MPLS - How does it work ?

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.

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.

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 10.1.1.1 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 10.1.1.1

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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