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QFX5100: Can't ping lo0 interface from directly connected devices

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  • 1.  QFX5100: Can't ping lo0 interface from directly connected devices

    Posted 04-29-2022 09:53
    I am assigning an IP address to the lo0 interface:

    
    # show interfaces lo0
    unit 0 {
    
            address 127.0.0.1/32;
            address 10.0.0.2/24;
        }
    }
    
    # show interfaces irb
    unit 1000 {
        family inet {
            address 10.0.0.1/24;
        }
    }
    
    # show vlans
    main_vlan {
        vlan-id 1000;
        l3-interface irb.1000;
    }
    
    # show interface xe-0/0/47
    
    xe-0/0/47 {
        unit 0 {
            family ethernet-switching {
                vlan {
                    members main_vlan;
                }
            }
        }
    }
    
    


    I am able to ping 10.0.0.1 and 10.0.0.2 on the switch itself.

    From remote devices, I can ping 10.0.0.1, but not 10.0.0.2 (ARP resolution fails).

    What could be causing this behavior?


  • 2.  RE: QFX5100: Can't ping lo0 interface from directly connected devices

     
    Posted 05-02-2022 05:56
    Do you have your routing protocol like ISIS or OSPF setup between the devices so they can learn the loopback address of the neighbor?

    ------------------------------
    Steve Puluka BSEET - Juniper Ambassador
    IP Architect - DQE Communications Pittsburgh, PA (Metro Ethernet & ISP)
    http://puluka.com/home
    ------------------------------



  • 3.  RE: QFX5100: Can't ping lo0 interface from directly connected devices
    Best Answer

    Posted 05-02-2022 15:48
    You can't have your loopback address in the same subnet as another directly connected Ethernet interface. This is not how loopbacks work. The loopback address is typically a /32 host route in a separate subnet from your other interfaces. Move your loopback IP to another subnet and either set up static routing on the other device to route that /32 to 10.0.0.1 or set up OSPF or IS-IS between the devices to advertise the loopback into the IGP.

    ------------------------------
    Eric Van Tol
    ------------------------------