From: Chris Lewis (chrlewiscsco@yahoo.com)
Date: Mon Nov 07 2005 - 00:28:52 GMT-3
Tags as configured below are indeed a nice way to stop routes from being fed back in to their IGP of origin. However, that is often not enough to eradicate sub-optimal routing. For example, take the simple topology below:
R1--------R2
| |
R3--------R4
Each has a loopback on it from 1.1.1.1 for R1, 2.2.2.2 for R2 etc.
Now say R2 and R3 both run OSPF and RIP,
R1 only runs OSPF and R4 only runs RIP.
The optimal position is to have R1 see equal cost paths to the loopback of R4 via both R2 and R3, however with tags alone, you will not be able to achieve this. It will only see one.
Netmasterclass has an excellent write up on this in their public PDF section.
Chris
"Schulz, Dave" <DSchulz@dpsciences.com> wrote:
This is a great subject, and one that I have been wrestling with for awhile.
I have used the ACLs for the distribution, but Kevin is right...you have to
maintain the ACLs. And, in a dynamic environment, this may take a lot more
admin than one would care to admit. I have found that easiest way to do the
redistribution is by using tags. I try to keep the same tag number as the
administrative distance to keep things straight. So, if I am redistributing
from OSPF to EIGRP....I use 110 as the tag and 90 in the reverse direction.
This seems to work well and is very easy to implement and keep things
straight.
The one thing that I have learned with the redistribution is applying the
metrics. For EIGRP, you must apply the metrics either as a default in the
routing process or on the redistribute command line. You cannot solely do
this within the metric. Here is an example of a route-map for redistribution
that I have used:
router eigrp 1
redistribute ospf 1 route-map Ospf2Eigrp metric 100000 1 255 1 1500
!
router ospf 1
redistribute eigrp 1 route-map Eigrp2Ospf metric 10 metric-type 1
!
route-map Eigrp2Ospf deny 10
match tag 110
!
route-map Eigrp2Ospf permit 20
set tag 90
!
route-map Ospf2Eigrp deny 10
match tag 90
!
route-map Ospf2Eigrp permit 20
set tag 110
I am interested in any other great ways to accomplish this. You can't know
enough of the ways to do things.
Dave
-----Original Message-----
From: nobody@groupstudy.com
To: Cisco Nuts
Cc: ccielab@groupstudy.com
Sent: 11/5/2005 10:13 AM
Subject: Re: Rip <--->Ospf Redistribution - using distribute-lists?
Both using distance and or distribute lists is a valid way
of stopping the loops. The advantage of the distance way
where possible is you do not have to maintain ACLs so
as new routes get advertised you do not have to update
the ACL's.
It is not always possible to use distance on its own.
Regards
Kevin
On 11/5/05, Cisco Nuts wrote:
> Hello: Is distribute-lists a good idea to use when doing 2-way
> redistribution b/w Rip and Ospf or for that matter b/w any 2 IGP's in
> general? I have been reading a very good example of this on CCO but
did
> not run into this kind of solution (if I recall correctly) when doing
the
> InetExp Labs. Even a sample lab from DoIt uses the distance 109 for
RIP.
> Permitting all RIP routes into Ospf via the distribute-list out rip
under
> Ospf while denying all RIP routes in via the distribute-list out ospf
> under Rip seems to nail it down. Any thoughts on this? Thanks!!
>
>
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