The problem with making a site an area in ospf is that it limits your expansion capabilities at that site from day zero - to connect a new site you must connect it later on to one of the routers (= sites) belonging to the backbone area instead of perhaps a site that is somehow better (like closer, cheaper circuits, services are there, etc). That is, unless you resort to virtual links which imho have no place in a well designed production network unless you're having to integrate something you purchased...
With ISIS you wouldn't have this particular problem as any L2 area will happily talk with another L2 area. That said I'm certainly not advocating the OP to deploy ISIS without a bit more understanding what he wants to do ;-) As for priority in a broadcast type of network.. Unless you want to be really deterministic it most likely doesn't matter who's the DR and who's not. Sups on the cats won't be having a problem with their DR role unless you're doing something really silly. Still if it's a /30 or /31 prefix on your link you pretty much know it's p2p and should configure so, too. Assuming the OP wanted L3 all the way to his cat4500s: routed ports (not SVIs *), /31 addressing on router-router ifs, ifs ospf p2p, area 0 everywhere, no igp hello/dead tuning - if you cannot rely on media detection use bfd with aggressive timers instead, if there is reason to believe that you're carrying more than a few lans at each site deploy ibgp from day 0 - you'll save yourself from grief later. *) On the 6500s SVIs consume limited vlan space just as routed ports while, again imho, the syntax for routed ports is easier to understand and one doesn't have to worry about what vlans are active on what port (assuming you don't want to permit 1-4094 everywhere ;)). Kaj > From: Joe Astorino <[email protected]> > Date: Fri, 14 Aug 2009 07:58:20 -0700 > To: Ryan Hughes <[email protected]> > Cc: <[email protected]> > Subject: Re: [OSL | CCIE_RS] OSPF Design Question > > A lot of different things come into play here. If this is a simple topology > there is no reason we can't have area 0 for everything. If you have a ton of > routes going back and forth between the sites, you may make each site an area > and leave area 0 for the core and distribution. With that design you would > just have type 3 summary LSAs going between the areas. > > If you are running point-to-point subinterfaces you will not have a DR and you > will not have to deal with priority at all. At the end of the day, it is more > of a design decision depending on your environment!
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