Brian,
sorry i took so long getting back to you....
i have read your naswer and understand what you are saying....and yes your
right...(sorry i got a bit confused with the wording)
i have been looking into this but am unable to find an answer as to why one
ASBR (your right that`s what there called) uses the RIP route and ine uses
the OSPF (re-dist rip route).i now ospf will prefur and INTRA area route to
an INTER but that rule dosen`t apply..it just doesn`r make sence why one
router would choose one route one-time and then not another...
thanks for the brainteeser thought .....i will look up somemore
steve
>From: "Brian Lodwick"
>Reply-To: "Brian Lodwick"
>To: [EMAIL PROTECTED]
>Subject: Re: OSPF scenario [7:7605]
>Date: Mon, 11 Jun 2001 10:33:11 -0400
>
>Steve,
>~you said: r1 and r3 to get to the ethernet sement would have to go thru
>RIP.
>
>~my reply:Well the wording is kindof wierd, but the way I think of it is r1
>will receive a route for the ethernet segment from r5 via RIP and from r2
>via OSPF and the same on r3 it will receive a route to the ethernet segment
>from r4 via RIP and from r2 via OSPF. I did say on r1 and r3 full
>redistribution was taking place (OSPF into RIP & RIP into OSPF).
>So what is happenning is r1 and r3 are receiving RIP routes to the /16
>network from the ethernet segment and they are also receiving OSPF External
>routes to the /16 ethernet segment. The reason I mention the mask is
>because
>one is not more specific than the other so administrative distance is next
>distinction for placement in the routing table.
>
>The rest of the questions I think are questioning concern how
>redistribution
>works. I'll try help, but Jeff Doyle will do a much better job since there
>were alot of other variables that played into this scenario (like a
>classless routing protocol into a classfull routing protocol)
>r1 and r3 will receive RIP routes and OSPF routes since one of their
>serial's are in the OSPF process and the other is in the RIP process, it is
>up to this router to determine which route goes into it's routing table if
>it receives 2 routes to a certain destination.
>The redistribution for lets say RIP into OSPF -says if you receive a route
>from RIP send these routes along with your other regular OSPF updates out
>of
>the designated OSPF interfaces and give them this metric when you send
>them.
>The redistribution doesn't effect how the redistributing router will
>determine it's best route, it just controls how this router sends routing
>updates.
>
>~I said: What ends up happening is one of the ASBR's uses the OSPF route
>and
>the other one uses the RIP route, dependancy upon which one comes to full
>first will use the RIP route, and the other one will use the OSPF route.
>
>~you said: THERE is no ospf route......R4 and R5 are using RIP ....you
>can`t
>get to the ethernet segment via ospf only rip .....
>you can go VIA a Re-distributed route ....but it`s a RIP re-distributed
>route not ospf...what i mean is the route to r4 and r5 is re-dis into ospf
>via rip .... r2 wants to get to the ether-link ... it uses the re-dist rip
>route andvertised via ospf...yes it`s an ospf route BUT it came from
>RIP..so
>what do you mean ...?????
>r2 wants to get to the ether-link ... it uses the re-dist rip route
>andvertised via ospf... yes it`s an ospf route BUT it came from RIP
>
>~my reply: I was talking about r1 and r3, I am considering them to be
>ASBR's
>(because they have a connection outside of the OSPF process -I'm not sure
>of
>the exact RFC terminology, but I believe these would be considered ASBR's)
>So thinking about r1 or r3 they can get to this ethernet segment via either
>a RIP route or an external OSPF route. (I call the redistributed RIP route
>an OSPF External route once it's in the OSPF process). Yea it originally
>came from RIP, but r2 just know's it's an external OSPF route r2 doesn't
>know it used to be a RIP route it just received it from r1 and r3 via OSPF.
>r2 is not running RIP.
>
>I've tried to explain as far as my knowledge level goes, but I'm not to
>sure
>if I fully understand your questions , or maybe I am overlooking something?
>Could you try asking the questions more directly or differently if I
>haven't
>helped?
>
> >>>Brian
>
> >From: "Stephen Skinner"
> >Reply-To: [EMAIL PROTECTED]
> >To: [EMAIL PROTECTED], [EMAIL PROTECTED]
> >Subject: Re: OSPF scenario [7:7605]
> >Date: Fri, 08 Jun 2001 09:29:12 -0000
> >
> >Hi
> >i don`t mean to be rude but ,for r1 and r3 to get to the ethernet
> >segment,you will have to go throught rip...??????
