R1:
interface Loopback0
 ip address 172.16.2.1 255.255.255.0 secondary
 ip address 172.16.1.1 255.255.255.0
 ip router isis 
 isis circuit-type level-1
interface Serial1/1
 ip address 172.16.255.1 255.255.255.252
 ip router isis 
 serial restart-delay 0
 isis circuit-type level-2-only
router isis 
 net 49.0001.ca00.0bbc.0000
 is-type level-1-2  //一般缺省值为level-1-2,不会显示出来

R2:
interface Serial1/0
 ip address 172.16.255.2 255.255.255.252
 ip router isis 
 isis circuit-type level-1-2  //一般缺省值为level-1-2,不会显示出来
interface Serial1/1
 ip address 172.16.255.5 255.255.255.252
 ip router isis 
 isis circuit-type level-2-only
router isis 
 net 49.0002.ca01.0bbc.0000

R3:
interface Serial1/0
 ip address 172.16.255.6 255.255.255.252
 ip router isis
interface Serial1/1
 ip address 172.16.255.9 255.255.255.252
 ip router isis 
 isis circuit-type level-2-only
router isis 
 net 49.0002.ca02.0bbc.0000

R4:
interface Serial1/0
 ip address 172.16.255.10 255.255.255.252
 ip router isis 
 isis circuit-type level-2-only
interface Serial1/1
 ip address 172.16.255.13 255.255.255.252
 ip router isis 
router isis 
 net 49.0003.ca03.0bbc.0000

R5:
interface Loopback0
 ip address 172.16.128.1 255.255.255.0
 ip router isis 
 isis circuit-type level-1
interface Loopback1
 ip address 172.16.129.1 255.255.255.0
 ip router isis 
interface Serial1/0
 ip address 172.16.255.14 255.255.255.252
 ip router isis 
router isis 
 net 49.0003.ca04.0bbc.0000

R5#show ip route isis
     172.16.0.0/16 is variably subnetted, 8 subnets, 2 masks
i L2    172.16.255.0/30 [115/40] via 172.16.255.13, Serial1/0
i L2    172.16.255.4/30 [115/30] via 172.16.255.13, Serial1/0
i L2    172.16.255.8/30 [115/20] via 172.16.255.13, Serial1/0
i L2    172.16.1.0/24 [115/50] via 172.16.255.13, Serial1/0
i L2    172.16.2.0/24 [115/50] via 172.16.255.13, Serial1/0

R1#show ip route isis 
     172.16.0.0/16 is variably subnetted, 8 subnets, 2 masks
i L2    172.16.128.0/24 [115/50] via 172.16.255.2, Serial1/1
i L2    172.16.129.0/24 [115/50] via 172.16.255.2, Serial1/1
i L2    172.16.255.4/30 [115/20] via 172.16.255.2, Serial1/1
i L2    172.16.255.8/30 [115/30] via 172.16.255.2, Serial1/1
i L2    172.16.255.12/30 [115/40] via 172.16.255.2, Serial1/1

R1#ping 172.16.128.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.128.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 48/60/88 ms

R5#ping 172.16.1.1 

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 60/73/84 ms

R1:
router isis
 summary-address 172.16.0.0 255.255.252.0

R4:
show ip route isis
     172.16.0.0/16 is variably subnetted, 7 subnets, 3 masks
i L1    172.16.128.0/24 [115/20] via 172.16.255.14, Serial1/1
i L1    172.16.129.0/24 [115/20] via 172.16.255.14, Serial1/1
i L2    172.16.255.0/30 [115/30] via 172.16.255.9, Serial1/0
i L2    172.16.255.4/30 [115/20] via 172.16.255.9, Serial1/0
i L2    172.16.0.0/22 [115/40] via 172.16.255.9, Serial1/0