晨星
实验介绍
了解 OSPF 通告缺省路由的方式与原理。
实验目的
R1与R2作为企业边界出口设备，构成双出口冗余以实现负载分担。企业内部部署并运行OSPF路由协议，使Client A与Client B能正常访问 Internet路由器的100.1.1.0网络。为减少路由表容量，在 R1与 R2上配置缺省路由，从而在提供连通性的同时保证网络的高可用性。
拓扑结构
接口信息
实验步骤
步骤一：配置接口IP
SW1为二层交换机，无需额外配置，正常开机即可。
以SW2为例，模拟器的三层交换机无法直接配置接口IP，需要使用VLAN子接口曲线救国。
[SW2-Vlanif1]dis th
#
interface Vlanif1
ip address 10.1.1.21 255.255.255.0
#
return
[SW2-Vlanif2]dis th
#
interface Vlanif2
ip address 20.1.1.2 255.255.255.0
#
return
[SW2-Vlanif3]dis th
#
interface Vlanif3
ip address 30.1.1.2 255.255.255.0
#
return
将端口加进对应VLAN。
VLAN 1默认放行。
[SW2-GigabitEthernet0/0/1]dis th
#
interface GigabitEthernet0/0/1
port link-type access
#
return
[SW2-GigabitEthernet0/0/2]dis th
#
interface GigabitEthernet0/0/2
port link-type access
port default vlan 2
#
return
[SW2-GigabitEthernet0/0/3]di th
#
interface GigabitEthernet0/0/3
port link-type access
port default vlan 3
#
return
其余类似，路由器直接在接口配置IP即可。
步骤二：配置NAT
以R1为例。
匹配内部源网段。
[R1-acl-basic-2001]dis th
[V200R003C00]
#
acl number 2001
rule 5 permit source 192.168.1.0 0.0.0.255
rule 10 permit source 172.16.1.0 0.0.0.255
#
return
[R1-GigabitEthernet0/0/1]dis th
[V200R003C00]
#
interface GigabitEthernet0/0/1
ip address 202.106.0.1 255.255.255.252
nat outbound 2001
#
return
配置缺省路由，指定去往任意网段的下一跳接口IP地址。
[R1]ip route-static 0.0.0.0 0 202.106.0.2步骤三：配置OSPF
R1、R2、SW2、SW3和SW4均需要配置OSPF。
仅R1和R2需要配置OSPF通告缺省路由。
以R1和SW2为例。
[R1-ospf-1]di th
[V200R003C00]
#
ospf 1
default-route-advertise always cost 10 type 1
area 0.0.0.0
network 10.1.1.0 0.0.0.255
#
return
[SW2-ospf-1]dis th
#
ospf 1
area 0.0.0.0
network 10.1.1.0 0.0.0.255
network 20.1.1.0 0.0.0.255
network 30.1.1.0 0.0.0.255
#
return
通过查看SW2的OSPF路由表项可知，其学习到2条完全等价的缺省路由【O_ASE】
[SW2]display ip routing-table protocol ospf
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Public routing table : OSPF
Destinations : 4 Routes : 6
OSPF routing table status : <Active>
Destinations : 4 Routes : 6
Destination/Mask Proto Pre Cost Flags NextHop Interface
0.0.0.0/0 O_ASE 150 11 D 10.1.1.1 Vlanif1
O_ASE 150 11 D 10.1.1.2 Vlanif1
40.1.1.0/24 OSPF 10 2 D 20.1.1.3 Vlanif2
OSPF 10 2 D 30.1.1.4 Vlanif3
172.16.1.0/24 OSPF 10 2 D 30.1.1.4 Vlanif3
192.168.1.0/24 OSPF 10 2 D 20.1.1.3 Vlanif2
OSPF routing table status : <Inactive>
Destinations : 0 Routes : 0
检测客户端到达Internet的Loopback接口的可达性
Welcome to use PC Simulator!
