Pinging the Directly Connected CE Routers from the PE Routers

Using traceroute from Router PE2 to Router CE2

To determine the path from the VPN interface on Router PE2 to the VPN and loopback interfaces on Router CE2, respectively, use the following traceroute commands:

user@vpn2> traceroute 10.255.10.5 interface
t3-0/0/3.0 source 192.168.193.2

traceroute to 10.255.10.5 (10.255.10.5) from 192.168.193.2, 30 hops max, 40 byte packets
 1  vpn5.isp-core.net (10.255.10.5)  1.009 ms  0.677 ms  0.633 ms
user@vpn2>  traceroute 192.168.193.5 interface t3-0/0/3.0 source 192.168.193.2  
traceroute to 192.168.193.5 (192.168.193.5) from 192.168.193.2, 30 hops max, 40 byte packets
 1  vpn5-t3-003.isp-core.net (192.168.193.5)  0.974 ms  0.665 ms  0.619 ms

Pinging the Remote CE Router from the Local PE Router

The following procedure is effective for Layer 3 VPNs only. To ping a remote CE router from a local PE router in a Layer 3 VPN, you need to configure the following:

Configure a logical unit for the loopback interface.
To configure an additional logical unit on the loopback interface of the PE router, configure the unit statement at the [edit interfaces lo0] hierarchy level:
[edit interfaces]lo0 {unit number {family inet {address address;}}}
Configure the loopback interface for the Layer 3 VPN routing instance on the local PE router. You can associate one logical loopback interface with each Layer 3 VPN routing instance, enabling you to ping a specific routing instance on a router.
Specify the loopback interface you configured in Step 1 using the interface statement at the [edit routing-instances routing-instance-name] hierarchy level:
[edit routing-instances routing-instance-name]interface interface-name;
The interface-name is the logical unit on the loopback interface (for example, lo0.1).
From the VPN interface on PE router, you can now ping the logical unit on the loopback interface on the remote CE router:
user@host> ping interface interface host
Use interface to specify the new logical unit on the loopback interface (for example, lo0.1). For more information about how to use the ping interface command, see the JUNOS Interfaces Command Reference.

Limitation on Pinging a Remote CE Router from a PE Router

If you attempt to ping a remote CE router from a PE router, ICMP echo requests are sent from the PE router, with the PE router’s VPN interface as the source. Other PE routers have a route back to that address with a VPN label. When the echo replies return, they include a label. The PE router pops the VPN label and sends the packet from the VPN interface to the local CE router. The local CE router sends it back to the PE router, its actual destination.

When a Juniper Networks routing platform receives a labeled packet, the label is popped (depending on the label operation specified), and the packet is forwarded to an interface, even if the packet is destined for that particular PE router. Labeled packets are not analyzed further for the IP information under the label.

If there is a problem with the connection to the local CE router, packets are sent out but do not return to the PE router, and the ping fails. If the connection between your PE router and local CE router is down, sending a ping to the remote CE router fails even though the connection to the remote CE router might be functional.

Pinging a Layer 3 VPN

You can ping from a PE router to a PE router in a Layer 3 VPN using the ping mpls l3vpn l3vpn-name prefix prefix <count count> command. For more information, see Pinging VPNs, VPLS, and Layer 2 Circuits.

For a detailed description of the ping mpls command, see the JUNOS Routing Protocols and Policies Command Reference.

Disabling Normal TTL Decrementing for Layer 3 VPNs

For information about how to disable normal TTL decrementing for Layer 3 VPNs, see Configuring the Local Site on PE Routers in Layer 2 VPNs.

Troubleshooting RSVP and LDP LSPs

You can use the show mpls lsp command to determine whether an LSP is up and running. However, this command displays information about RSVP LSPs only. If you have configured LDP LSPs, use the show route protocol ldp command. For more information about how to use show commands to troubleshoot RSVP LSPs, see the JUNOS MPLS Network Operations Guide.

Troubleshooting Inconsistently Advertised Routes from Gigabit Ethernet Interfaces

For direct routes on a LAN in a VRF, the JUNOS Software attempts to locate a CE that can be designated as the next hop. If this cannot be done, advertised routes from Gigabit Ethernet interfaces are dropped.

In such instances, do one of the following:

Use the static statement at the [edit routing-options] or [edit logical-systems logical-system-name routing-options] hierarchy levels in the VRF routing instance to a CE router on the LAN subnet, configuring the CE as the next hop. All traffic to directly destinations on this LAN will go to the CE. You can add two static routes to two CEs on the LAN for redundancy.

Configure the vrf-table-label statement at the [edit routing-instances routing-instance-name] hierarchy levels to map the inner label of a packet to a specific VRF routing table. This allows the examination of the encapsulated IP header to force IP lookups on the VRF routing instance for all traffic.

Note: The vrf-table-label statement is not available for every core-facing interface; for example, channelized interfaces are not supported. See Filtering Packets in Layer 3 VPNs Based on IP Headers for information about support for the vrf-table-label statement over Ethernet and SONET/SDH interfaces.