Cisco Cisco IOS Software Release 12.2(25)S

The Interfaces MIB (IF MIB) provides a Simple Network Management Protocol (SNMP)-based method 
for managing interfaces. Each entry in the IF MIB establishes indexing, statistics, and stacking 
relationships among underlying physical interfaces, subinterfaces, and Layer 2 protocols that exist 
within Cisco IOS.

The enhancements add an MPLS layer to the IF MIB as a Layer 2 protocol to provide statistics for traffic 
encapsulated as MPLS on an interface. In this new structure, MPLS-specific data, such as 
MPLS-encapsulated traffic counters and the MPLS maximum transmission unit (MTU), resides on top 
of the underlying physical or virtual interface to allow separation from non-MPLS data.

The enhancements also allow you to view indexing, statistics, and stacking relationships using the 
ifStackTable. MPLS layer interfaces are stacked above the underlying physical or virtual interface that 
is actually forwarding the MPLS traffic. MPLS traffic engineering tunnels are then stacked above those 
MPLS layers.

The IF MIB supports several types of interfaces. A virtual interface that provides protocol statistics for 
MPLS-encapsulated traffic has been added. This new interface is stacked above real Cisco IOS interfaces 
or subinterfaces, such as Ethernet (et0) or ATM (at1/1.1).

When any MPLS application starts, Cisco IOS creates a corresponding MPLS layer above each interface 
capable of supporting MPLS.

An IF MIB entry is created when you enable any MPLS application on an interface; the entry is removed 
when you disable the MPLS application.

The IF MIB consists of the following tables:

ifTable—Contains information on each interface in the network. Its definition of an interface 
includes any sublayers of the internetwork layer of the interface. MPLS interfaces fit into this 
definition of an interface. Therefore, each MPLS-enabled interface is represented by an entry in the 
ifTable. (See

.)

ifXTable—Contains objects that have been added to the IF MIB as a result of the interface evolution 
effort or replacements for objects from the original MIB-II ifTable. This table also contains objects 
that were previously in the ifExtsTable. (See

ifStackTable—Contains

 

objects that define the relationships among the sublayers of an interface. 

(See

.)

ifRcvAddressTable—Contains

 

objects that define the media-level addresses received by an 

interface.

 

(See

.)

There are objects that are not supported by some interface types. The corresponding MPLS layer objects 
might not be supported if they depend on an unsupported object at the underlying layer.

The notation used in the IF MIB follows the conventions defined in Abstract System Notation One 
(ASN.1). ASN.1 defines an Open System Interconnection (OSI) language used to describe data types 
independently from particular computer structures and presentation techniques. Each object in the MIB 
incorporates a DESCRIPTION field that includes an explanation of the object’s meaning and usage,