拓扑及地址规划如图所示,ASBR1和ASBR2引入同一条静态路由 ip route-static 2.2.2.0 24 192.168.3.2。但在三台路由器上只能看到一条第五类LSA。
在三台路由器的路由表中均可看到到2.2.2.0网段的路由,在中间的MSR3620上可看到两条到达2.2.2.0网段的路由。
<ASBR-1>dis ip r
Destinations : 18 Routes : 19
Destination/Mask Proto Pre Cost NextHop Interface
0.0.0.0/32 Direct 0 0 127.0.0.1 InLoop0
2.2.2.0/24 Static 60 0 192.168.3.2 GE0/1
127.0.0.0/8 Direct 0 0 127.0.0.1 InLoop0
127.0.0.0/32 Direct 0 0 127.0.0.1 InLoop0
127.0.0.1/32 Direct 0 0 127.0.0.1 InLoop0
127.255.255.255/32 Direct 0 0 127.0.0.1 InLoop0
192.168.1.0/24 Direct 0 0 192.168.1.1 GE0/0
192.168.1.0/32 Direct 0 0 192.168.1.1 GE0/0
192.168.1.1/32 Direct 0 0 127.0.0.1 InLoop0
192.168.1.255/32 Direct 0 0 192.168.1.1 GE0/0
192.168.2.0/24 O_INTRA 10 2 192.168.1.2 GE0/0
192.168.3.3 GE0/1
192.168.3.0/24 Direct 0 0 192.168.3.1 GE0/1
192.168.3.0/32 Direct 0 0 192.168.3.1 GE0/1
192.168.3.1/32 Direct 0 0 127.0.0.1 InLoop0
192.168.3.255/32 Direct 0 0 192.168.3.1 GE0/1
224.0.0.0/4 Direct 0 0 0.0.0.0 NULL0
224.0.0.0/24 Direct 0 0 0.0.0.0 NULL0
255.255.255.255/32 Direct 0 0 127.0.0.1 InLoop0
<ASBR-2>dis ip r
Destinations : 18 Routes : 19
Destination/Mask Proto Pre Cost NextHop Interface
0.0.0.0/32 Direct 0 0 127.0.0.1 InLoop0
2.2.2.0/24 Static 60 0 192.168.3.2 GE0/1
127.0.0.0/8 Direct 0 0 127.0.0.1 InLoop0
127.0.0.0/32 Direct 0 0 127.0.0.1 InLoop0
127.0.0.1/32 Direct 0 0 127.0.0.1 InLoop0
127.255.255.255/32 Direct 0 0 127.0.0.1 InLoop0
192.168.1.0/24 O_INTRA 10 2 192.168.2.2 GE0/0
192.168.3.1 GE0/1
192.168.2.0/24 Direct 0 0 192.168.2.1 GE0/0
192.168.2.0/32 Direct 0 0 192.168.2.1 GE0/0
192.168.2.1/32 Direct 0 0 127.0.0.1 InLoop0
192.168.2.255/32 Direct 0 0 192.168.2.1 GE0/0
192.168.3.0/24 Direct 0 0 192.168.3.3 GE0/1
192.168.3.0/32 Direct 0 0 192.168.3.3 GE0/1
192.168.3.3/32 Direct 0 0 127.0.0.1 InLoop0
192.168.3.255/32 Direct 0 0 192.168.3.3 GE0/1
224.0.0.0/4 Direct 0 0 0.0.0.0 NULL0
224.0.0.0/24 Direct 0 0 0.0.0.0 NULL0
255.255.255.255/32 Direct 0 0 127.0.0.1 InLoop0
[MSR3620]dis ip r
Destinations : 18 Routes : 20
Destination/Mask Proto Pre Cost NextHop Interface
0.0.0.0/32 Direct 0 0 127.0.0.1 InLoop0
2.2.2.0/24 O_ASE2 150 1 192.168.1.1 GE0/0
192.168.2.1 GE0/1
127.0.0.0/8 Direct 0 0 127.0.0.1 InLoop0
127.0.0.0/32 Direct 0 0 127.0.0.1 InLoop0
127.0.0.1/32 Direct 0 0 127.0.0.1 InLoop0
127.255.255.255/32 Direct 0 0 127.0.0.1 InLoop0
192.168.1.0/24 Direct 0 0 192.168.1.2 GE0/0
192.168.1.0/32 Direct 0 0 192.168.1.2 GE0/0
192.168.1.2/32 Direct 0 0 127.0.0.1 InLoop0
192.168.1.255/32 Direct 0 0 192.168.1.2 GE0/0
192.168.2.0/24 Direct 0 0 192.168.2.2 GE0/1
192.168.2.0/32 Direct 0 0 192.168.2.2 GE0/1
192.168.2.2/32 Direct 0 0 127.0.0.1 InLoop0
192.168.2.255/32 Direct 0 0 192.168.2.2 GE0/1
192.168.3.0/24 O_INTRA 10 2 192.168.1.1 GE0/0
192.168.2.1 GE0/1
224.0.0.0/4 Direct 0 0 0.0.0.0 NULL0
224.0.0.0/24 Direct 0 0 0.0.0.0 NULL0
255.255.255.255/32 Direct 0 0 127.0.0.1 InLoop0
但在三台路由器设备上的lsdb表项中只能看到一条第五类LSA。
<ASBR-1>dis ospf lsd
OSPF Process 1 with Router ID 192.168.3.1
