MPLS Enhancements to Interfaces MIB

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

• Simple Network Management Protocol (SNMP) must be installed and enabled on the label switching routers (LSRs)
• MPLS must be enabled on the LSRs
• MPLS IP must be enabled on an interface or an MPLS traffic engineering (TE) tunnel enabled on an interface

• Link up and link down traps for the MPLS layer are not supported in this release.
• Write capability using the SNMP SET command is not supported for the MPLS layer in this release.
• Some counters, including discard and multicast, increment on the underlying physical layer; therefore, they equal 0 because they never reach the MPLS layer.
• The high-capacity counters for the MPLS layer interfaces of the Interfaces MIB contain 64 bits of counter data. In previous versions, the high capacity counters displayed 32 bits of counter data.

The following MIB objects are affected:

• • ifHCInOctets
  • ifHCOutOctets
  • ifHCInUcastPkts
  • ifHCOutUcastPkts

When the 64-bit values are less than the value of 232, the 32-bit and 64-bit values are identical.

After the counter increases to more than 232, the counters are different; the 64-bit value is computed by the following formula:

X * (232) + Y

where:

• • X is the number of times the 32-bit counter has rolled.
  • Y is the residual value of the counter after the roll occurred. The Y value equals the 32-bit value.

When the high-capacity counter values are compared to their 32-bit values, there is a period of time that the counter values are not equal. The 64-bit values lag the 32-bit values when the counters poll the 32-bit hardware counters and computing the correct counter value. During the polling and computation interval, the following high-capacity counter values counters might be inconsistent:

• • ifInOctets
  • ifOutOctets
  • ifInUcastPkts
  • ifOutUcastPkts

The inconsistent values can occur if traffic is constantly flowing over an interface and a MIB walk is performed. The 32-bit value is correct at that moment. The 64-bit value lags slightly, because of the polling computations needed to generate it. Once traffic stops flowing over the interface, and a polling period has passed, the two counters are identical and correct.

The lag time depends on the following factors:

• • The polling interval used by the Interfaces MIB. The less time the polling interval takes, the more accurate the value is.
  • The size of the Interfaces MIB. A large MIB takes a long time to walk and might affect the values found at that instant.
  • The number of computations needed to generate the 64-bit value. The number of MPLS-enabled interfaces increases the number of 64-bit counter values that need to be computed.

• Feature Design of the MPLS Enhancements to Interfaces MIB
  
• Interfaces MIB Scalar Objects
  
• Stacking Relationships for MPLS Layer Interfaces
  
• Stacking Relationships for Traffic Engineering Tunnels
  
• MPLS Label Switching Router MIB Enhancements
  
• Benefits of the MPLS Enhancements to Interfaces MIB
  

• Enabling the SNMP Agent
  

• MPLS Enhancements to Interfaces MIB: Examples
  

Router# configure terminal
Router(config)# snmp-server community

Router(config)# snmp-server community public

Router(config)# snmp-server community comaccess ro 4

ATM -- Asynchronous Transfer Mode. The international standard for cell relay in which multiple service types (such as voice, video, or data) are conveyed in fixed-length (53-byte) cells. Fixed-length cells allow cell processing to occur in hardware, thereby reducing transit delays. ATM is designed to take advantage of high-speed transmission media, such as E3, SONET, and T3.

ATM-AAL5 --ATM adaptation layer 5. One of four AALs recommended by the ITU-T. AAL5 supports connection-oriented variable bit rate (VBR) services and is used predominantly for the transfer of classical IP over ATM and LAN emulation (LANE) traffic. AAL5 uses simple and efficient AAL (SEAL) and is the least complex of the current AAL recommendations. It offers low bandwidth overhead and simpler processing requirements in exchange for reduced bandwidth capacity and error-recovery capability.

encapsulation -- Wrapping of data in a particular protocol header. For example, Ethernet data is wrapped in a specific Ethernet header before network transit. Also, when bridging dissimilar networks, the entire frame from one network is simply placed in the header used by the data link layer protocol of the other network.

IETF --Internet Engineering Task Force. A task force (consisting of more than 80 working groups) that is developing standards for the Internet and the IP suite of protocols.

interface --The boundary between adjacent layers of the ISO model.

label --A short, fixed-length identifier that is used to determine the forwarding of a packet.

label switching--A term used to describe the forwarding of IP (or other network layer) packets using a label swapping algorithm based on network layer routing algorithms. The forwarding of these packets uses the exact match algorithm and rewrites the label.

LSR --label switching router. A device that forwards Multiprotocol Label Switching (MPLS) packets based on the value of a fixed-length label encapsulated in each packet.

MIB --Management Information Base. A database of network management information that is used and maintained by a network management protocol such as Simple Network Management Protocol (SNMP). The value of a MIB object can be changed or retrieved by means of SNMP commands, usually through a network management system. MIB objects are organized in a tree structure that includes public (standard) and private (proprietary) branches.

MPLS --Multiprotocol Label Switching. A method for forwarding packets (frames) through a network. It enables routers at the edge of a network to apply labels to packets (frames). ATM switches or existing routers in the network core can switch packets according to the labels with minimal lookup overhead.

MPLS interface--An interface on which Multiprotocol Label Switching (MPLS) traffic is enabled.

MTU --maximum transmission unit. Maximum packet size, in bytes, that a particular interface can handle.

NMS --network management system. System responsible for managing at least part of a network. An NMS is generally a reasonably powerful and well-equipped computer, such as an engineering workstation. NMSs communicate with agents to help keep track of network statistics and resources.

OID --object identifier. Values are defined in specific MIB modules. The Event MIB allows you or an NMS to watch over specified objects and to set event triggers based on existence, threshold, and Boolean tests. An event occurs when a trigger is fired; this means that a specified test on an object returns a value of true. To create a trigger, you or a network management system (NMS) configures a trigger entry in the mteTriggerTable of the Event MIB. This trigger entry specifies the OID of the object to be watched. For each trigger entry type, corresponding tables (existence, threshold, and Boolean tables) are populated with the information required for carrying out the test. The MIB can be configured so that when triggers are activated (fired) either a Simple Network Management Protocol (SNMP) Set is performed, a notification is sent out to the interested host, or both.

SNMP --Simple Network Management Protocol. A management protocol used almost exclusively in TCP/IP networks. SNMP provides a means for monitoring and controlling network devices, and for managing configurations, statistics collection, performance, and security.

traffic engineering tunnel--A label-switched tunnel that is used for traffic engineering. Such a tunnel is set up through means other than normal Layer 3 routing; it is used to direct traffic over a path different from the one that Layer 3 routing could cause the tunnel to take.

trap --A message sent by a Simple Network Management Protocol (SNMP) agent to a network management station, console, or terminal, indicating that a significant event occurred. Traps are less reliable than notification requests, because the receiver does not send an acknowledgment when it receives a trap. The sender cannot determine if the trap was received.

tunnel --A secure communication path between two peers, such as routers.