Juniper IGP - CONFIGURATION GUIDE V11.1.X Configuration Manual page 82

JUNOSe 11.0.x IP, IPv6, and IGP Configuration Guide
ip share-interface
ip share-nexthop
58
Shared IP Interfaces
host1(config)#interface ip si0
Use the no version to delete the IP interface.
See interface ip
Use to specify the layer 2 interface used by a shared IP interface. The command
fails if the layer 2 interface does not yet exist. The command is not supported
(that is, it fails) if you use an RSVP tunnel (for example, tunnel mpls:1) to identify
the layer 2 interface.
If you issue this command on a shared IP interface, you cannot issue the ip
share-nexthop command for the interface.
After creating the shared IP interface, you can configure it as you do any other
IP interface.
The shared interface is operationally up when the layer 2 interface is operationally
up.
You can create operational shared IP interfaces in the absence of a primary IP
interface.
Example
host1(config-if)#ip share-interface atm 5/3.101
Use the no version to remove the association between the layer 2 interface and
the shared IP interface. You can delete shared and primary IP interfaces
independently.
See ip share-interface
Use to specify that the shared IP interface dynamically tracks a next hop. If the
next hop changes, the shared IP interface moves to the new layer 2 interface
associated with the IP interface toward the new next hop.
If you issue this command on a shared IP interface, you cannot issue the ip
share-interface command for the interface.
If you issue this command on a shared IP interface, the shared interface cannot
dynamically track the next hop for the specified destination if the next-hop IP
address is resolvable over MPLS.
If you specify a virtual router, the command fails if the VR does not already exist.
If you do not specify a VR, the current VR is assumed.
After creating the shared IP interface, you can configure it as you do any other
IP interface.
The shared interface is operationally up when the layer 2 interface associated
with the specified next hop is operationally up. However, if the layer 2 interfaced
associated with the specified next hop is an MPLS next hop (for example, an
RSVP or LDP tunnel), the shared interface remains operationally down.