Configuring Miscellaneous MPLS Properties

This section discusses additional MPLS properties that are not directly related to creating LSPs.

Popping the Label on the Ultimate-Hop Router

You can control the label value advertised on the egress router of an LSP. The default advertised label is label 3 (implicit null label). If label 3 is advertised, the penultimate -hop router removes the label and sends the packet to the egress router. By enabling ultimate-hop popping, label 0 (IPv4 Explicit Null Label) is advertised. Ultimate hop-popping ensures that any packets traversing an MPLS network include a label.

To configure MPLS to pop the label on the ultimate hop, include the explicit-null statement:

 [edit protocols ldp]  explicit-null; 

Juniper Networks routers queue packets based on the incoming label. Routers from other vendors might queue packets differently. Keep this in mind when working with networks containing routers from multiple vendors .

Configuring Traffic Engineering for LSPs

Establishing an LSP installs a host route (a 32-bit mask) in the ingress router toward the egress router. The address of the host route is the destination address of the LSP. By default, only BGP can use LSPs in its route calculations. On the ingress router, to enable both BGP and the IGPs to use an LSP in forwarding traffic destined for the egress router of that LSP, include the traffic-engineering statement with the bgp-igp option:

 [edit protocol mpls]  traffic-engineering bgp-igp; 

To install the ingress routes in both the inet.0 and inet.3 routing tables, which are used to support VPNs, include the traffic engineering statement with the bgp-igp-both-ribs option:

 [edit protocol mpls]  traffic-engineering bgp-igp-both-ribs; 

Configuring MPLS to Gather Statistics

To configure MPLS so that it periodically gathers traffic statistics about all MPLS sessions, including transit sessions, include the statistics statement:

 [edit protocol mpls]  statistics {   file  filename  <size  size  files  number  >;   interval  seconds  ;   auto-bandwidth; } 

The default interval is 300 seconds.

The statistics are placed in a file, with one entry per LSP. During the specified interval, the following information is recorded in this file:

• Number of packets, number of bytes, packets per second, and bytes per second transmitted by each LSP.

• Percent of bandwidth transmitted over a given LSP in relation to the bandwidth percentage configured for that LSP. Note that if no bandwidth is configured for an LSP, 0 percent is recorded in the percentage column.

At the end of each periodic report, a summary shows the current time, total number of sessions, number of sessions read, number of sessions ignored, and read errors, if any. Ignored sessions are typically those not in the up state or those with a reserved (0 through 15) incoming label (typically the egress point of an LSP). The reason for a read error appears on the same line as the entry for the LSP on which the error occurred. Gathering statistics is an unreliable process; occasional read errors might affect their accuracy.

Controlling MPLS System Log Messages and SNMP Traps

For more information about the MPLS SNMP traps and the proprietary MPLS MIB, see the JUNOS technical documentation: MPLS.

Whenever an LSP makes a transition from up to down, or down to up, and whenever an LSP switches from one active path to another, the ingress router generates a system log message and sends an SNMP trap.

To disable the generation of system log messages and SNMP traps, include the following statements. For scalability reasons, only the ingress router generates SNMP traps. By default, MPLS issues traps for all configured LSPs. If you have many LSPs, the number of traps can become quite large.

 [edit protocols mpls]  log-updown {   no-syslog;   no-trap; } 

Tracing MPLS Protocol Packets and Operations

To trace MPLS protocol packets and operations, include the traceoptions statement:

 [edit protocol mpls]  traceoptions {   file  filename  <replace> <size  size  > <files  number  > <no-       stamp>     <(world-readable  no-world-readable)>;   flag  flag  <  flag-modifier  > <disable>; } 

For more information about tracing and global tracing options, see the JUNOS technical documentation.

You can specify the following MPLS-specific flags:

• connection ” All circuit cross-connect (CCC) activity

• connection-detail ” Detailed CCC activity

• cspf ” CSPF computations

• cspf-link ” Links visited during CSPF computations

• cspf-node ” Nodes visited during CSPF computations

• error ” MPLS error conditions

• state ” All LSP state transitions