开放最短路径优先前缀抑制

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已更新: 2018 年 6 月 13 日

文档 ID:213404

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简介

本文档介绍IOS®和IOS® -XE的开放最短路径优先(OSPF)前缀抑制功能。

背景信息

OSPF前缀抑制是减少区域内泛洪的链路状态通告(LSA)数量的有用功能。在主机之间有多条中转链路的OSPF区域中，主机之间有实际通信。无需向所有路由器通告传输链路LSA。您只能通告与终端主机相关的LSA。默认情况下，OSPF会通告包括中转链路LSA的所有LSA。

OSPF前缀抑制功能有助于克服此行为，并减少通告的第1类（路由器）和第2类（网络）LSA的数量。

此功能可在路由器上全局启用，也可在每个接口上全局启用。

由于数据库(DB)中的前缀数量较少，OSPF前缀抑制有助于加快最短路径优先(SPF)计算。OSPF第3类、第4类、第5类或第7类LSA不会被抑制。

先决条件

要求

本文档没有任何特定的要求。

使用的组件

本文档不限于特定的软件和硬件版本。

本文档中的信息都是基于特定实验室环境中的设备编写的。本文档中使用的所有设备最初均采用原始（默认）配置。如果您的网络处于活动状态，请确保您了解所有命令的潜在影响。

配置

网络图

ospf前缀抑制区域0

配置

在此图中，有2台PC、PC1和PC2通过包含4台路由器的网络连接。这里的目标是确保端到端可达性，您可以在R1、R2、R和R4的主干链路上启用OSPF前缀抑制，这有助于减少LSA的数量。

OSPF前缀抑制可以在全局模式或接口模式下配置：


Global mode configuration:

!
router ospf 1
prefix-suppression
!

Interface mode configuration:

R1:
R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#int e0/2
R1(config-if)#ip ospf prefix-suppression 
R1(config-if)#int e0/3
R1(config-if)#ip ospf prefix-suppression 
R1(config-if)#end
R1#

R2:

R2#
R2#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#int e0/0
R2(config-if)#ip ospf prefix-suppression 
R2(config-if)#int e0/1 
R2(config-if)#ip ospf prefix-suppression 
R2(config-if)#end
R2#
R2#

R3:

R3#
R3#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R3(config-if)#int e0/1 
R3(config-if)# ip ospf prefix-suppression 
R3(config-if)#int e0/0 
R3(config-if)# ip ospf prefix-suppression 
R3(config-if)#end
R3#
R3#

R4:

R4#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R4(config)#int e0/2
R4(config-if)#ip ospf prefix-suppression 
R4(config-if)#int e0/3
R4(config-if)#ip ospf prefix-suppression 
R4(config-if)#end
R4#
R4#

注意：如果通过OSPF通告管理或环回接口，则可能需要从OSPF前缀抑制中排除管理或环回接口。

验证

使用本部分可确认配置能否正常运行。

在配置前缀抑制之前：

R1:

R1#sh ip route
Codes: L - local, 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, H - NHRP, l - LISP
+ - replicated route, % - next hop override

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 9 subnets, 2 masks
C 10.1.1.0/24 is directly connected, Ethernet0/1
L 10.1.1.254/32 is directly connected, Ethernet0/1
C 10.1.12.0/24 is directly connected, Ethernet0/2
L 10.1.12.1/32 is directly connected, Ethernet0/2
C 10.1.13.0/24 is directly connected, Ethernet0/3
L 10.1.13.1/32 is directly connected, Ethernet0/3
O 10.1.24.0/24 [110/20] via 10.1.12.2, 00:02:29, Ethernet0/2
O 10.1.34.0/24 [110/20] via 10.1.13.3, 00:02:12, Ethernet0/3
O 10.2.2.0/24 [110/30] via 10.1.13.3, 00:04:22, Ethernet0/3
[110/30] via 10.1.12.2, 00:04:22, Ethernet0/2
R1#


R1#show ip ospf database network | i Mask|Attached Router|State ID
Link State ID: 10.1.12.2 (address of Designated Router)
Network Mask: /24
Attached Router: 10.1.24.2
Attached Router: 10.1.13.1
Link State ID: 10.1.13.3 (address of Designated Router)
Network Mask: /24
Attached Router: 10.1.34.3
Attached Router: 10.1.13.1
Link State ID: 10.1.24.4 (address of Designated Router)
Network Mask: /24
Attached Router: 10.2.2.254
Attached Router: 10.1.24.2
Link State ID: 10.1.34.4 (address of Designated Router)
Network Mask: /24
Attached Router: 10.2.2.254
Attached Router: 10.1.34.3
R1#

R4:

R4#sh ip route
Codes: L - local, 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, H - NHRP, l - LISP
+ - replicated route, % - next hop override

