Pinging VPNs, VPLS, and Layer 2 Circuits
For testing purposes, you can ping Layer 2 VPNs, Layer 3 VPNs, and Layer 2 circuits by using the ping mpls command. The ping mpls command helps to verify that a VPN or circuit has been enabled and tests the integrity of the VPN or Layer 2 circuit connection between the PE routers. It does not test the connection between a PE router and a CE router. To ping a VPLS routing instance, you issue a ping vpls instance command.
You issue the ping mpls command from the ingress PE router of the VPN or Layer 2 circuit to the egress PE router of the same VPN or Layer 2 circuit. When you execute the ping mpls command, echo requests are sent as MPLS packets.
The payload is a User Datagram Protocol (UDP) packet forwarded to the address 127.0.0.1. The contents of this packet are defined in RFC 4379, Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures. The label and interface information for building and sending this information as an MPLS packet is the same as for standard VPN traffic, but the time-to-live (TTL) of the innermost label is set to 1.
When the echo request arrives at the egress PE router, the contents of the packet are checked, and then a reply that contains the correct return is sent by means of UDP. The PE router sending the echo request waits to receive an echo reply after a timeout of 2 seconds (you cannot configure this value).
You must configure MPLS at the [edit protocols mpls] hierarchy level on the egress PE router (the router receiving the MPLS echo packets) to be able to ping the VPN or Layer 2 circuit. You must also configure the address 127.0.0.1/32 on the egress PE router’s lo0 interface. If this is not configured, the egress PE router does not have this forwarding entry and therefore simply drops the incoming MPLS pings.
The ping mpls command has the following limitations:
You cannot ping an IPv6 destination prefix.
You cannot ping a VPN or Layer 2 circuit from a router that is attempting a graceful restart.
You cannot ping a VPN or Layer 2 circuit from a logical system.
You can also determine whether an LSP linking two PE routers in a VPN is up by pinging the end point address of the LSP. The command you use to ping an MPLS LSP end point is ping mpls lsp-end-point address. This command tells you what type of LSP (RSVP or LDP) terminates at the address specified and whether that LSP is up or down.