1. MPLS - How does it work ?

2. 32-bits - Path Label - RSVP 32-bits - VPN Label - MP-BGP
MPLS Label Stack
IP Packet
TTL
Label (20-bits)
CoS S
32-bits - Path Label - RSVP
L2 Header
MPLS Header
32-bits - VPN Label - MP-BGP
Fields
Label
Experimental (CoS)
Stacking bit
Time to live
Always set to 255 in the GX Network
VPN Label
The originating PR device when announcing the VPN route to the rest of the network assigns the VPN label and announces it as part of the MP-BGP route announcement.
The Label refers to the egress interface on the originating PR device the packet should be forwarded out.
The originating PR device will perform a POP operation on any MPLS encapsulated packet received with a valid VPN Label
A routing lookup is performed on the destination address of the inbound packet on the inbound PR in the VPN specific routing table to find the VPN Label
Path Label
Provides a path from the Ingress PR device to the Egress PR device that originated the VPN route.
All BGP routes have a next hop address
This is always the originating PR router of the route
When the route lookup is performed to find the VPN Label a recursive lookup is performed on the next hop address and this will return the Path Label
This is derived from the RSVP TE Tunnel to reach the originating PR device
Remember: Traffic flows in the inverse direction to routing information.

3. Architecture – VPN Separation
WHIP
MPLS CORE PR
VRF
MPLS LSP
VRF
VRF
VRF
VRF PR PR
Talk about security
Talk about
Each customer interface is mapped into a VRF.
Holds routing and reachability information for the Customers VPN
Could hold a subset of the routes within a VPN as apposed to all the routes
BGP with VPN extensions, is used to transfer routes and reachability information between VRF’s on different PR’s.
On export from a VRF the route is tagged with a BGP community which defines which VPN it belongs to, as well as the topology type (I.e. Full Mesh, Hub and Spoke, etc)
The VPN extensions carry a VPN label to ensure packets are routed through the correct VRF.

4. MPLS/BGP IP-VPN 101 – MP-BGP -> VPN Label
Site 2
CPE-1
CPE-2
Site 1
PR-1
PR-2
IBGP session FT FT
CPE-3
CPE-4
Site 1
Site 2 (10/8) FT FT 2
Route lookup performed on in RED VPN
Returns Label value of 75
Next hop of PR-2
Route lookup on PR-2
Returns RSVP label of LSP to reach PR-2
Packet transmitted with label stack of
RSVP Label ¦ 75 3
Receives MPLS labelled packet with label of 75
POPs Label
Sends to CPE-4 1
IP Packet with Destination address of

5. Applications – Today and Tomorrow
Intranets – for company communications – LAN extension
Remote access solution for mobile workforce and remote locations
Extranets – for customers, partners, suppliers & communities of interest
Connections to Global Crossing Financial Extranet (content)
Analyst firm – customers download reports, video conferencing & streaming video
Hosted applications
Convergence of applications: voice, video, Internet and corporate data
VoIP
IP Videoconferencing
L2 Virtual Private Lines (VPLs) for legacy protocol transport (X.25, FR/ATM)
Business continuity
Redundant back-up with usage based-billing . . .
. . . also carries your extra traffic

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