From: ccie2be (ccie2be@nyc.rr.com)
Date: Thu Aug 28 2003 - 09:22:40 GMT-3
Hi David,
I'm sure I understand your question but I'll try to clarify what I said
earlier.
Some routing protocols - notably Eigrp and OSPF - treat routes learned from
external sources via redistribution differently than routes learned from the
protocol itself. You can see this very clearly when you redist routes into
OSPF or Eigrp and then look at the route table with the show ip route
command. Routes that have been redist into OSPF or Eigrp are "tagged" in
the route table as external.
To see how the routes are tagged, just configure the following:
R1---ospf ----R2---rip---R3
On R2 configure redist of rip into ospf and ospf into rip. Now look at the
route table on R1 and R3. On R1, routes that were redist into ospf are
"tagged" as External. On R3, how do routes that were redist into RIP
appear?
Now, do the same thing except this time, substitute Eigrp for ospf. Then
try it again, but this time substitute IS-IS for Eigrp.
Now, add a forth router, R4 and connect it to both R1 and R3 and like
before, run two routing protocols on it and redistribute between the two
protocols. First, don't filter any routes and see happens then filter ospf
or eigrp or is-is routes.
Hopefully, after doing this little excercise, all will be clear.
----- Original Message -----
From: "David zhao" <zhaobaolong@boco.com.cn>
To: "ccie2be" <ccie2be@nyc.rr.com>
Sent: Thursday, August 28, 2003 3:56 AM
Subject: Re: Multiple Point Route Redistribution
> hi
> i learn a lot from the your reply . it's very helpful.
> but i have a little confuse about the idea ,"one of the routing
protocols tagged routes as external but the
> other routing protocol doesn't," in the case ,why to filter and how to
filter, for the sub-optimal
> routes which reach to rip network ?
> thx for your kind reply .
>
>
> ----- Original Message -----
> From: "ccie2be" <ccie2be@nyc.rr.com>
> To: "Group Study" <ccielab@groupstudy.com>; "Jeff Colburn"
<willbccie@yahoo.com>
> Sent: Tuesday, August 26, 2003 8:31 PM
> Subject: Re: Multiple Point Route Redistribution
>
>
> > Hey Jeff,
> >
> > One of the things I do in this situation is determine the nature of the
> > issue; that is which routing protocols am I dealing with and do the
routing
> > protocols tag routes redistributed into them.
> >
> > For example, if the routing protocols are Eigrp and OSPF, I don't have
to
> > worry about route reflection. A route redist into Eigrp from OSPF won't
be
> > redist back into OSPF.
> >
> > If, however, one of the routing protocols tagged routes as external but
the
> > other routing protocol doesn't, then I have to filter - but only from
one
> > side. For example, if the 2 protocols are OSPF and RIP, then a filter
is
> > needed when redist from rip to ospf but not when redist from ospf to
rip.
> >
> > Another thing to keep in mind when configuring redist is classful versus
> > classless. This isn't specific to multi point redist but it's very
> > important. Make sure you know how to summarize routes in all the
classless
> > routing protocols, especially OSPF and BGP because when redist to a
classful
> > routing protocol only routes with the same subnet mask length as the
> > classful protocol is using will get redist. For example, you can't
redist
> > x.x.x.x/26 into RIP when RIP is only knows about y.y.y.y/24 routes.
> >
> > One last thought - I only learned about this one fairly recently. You
can't
> > redist routes multiple times on a single router. For example, let's say
a
> > router is running 2 routing protocols, rip and ospf and you have static
> > routes or connected routes on the router. You can't redist the static
into
> > rip and then expect the static routes to be redist from rip into ospf.
You
> > have to explicitly redist the static routes into both rip and ospf.
> >
> > As a second to last suggestion, I would read Doyle chapter on
redistribution
> > again and go through all the review questions and exercises at the end
of
> > the chapter until you know that stuff cold.
> >
> > Lastly, after configuring redist, I would verify with a show ip route on
all
> > the routers that all the routes that should be in the route table are
there.
> >
> > Hope this helps. dt
> > ----- Original Message -----
> > From: "Jeff Colburn" <willbccie@yahoo.com>
> > To: <ccielab@groupstudy.com>
> > Sent: Tuesday, August 26, 2003 7:24 AM
> > Subject: Multiple Point Route Redistribution
> >
> >
> > > I am quickly approaching my lab date and I feel that I still have one
> > critical weakness, route redistribution between multiple points. I have
> > been successful using distance commands and route maps when the points
are
> > between a protocol on the edge being redistributed into the core
protocol.
> > I have been running into difficulty when several protocols are running
and
> > redistribution is done at various points in the network. I feel I spend
too
> > much time tweaking distances and map statements to eliminate the
sub-optimal
> > routes.
> > > Does anyone have a good general practice or approach when tackling
this
> > task?
> > >
> > > Thanks,
> > >
> > > Jeff Colburn
> > >
> > >
> > > ---------------------------------
> > > Do you Yahoo!?
> > > Yahoo! SiteBuilder - Free, easy-to-use web site design software
> > >
> > >
> > >
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