> From stpeters@NetHeaven.com Sat Jul 26 17:28:23 1997
> Date: Sat, 26 Jul 1997 17:28:07 -0400
> From: "Dick St.Peters" <stpeters@NetHeaven.com>
> To: "David S. Graves" <admin@graves.com>
> Subject: Re: A (maybe dumb) static route question
>
> If you have your ospf set up correctly, you
> - do not need _any_ static routes
> - cannot have _any_ static routes <===
>
> With ospf, routers do not exchange routes. They tell each other what
> they are connected to.
>
> To see the implications of this, we need to label your routers
>
> INTERNET --[DS1]-----{1}ETHERA{2}----[DS1]--{3}ETHERB{4}---[DS1]---{5}ETHERC
>
> Now look what happens if you put a static route to ETHERC on router
> {1}: with ospf, router {1} can only tell other routers what it is
> connected to. It will import the static route into ospf by telling
> all the other routers that it is *connected* to ETHERC (or rather, to
> whatever IP network is running on ETHERC). Router {2} will then see
> its shortest path to ETHERC as being via router {1}, so when {1} sends
> a packet for ETHERC to {2}, {2} sends it right back to {1}
>
> If {1} and {2} are just different ports on the same router, that
> router will tell {3} that it is connected to ETHERC, so {3} will see
> its shortest path to ETHERC and being via {1,2}.
>
> When you run ospf you must let it handle all the routing interior to
> your ospf realm. Static routes can only be used at the ospf edges to
> tell the ospf interior how to reach things exterior to the ospf realm.
> In othe words, the only ospf-speaking router with a static route to
> anything not speaking ospf should be the router closest to it.
>
> A single static route inside the realm - even a correct route - will
> screw up the computed connection topology. That's the hardest thing
> about ospf to get used to: correct static routes can ruin the routing.
>
> David S. Graves writes:
> > I've got 3 ethers , all connected by ds1's through irx's.
> >
> > irx's are running ospf
> >
> > Let's call them ether A, B and C
> >
> > I've got a Class C routed to each ether.
> >
> > The internet is connected to ether A
> >
> > so it looks like this:
> >
> > INTERNET --[DS1]-----ETHERA----[DS1]---ETHERB---[DS1]---ETHERC
> >
> >
> > I've got 2 pm3's at the end of etherC
> >
> > Question:
> >
> > It appears that I MUST add static routes at the routers between ether A and
> > ether B
> > or the portmonsters at ether C can't be seen.
> >
> > Is this necessary with OSPF -- why doesn't the portmonster announce itself?
> >
> > -------------
> > I've got a coupla plain unix boxes on ether C -- it makes sense that they need
> > static routes, but what about the portmonsters?
>
> Your unix boxes on C do not need any routes. They are part of the IP
> network on C, and the ospf-speaking routers connected to C will make
> sure everyone else knows how to get to that network.
>
> Your ospf routers must be able to discover each other as neighbors.
> They must all have the same range for a given area, and all the
> ospf-speaking routers connected to a network must use the same netmask
> for their interface on that network.
>
> You also need to make sure your filters let through ospf multicast
> packets (sent to ospf-all.mcast.net = 224.0.0.5).
>
> --
> Dick St.Peters, stpeters@NetHeaven.com
> Gatekeeper, NetHeaven, Saratoga Springs, NY, 1-800-910-6671 (voice)
> Albany/Saratoga/Glens Falls/North Creek/Lake Placid/Blue Mountain Lake
> Soon: Elizabethtown/Greenwich/Keene/Plattsburgh/Saranac Lake/Ticonderoga
> First Internet service based in the 518 area code
>