Topology
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| OSPF Route Filtering Topology |
R1 (config) #int fa0/0
R1 (config-if) #ip add
172.10.1.1 255.255.255.0
R1 (config-if) #no shut
R1 (config) #int fa0/1
R1 (config-if) #ip add
172.10.2.1 255.255.255.0
R1 (config-if) #no shut
R1 (config) #int s0/0
R1 (config-if) #ip add
192.168.1.1 255.255.255.0
R1 (config-if) #no shut
R2 (config) #int fa0/0
R2 (config-if) #ip add
172.20.1.1 255.255.255.0
R2 (config-if) #no shut
R2 (config) #int fa0/1
R2 (config-if) #ip add
172.20.2.1 255.255.255.0
R2 (config-if) #no shut
R2 (config) #int s0/0
R2 (config-if) #ip add
192.168.2.1 255.255.255.0
R2 (config-if) #no shut
R2 (config-if) #int lo1
R2 (config-if) #ip add
172.168.1.1 255.255.255.0
R2 (config-if) #int lo2
R2 (config-if) #ip add
172.168.2.1 255.255.255.0
R2 (config-if) #int lo3
R2 (config-if) #ip add
172.168.3.1 255.255.255.0
R2 (config-if) #int lo4
R2 (config-if) #ip add
172.168.4.1 255.255.255.0
R2 (config-if) #int lo5
R2 (config-if) #ip add
172.168.5.1 255.255.255.0
R3 (config) #int fa0/0
R3 (config-if) #ip add
172.30.1.1 255.255.255.0
R3 (config-if) #no shut
R3 (config) #int fa0/1
R3 (config-if) #ip add
172.30.2.1 255.255.255.0
R3 (config-if) #no shut
R3 (config) #int s0/0
R3 (config-if) #ip add
192.168.3.1 255.255.255.0
R3 (config-if) #no shut
R4 (config) #int fa0/0
R4 (config-if) #ip add
172.40.1.1 255.255.255.0
R4 (config-if) #no shut
R4 (config) #int fa0/1
R4 (config-if) #ip add
172.40.2.1 255.255.255.0
R4 (config-if) #no shut
R4 (config) #int s0/0
R4 (config-if) #ip add
192.168.4.1 255.255.255.0
R4 (config-if) #no shut
R5 (config) #int s0/0
R5 (config-if) #ip add
192.168.1.2 255.255.255.0
R5 (config-if) #no shut
R5 (config) #int s0/1
R5 (config-if) #ip add
192.168.2.2 255.255.255.0
R5 (config-if) #no shut
R5 (config) #int s0/2
R5 (config-if) #ip add
192.168.3.2 255.255.255.0
R5 (config-if) #no shut
R5 (config) #int s0/3
R5 (config-if) #ip add
192.168.4.2 255.255.255.0
R5 (config-if) #no shut
R5#ping 192.168.1.1 to 4.1
successful
R1 (config) #int fa0/0
R1 (config-if) #ip os 100
area 1
R1 (config) #int fa0/1
R1 (config-if) #ip os 100
area 1
R1 (config) #int s0/0
R1 (config-if) #ip os 100
area 1
R2 (config) #int fa0/0
R2 (config-if) #ip os 100
area 0
R2 (config) #int fa0/1
R2 (config-if) #ip os 100
area 0
R2 (config) #int s0/0
R2 (config-if) #ip os 100
area 0
R3 (config) #int fa0/0
R3 (config-if) #ip os 100
area 2
R3 (config) #int fa0/1
R3 (config-if) #ip os 100
area 2
R3 (config) #int s0/0
R3 (config-if) #ip os 100
area 2
R4 (config) #int fa0/0
R4 (config-if) #ip os 100
area 3
R3 (config) #int fa0/1
R3 (config-if) #ip os 100
area 3
R3 (config) #int s0/0
R3 (config-if) #ip os 100
area 3
R5 (config) #int s0/0
R5 (config-if) #ip os 100
area 1
R5 (config) #int s0/1
R5 (config-if) #ip os 100
area 0
R5 (config) #int s0/2
R5 (config-if) #ip os 100
area 2
R5 (config) #int s0/3
R5 (config-if) #ip os 100
area 3
R1#sh ip route os
R2 (config) #router os 100
R2 (config-router)
#redistribute ei 100 subnets metric-type 1
R1#sh ip route os
R2 (config) #router ei 100
R2 (config-router) #no
auto-summary
R2 (config-router) #network
172.168.1.0 0.0.0.255
R2 (config-router) #network
172.168.2.0 0.0.0.255
R2 (config-router) #network
172.168.3.0 0.0.0.255
R2 (config-router) #network
172.168.4.0 0.0.0.255
R2 (config-router) #network
172.168.5.0 0.0.0.255
Apply
Access-List on R1
R1 (config) #access-list 10
deny 172.40.1.0 0.0.0.255
R1 (config) #access-list 10
deny 172.40.2.0 0.0.0.255
R1 (config) #access-list 10
permit any
R1 (config) #router os 100
R1 (config-router)
#distribute-list 10 in s0/0
R1#sh ip route os
We can see the effect here.
Now we will remove distribute list
R1 (config) #router os 100
R1 (config-router) #no
distribute-list 10 in s0/0
R1#sh ip route os
Now we will get all the routes.
This above was route filtering via access-list
Now we will perform route filtering via route-map
R1 (config) #route-map abc
deny 10
R1 (config) #match ip
address 10
R1 (config) #exit
R1 (config) #route-map abc
permit 20
We create here an access-list 10 and denied 40.1 and 40.2 IP.
Except this all routes are permit.
After that we created a route-map named ‘abc’
R1 (config) #router os 100
R1 (config-router)
#distribute-list route-map abc in
R1#sh ip route os
What we can see here all the routes are denied except the 40.1 and
40.2 routes.
Now we will remove this
R1 (config-router) #no
distribute-list route-map abc in
Now we will see prefix-list
R1#sh ip route os
R1 (config) #ip prefix-list abc
deny 172.30.0.0 /16 ge 24 le 24
R1 (config) #ip prefix-list abc
permit 0.0.0.0/0 le 32
R1 (config) #router os 100
R1 (config-router)
#distribute-list prefix abc in s0/0
R1#sh ip route os
We cannot see 172.30 routes here.
Now we will remove this
R1 (config) #router os 100
R1 (config-router) #no
distribute-list prefix abc in s0/0
R1#sh ip route os
Now we can see all the routes once again.
OSPF also offer route filtering via route tagging
Now we will go on R2
R2 (config) #router os 100
R2 (config-router) #no
redistribute ei 100 subnet metric-type 1
R2 (config) #router os 100
R2 (config-router)
#redistribute ei 100 subnets metric-type 1 tag 100
R1#sh ip route os
It contains external routes.
R1#sh ip os database
We can see tag is 100
R3#sh ip os database
Tag is 100
R4#sh ip os database
Tag is 100
R1 (config) #route-map as
100
R1 (config) #match tag 100
R1 (config) #exit
R1 (config) #router os 100
R1 (config) #distribute-list
route-map as 100 in
R1#sh ip route os
In ospf we can use area filter list. It will apply on ABR
Here ABR is R5
We will block 40 series
Area filter list only works with prefix-list.
R5 (config) #ip prefix-list abc
deny 172.40.0.0/16 ge 24 le 24
R5 (config) #ip prefix-list abc
permit 0.0.0.0 /0 le 32
R5 (config) #router os 100
R5 (config-router) #area 1
filter-list prefix abc in
R1#sh ip route os
R2#sh ip route os
R3#sh ip route os
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