Working of IP MPLS

MPLS Encapsulation: Label Stack

Penultimate Hop Popping

Label Switched Path and

Routers

Control and Data Plane

IP MPLS Tables

What is VRF?

Ankur Mittal

Senior

Manager/RailTel

Need for VRF

Route Distinguisher

Route Target

RD RT Working and MP-BGP

Switching Advantages

MPLS Performance

Certain link layer technologies can carry label as a part of their link layer header

e.g ATM & Frame Relay

Link layers that do not support labels in their header carry them in a “shim” label header MPLS header is pre-pended to packet with a push operation at ingress node

Label is added immediately after Layer 2 encapsulation header

Packet is restored at the end of the LSP with a pop operation

Normally the label stack is popped at penultimate node

MPLS Encapsulation: Label Stack

Layer 2 Header MPLS Label 1 MPLS Label 2 MPLS Label n Layer 3 Packet …

RFC 3032. MPLS

Label Stack Encoding

Forwarding via Label Swapping

417 data 288 data

Popping Labels

data 288 data

288 data 577 data 577

Pushing Labels

data 288 data

288 data 577 data 577

417 IP 666 IP 233 IP IP IP

POP

+

IP Lookup PUSH SWAP SWAP

666 IP 233 IP IP IP

IP Lookup PUSH POP SWAP

IP

Penultimate Hop Popping

Core Functions

Customer

IP Network

Edge Functions

LSP

Label Switched Path

Customer

IP Network

Label Switched Path

Label Switched Routers

The data plane

IP IP Forwarding Table

IP in IP out IP

Label Swapping Table

MPLS in MPLS out

77 data 23 data

represents IP Lookup + label push

represents label pop + IP lookup

Control and Data Plane

IP MPLS Tables

• RIB Routing Information Base

• FIB Forwarding Information Base

• LIB Label Information Base

• LFIB Label Forwarding Information Base

How it works?

Real-world Scenario

Customer isolation is achieved on the PE router by the virtual

routing table called VRF (VPN RF).

VRF also contains VPN identifiers as well as VPN membership

information (RD and RT)

VRF: Virtual Routing and Forwarding Table

Need for VRF

PE router provides isolation between customers using VRFs

Information needs to be carried between PE routers to

enable data transfer between customer sites via the MPLS

VPN backbone

A RD is a 64-bit unique identifier that is prepended to the 32-

bit customer prefix or route learned from a CE router, which

makes it a unique 96-bit address that can be transported

between the PE routers in the MPLS domain

Route Distinguisher

Additional identifiers used in the MPLS VPN domain in the

deployment of MPLS VPN that Identify membership of the

routes learned from that particular site

Use extended BGP community.

Export and import target is use.

The format of a RT is the same as an RD value.

These VPN labels are per route or per forwarding instances.

Route Targets

RD RT Working and MP-BGP

Overview

Advantages of switching over routing Performance

Faster transit time

Less Delay

Packet prioritization

Flexible routing

Scalability and simplicity

Ease of management

IP MPLS DLC

Data

Link

IP

MPLS

Label

IP DLC

IP Address

Switching Advantages

Data

Link

IP

MPLS

Routed Packet

Data

Link

IP

MPLS

Switched Packet

Forwarding

Table

Forwarding

Table

Forwarding

Table

MPLS faster transit over IP routing Requires less CPU and memory

Indexed lookup of forwarding table as opposed to best fit IP address lookup

Smaller forwarding table—only contains known LSRs as opposed to all known IP

networks Internet routing table contains more than 70,000 table entries

MPLS Performance

Batasia Loop of Darjeeling Himalayan Railways – A Heritage Railway under UNESCO

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