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comparing to Cisco IOS , we can create any number of loopbacks on router , but on Junos you can create only one loopback interface (even logical units from same loopback) in the routing instance , did any one suggest or think about the reason for this design ? and did Junos has another logical interface can be used in the place of loopback ?

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  • You still retain the ability to configure multiple addresses on the same interface as well as separating them logically with with different units (i.e. lo0.0 and lo0.5).
    – Ryan Foley
    Sep 5, 2014 at 7:30
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    no I have already tried out on Junos 12.1 and it is not posible
    – Mr.lock
    Sep 5, 2014 at 10:06
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    The Juniper Techlibrary includes documentation on how to apply multiple IP addresses to the same loopback interface.
    – Ryan Foley
    Sep 5, 2014 at 12:14
  • you can apply multiple IP to same unit , but for VPN configuration you can't tell Junos which IP should be used for VPN originating
    – Mr.lock
    Sep 15, 2014 at 8:12
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can post and accept your own answer.
    – Ron Maupin ♦
    Jan 3, 2021 at 4:13

2 Answers 2

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Because it's entirely unnecessary.

In JunOS you can have multiple addresses on a single logical interface.

> show configuration interfaces lo0.0
family inet {
    address 127.0.0.1/32;
    address 127.0.0.2/32;
}
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  • let us say we use loopback for VPN Termination , and because of management traffic are going to loopback 0 may be you apply some filters to the interface level , then it will be better to have totally independent loopbacks
    – Mr.lock
    Sep 9, 2014 at 5:26
  • You can apply filters at the network level. Or better yet, use security policies. Even better still use fxp0 for management.
    – bahamat
    Sep 9, 2014 at 15:56
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You can add an individual lo0.x to each routing-instance present. So if you configure multiple routing-instances, you can configure multiple, separate loopback interfaces.

And this is 'the proper way to do it', instead of multiple loopbacks per single routing-instance. The purpose of the loopback interface is to act as both an anchor interface for identification, but also an 'always-up' anchor interface. There should be no need for multiple anchors or identification points for a single instance of a network-computing entity (my ad hoc alternative term for a routing-instance). As others have stated here already, it's not just plausible but advisable to merely add more addresses to the single loopback interface instead of creating more interfaces.

Not being able to have that kind of functionality in a routing-instance would be disastrous for things like OSPF and others, so it's possible to place as many as necessary into each routing-instance you decide to configure (one being as many as necessary).

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  • then if you need independent loopback you have to create new routing instance and that will add more complexity , in netscreen you can create multiple loopbacks in virtual router , why they did not move that to SRX
    – Mr.lock
    Sep 9, 2014 at 5:28
  • To answer Mr.Iock, I think you've missed the point- you shouldn't have to need separate independent loopback interfaces in the same routing-instance. They didn't move to that in SRX from Netscreen because it's a bad habit they didn't want to carry over.
    – danno
    Sep 9, 2014 at 5:49

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