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Seamless MPLS network reliability can be improved using a variety of functions. If a network fault occurs, devices with reliability functions enabled immediately detect the fault and switch traffic from active links to standby links.
The following examples demonstrate the reliability functions used on an inter-AS seamless MPLS network.
  • A fault occurs on a link between a CSG and an AGG.
    As shown in Figure 1, the active link along the primary path between CSG1 and AGG1 fails. After BFD for LDP or BFD for CR-LSP detects the fault, the BFD module uses LDP FRR, TE Hot-standby or BGP FRR to switch traffic from the primary path to the backup path.
    Figure 1 Traffic protection triggered by a fault in the link between the CSG and AGG on the inter-AS seamless MPLS network

  • A fault occurs on an AGG.
    As shown in Figure 2 , BGP Auto FRR is configured on CSGs and AGG ASBRs to protect traffic on the BGP LSP between CSG1 and MASG1. If BFD for LDP or BFD for TE detects AGG1 faults, the BFD module switches traffic from the primary path to the backup path.
    Figure 2 Traffic protection triggered by a fault in an AGG on the inter-AS seamless MPLS network


  • A fault occurs on the link between an AGG and an AGG ASBR.
    As shown in Figure 3, a fault occurs on the link along the primary path between AGG1 and ASBR1. After BFD for LDP or BFD for CR-LSP detects the fault, the BFD module uses LDP FRR, TE hot-standby or BGP FRR to switch traffic from the primary path to the backup path.
    Figure 3 Traffic protection triggered by a fault in the link between an AGG and an AGG ASBR on the inter-AS seamless MPLS network


  • A fault occurs on an AGG ASBR.
    As shown in Figure 4, BFD for LDP or BFD for TE is configured on AGG1, and BFD for interface is configured on core ASBR1. If AGG ASBR1 fails, the BFD modules on AGG1 and core ASBR1 detect the fault and trigger the BGP Auto FRR function. BGP Auto FRR switches both upstream and downstream traffic from the primary path to backup paths.
    Figure 4 Traffic protection triggered by a fault in an AGG ASBR on the inter-AS seamless MPLS network

  • A fault occurs on the link between an AGG ASBR and a core ASBR.
    As shown in Figure 5, BFD for interface is configured on AGG ASBR1 and core ASBR1. If the BFD module detects a fault in the link between AGG ASBR1 and core ASBR1, the BFD module triggers the BGP Auto FRR function. BGP Auto FRR switches both upstream and downstream traffic from the primary path to backup paths.
    Figure 5 Traffic protection triggered by a fault in the link between an AGG ASBR and a core ASBR on the inter-AS seamless MPLS network


  • A fault occurs on a core ASBR.
    As shown in Figure 6, BFD for interface and BGP Auto FRR are configured on AGG ASBR1. BGP Auto FRR and BFD for LDP (or BFD for TE) are configured on MASGs to protect traffic on the BGP LSP between CSG1 and MASG1. If the BFD module detects a fault in core ASBR1, it switches both upstream and downstream traffic from the primary path to backup paths.
    Figure 6 Traffic protection triggered by a fault in a core ASBR on the inter-AS seamless MPLS network


  • A link fault occurs in the core area.
    As shown in Figure 7, BFD for LDP or BFD for CR-LSP is configured on core ASBR1. If the BFD module detects a fault in the link between core ASBR1 and MASG1, it triggers the LDP FRR, TE Hot-standby or BGP FRR function. LDP FRR, TE FRR, or BGP FRR switches both upstream and downstream traffic from the primary path to the backup path.
    Figure 7 Traffic protection triggered by a link fault in a core area on the inter-AS seamless MPLS network


  • A fault occurs on an MASG.
    As shown in Figure 8, BFD for BGP tunnel is configured on CSG1. BFD for BGP tunnel is implemented in compliance with RFC 5884 “Bidirectional Forwarding Detection (BFD) for MPLS Label Switched Paths (LSPs).” BFD for BGP tunnel monitors E2E BGP LSPs, including a BGP LSP connected to an LDP LSP. When MASG1 that functions as a provider edge (PE) device fails, BFD for BGP tunnel can rapidly detect the fault and trigger VPN FRR switching. The BFD module then switches both upstream and downstream traffic from the primary path to the backup path.
    Figure 8 Traffic protection triggered by a fault in an MASG on the inter-AS seamless MPLS network



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