Filtering LSA (3) of Type 3 on the ABR in OSPF Environment)

LSA for filtering Type 3 in the OSPF environment-test

Test-filter LSA of Type 3 that enters area 0 on R1

R1 (config-router) # area 0 filter-list prefix lsa3in in

View the R1 Database

 
 

  
  
R1#show ip ospf database  
  
  
 
  
  
OSPF Router with ID (1.1.1.1) (Process ID 1)  
  
  
 
  
  
Router Link States (Area 0)  
  
  
 
  
  
Link ID         ADV Router      Age         Seq#       Checksum Link count  
  
  
1.1.1.1         1.1.1.1         1348        0x80000004 0x0010BC 1  
  
  
2.2.2.2         2.2.2.2         1348        0x80000002 0x00D5EF 1  
  
  
 
  
  
Net Link States (Area 0)  
  
  
 
  
  
Link ID         ADV Router      Age         Seq#       Checksum  
  
  
10.1.1.2        2.2.2.2         1349        0x80000001 0x002CEB  
  
  
 
  
  
Summary Net Link States (Area 0)  
  
  
 
  
  
Link ID         ADV Router      Age         Seq#       Checksum  
  
  
192.168.4.0     2.2.2.2         1680        0x80000001 0x00794D  
  
  
192.168.5.0     2.2.2.2         1680        0x80000001 0x006E57  
  
  
192.168.6.0     2.2.2.2         1680        0x80000001 0x006361  
  
  
 
  
  
Router Link States (Area 2)  
  
  
 
  
  
Link ID         ADV Router      Age         Seq#       Checksum Link count  
  
  
1.1.1.1         1.1.1.1         1489        0x80000004 0x00CFF1 3  
  
  
 
  
  
Summary Net Link States (Area 2)  
  
  
 
  
  
Link ID         ADV Router      Age         Seq#       Checksum  
  
  
192.168.4.0     1.1.1.1         1335        0x80000001 0x001A70 
 
 

It is found that there are only three LSA entries in Type 3 of Region 0, because only one entry of 192.168.4.0/24 is allowed in the prefix list, so three entries of Region 0 are entered from R1, 192.168.1.0/24, 192.168.2.0/24, and 192.168.3.0/24 cannot enter area 0.

Test-filter LSA of Type 3 advertised from Area 1 on R1

In R1, the LSA of Type 3 advertised from Area 1 is filtered. Only 192.168.1.0/24 is allowed.

 
 

  
  
R1(config)#ip prefix-list lsa3out permit 192.168.1.0/24  
  
  
R1(config-router)#area 1 filter-list prefix lsa3out out 
 
 

View the R1 Database

 
 

  
  
R1#show ip ospf database  
  
  
 
  
  
OSPF Router with ID (1.1.1.1) (Process ID 1)  
  
  
 
  
  
Router Link States (Area 0)  
  
  
 
  
  
Link ID         ADV Router      Age         Seq#       Checksum Link count  
  
  
1.1.1.1         1.1.1.1         27          0x80000005 0x000EBD 1  
  
  
2.2.2.2         2.2.2.2         1902        0x80000002 0x00D5EF 1  
  
  
 
  
  
Net Link States (Area 0)  
  
  
 
  
  
Link ID         ADV Router      Age         Seq#       Checksum  
  
  
10.1.1.2        2.2.2.2         1903        0x80000001 0x002CEB  
  
  
 
  
  
Summary Net Link States (Area 0)  
  
  
 
  
  
Link ID         ADV Router      Age         Seq#       Checksum  
  
  
192.168.4.0     2.2.2.2         365         0x80000002 0x00774E  
  
  
192.168.5.0     2.2.2.2         365         0x80000002 0x006C58  
  
  
192.168.6.0     2.2.2.2         365         0x80000002 0x006162  
  
  
 
  
  
Router Link States (Area 2)  
  
  
 
  
  
Link ID         ADV Router      Age         Seq#       Checksum Link count  
  
  
1.1.1.1         1.1.1.1         27          0x80000005 0x00CDF2 3  
  
  
 
  
  
Summary Net Link States (Area 2)  
  
  
 
  
  
Link ID         ADV Router      Age         Seq#       Checksum  
  
  
192.168.4.0     1.1.1.1         30          0x80000002 0x001871 
 
 

We found that there are only three items in Area 0 because only 192.168.4.0/24 is allowed in the LSA filter of area 0 just made on R1, in this way, even if 192.168.1.0/24 is allowed in the outbound stack of Area 1, it still cannot enter area 0. Therefore, you must allow 192.168.1.0/24 in the prefix list.

R1 (config) # ip prefix-list lsa3in permit 192.168.1.0/24

View the OSPF database of R1

 
 

  
  
R1#show ip ospf database  
  
  
 
  
  
OSPF Router with ID (1.1.1.1) (Process ID 1)  
  
  
 
  
  
Router Link States (Area 0)  
  
  
 
  
  
Link ID         ADV Router      Age         Seq#       Checksum Link count  
  
  
1.1.1.1         1.1.1.1         27          0x80000005 0x000EBD 1  
  
  
2.2.2.2         2.2.2.2         1902        0x80000002 0x00D5EF 1  
  
  
 
  
  
Net Link States (Area 0)  
  
  
 
  
  
Link ID         ADV Router      Age         Seq#       Checksum  
  
  
10.1.1.2        2.2.2.2         1903        0x80000001 0x002CEB  
  
  
 
  
  
Summary Net Link States (Area 0)  
  
  
 
  
  
Link ID         ADV Router      Age         Seq#       Checksum  
  
  
192.168.1.0     1.1.1.1         4           0x80000001 0x00B815  
  
  
192.168.4.0     2.2.2.2         365         0x80000002 0x00774E  
  
  
192.168.5.0     2.2.2.2         365         0x80000002 0x006C58  
  
  
192.168.6.0     2.2.2.2         365         0x80000002 0x006162  
  
  
 
  
  
Router Link States (Area 2)  
  
  
 
  
  
Link ID         ADV Router      Age         Seq#       Checksum Link count  
  
  
1.1.1.1         1.1.1.1         27          0x80000005 0x00CDF2 3  
  
  
 
  
  
Summary Net Link States (Area 2)  
  
  
 
  
  
Link ID         ADV Router      Age         Seq#       Checksum  
  
  
192.168.4.0     1.1.1.1         30          0x80000002 0x001871 
 
 

The LSA of Type 3 of area 0 has an additional IP Address 192.168.1.0/24.
View route table on R2

R2 # show ip route ospf
O ia 192.168.1.0/24 [110/65] via 10.1.1.1, 00:05:08, Serial0
There is only one CIDR route for 192.168.1.0/24.

LSA of Type 3 in the OSPF environment-Summary

The LSA function provided by OSPF in the ABR filtering Type 3 allows you to filter a specific area in the in or out direction on the ABR. That is, LSA of Type 3 that is allowed to enter or exit the region.

Filtering LSA 1 of Type 3 on the ABR in OSPF environment)

Filtering LSA 2 of Type 3 on the ABR in OSPF environment)

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