As MPLS is widely deployed and the MPLS network transmits various types of traffic, the ISP must provide the capability to monitor the label switched path (LSP) status and locate MPLS forwarding faults. Virtual Circuit Connectivity Verification (VCCV) provides the service capability.
VCCV is an end-to-end PW fault detection and diagnosis mechanism. It tests and checks connectivity of the PW forwarding path. VCCV provides the control channel through which connectivity verification (CV) messages are sent between the PW ingress and egress.
Two VCCV modes are available: VCCV ping and VCCV tracert.
VCCV ping, as an extension of LSP ping, is used to manually test connectivity of a virtual circuit (VC). VCCV ping sends MPLS Echo Request messages through a PW to determine connectivity of the PW. VCCV defines a series of messages transmitted between PEs to verify connectivity of PWs. VCCV ping can be performed in control word channel mode or label alert channel mode:
Control word channel: End-to-end detection between UPEs is supported.
Label alert channel: Segment by segment detection between the UPE and SPE and end-to-end detection are supported.
VCCV tracert, as an extension of LSP tracert, is used to locate the faulty node on a PW. VCCV tracert sends MPLS Echo Request messages through a PW to collect information about nodes on the PW. VCCV tracert is classified into PWE3 single-segment tracert and PWE3 multi-segment tracert.
To ensure that both VCCV packets and PW packets are transmitted along the same path, VCCV packets must be encapsulated in the same way and transmitted in the same channel as PW packets.