From: alsontra@hotmail.com
Date: Sun Jan 25 2004 - 04:40:27 GMT-3
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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