PC>ipconfig
Link local IPv6 address...........: fe80::5689:98ff:fefa:5a5c
IPv6 address......................: :: / 128
IPv6 gateway......................: ::
IPv4 address......................: 192.168.1.1
Subnet mask.......................: 255.255.255.0
Gateway...........................: 192.168.1.3
Physical address..................: 54-89-98-FA-5A-5C
DNS server........................:
PC>ping 100.1.1.1
Ping 100.1.1.1: 32 data bytes, Press Ctrl_C to break
From 100.1.1.1: bytes=32 seq=1 ttl=252 time=62 ms
From 100.1.1.1: bytes=32 seq=2 ttl=252 time=110 ms
From 100.1.1.1: bytes=32 seq=3 ttl=252 time=78 ms
From 100.1.1.1: bytes=32 seq=4 ttl=252 time=94 ms
From 100.1.1.1: bytes=32 seq=5 ttl=252 time=93 ms
--- 100.1.1.1 ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 62/87/110 ms
PC>Welcome to use PC Simulator!
PC>ipconfig
Link local IPv6 address...........: fe80::5689:98ff:feaf:9f0
IPv6 address......................: :: / 128
IPv6 gateway......................: ::
IPv4 address......................: 172.16.1.1
Subnet mask.......................: 255.255.255.0
Gateway...........................: 172.16.1.4
Physical address..................: 54-89-98-AF-09-F0
DNS server........................:
PC>ping 100.1.1.1
Ping 100.1.1.1: 32 data bytes, Press Ctrl_C to break
From 100.1.1.1: bytes=32 seq=1 ttl=252 time=78 ms
From 100.1.1.1: bytes=32 seq=2 ttl=252 time=78 ms
From 100.1.1.1: bytes=32 seq=3 ttl=252 time=78 ms
From 100.1.1.1: bytes=32 seq=4 ttl=252 time=78 ms
From 100.1.1.1: bytes=32 seq=5 ttl=252 time=94 ms
--- 100.1.1.1 ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 78/81/94 ms
PC>注意事项
注1
在使用OSPF VPN实例的环境下，若想要发布指定缺省路由的Type-3 LSA，则需要使用summary参数【无论本机是否存在激活的非本OSPF缺省路由，该参数都将会产生并发布一个描述缺省路由的LSA】
R1:
ospf 1 vpn-instance VPNA
default-route-advertise summary cost 10注2
在上述案例中，若R1配置的缺省路由的优先级值为200，而R2配置的缺省路由的优先级值为默认的60时，R1与R2各自的路由表项中，都将使用自身所配置的缺省路由
[R1]ip route-static 0.0.0.0 0 202.106.0.2 preference 200
Info: Succeeded in modifying route.
[R1]dis ip routing-table
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Tables: Public
Destinations : 16 Routes : 16
Destination/Mask Proto Pre Cost Flags NextHop Interface
0.0.0.0/0 Static 200 0 RD 202.106.0.2 GigabitEthernet0/0/1
10.1.1.0/24 Direct 0 0 D 10.1.1.1 GigabitEthernet0/0/0
10.1.1.1/32 Direct 0 0 D 127.0.0.1 GigabitEthernet0/0/0
10.1.1.255/32 Direct 0 0 D 127.0.0.1 GigabitEthernet0/0/0
20.1.1.0/24 OSPF 10 2 D 10.1.1.21 GigabitEthernet0/0/0
30.1.1.0/24 OSPF 10 2 D 10.1.1.21 GigabitEthernet0/0/0
40.1.1.0/24 OSPF 10 3 D 10.1.1.21 GigabitEthernet0/0/0
127.0.0.0/8 Direct 0 0 D 127.0.0.1 InLoopBack0
127.0.0.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
127.255.255.255/32 Direct 0 0 D 127.0.0.1 InLoopBack0
172.16.1.0/24 OSPF 10 3 D 10.1.1.21 GigabitEthernet0/0/0
