This article outlines one of the reasons for the internal ".local." interface to report incrementing input errors and gives possible workarounds to prevent these errors, while indicating the release in which the issue is resolved.

It is observed that the error count increases for the ".local." (internal) interface in Junos OS with Upgraded FreeBSD kernel (FreeBSD 10.x or later) when receiving any packets from the management interface (fxp0 or em0).

id@router> show interfaces .local.. extensive

Physical interface: .local., Enabled, Physical link is Up
  Interface index: 0, SNMP ifIndex: 0, Generation: 1
  Type: Loopback, Link-level type: Interface-Specific, MTU: Unlimited,
  Clocking: Unspecified, Speed: Unlimited
  Device flags   : Present Running Loopback
  Interface flags: Point-To-Point
  Link type      : Unspecified
  Link flags     : None
  Physical info  : Unspecified
  Hold-times     : Up 0 ms, Down 0 ms
  Damping        : half-life: 0 sec, max-suppress: 0 sec, reuse: 0, suppress: 0, state: unsuppressed
  Current address: Unspecified, Hardware address: Unspecified
  Alternate link address: Unspecified
  Last flapped   : Never
  Statistics last cleared: Never
  Traffic statistics:
   Input  bytes  :                    0
   Output bytes  :                    0
   Input  packets:                    0
   Output packets:                    0
   IPv6 transit statistics:
    Input  bytes  :                   0
    Output bytes  :                   0
    Input  packets:                   0
    Output packets:                   0
  Input errors:
    Errors: 102, Drops: 0, Framing errors: 0, Runts: 0, Giants: 0,
    Policed discards: 0, Resource errors: 0
  Output errors:
    Carrier transitions: 0, Errors: 0, Drops: 0, MTU errors: 0,
    Resource errors: 0


id@router> show interfaces .local.. extensive | match errors
  Input errors:
    Errors: 104, Drops: 0, Framing errors: 0, Runts: 0, Giants: 0, Policed discards: 0,
    Resource errors: 0
  Output errors:
    Carrier transitions: 0, Errors: 0, Drops: 0, MTU errors: 0, Resource errors: 0


id@router> run show interfaces .local.. extensive | match errors   
  Input errors:
    Errors: 115, Drops: 0, Framing errors: 0, Runts: 0, Giants: 0, Policed discards: 0,
    Resource errors: 0
  Output errors:
    Carrier transitions: 0, Errors: 0, Drops: 0, MTU errors: 0, Resource errors: 0

The errors are observed when the physical link of the management interface (fxp0 or em0) is UP but there is no logical interface (IFL) configured.

id@router> show interfaces fxp0

Physical interface: fxp0, Enabled, Physical link is Up
  Interface index: 64, SNMP ifIndex: 1
  Type: Ethernet, Link-level type: Ethernet, MTU: 1514, Speed: 1000mbps
  Device flags   : Present Running
  Interface flags: SNMP-Traps
  Link type      : Full-Duplex
  Current address: 00:a0:a5:89:c3:9a, Hardware address: 00:a0:a5:89:c3:9a
  Last flapped   : 2019-06-05 17:14:44 AEST (1d 19:24 ago)
    Input packets : 145                                <<< Packets are received.
    Output packets: 0


id@router> show interfaces terse | grep fxp0           <<< fxp0 interface is UP.
fxp0                    up    up


id@router> show configuration interfaces fxp0 | display inheritance  <<< No fxp0 interface configured

id@router> 

This issue has been resolved in Junos OS releases 17.4 and later as documented in PR1148794 .

Meanwhile, to prevent these errors from being reported, use one of the following workarounds:

• Disable the management interface (fxp0/em0):

set interfaces <mgmt interface> disable

OR

• Add an IFL under the management interface (fxp0/em0):

set interfaces <mgmt interface> unit 0