IS-IS uses L1 (intra-area) and L2 (inter-area/backbone) adjacencies. Routers at area boundaries run both levels simultaneously. NET format:
49.AREA.SYSID.00.Topology
Basic connectivity without traffic engineering. Three areas: 49.0001, 49.0002, 49.0003, 49.0004.
Configurations
R1 — L1 only (area 49.0003)
interface Ethernet0/0
no shutdown
ip address 10.0.12.1 255.255.255.0
ip router isis
!
interface Ethernet0/1
no shutdown
ip address 10.0.13.1 255.255.255.0
ip router isis
!
router isis
net 49.0003.0000.0000.0001.00
is-type level-1
R2 — L1/L2 boundary (area 49.0003)
interface Ethernet0/0
no shutdown
ip address 10.0.24.2 255.255.255.0
ip router isis
!
interface Ethernet0/1
no shutdown
ip address 10.0.12.2 255.255.255.0
ip router isis
isis circuit-type level-1
!
interface Ethernet0/2
no shutdown
ip address 10.0.25.2 255.255.255.0
ip router isis
isis circuit-type level-2-only
!
router isis
net 49.0003.0000.0000.0002.00
R3 — L1 only (area 49.0003)
interface Ethernet0/0
no shutdown
ip address 10.0.34.3 255.255.255.0
ip router isis
isis circuit-type level-1
!
interface Ethernet0/1
no shutdown
ip address 10.0.13.3 255.255.255.0
ip router isis
isis circuit-type level-1
!
router isis
net 49.0003.0000.0000.0003.00
is-type level-1
R4 — L1/L2 boundary (area 49.0003)
interface Ethernet0/0
no shutdown
ip address 10.0.24.4 255.255.255.0
ip router isis
!
interface Ethernet0/1
no shutdown
ip address 10.0.34.4 255.255.255.0
ip router isis
isis circuit-type level-1
!
interface Ethernet0/2
no shutdown
ip address 10.0.47.4 255.255.255.0
ip router isis
isis circuit-type level-2-only
!
router isis
net 49.0003.0000.0000.0004.00
R5 — L2 only (area 49.0004)
interface Ethernet0/0
no shutdown
ip address 10.0.25.5 255.255.255.0
ip router isis
isis circuit-type level-2-only
!
router isis
net 49.0004.0000.0000.0005.00
R6 — L1 only (area 49.0001)
interface Ethernet0/0
no shutdown
ip address 10.0.67.6 255.255.255.0
ip router isis
isis circuit-type level-1
!
router isis
net 49.0001.0000.0000.0006.00
is-type level-1
R7 — L1/L2 boundary (area 49.0001)
interface Ethernet0/0
no shutdown
ip address 10.0.47.7 255.255.255.0
ip router isis
isis circuit-type level-2-only
!
interface Ethernet0/1
no shutdown
ip address 10.0.67.7 255.255.255.0
ip router isis
isis circuit-type level-1
!
interface Ethernet0/2
no shutdown
ip address 10.0.78.7 255.255.255.0
ip router isis
isis circuit-type level-2-only
!
router isis
net 49.0001.0000.0000.0007.00
R8 — L1/L2 boundary (area 49.0002)
interface Ethernet0/0
no shutdown
ip address 10.0.78.8 255.255.255.0
ip router isis
isis circuit-type level-2-only
!
interface Ethernet0/1
no shutdown
ip address 10.0.89.8 255.255.255.0
ip router isis
isis circuit-type level-1
!
router isis
net 49.0002.0000.0000.0008.00
R9 — L1 only (area 49.0002)
interface Ethernet0/0
no shutdown
ip address 10.0.89.9 255.255.255.0
ip router isis
isis circuit-type level-1
!
router isis
net 49.0002.0000.0000.0009.00