Router 1 Configuration
!
interface Loopback0
ip address 172.16.1.1 255.255.255.255
!--- Creates loopback interface and assigns
!--- IP address to interface Loopback0.
!
interface Ethernet0
ip address 172.16.12.1 255.255.255.0
ip router isis
!--- Assigns IP address to interface Ethernet0
!--- and enables IS-IS for IP on the interface.
!
router isis
passive-interface Loopback0
net 49.0001.1720.1600.1001.00
!
!--- Enables the IS-IS process on the router,
!--- makes loopback interface passive
!--- (does not send IS-IS packets on interface),
!--- and assigns area and system ID to router.
Router 2 Configuration
!
interface Loopback0
ip address 172.16.2.2 255.255.255.255
!--- Creates loopback interface and assigns
!--- IP address to interface Loopback0.
!
Interface Ethernet0
ip address 172.16.12.2 255.255.255.0
ip router isis
!--- Assigns IP address to interface Ethernet0
!--- and enables IS-IS for IP on the interface.
!
Interface Serial0
ip address 172.16.23.1 255.255.255.252
ip router isis
!--- Assigns IP address to interface Serial0
!--- and enables IS-IS for IP on the interface.
!
router isis
passive-interface Loopback0
net 49.0001.1720.1600.2002.00
!
!--- Enables the IS-IS process on the router,
!--- makes loopback interface passive
!--- (does not send IS-IS packets on interface),
!--- and assigns area and system ID to router.
Router 3 Configuration
!
interface Loopback0
ip address 172.16.3.3 255.255.255.255
!--- Creates loopback interface
!--- and assigns IP address to
!--- interface Loopback0.
!
Interface Serial0
ip address 172.16.23.2 255.255.255.252
ip router Isis
!--- Assigns IP address to
!--- interface Serial0 and enables
!--- IS-IS for IP on the interface.
!
router isis
passive-interface Loopback0
net 49.0001.1234.1600.2231.00
!
!--- Enables the IS-IS process on the router,
!--- makes loopback interface passive
!--- (does not send IS-IS packets on interface),
!--- and assigns area and system ID to router.