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Leading Edge Routing MPLS Enhancements to Support Layer 2 Transport Services Jeremy Brayley firstname.lastname@example.org
Copyright © 2001, Laurel Networks, Inc. Agenda Introduction –Why Layer 2 service over MPLS? Provisioning Signaling Layer 2 encapsulations Summary and future work
Copyright © 2001, Laurel Networks, Inc. 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
Copyright © 2001, Laurel Networks, Inc. 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)
Copyright © 2001, Laurel Networks, Inc. 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
Copyright © 2001, Laurel Networks, Inc. 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
Copyright © 2001, Laurel Networks, Inc. Scalability through label stacking IP/MPLS network Tunnel to 184.108.40.206 Layer 2 VCs 220.127.116.11 18.104.22.168 Tunnel label determines path to remote edge VC label designates connection at tunnel endpoint Tunnel label VC label P P PE
Copyright © 2001, Laurel Networks, Inc. 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 Tunnel label VC label Layer 2 frame Port/DLCI VCID
Copyright © 2001, Laurel Networks, Inc. Provisioning a Layer 2 transport service 22.214.171.124 126.96.36.199 1A, 100 1B, 200 Port 1A, VLAN 100 -> peer 188.8.131.52, VCID 50 Port 1B, VLAN 200 -> peer 184.108.40.206, VCID 50 LDP advertises label 501 for VCID 50 LDP advertises VC label 500 for VCID 50 PE chooses tunnel to 220.127.116.11, label 600 600501 Ethernet PE chooses tunnel to 18.104.22.168, label 601 601500 Ethernet 600 601 indirect LDP session to advertise VC labels PE P P
Copyright © 2001, Laurel Networks, Inc. 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
Copyright © 2001, Laurel Networks, Inc. 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
Copyright © 2001, Laurel Networks, Inc. Withdrawing labels to indicate connection status 22.214.171.124 126.96.36.199 DCLI 100 DCLI 200 X PE withdraws VC label for connection ID 50 Incoming frames on DLCI 200 are dropped until a new VC label is received LMI indicates status=down VCID is down PE P P
Copyright © 2001, Laurel Networks, Inc. Layer 2 encapsulation Martini drafts define the following encapsulations over MPLS –Frame Relay –Ethernet port / 802.1q VLAN –ATM AAL5 –ATM cell –PPP/HDLC
Copyright © 2001, Laurel Networks, Inc. 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 Tunnel label VC label 4 octets Control word Frame Relay PDU 4 octets RsvdBFDC bits 41111 Length 8 Sequence Number 16 Control Word payload Q.922 address FCS Frame Relay frame Frame Relay over MPLS
Copyright © 2001, Laurel Networks, Inc. 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 Tunnel label VC label 4 octets Ethernet header Ethernet payload DASATFCS Ethernet frame Ethernet over MPLS
Copyright © 2001, Laurel Networks, Inc. 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 Tunnel label VC label 4 octets Control word AAL5 CPCS-PDU 4 octets RsvdTELC bits 411 Length 8 Sequence Number 16 Control Word AAL5 over MPLS 11
Copyright © 2001, Laurel Networks, Inc. ATM cell mode Ingress performs no reassembly Control word is optional: –Length may be used to infer number of cells –Flags set to zero Tunnel label VC label 4 octets Control word ATM cell #1 minus HCS 4 octets Rsvd bits 4 Length 8 Sequence Number 16 Control Word Flags 4 52 octets ATM cell #2 minus HCS 52 octets … ATM cells over MPLS
Copyright © 2001, Laurel Networks, Inc. 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. Rsvd bits 4 Length 8 Sequence Number 16 Control Word Flags 4
Copyright © 2001, Laurel Networks, Inc. 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 Set Tunnel and VC label EXP to 010 Treat according to VC label EXP Treat according to Tunnel label EXP PE P P P P
Copyright © 2001, Laurel Networks, Inc. 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
Copyright © 2001, Laurel Networks, Inc. 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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