Routing query on EIGRP and OSPF

[Ganesan Palaniappan]

Hi,

Suppose i have 2 routers connected by using ethernet link. I have 2 internal network connected to each routers.

Now i am using OSPF routing protocol between the routers and i made adjancies only with the ethernet interface ip address ie /30 subent.

Now my query, will my internal network will get advertised by learning internally or do i want to advertise by using network command.

Again.. do i want to advertise with passive interface command or not. what is the difference in enabling ospf for all networks.

Attached a sample diagram which my setup clearly.

I want to know, what the is difference if i advertise the internal network with passive interface enabled and not.

May be the query is simple, but i am missing to understand one point and looking for the someone to explain that.

Also the sme using EIGRP, will it make any difference. As i understood the network command in IGP is same,

Regards,Gan

[Ganesan Palaniappan]

forgot to add the image

[mhnedirli]

Hi, 

You need to advertise your subnets which do you want to advertise such as if you want to R1 can see 30.30.30.0/24 subnet you need to advertise this subnet on R2 with network command. Passive interface stops the sending advertisement on an interface which you enabled.

[Ganesan Palaniappan]

Hi,

 If i understood correctly, i need to advertise the network by using network command. So if i enable passive interface for the network for 30.30.30.0/24 interface on LAN  side,then it will not send any EIGRP messages on that link to the switches.

But i can see the network on the R1 router for the LAN which also works fine. Correct me if i am wrong!

Regards,

Gan

[Richard Burts]

Gan

You have choices about how you can get OSPF and EIGRP to advertise the LAN subnets that you have configured. Let me start with the obvious point that you must have a network statement for the subnet that connects the two routers. The network statement is necessary to have the routing protocol run on those connecting interfaces.

Beyond the connecting interfaces you have a choice about how to get the routing protocol to advertise the LAN subnets. You could use network statements that match the LAN subnets. This will result in the routing protocol running on the LAN interfaces as well as the connecting interface. This is the approach that is frequently used but not the only option. You can also redistribute connected into the routing protocol. Redistribute connected will result in the routing protocol advertising the subnets but the routing protocol will not run on the LAN interfaces. The other thing to consider is that if you redistribute the subnets they will be advertised as External routes in the routing protocol.

If you do use network statements for the LAN subnets then there is the question of whether to use passive interface for the LAN subnets. When you use passive interface the routing protocol does not send any hello messages on those interfaces, will not create any neighbor relationships on those interfaces, and will not accept any routing updates from those interfaces. If there are no routers connected on those interfaces and no other devices that need to participate in the routing protocol then passive interface may be a good option to consider as it reduces the overhead processing on the interface.

HTH

Rick