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Leading Edge Routing

Leading Edge Routing. MPLS Enhancements to Support Layer 2 Transport Services. Jeremy Brayley jbrayley@laurelnetworks.com. Agenda. Introduction Why Layer 2 service over MPLS? Provisioning Signaling Layer 2 encapsulations Summary and future work. What is MPLS?.

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Leading Edge Routing

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  1. LeadingEdge Routing MPLS Enhancements to Support Layer 2 Transport Services Jeremy Brayley jbrayley@laurelnetworks.com

  2. Agenda • Introduction • Why Layer 2 service over MPLS? • Provisioning • Signaling • Layer 2 encapsulations • Summary and future work

  3. What is MPLS? Multiprotocol Label Switching • Label switching mechanism with IP control plane initially designed to increase forwarding performance • Label stacking allows tunnel hierarchy for superior scalability • New signaling protocols (LDP, RSVP-TE, CR-LDP, and even mBGP) • First application - IP Traffic Engineering • Subsequently several new applications have been proposed

  4. New applications for MPLS • MPLS has been viewed as an IP traffic engineering technology • Allows a carrier to increase operational efficiency, but service remains the same • Layer 2 transport is a new application of MPLS • MPLS becomes forwarding infrastructure for a number of services • IP services • Private Data (Frame Relay, ATM, Ethernet)

  5. What problems are we solving? • Network consolidation • For carriers offering Private Data and IP services • Additional service revenue opportunities • For carriers currently only offering IP services • Scalability • Core switches MPLS tunnels and manages far fewer connections • Ease of provisioning • Touch only edge devices

  6. Methods of providing layer 2 services over MPLS • MPLS-based Layer 2VPNs (L2VPN) • draft-kompella-mpls-12vpn-02.txt • L2VPN method eases provisioning of full mesh VPNs • Policies can be formed to provision hub and spoke topologies • Transport of Layer 2 frames over MPLS • draft-martini-l2circuit-trans-mpls-05.txt • Defines point-to-point transport using LDP • draft-martini-l2circuit-encap-mpls-01.txt • Defines encapsulations for multiple layer 2 services • Full or partial mesh provisioning requires automated management tools • Both techniques use label stacking for scalability

  7. Scalability through label stacking P Layer 2 VCs 2.2.2.2 Tunnel to 2.2.2.2 PE PE 1.1.1.1 IP/MPLS network P Tunnel label VC label VC label VC label Tunnel label determines path to remote edge VC label designates connection at tunnel endpoint

  8. Martini method for L2 transport • All services look like a Virtual Circuit to MPLS network • Provision service by associating each endpoint with a common VC Identifier(VCID) • Network automatically determines VC label and Tunnel label to push on L2 frame Port/DLCI Port/DLCI VCID Tunnel label VC label Layer 2 frame

  9. Provisioning a Layer 2 transport service indirect LDP session to advertise VC labels LDP advertises label 501 for VCID 50 LDP advertises VC label 500 for VCID 50 PE chooses tunnel to 2.2.2.2, label 600 PE chooses tunnel to 1.1.1.1, label 601 600 501 Ethernet 601 500 Ethernet Port 1B, VLAN 200 -> peer 1.1.1.1, VCID 50 Port 1A, VLAN 100 -> peer 2.2.2.2, VCID 50 P 1B, 200 1A, 100 601 600 PE PE 2.2.2.2 1.1.1.1 P

  10. LDP in review • VC label established via indirect LDP session • New Virtual Circuit FEC element defined • Used in Label Mapping and Label Withdraw messages • PE binds VC label to VC Identifier(VCID) and advertises to remote peer • LDP message includes: • Local port identifier • VC type (FR, ATM, VLAN, etc) • Local MTU

  11. Tunnel creation and selection • Tunnels must exist between PE endpoints before transport connection may be established • Same tunnel may be used for IP and L2 transport traffic • Eases provisioning • Scalable • Service determined by tunnel creation • RSVP-TE tunnels allow traffic engineering and resource reservation • LDP tunnels are plug & play

  12. Withdrawing labels to indicate connection status LMI indicates status=down VCID is down X PE withdraws VC label for connection ID 50 P DCLI 100 DCLI 200 PE PE 2.2.2.2 1.1.1.1 P Incoming frames on DLCI 200 are dropped until a new VC label is received

  13. Layer 2 encapsulation • Martini drafts define the following encapsulations over MPLS • Frame Relay • Ethernet port / 802.1q VLAN • ATM AAL5 • ATM cell • PPP/HDLC

  14. Frame Relay encapsulation • Ingress device strips the Frame Relay header and FCS and appends label stack and control word • Control word carries FECN, BECN, DE, C/R bits plus PDU length • Sequence number is optional. It is used to guarantee in-order delivery of frames Q.922 address payload FCS Frame Relay frame 4 octets 4 octets 4 octets Tunnel label VC label Control word Frame Relay PDU Frame Relay over MPLS 4 1 1 1 1 8 16 bits Rsvd B F D C Length Sequence Number Control Word

  15. Ethernet encapsulation • Ingress device strips the Ethernet preamble and CRC, but transports the entire header • Control word is not used • 802.1q VLAN ID may be overwritten at egress DA SA T payload FCS Ethernet frame 4 octets 4 octets Tunnel label VC label Ethernet header Ethernet payload Ethernet over MPLS

  16. ATM AAL5 encapsulation • Ingress reassembles AAL5 frames and strips 8 octet AAL5 trailer • Required control word includes: • Transport type (AAL5 CPCS-PDU or ATM cell) • EFCI, CLP, and C/R bits (CPCS-UU’s LSB) • (CPCS-PDU + control word) length • Sequence number 4 octets 4 octets 4 octets Tunnel label VC label Control word AAL5 CPCS-PDU AAL5 over MPLS 4 1 1 1 1 8 16 bits Rsvd T E L C Length Sequence Number Control Word

  17. ATM cell mode • Ingress performs no reassembly • Control word is optional: • Length may be used to infer number of cells • Flags set to zero 4 octets 4 octets 4 octets 52 octets 52 octets Tunnel label VC label Control word ATM cell #1 minus HCS ATM cell #2 minus HCS … ATM cells over MPLS 4 4 8 16 bits Rsvd Flags Length Sequence Number Control Word

  18. Control word in review • Layer 2 header fields may be discarded at ingress • Control word carries variable “flag” bits • (FR FECN, BECN, C/R, DE, ATM CLP, EFCI, etc) • Length required when padding small frames on links which have a minimum frame size • Sequence number is optional. It is used to detect out of order delivery of frames. 4 4 8 16 bits Rsvd Flags Length Sequence Number Control Word

  19. Class of Service considerations • Ingress device may set MPLS EXP bits to denote class of service on MPLS network • Should set EXP on both Tunnel and VC labels • Tunnel label stripped before egress if PHP is used • Allows user to keep 802.1p classification across MPLS network P Treat according to Tunnel label EXP Set Tunnel and VC label EXP to 010 Treat according to VC label EXP P P P PE PE

  20. Future work • Interworking between different frame types • Frame Relay / ATM service interworking (FRF.8.1) • FR/ATM/Ethernet interworking for IP • OA&M improvements & SLA measurement • In-band performance monitoring and continuity check

  21. Summary • L2 transport is a new application of MPLS • Not just for traffic engineering anymore • Allows a service provider to expand IP/MPLS network while offering Layer 2 services • MPLS label stacking mechanism allows for core network scalability • Far fewer connections to manage in core • Services provisioned at edge

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