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Logical interface lo0.* flags ''Down'' on QFX5100 running Junos 14.1X53-D30.3

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Article ID: KB35594 KB Last Updated: 04 May 2020Version: 1.0
Summary:

Interface lo0 is up, but logical interface lo0.* Flags ''Down'' . This phenomenon only occurs on loopback interface on Junos 14.1X53-D30.3. The physical interfaces shows normal on Junos 14.1X53-D30.3. 

Symptoms:

*Junos: 14.1X53-D30.3

interface loopback0
-------------------
{master:0}
user@switch> show interfaces terse
Interface               Admin Link Proto    Local                 Remote
ge-0/0/0                up    up
ge-0/0/0.0              up    up   inet     1.1.1.1/24
 
lo0                     up    up
lo0.0                   up    up   inet     127.0.0.1           --> 0/0
                                            192.168.140.251     --> 0/0
lo0.1                   up    up   inet     127.0.0.1           --> 0/0
                                            218.251.248.15      --> 0/0
 
user@switch> show interfaces lo0
Physical interface: lo0, Enabled, Physical link is Up
  Interface index: 6, SNMP ifIndex: 6
  Type: Loopback, MTU: Unlimited
  Device flags   : Present Running Loopback
  Interface flags: SNMP-Traps
  Link flags     : None
  Last flapped   : Never
    Input packets : 141714
    Output packets: 141714
 
  Logical interface lo0.0 (Index 565) (SNMP ifIndex 16)
    Description:  -> loopback
    Flags: Down   <<<   SNMP-Traps Encapsulation: Unspecified
 
  Logical interface lo0.1 (Index 566) (SNMP ifIndex 514)
    Description:  -> [global-VR] loopback
    Flags: Down   <<<    SNMP-Traps Encapsulation: Unspecified
 

From the PFE (ASIC level):

TFXPC0(vty)# show interface lo0
 
Physical device lo0 (Index 6, context 0x0)
  Administration interface
  Device flags: (0x0000000000000103)  Present Running Loopback
  Flags: (0x0000000000000000) Up
 
Logical interface lo0.0 (Index 565, Alias-Index 0 Peer-Index 0 ifl address 0x246c04d8)
Channel Mode DISABLED (channel1 0  channel2 0)
  Flags: (0x0000000000008052) Shutdown  <<< Point-To-Point No-Multicast SNMP-Traps
  GEN Flags: (0x0000)
 
Logical interface lo0.1 (Index 566, Alias-Index 0 Peer-Index 0 ifl address 0x246bd700)
Channel Mode DISABLED (channel1 0  channel2 0)
  Flags: (0x0000000000008052) Shutdown  <<< Point-To-Point No-Multicast SNMP-Traps
  GEN Flags: (0x0000)

Compared to physical port:

*Junos: 14.1X53-D30.3

physical interface ge-0/0/0
-------------------
user@switch# run show interfaces ge-0/0/0
Physical interface: ge-0/0/0, Enabled, Physical link is Up
  Interface index: 647, SNMP ifIndex: 1874
  Link-level type: Ethernet, MTU: 1514, MRU: 0, Speed: Auto, Duplex: Auto,
  BPDU Error: None, MAC-REWRITE Error: None, Loopback: Disabled,
  Source filtering: Disabled, Flow control: Disabled, Auto-negotiation: Enabled,
  Remote fault: Online, Media type: Copper
  Device flags   : Present Running
  Interface flags: SNMP-Traps Internal: 0x4000
  Link flags     : None
  CoS queues     : 12 supported, 12 maximum usable queues
  Current address: 5c:45:27:9e:5f:c3, Hardware address: 5c:45:27:9e:5f:c3
  Last flapped   : 2020-02-02 04:43:51 JST (00:49:01 ago)
  Input rate     : 248 bps (0 pps)
  Output rate    : 0 bps (0 pps)
  Active alarms  : None
  Active defects : None
  Interface transmit statistics: Disabled
 
  Logical interface ge-0/0/0.0 (Index 549) (SNMP ifIndex 507)
    Flags: Up  <<<   SNMP-Traps 0x4004000 Encapsulation: ENET2
    Input packets : 4
    Output packets: 5
    Protocol inet, MTU: 1500
      Flags: Sendbcast-pkt-to-re , Is-Primary
      Addresses, Flags: Is-Preferred Is-Primary
        Destination: 1.1.1/24, Local: 1.1.1.1, Broadcast: 1.1.1.255

From the PFE (ASIC level):

TFXPC0(vty)# show interface ge-0/0/0                                 
 
Physical device ge-0/0/0 (Index 647, context 0x215fc448)
  PFE:  Local, PIC:  Local, FPC Slot: 0, Global PFE: 0, Chassis ID: 0
  Chassis slot = 0, Type: Gig Ethernet, Port: 0, Subport: 0, pic_i2cid: 0xf0ad
  Device flags: (0x0000000000000001)  Present
  Flags: (0x0000000000008000) Up SNMP-Traps
 
Logical interface ge-0/0/0.0 (Index 567, Alias-Index 0 Peer-Index 0 ifl address 0x24a47d10)
Channel Mode DISABLED (channel1 4095  channel2 0)
  Flags: (0x000000000400c000) Up   <<<  SNMP-Traps Subset-iif
Solution:

 This has no service impact. It is a cosmetic issue in PFE level. To check loopback interface state, use 'show interface terse' instead.

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