mpls技術(shù)綜述(已修改)
2025-08-03 08:42 本頁(yè)面
【正文】 MPLS Architecture Overview Adopted from Stefano Previdi’s presentation 麟瑞科技 技術(shù)經(jīng)理 張晃崚 Agenda ? MPLS Concepts ? LSRs and labels ? Label assignment and distribution ? Label Switch Paths ? ATM LSRs ? Loops and TTL ? LDP overview ? Day in the Life of a Packet MPLS Concepts ? MPLS: Multi Protocol Label Switching ? MPLS is a layer 2+ switching ? Developed to integrate IP and ATM ? MPLS forwarding is done in the same way as in ATM switches ? Packet forwarding is done based on Labels MPLS Concepts ? Unlike IP, classification/label can be based on: Destination Unicast address Traffic Engineering VPN QoS ? FEC: Forwarding Equivalence Class ? A FEC can represent a: Destination address prefix, VPN, Traffic Engineering tunnel, Class of Service. Agenda ? MPLS Concepts ? LSRs and labels ? Label assignment and distribution ? Label Switch Paths ? ATM LSRs ? Loops and TTL ? LDP overview ? Summary LSRs and Labels ? LSR: Label Switch Router ? EdgeLSR: LSRs that do label imposition and disposition ? ATMLSR: An ATM switch with Label Switch Controller LSRs and Labels IGP domain with a label distribution protocol ? An IP routing protocol is used within the routing domain (.:OSPF, iISIS) ? A label distribution protocol is used to distribute address/label mappings between adjacent neighbors ? The ingress LSR receives IP packets, performs packet classification, assign a label, and forward the labelled packet into the MPLS work ? Core LSRs switch packets/cells based on the label value ? The egress LSR removes the label before forwarding the IP packet outside the MPLS work LSRs and Labels ? Uses new Ethertypes/PPP PIDs/SNAP values/etc ? More than one Label is allowed Label Stack ? MPLS LSRs always forward packets based on the value of the label at the top of the stack Label = 20 bits Exp = Experimental, 3 bits S = Bottom of stack, 1bit TTL = Time to live, 8 bits 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 Label | Exp|S| TTL LSRs and Labels PPP Header Layer 3 Header Shim Header PPP Header(Packet over SONET/SDH) Ether Hdr Layer 3 Header Shim Header Ether FR Hdr Layer 3 Header Shim Header Frame Relay ATM Cell Header HEC DATA CLP PTI VCI GFC VPI Label HEC DATA CLP PTI VCI GFC VPI Label Subsequent cells Agenda ? MPLS Concepts ? LSRs and labels ? Label assignment and distribution ? Label Switch Paths ? ATM LSRs ? Loops and TTL ? LDP overview ? Day in the Life of a Packet Label Assignment and Distribution ? Labels have linklocal significance Each LSR binds his own label mappings ? Each LSR assign labels to his FECs ? Labels are assigned and exchanged between adjacent neighboring LSR ? Applications may require nonadjacent neighbors Label Assignment and Distribution ? RtrC is the downstream neighbor of RtrB for destination ? RtrB is the downstream neighbor of RtrA for destination ? LSRs know their downstream neighbors
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