OSPF Question

[cisconoobie]

Why is there a need to create multiple OSPF areas? Why cant all routers just be in Area 0?

Also, can someone give me a scenario where you would use different OSPF process id's instead of just using 1 for all areas?

[vladrac-ccna]

Hello there,

Imagine your network with 100 routers or more all connected to the same area. Do you know what will be the size of your ospf database and the ammount of memory and cpu needed to calculate it, and to run SPF in the entire network?

Besides, every single link flap will affect your entire network.

So, its always good to plan and divide your network into multiple areas (when you have a mid-big network).

Second question,

imagine you connect 2 network and you dont want them to route between each other (maybe 2 customers...) then you'd use 2 ospf instances. you'd have 2 separated dabatase in your router and unless you redistribute between them routers you wont be able to route between the 2 networks.

I've only seen in when working on CCIE work books, but I bet someone is using it somewhere.

Vlad

[cisconoobie]

thanks for responding, I understand now.

If I had just 3 inside core routers, 2 firewalls in active/standby and 2 outside routers in HSRP for Internet access

would it make sense to create multiple areas ?

What is best practice when creating area 0?

[vladrac-ccna]

Hello,

check the following link for more details:

http://www.cisco.com/warp/public/104/1.html

but I'd put the 3 routers in area 0 and the 2 outside routers in area 1.

btw,

rate posts you find helpfull.

Vlad