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Explanation of "ifd" and "ifl" indexes and how to map them to an interface

  [KB2820] Show Article Properties


Summary:

ifd and ifl are referenced in log and show commands. This article briefly explains these acronyms and shows how to map them to the interface in question in order to gather more information.

Symptoms:
  • What do the acronyms ifd, ifl, iff, ifa, and iif stand for?

  • How can I get more information on the reference to ifd and ifl when analyzing logs or viewing show commands? 

    For example, ifl:85 is displayed in this log:
    Nov 24 20:58:34 2015 hostname master Failed to send the packet (discard), ifl:85, to SFI.
Solution:

Description:

Here's a brief description of the interface acronyms:

 Acronym Meaning
 ifd  Refers to a physical device
 ifl  Refers to a logical device
 iff  Refers to an address family
 ifa  Refers to an address entry
 iif  Refers to an incoming interface, either an ifd or an ifl (uses a kernel interface index, not an SNMP index)

ifd is the physical interface device, while ifl is the logical interface usually called unit.
Logical interfaces are always related to a physical interface.

For example, interface ge-1/2/3 would be a physical interface, while ge-1/2/3.0 would be a logical unit.

The organization hierarchy continues down with address families (iff) as [... family inet] and addresses (ifa) as [... address 10.1.2.3/24].

interfaces {
     ge-1/2/3 {    /* ifd */
          unit 0 { /* ifl */
               family inet { /* iff */
                    address 10.1.2.3/24 { /* ifa */
                         primary;
                    } 
               } 
          } 
     } 

}

 

 

Mapping the acronyms to an interface:

To identify which interface is referenced in a log message or show command output, use the following hidden commands:

> show interfaces ifl-index <index>
> show interfaces ifd-index <index>

For example, if the log references ifd:1, then run the command:

> show interfaces ifd-index 1
Physical interface: me0, Enabled, Physical link is Up
Interface index: 1, SNMP ifIndex: 33
Type: Ethernet, Link-level type: Ethernet, MTU: 1514, Speed: 100mbps
Device flags : Present Running
Interface flags: SNMP-Traps
Link type : Full-Duplex
Current address: 2c:6b:f5:8f:d7:bf, Hardware address: 2c:6b:f5:8f:d7:bf
Last flapped : 2015-09-10 23:08:06 UTC (11w0d 00:45 ago)
Input packets : 3528290
Output packets: 1595143

Logical interface me0.0 (Index 3) (SNMP ifIndex 34)
Flags: Up SNMP-Traps Encapsulation: ENET2
Input packets : 3528290
Output packets: 1595143
Protocol inet, MTU: 1500
Flags: Is-Primary
Addresses, Flags: Is-Preferred Is-Primary
Destination: 172.16.202/24, Local: 172.16.202.244,
Broadcast: 172.16.202.255

If the log references ifl:3, then run the command:

> show interfaces ifl-index 3
Logical interface me0.0 (Index 3) (SNMP ifIndex 34)
Flags: Up SNMP-Traps Encapsulation: ENET2
Input packets : 3528256
Output packets: 1595117
Protocol inet, MTU: 1500
Flags: Is-Primary
Addresses, Flags: Is-Preferred Is-Primary
Destination: 172.16.202/24, Local: 172.16.202.244,
Broadcast: 172.16.202.255

It is possible to obtain the index numbers with this command:

> show interfaces extensive | match "interface|index"| except "stat|flag|descript|speed"
Physical interface: ge-3/1/0, Enabled, Physical link is Up
  Interface index: 138, SNMP ifIndex: 8119, Generation: 141
Modification History:

2019-10-02: Minor, non-technical edits.

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