The document provides an overview of MPLS (Multi-Protocol Label Switching) concepts and components. It discusses how MPLS separates routing from forwarding by using labels to forward packets based on the label rather than the IP address. It describes MPLS components like edge label switching routers (ELSR or PE), label switching routers (LSR or P), and the label distribution protocol (LDP). It also provides examples of MPLS forwarding and MPLS VPN operation.
6. IP Routing 171.69 Packets Forwarded Based on IP Address Data Address Prefix 128.89 171.69 1 1 I/F … Address Prefix 128.89 171.69 0 1 … 0 1 I/F 128.89 0 1 128.89.25.4 Data Address Prefix 128.89 0 … … I/F Data Data 128.89.25.4 128.89.25.4 128.89.25.4 Route Update
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8. Label Header Label 1 2 3 4 5 6 7 8 EXP S TTL Bit 2 3 4 1 Byte Label EXP S TTL Label Value (20 bits) Class of Service (3 bits) Bottom of Stack (1 bit) Time to Live
9. Label Encapsulation PPP Ethernet Frame Relay Label IP header Label Label IP Header IP Header Data ATM Header Label Data ATM Header Packet over SONET/SDH Ethernet Frame Relay PVC ATM PVC’s Subsequent cells Data Data Data IP Header FRAME
13. MPLS Components LSR LSR LSR LSR ELSR ELSR P Network (Provider Control) PE CE CE PE ELSR ELSR C Network (Customer Control) C Network (Customer Control) P
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16. Control and Forward Plane Separation MPLS Process Route Updates/ Adjacency Label Bind Updates/ Adjacency IP Traffic MPLS Traffic Control Plane Data Plane LFIB Routing Process RIB LIB FIB
19. MPLS: Forwarding Label Distribution Protocol (e.g., LDP) establishes label to routes mappings
20. MPLS: Forwarding Label Distribution Protocol (e.g., LDP) creates LFIB entries on LSRs IN OUT I/F MAC Null - E0/0 aa-00-bb Null - E0/1 aa-00-cc IN OUT I/F MAC 16 32 S0/0 aa-00-bb 18 27 S0/0 aa-00-cc IN OUT I/F MAC 32 64 S0/0 aa-00-bb 27 18 S0/1 aa-00-cc IN OUT I/F MAC 64 POP S0/0 aa-00-bb 65 POP S0/1 aa-00-cc
21. MPLS: Forwarding Ingress edge LSR receives packet, performs Layer 3 value-added services, and “label” packets IN OUT I/F MAC Null - E0/0 aa-00-bb Null - E0/1 aa-00-cc IN OUT I/F MAC 16 32 S0/0 aa-00-bb 18 27 S0/0 aa-00-cc IN OUT I/F MAC 32 64 S0/0 aa-00-bb 27 18 S0/1 aa-00-cc IN OUT I/F MAC 64 POP S0/0 aa-00-bb 65 POP S0/1 aa-00-cc
22. MPLS: Forwarding LSRs forward labelled packets using label swapping IN OUT I/F MAC Null - E0/0 aa-00-bb Null - E0/1 aa-00-cc IN OUT I/F MAC 16 32 S0/0 aa-00-bb 18 27 S0/0 aa-00-cc IN OUT I/F MAC 32 64 S0/0 aa-00-bb 27 18 S0/1 aa-00-cc IN OUT I/F MAC 64 POP S0/0 aa-00-bb 65 POP S0/1 aa-00-cc
23. MPLS: Forwarding Edge LSR at egress removes remaining label * and delivers packet * Pentulimate hop popping actually occurs. There may may not necessarily be a label in the packet at the ultimate or egress LSR. IN OUT I/F MAC Null - E0/0 aa-00-bb Null - E0/1 aa-00-cc IN OUT I/F MAC 16 32 S0/0 aa-00-bb 18 27 S0/0 aa-00-cc IN OUT I/F MAC 32 64 S0/0 aa-00-bb 27 18 S0/1 aa-00-cc IN OUT I/F MAC 64 POP S0/0 aa-00-bb 65 POP S0/1 aa-00-cc
45. MPLS VPN Operation P P PE PE PE CE CE CE CE PE RR RR MP-BGP between PE router to distribute routes between VPNs IGP (OSPF,ISIS) used to establish reachability to destination networks. Label Distribution Protocol establishes mappings to IGP addresses CE-PE dynamic routing (or static) populate the VRF routing tables Customer routes placed into separate VRF tables at each PE = RT? = RT? Import routes into VRF if route-targets match (export = import) RD + RD + RD + RD + RD + VPN labels, RTs VPN labels, RTs
46. MPLS VPN Forwarding Example PE P P PE CE CE PE PE CE CE Push VPN Label (Red Route) Push IGP Label (Green PE Router) Swap IGP Label (From LFIB) POP IGP Label (Pentultimate Hop) Pop VPN Label (Red Route)