5. Implementing Basic OSPF
5.1 Core OSPF Configuration
1. Configure OSPF for the above network diagram. R1 will act as an ASBR by by redistributing a
series of static routes into the OSPF network. These routes should NOT increment their metric
as they pass through the network and should have an initial OSPF cost of 200. All routers
have a router-id reflecting their hostname; you should be able to ping this router-id
throughout the entire OSPF network.
5.3 Redistribute the statics
E1 increment their metric. That means cost of 200 + 10 + 100 for example.
E2 doesn’t increment their metric.
R1(config-router)#redistribute static subnets metric 200 metric-type ?
1 Set OSPF External Type 1 metrics
2 Set OSPF External Type 2 metrics
R1(config-router)#redistribute static subnets metric 200 metric-type 2
On R5 you can see the InterArea routes for example for R6 with
show ip route ospf
O IA 18.104.22.168 [110/66] via 172.30.10.2, 01:19:03, Serial2/0
and also see the external static routes on R5
O E2 172.16.0.0 [110/200] via 172.30.10.2, 00:00:02, Serial2/0
O E2 172.16.1.0 [110/200] via 172.30.10.2, 00:00:02, Serial2/0
O E2 172.16.2.0 [110/200] via 172.30.10.2, 00:00:02, Serial2/0
O E2 172.16.3.0 [110/200] via 172.30.10.2, 00:00:02, Serial2/0
The metric for E2 will be always the same = 200 (no increment)
perfect. we can go ahead !
5.4 Configuring the loopback adresses on R4 and R5
5.5 Network Statement
On R4 do a ‘show ip route’ end press enter.
you can see that the loopback addresses from R5 are shown with a 32bit mask.
a network statement must be forcefully dedicated to an physical interface
wrong: network 172.30.0.0 0.0.0.0 area 0
right: network 172.30.0.1 0.0.0.0 area 0
5.6 Route summarization on ABR and ASBR
5.7 auto-cost command
If you want adjust your auto-costs, you can type in the following command.
If 1 Gbit/s is your fastest line in your environment, go to the router process and type in the auto-cost command.
R2(config-router)#auto-cost reference-bandwidth ?
<1-4294967> The reference bandwidth in terms of Mbits per second
R2(config-router)#auto-cost reference-bandwidth 1000
But you have to do this for all your routers in your areas and environment.
Be carefully with this command and do not use a to high number of auto-cost. Maximum possible value is 4294967. But you run the risk, that lower
bandwidth lines ar never been calculated and drop out of the ospf process.
5.8 Interface priority command
Each broadcast and Non-Broadcast Multi-Access (NBMA) network has a designated router. If the network is a transit network, the designated
router generates a link state advertisement (LSA) for the network and has other responsibilities required for the running of the protocol. The
designated router is elected by the Hello Protocol.
The designated router concept reduces the amount of routing protocol traffic and reduces the size of the link-state database by enabling a
reduction in the number of adjacencies required on a broadcast or non-broadcast multi-access network.
When two routers attached to a network both attempt to become the designated router, the router with the highest priority becomes the
designated router. A router whose priority is set to 0 is ineligible to become designated router or backup designated router.
Use the ip ospf priority [1 - 255] command to set the priority to a value between 1 and 255.
Use the ip ospf priority 0 command to configure the router to never function as the designated router or backup designated router.
Use the no ip ospf priority command to set the priority at the default value of 1.
Factory Default: 1.
Command Mode: Interface configuration.
5.9 Tie break for the Router ID
1. Router ID is the router name
2. Highest active Interface IP Adress when ospf starts.
3. Loopback beat physical Interfaces.
4. Router-ID command
5. Priority (the higher wins)
If the priority not handled in the right way, clear the ospf process
Router# clear ip ospf process
Reset ALL OSPF process? [no]:
conform with yes