1b Label Distribution Protocol LDP establishes label to destination network

1b label distribution protocol ldp establishes label

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establish reachability to destination networks. 1b. Label Distribution Protocol (LDP) establishes label to destination network mappings. 2. Ingress Edge LSR receives packet, performs Layer 3 value- added services, and labels(PUSH) packets. 3. LSR switches packets using label swapping(SWAP) . 4. Edge LSR at egress removes(POP) label and delivers packet. 47
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MPLS Operation… Here is how MPLS actually works. Step 1A : a routing protocol such as OSPF, RIP or IS-IS determines the layer 3 topology. A router builds a routing table as it “listens” to the network. A Cisco router or IP+ATM switch can have a routing function inside that does this. All devices in the network are building the layer 3 topology. Step 1B : The Label Distribution Protocol (LDP) establishes label values for each device according to the routing topology, to pre-configure maps to destination points. Unlike ATM PVCs where the VPI/VCIs are manually assigned, labels are assigned automatically by LDP. 48
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MPLS Operation… Here is how MPLS actually works… Step 2 : An ingress packet enters the Edge LSR. The LSR labels it, does all the layer 3 value-added services, including QoS, Bandwidth management, and so forth. It then applies a label to it based on the information in the forwarding tables. Step 3 : the core LSR read the labels on each packet on the ingress interface, and based on what the label says, sends the packet out the appropriate egress interface with a new label. Step 4 : the egress Edge LSR strips the label and sends the packet to its destination. 49
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Router Example: Forwarding Packets 0 171.69 Packets Forwarded Based on IP Address Data Addres s Prefix 128.89 128.89 171.69 1 1 I/F Addres s Prefix 128.89 128.89 171.69 0 1 0 1 I/F 128.89 0 1 128.89.25.4 Data Addres s Prefix 128.89 128.89 0 I/F Data Data 128.89.25.4 128.89.25.4 128.89.25.4 128.89.25.4 128.89.25.4 128.89.25.4 3-50
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MPLS Example: Routing Information 128.89 1 0 1 0 Routing Updates (OSPF, RIP, …) You Can Reach 128.89 and 171.69 Thru Me You Can Reach 171.69 Thru Me You Can Reach 171.69 Thru Me You Can Reach 128.89 Thru Me You Can Reach 128.89 Thru Me In Label Addres s Prefix 128.89 171.69 1 1 Out I’face Out Label In Label Addres s Prefix 128.89 171.69 0 1 Out I’face Out Label In Label Addres s Prefix 128.89 0 Out I’face Out Label 171.69 3-51
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MPLS Example: Assigning Labels 128.89 1 0 1 0 Label Distribution Protocol (LDP) (downstream allocation) Use Label 4 for 128.89 and Use Label 5 for 171.69 Use Label 4 for 128.89 and Use Label 5 for 171.69 Use Label 7 for 171.69 Use Label 7 for 171.69 Use Label 9 for 128.89 Use Label 9 for 128.89 In Label Addres s Prefix 128.89 171.69 1 1 Out I’face Out Label In Label Addres s Prefix 128.89 171.69 0 1 Out I’face Out Label In Label Addres s Prefix 128.89 0 Out I’face Out Label - 9 9 7 4 5 4 5 - - 171.69 3-52
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In Label Addres s Prefix 128.89 128.89 171.69 1 1 Out I’face Out Label 4 5 - - MPLS Example: Forwarding Packets Label Switch Forwards Based on Label In Label Addres s Prefix 128.89 171.69 0 1 Out I’face Out Label 9 7 4 4 5 In Label Addres s Prefix 128.89 0 Out I’face Out Label - 9 Data 128.89.25.4 Data 128.89.25.4 Data 128.89.25.4 Data 128.89 1 0 1 0 128.89.25.4 128.89.25.4 4 4 9 9 3-53
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MPLS Encapsulations Label Header Label Header PPP Header PPP Header
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