OSPF advanced features - distribute list filtering, modifying interface OSPF priority configuration, OSPF - detailed explanation of passive interface, and modifying reference bandwidth value

Posted by nephish on Sat, 19 Feb 2022 03:22:46 +0100

catalogue

1, Brief description of route filtering:

2, Distribution list filtering configuration:

——- (1) use ACL to match route entries (used by OSPF process)

——- (2) use prefix list to match routing entries (used by OSPF process)

——- (3) OSPF process + interface usage

——- (4) Note:

3, Modify interface OSPF priority:

4, OSPF - passive interface:

V.: modify the reference bandwidth value

——(1) Modification in OSPF process

——(2) Interface modification:

1, Brief description of route filtering:

- LSA-3 filtering - database level

- distribute list filtering - between database and routing table

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2, Distribution list filtering configuration:

In general, matching routes generally use prefix lists

——- (1) use ACL to match route entries (used by OSPF process)

r1(config)#access-list 1 deny 3.3.3.0 0.0.0.255

r1(config)#access-list 1 deny 4.4.4.0 0.0.0.255

r1(config)#access-list 1 permit any

r1(config)#router ospf 100 

r1(config-router)#distribute-list 1 in

Filter the route matched by acl into my route table, but it is still in the database and will be updated to others

——- (2) use prefix list to match routing entries (used by OSPF process)

r1(config)#ip prefix-list aaa seq 1 deny 192.168.100.0/24 

r1(config)#ip prefix-list aaa seq 2 permit 0.0.0.0/0 le 32

r1(config)#router ospf 100

r1(config-router)# distribute-list prefix aaa in

r1(config-router)# exit

——- (3) OSPF process + interface usage

r1(config)#access-list 1 deny 3.3.3.0 0.0.0.255

r1(config)#access-list 1 deny 4.4.4.0 0.0.0.255

r1(config)#access-list 1 permit any

r1(config)#router ospf 100

r1(config-router)#distribute-list 1 in f0/0

r1(config-router)#distribute-list 1 in f0/0

LSA S of 3.3.3.0 and 4.4.4.0 from f0/0 interface are ignored when calculating routes; You can't enter my routing table, but you should prevent it from entering from other interfaces

——- (4) Note:

r1(config-router)#distribute-list 1 out

r1(config-router)#distribute-list 1 out f0/0

ospf does not advertise its own routing entries, but ospf advertises lsa, so these two commands are invalid for ospf

——- (5) filter LSA-5 in ASBR router

r1(config)#access-list 1 permit 4.4.4.0 0.0.0.255

r1(config)#router ospf 100

r1(config-router)#distribute-list 1 out bgp

Only bgp routes 4.4.4.0 are allowed to enter my database, which is used to control the redistributed routes to enter my database (configured at ASBR)

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3, Modify interface OSPF priority:

r1(config-router)#nei 1.1.1.1 priority 10 - for 1.1.1.1, my priority is 10

r1(config-if)#ip ospf priority 10 ------- the priority of my interface is 10 (1 by default)

The maximum router ID is DR

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4, OSPF - passive interface:

(config-router)#passive-interface s0/1

[(config-router)#passive-interface  vlan 10)

This interface does not send ospf hello message (the establishment of OSPF neighbor relationship depends on the hello packet)

r1(config-router)#passive-interface default

r1(config-router)#no passive-interface s0/1

All interfaces are set to passive except S0/1. R1 connects 100 branches and only establishes ospf neighbors with R2. These 100 branches are included in the network statement

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V.: modify the reference bandwidth value

——(1) Modification in OSPF process

r1(config)#router ospf 100

r1(config-router)#auto-cost reference-bandwidth 1000

A router has a G excuse and an F interface, but the calculated cost value is 1, which is unfair! Global effect. The unit is M

This 1000M is actually the eighth power of 10

1G==1 000 000 000

100M==1 000 000 00

Note: in the same OSPF network, if one is modified, all routers need to be modified to unify the routing standard

——(2) Interface modification:

Topics: network ospf CCNP