Link State Database
Area: 0.0.0.0
Type LinkState ID AdvRouter Age Len Sequence Metric
Router 192.168.2.2 192.168.2.2 290 48 8000001C 0
Router 192.168.3.3 192.168.3.3 683 48 80000017 0
Router 192.168.3.1 192.168.3.1 302 48 8000001A 0
Network 192.168.1.2 192.168.2.2 282 32 80000012 0
Network 192.168.2.1 192.168.3.3 807 32 80000011 0
Network 192.168.3.3 192.168.3.3 679 32 80000010 0
AS External Database
Type LinkState ID AdvRouter Age Len Sequence Metric
External 2.2.2.0 192.168.3.3 689 36 80000014 1
<ASBR-2>dis ospf lsd
OSPF Process 1 with Router ID 192.168.3.3
Link State Database
Area: 0.0.0.0
Type LinkState ID AdvRouter Age Len Sequence Metric
Router 192.168.2.2 192.168.2.2 322 48 8000001C 0
Router 192.168.3.3 192.168.3.3 714 48 80000017 0
Router 192.168.3.1 192.168.3.1 335 48 8000001A 0
Network 192.168.1.2 192.168.2.2 314 32 80000012 0
Network 192.168.2.1 192.168.3.3 838 32 80000011 0
Network 192.168.3.3 192.168.3.3 710 32 80000010 0
AS External Database
Type LinkState ID AdvRouter Age Len Sequence Metric
External 2.2.2.0 192.168.3.3 720 36 80000014 1
<MSR3620>dis ospf lsdb
OSPF Process 1 with Router ID 192.168.2.2
Link State Database
Area: 0.0.0.0
Type LinkState ID AdvRouter Age Len Sequence Metric
Router 192.168.2.2 192.168.2.2 336 48 8000001C 0
Router 192.168.3.3 192.168.3.3 729 48 80000017 0
Router 192.168.3.1 192.168.3.1 350 48 8000001A 0
Network 192.168.1.2 192.168.2.2 328 32 80000012 0
Network 192.168.2.1 192.168.3.3 853 32 80000011 0
Network 192.168.3.3 192.168.3.3 725 32 80000010 0
AS External Database
Type LinkState ID AdvRouter Age Len Sequence Metric
External 2.2.2.0 192.168.3.3 735 36 80000014 1
无
在两台ASBR设备中可以看到,到达目的网段2.2.2.0的FA地址是完全相同的,引入的静态路由也完全相同。
<ASBR-1>dis ospf lsdb ase
OSPF Process 1 with Router ID 192.168.3.1
Link State Database
Type : External
LS ID : 2.2.2.0
Adv Rtr : 192.168.3.3
LS age : 1194
Len : 36
Options : O E
Seq# : 80000014
Checksum : 0xd8c
Net mask : 255.255.255.0
MTID 0 Metric : 1
E Type : 2
Forwarding Address: 192.168.3.2
Tag : 1
<ASBR-2>dis ospf lsdb ase
OSPF Process 1 with Router ID 192.168.3.3
Link State Database
Type : External
LS ID : 2.2.2.0
Adv Rtr : 192.168.3.3
LS age : 1244
Len : 36
Options : O E
Seq# : 80000014
Checksum : 0xd8c
Net mask : 255.255.255.0
MTID 0 Metric : 1
E Type : 2
Forwarding Address: 192.168.3.2
Tag : 1
造成这个现象的原因是:当路由器收到一个5类LSA,如果这个5类LSA包含的路由和本地静态路由的ip、掩码都相同,并且其中的FA地址和本地静态路由的下一跳地址也相同,那么这台路由器会去比较这个5类LSA产生者的router id和自己的router id如果自己的router id小,那么自己就不会再将这个静态路由引入到ospf中,也不会再产生5类LSA。也就是说当两条外部5类LSA的fa地址相同时,lsdb中确实只能看到一条。Router id小的asbr会撤销自己发布的5类LSA。
路由器在选路时实际上是根据FA地址来选路的,如果两个LSA的ip、掩码、FA都相同,那么这两个LSA的功能就是一样的,没有必要把这两个LSA都发布出去,占用路由器的资源。
本实验中到达目的地址2.2.2.2有两条相同的fa地址,分别为router id是192.168.3.1的ASBR1和router id为192.168.3.3的ASBR2。选取id较大的192.168.3.3这一边的第五类LSA显示在lsdb中。
如果有需要将两条第五类LSA均显示在ospf区域内的lsdb中,可修改引入的静态路由,使他们的下一跳不一致。或使该目的地址的fa地址为全零(例如不将ASBR的出接口加入ospf进程中),路由器将不比较route id,会将两条五类LSA均引入。
无
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