From: Joe Chang (changjoe@earthlink.net)
Date: Sun Jan 25 2004 - 06:54:43 GMT-3
This is a really interesting scenario, thanks for bringing it up. IMHO the
simplest solution would be to make sure EIGRP redistributes only summary
addresses into OSPF. For example if you redistribute 1.0.0.0/8 into OSPF,
the R2 in your scenario would be able to discern that the best route to
1.1.1.1 is through its SW1 interface by virtue of closest-match routing
(assuming R2 has, say, 1.1.1.0/24 in its routing table).
----- Original Message -----
From: <alsontra@hotmail.com>
To: <ccielab@groupstudy.com>; "Kenneth Wygand" <KWygand@customonline.com>
Sent: Saturday, January 24, 2004 11:40 PM
Subject: Re: OSPF, EIGRP redistribution
> Sorry if there is confusion. Using route tags prevents routing loops when
> doing mutual distribution between OSPF-and -EIGRP, but it does not always
> provide optimal routing.When I advertise routes from SW1 into the Eigrp
> domain they are redistributed into the OSPF domain with "either" R2 or R6
as
> the gateway. This cause which ever router is the current gateway for the
> SW1 routes to experience less than optimal routing.
>
> After spending sometime with this, I have come to the following
conclusions:
>
> 1. Tagging routes prevents route-feed back and loops in your topology
> 2. Tagging does not prevent less than optimal routing. i.g. R2 sometimes
> traverses R5,R6 and SW1 to get to R7.
> 3. The primary way to prevent this is through the use of the distance
> command.
> 4. If you use the distance command without tagging, redistribution seems
to
> work, but the SPF and DUAL are constantly nagging.
>
> --------R5--------
> | |
> R6 R2
> | |
> -------SW1------
> -
> -
> R7 (network 1.1.1.1)
>
> I've configured this scenarios several times and as long as the router
> acting as the R7 (networks next_hop) is up, one router will experience
less
> than optimal routing. My main question is whether or not my conclusions,
> configs, reasoning... are correct??? maybe??? or at least in the ball
park?
>
>
>
> ----- Original Message -----
> From: "Kenneth Wygand" <KWygand@customonline.com>
> To: <alsontra@hotmail.com>; <ccielab@groupstudy.com>
> Sent: Saturday, January 24, 2004 9:10 PM
> Subject: RE: OSPF, EIGRP redistribution
>
>
> > Alsontra,
> >
> > I don't understand what you mean when you say "As I understand it, this
> > configuration causes either R6 or R2 to become an ASBR and that ASBR
then
> > advertises all routes learned from SW1. Which puts you in situation
that
> > causes less than optimal routing on R6 or R2." The configuration you
have
> listed simply prevents loops from a potential "chained" redistribution.
It
> just "tags" routes so once they pass through one distribution, they will
not
> be redistributed back to the original protocol.
> >
> > Can you please explain further, and let us know what routing protocols
are
> running on which routers?
> >
> > Thanks!
> > Ken
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com on behalf of alsontra@hotmail.com
> > Sent: Sat 1/24/2004 8:36 PM
> > To: ccielab@groupstudy.com
> > Cc:
> > Subject: OSPF, EIGRP redistribution
> >
> >
> >
> > ****Let me start by saying I've read about 100 posts on this subject,
but
> I
> > haven't found a definitive answer. ****
> >
> > I am working on scenario that involves mutual distribution of OSPF and
> EIGRP
> > using route maps. The topology looks something like this:
> >
> >
> > --------R5--------
> > | |
> > R6 R2
> > | |
> > -------SW1------
> >
> > Using the following route maps on R2 and R6:
> >
> > <snip>
> > route-map OSPF-TO-EIGRP deny 10
> > match tag 111
> > !
> > route-map OSPF-TO-EIGRP permit 20
> > set tag 90
> > !
> > route-map EIGRP-TO-OSPF deny 10
> > match tag 90
> > !
> > route-map EIGRP-TO-OSPF permit 20
> > set tag 111
> > !
> > </snip>
> >
> > R6 and R2 are doing mutual distribution using route-maps and all is well
> > until I advertise any networks connected to SW1. As I understand it,
this
> > configuration causes either R6 or R2 to become an ASBR and that ASBR
then
> > advertises all routes learned from SW1. Which puts you in situation
that
> > causes less than optimal routing on R6 or R2.
> >
> > Is it possible to use "just" route tagging in a mutual OSPF-EIGRP
> > retribution situation and avoid less that optimal routing? I know from
> > previous posts that I can use the distance command in the following
> fashion
> > to elevate the situation. <see below> However, is route tagging alone
> > capable of solving mutual distribution scenarios without causing less
> than
> > optimal routing? Or is it just possible that I've misconfigured
something
> > somewhere, and that's the cause of the less that optimal routing?
> >
> > access-list 10 permit <networks>
> >
> > access-list 10 permit <networks>
> >
> > and applying it under router OSPF:
> >
> > router ospf 100
> >
> > distance 171 <neighbors address> 255.255.255.255 10
> >
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