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Configuring network management-specific interface
index
Interface index (ifindex) and network management (NM)-specific ifindex are both interface identifications.
ifindex is an internal parameter for software implementation of the device, and it uniquely identifies an
interface for internal resource allocation and management. NM-specific ifindex is a parameter provided
by the device to the NMS. It is the index for ifTable entries.
An NM-specific ifindex is in either of the following formats:
• 16-bit NM-specific ifindex—A 16-bit NM-specific ifindex value contains 16 bits and ranges from 1 to
65534. The NM-specific ifindex value of each interface is allocated dynamically and increased
sequentially. The 16-bit NM-specific ifindex is an index value without any syntax explanation, and
only uniquely identifies an interface.
• 32-bit NM-specific ifindex—A 32-bit NM-specific ifindex value contains 32 bits, as shown in Figure
37. T
he value is composed of the following parts: Chassis ID, Slot ID, interface type, and interface
offset.
Figure 37 32-bit NM-specific ifindex
• Offset— 16 bits in length and distinguishes different interfaces of the same type on the same
interface board.
• Interface type—7 bits in length and is the enumerated value corresponding to the interface type. It
supports up to 128 different interface types and supports more than 80 interface types.
• Slot ID—Number of the physical slot in which the interface resides, with the length of 5 bits.
• Chassis ID—4 bits in length. For a distributed IRF virtual device, this field indicates the member ID of
the device to which the interface belongs; for other devices, this field has no meanings and the
value is 0.
Switching the format of an NM-specific ifindex
An NM-specific ifindex adopts the default format (16-bit format). When either of the following scenarios
appears, you must switch the format of the NM-specific ifindex using the following guidelines:
• If the NMS requires a 32-bit NM-specific ifindex, switch the NM-specific ifindex format to 32-bit,
which carries interface information such as the number of the slot in which the interface resides. If
the NMS only supports 16-bit NM-specific ifindex values, the NMS cannot recognize 32-bit NM-
specific ifindex values so make sure that the NM-specific ifindex values on the device are 16-bit.
• If the network protocol operating on the device does not support 32-bit NM-specific ifindex values,
make sure that NM-specific ifindex values on the device are 16-bit. For example, each packet of
NetStream version 5 or version 8 only reserves 16 bits for the ifindex, and the NM-specific ifindexes
must be in the 16-bit format. Each packet of NetStream version 9 reserves 32 bits for the ifindex, and
the NM-specific ifindexes can be in either the 16-bit format or the 32-bit format.
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