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