Subscriber interfaces operate only with basic (or enhanced) subscriber management. At the very least, a host, either statically configured or dynamically learned by DHCP must be present in order for the interface to be useful.
The following example displays a subscriber interface configuration for the 7750 SR:
A:ALA-48>config>service>ies>sub-if# info
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address 192.168.140.1/24
group-interface "abc-if" create
sap 1/1/19:0 create
ingress
qos 2
filter ip 10
exit
static-host ip 192.168.145.100 mac 00:01:00:00:00:01 create
exit
exit
exit
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A:ALA-48>config>service>ies>sub-if#