对于从其他协议（例EIGRP）重分发到OSPF的每条外部路由，都使用一个外部LSA（5类LSA）进行通告。在ASBR中，可对5类LSA（重分发而来的的路由）进行汇总，然后将其注入OSPF域中。
R1配置：
interface Loopback1
ip address 1.1.1.1 255.255.255.255
!
interface Loopback2
ip address 1.1.2.1 255.255.255.255
!
interface Loopback3
ip address 1.1.3.1 255.255.255.255
!
interface Loopback4
ip address 1.1.4.1 255.255.255.255
!
interface Serial1/1
ip address 10.0.1.1 255.255.255.0
serial restart-delay 0
!
router ospf 1
log-adjacency-changes
network 1.1.1.0 0.0.0.255 area 0
network 1.1.2.0 0.0.0.255 area 0
network 1.1.3.0 0.0.0.255 area 0
network 1.1.4.0 0.0.0.255 area 0
network 10.0.1.0 0.0.0.255 area 0
!
R2配置：
interface Serial1/0
ip address 10.0.1.2 255.255.255.0
serial restart-delay 0
!
interface Serial1/1
ip address 10.0.2.1 255.255.255.0
serial restart-delay 0
!
router eigrp 1
network 10.0.2.0 0.0.0.255
auto-summary
!
router ospf 1
redistribute eigrp 1 subnets//将EIGRP网络的路由生分发到OSPF中
network 10.0.1.0 0.0.0.255 area 0
!
R3配置：
interface Loopback1
ip address 3.3.3.3 255.255.255.255
!
interface Loopback2
ip address 3.3.2.3 255.255.255.0
!
interface Loopback3
ip address 3.3.1.3 255.255.255.0
!
interface Loopback4
ip address 3.3.4.3 255.255.255.0
!
interface Serial1/0
ip address 10.0.2.2 255.255.255.0
serial restart-delay 0
!
router eigrp 1
network 3.3.1.0 0.0.0.255
network 3.3.2.0 0.0.0.255
network 3.3.3.0 0.0.0.255
network 3.3.4.0 0.0.0.255
network 10.0.2.0 0.0.0.255
no auto-summary
!
ip route 0.0.0.0 0.0.0.0 10.0.2.1//创建一条默认路由
上述配置完成后查看R1的路由表：
R1#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 4 subnets
C 1.1.1.1 is directly connected, Loopback1
C 1.1.3.1 is directly connected, Loopback3
C 1.1.2.1 is directly connected, Loopback2
C 1.1.4.1 is directly connected, Loopback4
3.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
O E2 3.3.3.3/32 [110/20] via 10.0.1.2, 00:00:10, Serial1/1
O E2 3.3.1.0/24 [110/20] via 10.0.1.2, 00:00:10, Serial1/1
O E2 3.3.2.0/24 [110/20] via 10.0.1.2, 00:00:10, Serial1/1
O E2 3.3.4.0/24 [110/20] via 10.0.1.2, 00:00:10, Serial1/1
10.0.0.0/24 is subnetted, 2 subnets
O E2 10.0.2.0 [110/20] via 10.0.1.2, 00:29:44, Serial1/1
C 10.0.1.0 is directly connected, Serial1/1
显示了EIGRP网络中的明细路由，其中3.3.1.0-3.3.4.0是连续网段，我们可以将其汇总成一条3.3.0.0/21的路由通告给R1，这将减少R1的路由条目。
在R2（ASBR）上做OSPF路由汇总：
R2#conf ter
R2(config)#router ospf 1
R2(config-router)#summary-address 3.3.0.0 255.255.248.0
再次查看R1的路由表：
R1#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 4 subnets
C 1.1.1.1 is directly connected, Loopback1
C 1.1.3.1 is directly connected, Loopback3
C 1.1.2.1 is directly connected, Loopback2
C 1.1.4.1 is directly connected, Loopback4
3.0.0.0/21 is subnetted, 1 subnets
O E2 3.3.0.0 [110/20] via 10.0.1.2, 00:02:42, Serial1/1
10.0.0.0/24 is subnetted, 2 subnets
O E2 10.0.2.0 [110/20] via 10.0.1.2, 00:27:40, Serial1/1
C 10.0.1.0 is directly connected, Serial1/1
