same IP address on two interfaces

m4rtin

Am I correct that JUNOS allows one to configure two interfaces with the same IP address? Looks like it's possible to configure this:

root@M10i> show configuration 
## Last commit: 2012-05-31 07:44:58 UTC by root
version 10.4R8.5;
system {
    root-authentication {
        encrypted-password "$1$X62k3nip$rneAWXEDwHxYDo9T6rjL0."; ## SECRET-DATA
    }
    syslog {
        user * {
            any emergency;
        }
        file messages {
            any notice;
            authorization info;
        }
        file interactive-commands {
            interactive-commands any;
        }
    }
}
interfaces {
    ge-1/1/0 {
        unit 0 {
            family inet {
                address 10.10.10.1/30;  
            }
        }
    }
    ge-1/2/0 {
        unit 0 {
            family inet {
                address 10.10.10.1/30;
            }
        }
    }
}

root@M10i>

But of course only one of those ports can have the configuration active:

root@M10i> show interfaces ge-1/1/0 terse 
Interface               Admin Link Proto    Local                 Remote
ge-1/1/0                up    up  
ge-1/1/0.0              up    up   inet     10.10.10.1/30   

root@M10i> show interfaces ge-1/2/0 terse    
Interface               Admin Link Proto    Local                 Remote
ge-1/2/0                up    up  
ge-1/2/0.0              up    up   inet    

root@M10i>

Is the configuration actually applied always to the first port? Are there any useful user-cases where ability to configure same IP address to more than one interface comes in handy?

Forsaken_GA

It can be useful in cutover situations, when you need to move the IP from one port to another. Then you just need to down one port, bring the other up, and you're failover time is kept to a minimum