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SR-MPLS OAM
SR-MPLS Operation, Administration, and Maintenance (OAM) monitors LSP connectivity and rapidly detects faults. SR-MPLS OAM is implemented using ping and tracert.
SR-MPLS ping and tracert send MPLS Echo Request packets during forward detection based on MPLS label forwarding. The SR-MPLS ping and tracert backhaul MPLS Echo Reply message is forwarded using multi-hop IP path. Ping and tracert can specify the source IP address. If no source IP address is specified, the local MPLS LSR-ID is used as the source IP address. The source IP address in the MPLS Echo Request packet is used as the destination IP address for the MPLS Echo Reply packet.
SR-MPLS BE Ping
On the network shown in Figure 2-79, PE1, P1, P2, and PE2 are all capable of SR-MPLS. An SR LSP is established between PE1 and PE2.
The process of initiating an SR-MPLS BE ping test from PE1 is as follows:
- PE1 initiates a ping test and checks whether the specified tunnel type is SR-MPLS BE IPv4.
- If the specified tunnel type is not SR-MPLS BE IPv4, PE1 reports an error message indicating a tunnel type mismatch and stops the ping test.
- If the specified tunnel type is SR-MPLS BE IPv4, the following operations are performed:
- PE1 constructs an MPLS Echo Request packet encapsulating the outer label of the initiator and carrying destination address 127.0.0.0/8 in the IP header of the packet.
- PE1 forwards the packet to P1. After receiving the packet, P1 swaps the outer MPLS label of the packet and forwards the packet to P2.
- Similar to P1, P2 swaps the outer MPLS label of the received packet and determines whether it is the penultimate hop. If yes, P2 removes the outer label and forwards the packet to PE2. PE2 sends the packet to the Rx/Tx module for processing.
- PE2 returns an MPLS Echo Reply packet to PE1 and generates the ping test result.
SR-MPLS BE Tracert
On the network shown in Figure 2-79, the process of initiating an SR-MPLS BE tracert test from PE1 is as follows:
- PE1 initiates a ping test and checks whether the specified tunnel type is SR-MPLS BE IPv4.
- If the specified tunnel type is not SR-MPLS BE IPv4, PE1 reports an error message indicating a tunnel type mismatch and stops the tracert test.
- If the specified tunnel type is SR-MPLS BE IPv4, the following operations are performed:
- PE1 constructs an MPLS Echo Request packet encapsulating the outer label of the initiator and carrying destination address 127.0.0.0/8 in the IP header of the packet.
- PE1 forwards the packet to P1. After receiving the packet, P1 determines whether the TTL–1 value in the outer label of the received packet is 0.
- If the TTL–1 value is 0, an MPLS TTL timeout occurs. P1 sends the packet to the Rx/Tx module for processing and returns a reply packet to PE1.
- If the TTL–1 value is greater than 0, P1 swaps the outer MPLS label of the packet, searches the forwarding table for the outbound interface, and forwards the packet to P2.
- Similar to P1, P2 also performs the following operations:
- If the TTL–1 value is 0, an MPLS TTL timeout occurs. P2 sends the packet to the Rx/Tx module for processing and returns a reply packet to PE1.
- If the TTL–1 value is greater than 0, P2 swaps the outer MPLS label of the received packet and determines whether it is the penultimate hop. If yes, P2 removes the outer label, searches the forwarding table for the outbound interface, and forwards the packet to PE2.
- PE2 sends the packet to the Rx/Tx module for processing, returns an MPLS Echo Reply packet to PE1, and generates the tracert test result.
SR-MPLS TE Ping
On the network shown in Figure 2-80, PE1, P1, and P2all support SR-MPLS. An SR-MPLS TE tunnel is established between PE1 and PE2. The devices assign adjacency labels as follows:
- PE1 assigns adjacency label 9001 to PE1-P1 adjacency.
- P1 assigns adjacency label 9002 to P1-P2 adjacency.
- P2 assigns adjacency label 9005 to P2-PE2 adjacency.
The process of initiating an SR-MPLS TE ping test from PE1 is as follows:
- PE1 initiates a ping test and checks whether the specified tunnel type is SR-MPLS TE.
- If the specified tunnel type is not SR-MPLS TE, PE1 reports an error message indicating a tunnel type mismatch and stops the ping test.
- If the specified tunnel type is SR-MPLS TE, the following operations are performed.
- PE1 constructs an MPLS Echo Request packet encapsulating label information about the entire tunnel and carrying destination address 127.0.0.0/8 in the IP header of the packet.
- PE1 forwards the packet to P1. P1 removes the outer label (9002) of the received packet and forwards the packet to P2.
- P2 removes the outer label (9005) of the received packet and forwards the packet to PE2 for processing.
- PE2 returns an MPLS Echo Reply packet to PE1.
SR-MPLS TE Tracert
On the network shown in Figure 2-80, the process of initiating an SR-MPLS TE tracert test from PE1 is as follows:
- PE1 initiates a tracert test and checks whether the specified tunnel type is SR-MPLS TE.
- If the specified tunnel type is not SR-MPLS TE, PE1 reports an error message indicating a tunnel type mismatch and stops the tracert test.
- If the specified tunnel type is SR-MPLS TE, the following operations are performed.
- PE1 constructs an MPLS Echo Request packet encapsulating label information about the entire tunnel and carrying destination address 127.0.0.0/8 in the IP header of the packet.
- PE1 forwards the packet to P1. After receiving the packet, P1 determines whether the TTL-1 value in the outer label is 0.
- If the TTL-1 value is 0, an MPLS TTL timeout occurs. P1 sends the packet to the Rx/Tx module for processing and returns an MPLS Echo Reply packet to PE1.
- If the TTL-1 value is greater than 0, P1 removes the outer MPLS label of the packet, buffers the TTL-1 value, copies the value to the new outer MPLS label, searches the forwarding table for the outbound interface, and forwards the packet to P2.
- Similar to P1, P2 also determines whether the TTL-1 value in the outer label of the received packet is 0.
- If the TTL-1 value is 0, an MPLS TTL timeout occurs. P2 sends the packet to the Rx/Tx module for processing and returns an MPLS Echo Reply packet to P1.
- If the TTL-1 value is greater than 0, P2 removes the outer MPLS label of the packet, buffers the TTL-1 value, copies the value to the new outer MPLS label, searches the forwarding table for the outbound interface, and forwards the packet to PE2.
- P2 forwards the packet to PE2, and PE2 returns an MPLS Echo Reply packet to PE1.
