distribution message: Used to create, change and delete label mappings related to FEC
Notification message: Used to provide recommendation or error notification information

33. Session initialization
LDP Message Switching
UDP-Hello
Discovery stage
UDP-Hello
TCP connection establishment
Session creation and maintenance
Session initialization
Label request
FEC
LSP creation and maintenance
Label mapping
Label

34. Basic MPLS Configurations (1)
Designate ID for LSR
It is necessary to configure the LSR with an ID before configuring other MPLS commands. The ID is generally in the format of IP address, and shall be unique within the domain.
mpls lsr-id X.X.X.X
Note: make configurations in the system view.
Activate/deactivate the LDP or enter the LDP view
To configure LDP, first activate the LDP and enter the LDP view
mpls ldp
Note: make configurations in the system view

35. Basic MPLS Configurations (2)
Enable interface LDP
mpls ldp enable
Note: make configurations in the interface view
LDP loop detection control
Enable loop detection
Loop-detect
Set the maximum hot number for loop detection
hops-count hop-number

36. MPLS Debugging MPLS display commands
Display information about LDP and LSR
display mpls ldp
Display information about LDP-enabled interface
display mpls ldp interface
Display information about all LSPs established in the public network
display mpls lsp

37. Configuration Example
Suppose a network consists of four NE routers, where Router B is connected to Router C via SDH, while Router B is connected to Router A and Router D via Ethernet.
The four routers all support MPLS. LSP can be set up between any two routers. The operational routing protocol is OSPF
Router B
Router A
Router C
Router D
ethernet8/0/0
ethernet1/0/0
ethernet1/0/1
ethernet2/0/1
pos2/0/1
pos7/0/0
Router C is configured with:
[Quidway] interface pos 7/0/0
[Quidway-Pos7/0/0] ip address
[Quidway] router id
[Quidway] ospf
[Quidway-ospf] area 0
[Quidway-ospf-area ] network
[Quidway] mpls lsr-id
[Quidway] mpls ldp
[Quidway-Pos7/0/0] mpls ldp enable
Configuration procedure
Configure ip address for the interface
Configure the ospf protocol
Configure the MPLS LDP

38. Summary Grasp the basic concepts and working process of MPLS
Grasp label allocation and distribution
Grasp MPLS LDP configuration

39. Thank you