ODA000015 MPLS Basic Knowledge 1.0 This related to MPLS basics

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

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

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

Connection-oriented Features 1 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

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.

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

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

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

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

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

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

MPLS Encapsulation Format and Label 20 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

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

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.

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

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

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

Transmitting interface Transmitting interface NHLFE A: FEC NHLFE next hop Transmitting interface Label operation Others 10.0.1.0/24 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 …

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.

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

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

Label Allocation Mode: DoD Label 18 is allocated to 171.68.10/24 Route triggering 分配到 171.68.10/24 Label 20 is allocated to 171.68.10/24 分配到 171.68.10/24 的标签为 18 的标签为 20 171.68.40/24 171.68.10/24 LSR1 LSR2 LSR3 Upstream Downstream Requesting labels destined for 171.68.10/24 请求到目的地址 Requesting labels destined for 171.68.10/24 171.68.10/24 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.

Label Allocation Mode: DU Route triggering Label 18 can be used to reach 171.68.10/24 到 171.68.10/24 到 171.68.10/24 Label 20 can be used to reach 171.68.10/24 Downstream Upstream 可以使用标签 18 可以使用标签 20 171.68.40/24 171.68.10/24 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.

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

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.

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

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

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

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

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.

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

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

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

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

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

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 ethernet8/0/0 168.1.1.1 ethernet1/0/0 168.1.1.2 ethernet1/0/1 172.17.1.1 ethernet2/0/1 172.17.1.2 pos2/0/1 100.10.1.2 pos7/0/0 100.10.1.1 Router C is configured with: [Quidway] interface pos 7/0/0 [Quidway-Pos7/0/0] ip address 100.10.1.1 255.255.255.0 [Quidway] router id 172.16.1.2 [Quidway] ospf [Quidway-ospf] area 0 [Quidway-ospf-area-0.0.0.0] network 100.10.1.0 0.0.0.255 [Quidway] mpls lsr-id 172.16.1.2 [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

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

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