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Multiple OSPF Processes

visitor68
Level 4
Level 4

Why would someone run multiple OSPF processes on the same router?

What are the implications?

Are there two SEPARATE databases that are established, one for each process?

Are these processes totally isolated?

What about the RIB? Are there effectively separate routing tables?

lets say a route is learned through both OSPF processes, what happens then....?

Another quick question:

router ospf 499

router-id 10.199.254.38

log-adjacency-changes

auto-cost reference-bandwidth 1000000

nsf

area 1 authentication message-digest

redistribute static metric-type 1 subnets route-map into-ospf

network 10.195.48.40 0.0.0.7 area 1

network 10.195.48.48 0.0.0.15 area 1

network 10.199.254.38 0.0.0.0 area 1

network 99.207.255.8 0.0.0.0 area 1

!

router ospf 599

log-adjacency-changes

auto-cost reference-bandwidth 1000000

nsf

area 0 authentication message-digest

area 2 authentication message-digest

redistribute static

passive-interface default

no passive-interface GigabitEthernet4/1

no passive-interface Vlan98

no passive-interface Vlan99

network 10.195.48.8 0.0.0.3 area 2

network 10.195.48.32 0.0.0.7 area 2

network 10.195.48.248 0.0.0.7 area 0

network 10.195.49.0 0.0.0.127 area 2

network 10.195.50.0 0.0.0.127 area 2

network 10.195.64.0 0.0.15.255 area 2

network 10.195.80.0 0.0.0.255 area 2

<b>interface GigabitEthernet4/1

ip address 10.195.48.53 255.255.255.240</b>

Notice the IP address of this interface. OSPF 499 is running OSPF on this interface (see the network statement), yet the interface is un-passived out in OSPF599....why is that? Typos?

Thanks

1 Accepted Solution

Accepted Solutions

Joe

You are pretty close. Let me try to clarify one of the things that you say:"it is not the fact that the network statement under OSPF encompasses the whole range of subnets that determines which LSAs are created and sent, but the actual interfaces that are configured on each router."

It is not just the network statement and it is not just the interfaces on the router that are configured. It is the combination of the network statement and the configured interfaces that determine what is advertised by OSPF.

To explain in a bit more detail:

When the OSPF process starts it looks at its configured network statements (and the address ranges defined by the address and the mask) and it looks at every interface on the router (that is in up/up state) and if an interface falls into the range defined by a network statement then that interface is included into OSPF. Then OSPF looks at the subnet defined on that interface (including its mask) and advertises that subnet.

So to clarify a couple of points:

- the network statement does not tell OSPF what to advertise but tells OSPF what interfaces to process.

- the network statement does not tell OSPF to summarize (there are separate commands to control summarization).

- OSPF will determine what to advertise based on the configured subnets on the interfaces that it includes in its processing.

HTH

Rick

HTH

Rick

View solution in original post

28 Replies 28

Manish Prasad
Level 5
Level 5

Why would someone run multiple OSPF processes on the same router? --you can do it but to able to achieve routing between them you have to use the redistribution.

Yes they have their own separate databases.

What about the RIB? Are there effectively separate routing tables? -yes

lets say a route is learned through both OSPF processes, what happens then....?

it will only happen when you redistribute.