The text identifier of the numbered interface, associated with the specified virtual router, whose IPv6 address is used as the source address when transmitting IPv6 packets on unnumbered remote access user links. Types/formats/examples for this string include: Loopback loopback <id> 'loopback 0' ATM Virtual Circuit atm <slot>/<port>.<distinguisher> 'atm 3/1.100' Ethernet { fastEthernet | gigabitEthernet } <slot>/<port> 'fastEthernet 3/0' 'gigabitEthernet 3/0' Ethernet VLAN { fastEthernet | gigabitEthernet } <slot>/<port>:<vlanID> 'fastEthernet 3/0:1000' 'gigabitEthernet 3/0:1000' Channelized Serial serial <slot>/<port>:<channelSpecifier>[/<channelSpecifier>]* 'serial 3/0:4' (T1/E1) 'serial 3/0:2/4' (T3/E3) 'serial 3/0:2/1/1/4' (OC3/OC12 - channelized DS3) 'serial 3/0:2/1/1/1/4' (OC3/OC12 - virtual tributaries) Other formats may be supported over time. An empty string indicates the referenced interface is unspecified, e.g., when this IPv6 interface is numbered.