Example for Configuring OSPF Stub Areas
Networking Requirements
As shown in Figure 5-38, all routers run OSPF, and the entire AS is divided into three areas. Router A and Router B serve as ABRs to forward routes between areas. Router D serves as an ASBR to import external routes (static routes).
It is required to configure Area 1 as a stub area to reduce the LSAs advertised to this area without affecting the route reachability.
Configuration Roadmap
The configuration roadmap is as follows:
Enable OSPF on each router, and configure basic OSPF functions.
Configure static routes on Router D, and import them into OSPF.
Configure Area 1 as a stub area, and check the OSPF routing information on Router C.
Stop Router A from advertising Type 3 LSAs to the stub area, and check the OSPF routing information on Router C.
Procedure
- Configure an IP address for each interface.
# Configure Router A.
<Huawei> system-view
[Huawei] sysname RouterA[RouterA] interface gigabitethernet 1/0/0[RouterA-GigabitEthernet1/0/0] ip address 192.168.0.1 24[RouterA-GigabitEthernet1/0/0] quit[RouterA] interface gigabitethernet 2/0/0[RouterA-GigabitEthernet2/0/0] ip address 192.168.1.1 24[RouterA-GigabitEthernet2/0/0] quitThe configurations of Router B, Router C, Router D, Router E, and Router F are similar to the configuration of Router A, and are not mentioned here.
- Configure basic OSPF functions.
# Configure Router A.
[RouterA] router id 1.1.1.1[RouterA] ospf[RouterA-ospf-1] area 0[RouterA-ospf-1-area-0.0.0.0] network 192.168.0.0 0.0.0.255[RouterA-ospf-1-area-0.0.0.0] quit[RouterA-ospf-1] area 1[RouterA-ospf-1-area-0.0.0.1] network 192.168.1.0 0.0.0.255[RouterA-ospf-1-area-0.0.0.1] quit[RouterA-ospf-1] quit# Configure Router B.
[RouterB] router id 2.2.2.2[RouterB] ospf[RouterB-ospf-1] area 0[RouterB-ospf-1-area-0.0.0.0] network 192.168.0.0 0.0.0.255[RouterB-ospf-1-area-0.0.0.0] quit[RouterB-ospf-1] area 2[RouterB-ospf-1-area-0.0.0.2] network 192.168.2.0 0.0.0.255[RouterB-ospf-1-area-0.0.0.2] quit[RouterB-ospf-1] quit# Configure Router C.
[RouterC] router id 3.3.3.3[RouterC] ospf[RouterC-ospf-1] area 1[RouterC-ospf-1-area-0.0.0.1] network 192.168.1.0 0.0.0.255[RouterC-ospf-1-area-0.0.0.1] network 172.16.1.0 0.0.0.255[RouterC-ospf-1-area-0.0.0.1] quit[RouterC-ospf-1] quit# Configure Router D.
[RouterD] router id 4.4.4.4[RouterD] ospf[RouterD-ospf-1] area 2[RouterD-ospf-1-area-0.0.0.2] network 192.168.2.0 0.0.0.255[RouterD-ospf-1-area-0.0.0.2] network 172.17.1.0 0.0.0.255[RouterD-ospf-1-area-0.0.0.2] quit[RouterD-ospf-1] quit# Configure Router E.
[RouterE] router id 5.5.5.5[RouterE] ospf[RouterE-ospf-1] area 1[RouterE-ospf-1-area-0.0.0.1] network 172.16.1.0 0.0.0.255[RouterE-ospf-1-area-0.0.0.1] quit[RouterE-ospf-1] quit# Configure Router F.
[RouterF] router id 6.6.6.6[RouterF] ospf[RouterF-ospf-1] area 2[RouterF-ospf-1-area-0.0.0.2] network 172.17.1.0 0.0.0.255[RouterF-ospf-1-area-0.0.0.2] quit[RouterF-ospf-1] quit - Configure Router D to import static routes.
[RouterD] ip route-static 200.0.0.0 8 null 0[RouterD] ospf[RouterD-ospf-1] import-route static type 1[RouterD-ospf-1] quit# View ABR/ASBR information on Router C.
[RouterC] display ospf abr-asbrOSPF Process 1 with Router ID 3.3.3.3
Routing Table to ABR and ASBR
RtType Destination Area Cost Nexthop Type
Intra-area 1.1.1.1 0.0.0.1 1 192.168.1.1 ABR
Inter-area 4.4.4.4 0.0.0.1 3 192.168.1.1 ASBR
# View the OSPF routing table of Router C.
When Router C is in a common area, there are AS external routes in the routing table.
[RouterC] display ospf routingOSPF Process 1 with Router ID 3.3.3.3
Routing Tables
Routing for Network
Destination Cost Type NextHop AdvRouter Area
172.16.1.0/24 1 Transit 172.16.1.1 3.3.3.3 0.0.0.1
172.17.1.0/24 4 Inter-area 192.168.1.1 1.1.1.1 0.0.0.1
192.168.0.0/24 2 Inter-area 192.168.1.1 1.1.1.1 0.0.0.1
192.168.1.0/24 1 Transit 192.168.1.2 3.3.3.3 0.0.0.1
192.168.2.0/24 3 Inter-area 192.168.1.1 1.1.1.1 0.0.0.1
Routing for ASEs
Destination Cost Type Tag NextHop AdvRouter
200.0.0.0/8 4 Type1 1 192.168.1.1 4.4.4.4
Total Nets: 6
Intra Area: 2 Inter Area: 3 ASE: 1 NSSA: 0
- Configure Area 1 as a stub area.
