[nsp] OSPF Area Design

Matthew Crocker matthew at crocker.com
Wed Feb 25 21:21:55 EST 2004

On Feb 25, 2004, at 7:34 PM, Vandy Hamidi wrote:

> Matt, thanks for the great reply, that's what I was thinking too.
> The dedicated internet connections at our remote offices are not on 
> the same routers as the frame relay.  It's typically:
>    ISP-----Router----FW-----Router----Frame-Relay full mesh
>                               |
>                           Office LAN
> Couple other considerations:
> the 4 remote offices are on the east coast and the main is on the west 
> with the 2 data centers.
> 1) I want the default routes needed by the east coast offices routed 
> to internet capable sites on the east coast.  Because I have fully 
> meshed 1.5Mbps, OSPF may consider our New York site as close to our 
> San Francisco office as it is to the Chicago office (same hop-count 
> and bandwidth).  NY's internet traffic may be routed across a 70ms 
> link to exit at SF instead of the 20ms link to CH.  How do I keep the 
> internet traffic going over closest link.

You can handle that with some local preference settings so the CH link 
is favored over the SF link so long as both are up.

> 2) We want the DC's IP's to be routable from the offices as well, but 
> it isn't directly connected to the WAN Cloud/FR Net.  I want to avoid 
> using virtual OSPF links if possible.  How can I accomplish that?

How is the DC office connected to your network?  Does it VPN in?  If 
so, can the VPN device run OSPF to announce routes from connected 

> Can I have two separate instances of OSPF and inject the DC's routes 
> into the other?

You can have separate OSPF areas on the same router

> 	-=Vandy=-
> -----Original Message-----
> From: Matthew Crocker [mailto:matthew at crocker.com]
> Sent: Wednesday, February 25, 2004 3:21 PM
> To: Vandy Hamidi
> Cc: cisco-nsp at puck.nether.net
> Subject: Re: [nsp] OSPF Area Design
> Are the routers that connect the frame network to the offices also the
> ones that handle the direct Inet links?  Or, do you have 2 routers in
> each office?  I would set the frame-relay network as area 0 and create
> a different area for each office.
> Example,
>   Office A:
>    has internet connection on router R.A1
>    has frame connection on router R.A2
>    has LAN segment
> Office B:
>    has internet connection on R.B2
>    has frame connection on router R.B2
>    has LAN segment
>   Main Office
>    has Internet connection on R.M1
>    has frame connection on route R.M2
>    has T1 to data center 1 on router R.M3
>    has T1 to data center 2 on router R.M4
>    has LAN segment
>   Datacenter 1
>     has T1 to main office on router R.D1
>     has T1 to datacenter 2 on router R.D2
>     has LAN segment
> OSPF area 0 contains R.A2, R.B2, R.M2,   PVCs interfaces on all routers
> listen for OSPF from all other routers (full mesh)
> OSPF area contains R.A1, R.A2
> OSPF area contains R.B1, R.B2
> OSPF area contains R.M1, R.M2, R.M3, R.M4
> OSPF area contains R.D1, R.D2
> router R.A1 originates default 0/0
> router R.B1 originates default 0/0
> router R.M1 originates default 0/0
> On Feb 25, 2004, at 5:15 PM, Vandy Hamidi wrote:
>> Current State:
>>  -4 Remote offices
>> 	-3 have dedicated Internet
>>  -1 Main Office
>> 	-Offices fully meshed through Frame-Relay
>> 	-Has dedicated INet
>>  -2 Remote Data Centers
>> 	-Data Centers fully meshed with Main office
>> We're Configuring OSPF for our 4 remote and Main offices using
>> Frame-Relay to fully mesh all locations.
>> Our main office also has a fully meshed point-to-point network with
>> our 2 data centers.
>> We'll have 4 connections to the internet from our 5 offices and we'd
>> like to be able to provide (originate 0/0) internet access to all
>> offices (current and new) as a backup for those that have dedicated
>> Inet and primary for offices w/o dedicated Inet.
>> All offices need to communicate directly with each other over the WAN.
>> We're currently using Static routes, but want to move to dynamic
>> routing for resiliency and ease of scalability.  We chose OSPF because
>> it's compatible with our Cisco and non-Cisco equipment.
>> What's the best way to design the OSPF Areas that will give us the
>> most effective routing and resiliency to failures while still
>> maintaining a simple configuration?
>> 	-=Vandy=-
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