> >
> >
> >
> >>I had originally thought that both of the ASBR's would choose the OSPF
> >>route
> >>to the ethernet segment between the 2 routers running only RIP, since
>the
> >>routes are identical in mask length,
> >
> >
> >R4 and R5 are only running rip ...yes.....
> >so how do you get to the ethernet segment between them Via an ospf path
>if
> >the are only running RIP???????
> >
> >the rip path will be advertised as an OSPF E2 path ..yes...
> >so there is NO rip path.....there are only OSPF paths...that is what
> >re-distribution does right...?????
> >
> >HELP..... i am confused
> >
> >
> >>What ends up happening is one of the ASBR's uses the OSPF route and the
> >>other one uses the RIP route, dependancy upon which one comes to full
> >>first
> >>will use the RIP route, and the other one will use the OSPF route.
> >
> >THERE is no ospf route......R4 and R5 are using RIP ....you can`t get to
> >the ethernet segment via ospf only rip .....
> >
> >you can go VIA a Re-distributed route ....but it`s a RIP re-distributed
> >route not ospf...
> >
> >what i mean is
> >
> >the route to r4 and r5 is re-dis into ospf via rip ....
> >r2 wants to get to the ether-link ...
> >it uses the re-dist rip route andvertised via ospf...
> >
> >yes it`s an ospf route BUT it came from RIP..
> >
> >so what do you mean ...?????
> >
> >i thought i knew OSPF but you have confused me totally..
> >
> >if i need help understanding this please help
> >
> >steve(.............me nogggin`s gone all soft,Guv)
> >
> >
> >
> >
> >>From: "Brian Lodwick"
> >>Reply-To: "Brian Lodwick"
> >>To: [EMAIL PROTECTED]
> >>Subject: OSPF scenario [7:7605]
> >>Date: Thu, 7 Jun 2001 17:17:54 -0400
> >>
> >>I've come across a wierd OSPF issue in a lab scenario I thought might be
> >>fun
> >>for everyone to comment on (instead of a bunch of gossip on salaries and
> >>brain dumps)
> >>
> >>The scenario has 5 routers (NLI-lab 7) and the last thing I want to do
>is
> >>upset NLI by divulging their lab scenario so I'll try to briefly go over
> >>what I thought was interesting without divulging the whole thing.
> >>
> >>There are 3 routers running OSPF on the top. 2 of the 3 have OSPF on one
> >>serial interface and RIP on the other serial interface -fully
> >>redistributing
> >>both ways. On the bottom there are 2 routers running RIP on their serial
> >>interfaces (which are connected to the RIP serials on the redistributing
> >>routers) then those 2 bottom RIP only routers are connected together via
> >>an
> >>ethernet segment which are both running RIP on the ethernets as well.
> >>
> >>r1 --- r2 --- r3
> >>| |
> >>| |
> >>r4 --------- r5
> >>
> >>I believe the two redistributing routers would be considered ASBR's in
> >>OSPF.
> >>I had originally thought that both of the ASBR's would choose the OSPF
> >>route
> >>to the ethernet segment between the 2 routers running only RIP, since
>the
> >>routes are identical in mask length, the next thing is to look at the
> >>administrative distance. Since OSPF has is lower it should choose the
>OSPF
> >>route, but if they both use the OSPF route you would obviosly create a
> >>routing loop, which cannot happen in OSPF since it creates a topological
> >>database.
> >>What ends up happening is one of the ASBR's uses the OSPF route and the
> >>other one uses the RIP route, dependancy upon which one comes to full
> >>first
> >>will use the RIP route, and the other one will use the OSPF route.
> >>It seems OSPF will only allow one external exit point for each outside
> >>subnet. But why don't both of the ASBR's choose the RIP routes and equal
> >>cost load balance out of the external links as it does internally?
> >>I think it's a neat scenario. I really liked it, the overall issue was
>to
> >>learn how to control the routing process to most efficiently route to
>the
> >>destination, but I learned alot about the way OSPF works too.
> >>
> >> >>>Brian
> >>_________________________________________________________________
> >>Get your FREE download of MSN Explorer at http://explorer.msn.com
>_________________________________________________________________
>Get your FREE download of MSN Explorer at http://explorer.msn.com
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