192.168.1.0/24 OSPF 10 3 D 10.1.1.21 GigabitEthernet0/0/0
202.106.0.0/30 Direct 0 0 D 202.106.0.1 GigabitEthernet0/0/1
202.106.0.1/32 Direct 0 0 D 127.0.0.1 GigabitEthernet0/0/1
202.106.0.3/32 Direct 0 0 D 127.0.0.1 GigabitEthernet0/0/1
255.255.255.255/32 Direct 0 0 D 127.0.0.1 InLoopBack0
[R1]
[R2]dis ip routing-table
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Tables: Public
Destinations : 16 Routes : 16
Destination/Mask Proto Pre Cost Flags NextHop Interface
0.0.0.0/0 Static 60 0 RD 69.151.202.2 GigabitEthernet0/0/1
10.1.1.0/24 Direct 0 0 D 10.1.1.2 GigabitEthernet0/0/0
10.1.1.2/32 Direct 0 0 D 127.0.0.1 GigabitEthernet0/0/0
10.1.1.255/32 Direct 0 0 D 127.0.0.1 GigabitEthernet0/0/0
20.1.1.0/24 OSPF 10 2 D 10.1.1.21 GigabitEthernet0/0/0
30.1.1.0/24 OSPF 10 2 D 10.1.1.21 GigabitEthernet0/0/0
40.1.1.0/24 OSPF 10 3 D 10.1.1.21 GigabitEthernet0/0/0
69.151.202.0/30 Direct 0 0 D 69.151.202.1 GigabitEthernet0/0/1
69.151.202.1/32 Direct 0 0 D 127.0.0.1 GigabitEthernet0/0/1
69.151.202.3/32 Direct 0 0 D 127.0.0.1 GigabitEthernet0/0/1
127.0.0.0/8 Direct 0 0 D 127.0.0.1 InLoopBack0
127.0.0.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
127.255.255.255/32 Direct 0 0 D 127.0.0.1 InLoopBack0
172.16.1.0/24 OSPF 10 3 D 10.1.1.21 GigabitEthernet0/0/0
192.168.1.0/24 OSPF 10 3 D 10.1.1.21 GigabitEthernet0/0/0
255.255.255.255/32 Direct 0 0 D 127.0.0.1 InLoopBack0
但由于R1与R2自身所配置的缺省路由的优先级值与其通过OSPF发布的缺省路由优先级值无关，因此SW2的OSPF路由表项中，依然存在着2条完全等价的缺省路由
[SW2]dis ip routing-table protocol ospf
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Public routing table : OSPF
Destinations : 4 Routes : 6
OSPF routing table status : <Active>
Destinations : 4 Routes : 6
Destination/Mask Proto Pre Cost Flags NextHop Interface
0.0.0.0/0 O_ASE 150 11 D 10.1.1.1 Vlanif1
O_ASE 150 11 D 10.1.1.2 Vlanif1
40.1.1.0/24 OSPF 10 2 D 30.1.1.4 Vlanif3
OSPF 10 2 D 20.1.1.3 Vlanif2
172.16.1.0/24 OSPF 10 2 D 30.1.1.4 Vlanif3
192.168.1.0/24 OSPF 10 2 D 20.1.1.3 Vlanif2
OSPF routing table status : <Inactive>
Destinations : 0 Routes : 0
此时，若希望SW2将R2发布的缺省路由作为主路由，则需要在R1的OSPF 进程下发布缺省路由时，使用【permit-calculate-other】参数
permit-calculate-other 配置允许在本机存在激活的非本OSPF缺省路由时，将会产生并发布一个缺省路由的LSA，且当前设备仍然计算来自于其它设备的缺省路由
R1:
ospf 1
default-route-advertise permit-calculate-other再次查看R1的路由表项，发现 RT1此时已经使用R2【10.1.1.2】通过OSPF发布的优先级值为150的缺省路由
~SW2的OSPF路由表项中,此时也只存在1条由R2【10.1.1.2】所发布的缺省路由
[SW2]dis ip routing-table protocol ospf
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Public routing table : OSPF
Destinations : 4 Routes : 5
OSPF routing table status : <Active>
Destinations : 4 Routes : 5
Destination/Mask Proto Pre Cost Flags NextHop Interface
0.0.0.0/0 O_ASE 150 11 D 10.1.1.2 Vlanif1
40.1.1.0/24 OSPF 10 2 D 30.1.1.4 Vlanif3
OSPF 10 2 D 20.1.1.3 Vlanif2
