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LAN routing (OSPF)

Hi Ciscoer,

Need advice to design LAN routing (attached the image). Planning to use OSPF, so how to breakdown the area?

and Other advice really appreacited.

The current design has 3 pairs Distribution Switch (A&B) and edge switches (access Sw) will attach to each Distribuition.

So far only 3 pairs, it will be expanded to be more than 10 pairs Distribution.

Servers or IP PBX will be in different vlan. Connection to WAN is via router (mpls/vpn/BGP).

Admin&Access Building is just access switches.

Many thanks in advance .




Re: LAN routing (OSPF)


The rule of thumb is do not have more than 50 routers in an OSPF area, You design is pretty clean so you can have core's in area 0, all distribution in single area or you may have each distribution in  separate areas. I have few suggestions here to make, could work for you and may not

1. the uplinks are 10g from Core to Dist, use Auto-cost reference bandwidth command on all core and dist so that 10g has  cost of 1, otherwise any thing with 100 megs or above will have the same cost of 1.

2. Design areas where you can summarize the subnets, so that only summarize routes are advertised by ABR (Dist)

3. if DR and BDR are not required use point to point interface type for OSPF btw dist and core.

4. Design the serverfarm in such a way that if later point of time firewall is introduced to protect SF, you may need not stress at that point of time.

5. User RPVST+ at access switches with root as the active router of First hop redundancy protocol.

6. Think of any future link to be introduced between Distributions, if there is possibility, merge those distribution as single area ( for the sake of simplicity)


Hitesh Vinzoda

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Community Member

Re: LAN routing (OSPF)

Hi Hitesh,

Thanks for your prompt advice.

Do you mean the number of my Distribution Sw not more than 50?

If the Core will be are 0, the distribution will be area 1, how about WAN link?

can I say area 2 or other area?

Point 1, Why do you suggest for point 1?

Point 3, Means, I need to create each D-S owns its area, e.g D-S pair 1 -> area 1, D-S pair 2 -> area 2, so on.

Point 5, Meaning, the gw of the Access SW will be D-S active and GW for D-S is core active.

So, then This will apply on config portion?

Thanks again in advance



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