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 9 subnets, 2 masks
O 10.1.1.0/24 [110/30] via 10.1.34.3, 00:04:59, Ethernet0/3
 [110/30] via 10.1.24.2, 00:04:59, Ethernet0/2
O 10.1.12.0/24 [110/20] via 10.1.24.2, 00:04:59, Ethernet0/2
O 10.1.13.0/24 [110/20] via 10.1.34.3, 00:04:59, Ethernet0/3
C 10.1.24.0/24 is directly connected, Ethernet0/2
L 10.1.24.4/32 is directly connected, Ethernet0/2
C 10.1.34.0/24 is directly connected, Ethernet0/3
L 10.1.34.4/32 is directly connected, Ethernet0/3
C 10.2.2.0/24 is directly connected, Ethernet0/1
L 10.2.2.254/32 is directly connected, Ethernet0/1
R4#



R4#show ip ospf database network | i Mask|Attached Router|State ID
Link State ID: 10.1.12.2 (address of Designated Router)
Network Mask: /24
Attached Router: 10.1.24.2
Attached Router: 10.1.13.1
Link State ID: 10.1.13.3 (address of Designated Router)
Network Mask: /24
Attached Router: 10.1.34.3
Attached Router: 10.1.13.1
Link State ID: 10.1.24.4 (address of Designated Router)
Network Mask: /24
Attached Router: 10.2.2.254
Attached Router: 10.1.24.2
Link State ID: 10.1.34.4 (address of Designated Router)
Network Mask: /24
Attached Router: 10.2.2.254
Attached Router: 10.1.34.3
R4#

配置前缀抑制后：

Please note that now we see only one OSPF route on Router1 and Router4.

R1:

[110/30] via 10.1.12.2, 00:04:22, Ethernet0/2
R1#sh ip route
Codes: L - local, 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, H - NHRP, l - LISP
+ - replicated route, % - next hop override

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 7 subnets, 2 masks
C 10.1.1.0/24 is directly connected, Ethernet0/1
L 10.1.1.254/32 is directly connected, Ethernet0/1
C 10.1.12.0/24 is directly connected, Ethernet0/2
L 10.1.12.1/32 is directly connected, Ethernet0/2
C 10.1.13.0/24 is directly connected, Ethernet0/3
L 10.1.13.1/32 is directly connected, Ethernet0/3
O 10.2.2.0/24 [110/30] via 10.1.13.3, 00:07:38, Ethernet0/3
[110/30] via 10.1.12.2, 00:07:38, Ethernet0/2
R1#



R1#show ip ospf database network | i Mask|Attached Router|State ID
Link State ID: 10.1.12.1 (address of Designated Router)
Network Mask: /32
Attached Router: 10.1.13.1
Attached Router: 10.1.24.2
Link State ID: 10.1.13.1 (address of Designated Router)
Network Mask: /32
Attached Router: 10.1.13.1
Attached Router: 10.1.34.3
Link State ID: 10.1.24.2 (address of Designated Router)
Network Mask: /32
Attached Router: 10.1.24.2
Attached Router: 10.2.2.254
Link State ID: 10.1.34.4 (address of Designated Router)
Network Mask: /32
Attached Router: 10.2.2.254
Attached Router: 10.1.34.3
R1#


R4:

R4#sh ip route
Codes: L - local, 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, H - NHRP, l - LISP
+ - replicated route, % - next hop override

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 7 subnets, 2 masks
O 10.1.1.0/24 [110/30] via 10.1.34.3, 01:15:37, Ethernet0/3
 [110/30] via 10.1.24.2, 01:15:47, Ethernet0/2
C 10.1.24.0/24 is directly connected, Ethernet0/2
L 10.1.24.4/32 is directly connected, Ethernet0/2
C 10.1.34.0/24 is directly connected, Ethernet0/3
L 10.1.34.4/32 is directly connected, Ethernet0/3
C 10.2.2.0/24 is directly connected, Ethernet0/1
L 10.2.2.254/32 is directly connected, Ethernet0/1
R4#




R4#show ip ospf database network | i Mask|Attached Router|State ID
Link State ID: 10.1.12.1 (address of Designated Router)
Network Mask: /32
Attached Router: 10.1.13.1
Attached Router: 10.1.24.2
Link State ID: 10.1.13.1 (address of Designated Router)
Network Mask: /32
Attached Router: 10.1.13.1
Attached Router: 10.1.34.3
Link State ID: 10.1.24.2 (address of Designated Router)
Network Mask: /32
Attached Router: 10.1.24.2
Attached Router: 10.2.2.254
Link State ID: 10.1.34.4 (address of Designated Router)
Network Mask: /32
Attached Router: 10.2.2.254
Attached Router: 10.1.34.3
R4#

故障排除

目前没有针对此配置的故障排除信息。

由思科工程师提供

Chandrashekar Hegde
Cisco TAC Engineer

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