# Configure Router A.
[RouterA] ospf[RouterA-ospf-1] area 1[RouterA-ospf-1-area-0.0.0.1] stub[RouterA-ospf-1-area-0.0.0.1] quit[RouterA-ospf-1] quit# Configure Router C.
[RouterC] ospf[RouterC-ospf-1] area 1[RouterC-ospf-1-area-0.0.0.1] stub[RouterC-ospf-1-area-0.0.0.1] quit[RouterC-ospf-1] quit# Configure Router E.
[RouterE] ospf[RouterE-ospf-1] area 1[RouterE-ospf-1-area-0.0.0.1] stub[RouterE-ospf-1-area-0.0.0.1] quit[RouterE-ospf-1] quit# View the routing table of Router C.
After the area where Router C resides is configured as a stub area, AS external routes are invisible. Instead, there is a default route.
[RouterC] display ospf routingOSPF Process 1 with Router ID 3.3.3.3
Routing Tables
Routing for Network
Destination Cost Type NextHop AdvRouter Area
0.0.0.0/0 2 Inter-area 192.168.1.1 1.1.1.1 0.0.0.1
172.16.1.0/24 1 Transit 172.16.1.1 3.3.3.3 0.0.0.1
172.17.1.0/24 4 Inter-area 192.168.1.1 1.1.1.1 0.0.0.1
192.168.0.0/24 2 Inter-area 192.168.1.1 1.1.1.1 0.0.0.1
192.168.1.0/24 1 Transit 192.168.1.2 3.3.3.3 0.0.0.1
192.168.2.0/24 3 Inter-area 192.168.1.1 1.1.1.1 0.0.0.1
Total Nets: 6
Intra Area: 2 Inter Area: 4 ASE: 0 NSSA: 0
- Stop Router A from advertising Type 3 LSAs to the stub area.
[RouterA] ospf[RouterA-ospf-1] area 1[RouterA-ospf-1-area-0.0.0.1] stub no-summary[RouterA-ospf-1-area-0.0.0.1] quit[RouterA-ospf-1] quit - Verify the configuration.
# View the OSPF routing table of Router C.
[RouterC] display ospf routingOSPF Process 1 with Router ID 3.3.3.3
Routing Tables
Routing for Network
Destination Cost Type NextHop AdvRouter Area
0.0.0.0/0 2 Inter-area 192.168.1.1 1.1.1.1 0.0.0.1
172.16.1.0/24 1 Transit 172.16.1.1 3.3.3.3 0.0.0.1
192.168.1.0/24 1 Transit 192.168.1.2 3.3.3.3 0.0.0.1
Total Nets: 3
Intra Area: 2 Inter Area: 1 ASE: 0 NSSA: 0
After the advertisement of summary LSAs to a stub area is disabled, the routing entries of the stub router are further reduced, and only the default route to a destination outside the AS is reserved.
Configuration Files
Configuration file of Router A
#
sysname RouterA#
router id 1.1.1.1
#
interface GigabitEthernet1/0/0ip address 192.168.0.1 255.255.255.0
#
interface GigabitEthernet2/0/0ip address 192.168.1.1 255.255.255.0
#
ospf 1
area 0.0.0.0
network 192.168.0.0 0.0.0.255
area 0.0.0.1
network 192.168.1.0 0.0.0.255
stub no-summary
#
return
Configuration file of Router B
#
sysname RouterB#
router id 2.2.2.2
#
interface GigabitEthernet1/0/0ip address 192.168.0.2 255.255.255.0
#
interface GigabitEthernet2/0/0ip address 192.168.2.1 255.255.255.0
#
ospf 1
area 0.0.0.0
network 192.168.0.0 0.0.0.255
area 0.0.0.2
network 192.168.2.0 0.0.0.255
#
return
Configuration file of Router C
#
sysname RouterC#
router id 3.3.3.3
#
interface GigabitEthernet1/0/0ip address 192.168.1.2 255.255.255.0
#
interface GigabitEthernet2/0/0ip address 172.16.1.1 255.255.255.0
#
ospf 1
area 0.0.0.1
network 192.168.1.0 0.0.0.255
network 172.16.1.0 0.0.0.255
stub
#
return
Configuration file of Router D
#
sysname RouterD#
router id 4.4.4.4
#
interface GigabitEthernet1/0/0ip address 192.168.2.2 255.255.255.0
#
interface GigabitEthernet2/0/0ip address 172.17.1.1 255.255.255.0
#
ospf 1
import-route static type 1
area 0.0.0.2
network 192.168.2.0 0.0.0.255
network 172.17.1.0 0.0.0.255
#
ip route-static 200.0.0.0 255.0.0.0 NULL0
#
return
Configuration file of Router E
#
sysname RouterE#
router id 5.5.5.5
#
interface GigabitEthernet2/0/0ip address 172.16.1.2 255.255.255.0
#
ospf 1
area 0.0.0.1
network 172.16.1.0 0.0.0.255
stub
#
return
Configuration file of Router F
#
sysname RouterF#
router id 6.6.6.6
#
interface GigabitEthernet2/0/0ip address 172.17.1.2 255.255.255.0
#
ospf 1
area 0.0.0.2
network 172.17.1.0 0.0.0.255
#
return