172.16.1.0/24 OSPF 10 2 D 30.1.1.4 Vlanif3
192.168.1.0/24 OSPF 10 2 D 20.1.1.3 Vlanif2
OSPF routing table status : <Inactive>
Destinations : 0 Routes : 0
注3
在上述案例中，若希望SW2从R1学习到的缺省路由带有标记5，而从R2学习到的缺省路由带有标记7，则需要使用【route-policy】参数
route-policy easthome permit node 10创建路由策略，并定义为允许策略，序列号为10
apply tag 5 配置其标记为5
default-route-advertise route-policy easthome cost 10 type 1 配置在路由表中有匹配的非OSPF产生的缺省路 由表项时，按策略发布缺省路由，并设置其代价值为10，且以外部类型1的方式进行发布
RTA:
route-policy R1 permit node 10
apply tag 5
ospf 1
default-route-advertise route-policy R1 cost 10 type 1RTB:
route-policy R2 permit node 10
apply tag 7
ospf 1
default-route-advertise route-policy R2 cost 10 type 1在SWB上查看其OSPF路由表项的详细信息
[SW2]dis ip routing-table protocol ospf verbose
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Tables: Public
Destinations : 4 Routes : 6
Destination: 0.0.0.0/0
Protocol: O_ASE Process ID: 1
Preference: 150 Cost: 11
NextHop: 10.1.1.1 Neighbour: 0.0.0.0
State: Active Adv Age: 00h01m14s
Tag: 5 Priority: low
Label: NULL QoSInfo: 0x0
IndirectID: 0x0
RelayNextHop: 0.0.0.0 Interface: Vlanif1
TunnelID: 0x0 Flags: D
Destination: 0.0.0.0/0
Protocol: O_ASE Process ID: 1
Preference: 150 Cost: 11
NextHop: 10.1.1.2 Neighbour: 0.0.0.0
State: Active Adv Age: 00h00m28s
Tag: 7 Priority: low
Label: NULL QoSInfo: 0x0
IndirectID: 0x0
RelayNextHop: 0.0.0.0 Interface: Vlanif1
TunnelID: 0x0 Flags: D
Destination: 40.1.1.0/24
Protocol: OSPF Process ID: 1
Preference: 10 Cost: 2
NextHop: 30.1.1.4 Neighbour: 0.0.0.0
State: Active Adv Age: 00h48m17s
Tag: 0 Priority: low
Label: NULL QoSInfo: 0x0
IndirectID: 0x0
RelayNextHop: 0.0.0.0 Interface: Vlanif3
TunnelID: 0x0 Flags: D
Destination: 40.1.1.0/24
Protocol: OSPF Process ID: 1
Preference: 10 Cost: 2
NextHop: 20.1.1.3 Neighbour: 0.0.0.0
State: Active Adv Age: 00h43m44s
Tag: 0 Priority: low
Label: NULL QoSInfo: 0x0
IndirectID: 0x0
RelayNextHop: 0.0.0.0 Interface: Vlanif2
TunnelID: 0x0 Flags: D
Destination: 172.16.1.0/24
Protocol: OSPF Process ID: 1
Preference: 10 Cost: 2
NextHop: 30.1.1.4 Neighbour: 0.0.0.0
State: Active Adv Age: 00h48m06s
Tag: 0 Priority: low
Label: NULL QoSInfo: 0x0
IndirectID: 0x0
RelayNextHop: 0.0.0.0 Interface: Vlanif3
TunnelID: 0x0 Flags: D
Destination: 192.168.1.0/24
Protocol: OSPF Process ID: 1
Preference: 10 Cost: 2
NextHop: 20.1.1.3 Neighbour: 0.0.0.0
State: Active Adv Age: 00h52m49s
Tag: 0 Priority: low
Label: NULL QoSInfo: 0x0
IndirectID: 0x0
RelayNextHop: 0.0.0.0 Interface: Vlanif2
TunnelID: 0x0 Flags: D
通过查看可知，SW2通过10.1.1.1【R1】学习到的缺省路由所携带的标记值为5，而通过10.1.1.2【R2】学习到的缺省路由所携带的标记值为7
注4
【match-any】参数指定OSPF路由表中有匹配的路由表项时【无论是否是OSPF产生的缺省路由】，若有多条路由通过策略，则选取最优者来生成缺省LSA；路由通过策略时，选取最优者的原则按照优先级由高至低的顺序如下：
-
路由设置了
Type的优先于未设置的，若均设置了Type，则数值越小越优选； -
路由设置了
Cost的优先于未设置的，若均设置了Cost，则数值越小越优选； -
路由设置了
Tag的优先于未设置的，若均设置了Tag，则数值越小越优选