OSPF Design question

Cisco gurus,

Need some help designing an OSPF routing infrastructure.

Cisco A has 192.168.50.x and 51.x networks (and a few more) b/h it Cisco B has 192.168.12.x and 13.x networks (and a lot more all directly connected) b/h it Cisco C has 192.168 13.x and 60.x networks b/h it

----------------------- ciscoA eth0 eth2:


----------------------- | | area 0? |

----------------------- cisco B (ABR?) eth0

eth1 eth2 eth3: eth4... eth5....

----------------------- | | area1? |

----------------------- cisco C eth0

eth1 eth2 eth3... eth4...


I read the OSPF design guide off of ciscos website and came up with the folloing plan,

- Cisco B should be ABR.

- Cisco A and B will be in area0

- Cisco B and C will be in area1

is that okay? someone has a better design in mind? comments?

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Sounds to me like you can use just one area (Area 0). Although it really depends on each case, I've seen some Cisco "rule of thumb" recommendation saying that multiple areas should be considered when reaching around 50 routers and few hundred subnets... is that really your case? James

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James Schnack

not even close to 50 routers, maybe around 5-6 more in area0 down the road. We do have a few hundred subnets on ciscoB. Cisco A and cisco C are just extention of our (class B) network.

any security reasons to use 2 areas vs. put all in area 0

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main advantage in your case of an ABR is that you can only summarise OSPF routes @ ABR.

BTW - you should only have OSPF full interfaces on places where routers need to form an adjacency - ie. networks / subnet that may carry transit traffic.

you can set other interfaces to OSPF passive, or leave them out of OSPF if you leave the interfaces out then you need to redistribute the routes into OSPF - but you can summarise as part of the redistribution.

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