How good is such design!!!!

CCIE_2011

Hi there,
I just wondering, can we create an ospf area with only ABR routers and the rest are all L2 switches for users in such broadcast domain.

http://g.imagehost.org/0627/Untitled_1.jpg

Will there be any benefit in creating such areas? or simply if all routers are in Area 0 this will have less admin work and better performance.

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Comments

dtlokee

Based on the design there is no advantage to making those routers ABR unless you have plans to expand those areas in the future. An ABR that is connected to area 0 will still contain a full routing table.

APA

what dtlokee said....

Fruitless exercise, unless thinking of the bigger picture.... where those areas might be further expanded to include more L3\L4 devices therefore wanting to keep them out of the backbone and segregated within a seperate area.

CCIE_2011

Thanks alot for the clarification. I was sure that this is the answer .... i just want to hear it from experts

.... I'm not very self confidante about networking yet

Thanks again

CCIE_2011

regarding my Question above. While studying for BSCI i came up with the following conclusion.

I would go with such design
http://g.imagehost.org/0627/Untitled_1.jpg

and apply summrization at ABR's. With this i will reduce routing table look up for the core routers and other distributors.

What do you think experts ?

networker050184

If you only have the amount of devices in the picture I don't see the point of using more than one area. You are adding complexity with little (if any) reward in the way of performance. Unless I'm mistaken, ts the same design you originally had so the same answers still apply.

CCIE_2011

networker050184, I'm assuming each area will have more than 15 access layer switch, and with more than 30 /24 subnet. This is our company's network

for sure such thing will reduce a lot of routing table entries.

networker050184

CCIE_2011 wrote: »

networker050184, I'm assuming each area will have more than 15 access layer switch, and with more than 30 /24 subnet. This is our company's network

for sure such thing will reduce a lot of routing table entries.

Sure it will reduce entries, but will the reduction be worth the added complexity? 30 routes isn't going to kill a modern router. I've always been a believer in the K.I.S.S. method.

Turgon

networker050184 wrote: »

Sure it will reduce entries, but will the reduction be worth the added complexity? 30 routes isn't going to kill a modern router. I've always been a believer in the K.I.S.S. method.

Inclined to agree.

tech-airman

CCIE_2011 wrote: »

regarding my Question above. While studying for BSCI i came up with the following conclusion.

I would go with such design
http://g.imagehost.org/0627/Untitled_1.jpg

and apply summrization at ABR's. With this i will reduce routing table look up for the core routers and other distributors.

What do you think experts ?

CCIE_2011,

OSPF is a classless routing protocol with NO option for becoming a classful routing protocol. Since OSPF is a classless routing protocol, you're required to use VLSM. VLSM is the process of "subnetting a subnet." At each subnet boundary is the "summarization" IP network address. So you're going to use "summarization" with every OSPF router interface, regardless if it's an ABR or not.

The problem that you might end up with in the future is the issue of scalability. If you didn't originally allow for enough IP addresses (both network and host) for each sub-subnet, then if you want to grow a certain area more than it was originally designed for, you'll have to re-subnet the entire network from top-down then implement it.

What is a "distributors?"

CCIE_2011

tech-airman wrote: »

What is a "distributors?"

distributors are Switches in the Distribution layer. is the my correct?

The problem that you might end up with in the future is the issue of scalability. If you didn't originally allow for enough IP addresses (both network and host) for each sub-subnet, then if you want to grow a certain area more than it was originally designed for, you'll have to re-subnet the entire network from top-down then implement it.
"

I totally agree. If we go with this approach, it is not necessary to just have one summary route for every ABR. we have just to summarize as much as possible. it won't harm to more than a route but to summarize whenever possible.

I really appreciate every body's participation. I learned alot although not yet a network admin.