Troubleshooting MPLS

Issues of basic MPLS

Failure to forward packets through an LSP

Symptom

Packets sent by a host in the network cannot be forwarded through an LSP tunnel.

Common causes

The following are the common causes of this type of issue:

·     The route does not exist.

·     The LSP does not exist

·     The route has not been recursed to the LSP tunnel.

·     The forwarding state of the LSP tunnel is not ACTIVE.

·     The BFD session state is down.

·     The CPU usage is too high.

Troubleshooting flow

Figure 1 shows the troubleshooting flowchart.

Figure 1 Flowchart for troubleshooting packet forwarding failure on LSP

 

Solution

To resolve the issue:

1.     Check if the IGP route exists.

Execute the display ip routing-table command to identify whether there is a subnet route destined for the Loopback interface address of the LSP destination node.

<Sysname> display ip routing-table 1.1.1.1

 

Summary count : 1

 

Destination/Mask   Proto   Pre Cost        NextHop         Interface

1.1.1.2/32         IS_L1   15  10          1.1.1.1         LoopBack1

¡     If the route does not exist, enable the IGP protocol on the Loopback interface and the public network interfaces to ensure the advertisement of the corresponding subnet route.

¡     If the route exists, proceed to step 2.

2.     Check if the LSP exists.

Execute the display mpls lsp command to identify if there is an LSP destined for the Loopback interface address of the destination node.

¡     If no such LSP exists, establish one of the specified type:

-     To establish an LDP LSP, enable MPLS and MPLS LDP on interfaces.

-     To establish an SRLSP, execute the segment-routing mpls command in IS-IS IPv4 unicast address family view, OSPF view, or BGP IPv4 unicast address family view to enable MPLS-based SR.

-     To establish an SR-MPLS TE policy, create the SR-MPLS TE policy correctly in SR TE view.

¡     If the LSP exists, proceed to step 3.

<Sysname> display mpls lsp

FEC                         Proto    In/Out Label    Out Inter/NHLFE/LSINDEX

1.1.1.2/32                  LDP      -/1049          GE0/0/1

3.     Check whether the route has been recursed to the LSP tunnel.

Execute the display mpls tunnel all command to view the information of all tunnels. Execute the display fib command to view the FIB entry of the specified nexthop address. Find out the FIB entry where the Nexthop field value is the same as the Destination field value in the tunnel information, and then check if the LSP index (value of the Token field) of the FIB entry is the same as the NHLFE ID of the tunnel.

¡     If they are different, it indicates that the route has not recursed to the LSP tunnel. Identify whether the tunnel type (Type field) of the specified FEC matches the tunnel type specified in the tunnel policy.

-     If the tunnel types are different, modify the tunnel policy in tunnel policy view to make the tunnel policy configuration match with the specified FEC tunnel type.

-     If the tunnel types are the same, proceed to step 7.

<Sysname> display tunnel-policy

Tunnel policy name: abc

  Select-Seq: LSP

    Load balance number   : 1

    Strict                : No

¡     If the LSP index and the tunnel NHLFE ID are the same, it indicates that the route has recursed to the LSP tunnel. Proceed to step 4.

<Sysname> display mpls tunnel all

Destination      Type     Tunnel/NHLFE      VPN Instance

2.2.2.9          LSP      NHLFE3            -

3.3.3.9          SRLSP    NHLFE2            -

4.4.4.9          SRPolicy NHLFE23068673     -

<Sysname> display fib

Destination count: 1 FIB entry count: 1

Flag:

  U:Usable   G:Gateway   H:Host   B:Blackhole   D:Dynamic   S:Static

  R:Relay    F:FRR

 

Destination/Mask   Nexthop         Flag     OutInterface/Token       Label

55.55.55.55/32     2.2.2.9         UGHR     3                        Null

…

4.     Check if the forwarding state of the LSP tunnel is normal.

Execute the display mpls forwarding nhlfe command to view information about NHLFE entries.

¡     If the forwarding tags don't contain tag A, it implies that the LSP tunnel is not usable. Proceed to step 5.

¡     If the forwarding tags contain flag A, it implies that the LSP tunnel is functioning normally. Proceed to step 6.

<Sysname> display mpls forwarding  nhlfe  3

Flags: T - Forwarded through a tunnel

       N - Forwarded through the outgoing interface to the nexthop IP address

       B - Backup forwarding information

       A - Active forwarding information

       M - P2MP forwarding information

       S - Secondary backup path

 

NID        Tnl-Type   Flag OutLabel Forwarding Info

--------------------------------------------------------------------------------

3          LSP        NA   1040127  GE0/0/3                  10.0.3.2

5.     Check if BFD is functioning properly.

Execute the display mpls bfd command or the display mpls sbfd command to view BFD/SBFD information for LSP tunnels.

¡     If the BFD/SBFD session state is Down, execute the mpls bfd enable command in system view to enable BFD/SBFD for MPLS, and make sure the BFD/SBFD session state is up.

¡     If the BFD/SBFD session state is Up, proceed with step 6.

<Sysname> display mpls bfd ipv4 22.22.2.2 32

 Total number of sessions: 1, 1 up, 0 down, 0 init

 

 FEC Type: LSP

 FEC Info:

   Destination: 22.22.2.2

   Mask Length: 32

 NHLFE ID: 1025

 Local Discr: 513                    Remote Discr: 513

 Source IP: 11.11.1.1                Destination IP: 127.0.0.1

 Session State: Up                   Session Role: Passive

 Template Name: -

<Sysname> display mpls sbfd ipv4 22.22.2.2 32

 Total number of sessions: 1, 1 up, 0 down, 0 init

 

 FEC Type: LSP

 FEC Info:

   Destination: 22.22.2.2

   Mask Length: 32

 NHLFE ID: 1025

 Local Discr: 513                    Remote Discr: 513

 Source IP: 11.11.1.1                Destination IP: 127.0.0.1

 Session State: Up

 Template Name: -

6.     Check if CPU is functioning properly.

Execute the display cpu-usage command to view CPU usage statistics.

¡     If the CPU usage is too high, disable some unnecessary features to reduce the device's CPU usage.

¡     If the CPU usage is normal, proceed to step 7.

7.     If the issue persists, collect the following information and contact Technical Support:

¡     Results of each step.

¡     The configuration file, log messages, and alarm messages.

Related alarm and log messages

Alarm messages

N/A

Log messages

N/A