From: Connary, Julie Ann (jconnary@xxxxxxxxx)
Date: Tue Jan 16 2001 - 11:47:56 GMT-3
Hi,
I emphasize with you because I am always hung up on this issue.
How I have come to resolve it is this:
1. remember that IGRP can only accept routes with the same subnet mask as
it's interface. So if the IGRP interface
is a 24 bit subnet mask, then you will only get 24 bit routes redistributed
from OSPF into IGRP (same applies to RIP V1). This rule does not apply if
the route is in a different classfull network and then it will summarize to
the classfull boundary.
2. to solve this problem you have 3 choices:
a. if possible - summarize at OSPF Area border routers. Say if you
have an area 3 with a /28 bit subnet mask, use area 3 range x.x.x.x
255.255.255.0 to summarize to the /24 bit mask and then it will get
redistributed into IGRP.
b. on the redistribution router create a static route to null 0 to
summarize to the 24 bit boundary, ip route x.x.x.x 255.255.255.0 null 0 and
redistribute static into IGRP.
c. use a ip default-network on the redistribution router or a
downstream IGRP router. Remember that the default network must
point to another address range. so if your address range is
x.x.x.x the default route must point to y.y.y.y. This installs
a gateway of last resort into your routing table. Remember that
IGRP does not use the 0.0.0.0 route.
3. Always look at your ospf database to make sure that you did not
redistribute in connected routes that you specified as
passive under IGRP. do a show ip ospf database and go to the very bottom
and look at your external LSA's. Make sure that
you only have the external LSA's that you expected. Use route-maps to
filter connected subnets and other network as necessary and
then recheck the IP OSPF database. Unfortunately IGRP does not have a
database to check - so you always have to
do a debug on igrp routing or check a downstream router. If you are doing
EIGRP you can do
a show ip eigrp topology to make sure that you have only redistributed into
eigrp the routes that you expected.
good luck - I go in 10 days. eeeeeeeeeeeeeeeeeeeeeeeeeeeee!!!!!!!!
read up on VLSM. check out the tech tips on CCO. Set up 4 routers and
redistribute between protocols. Make sure that
you do it very deliberately. That is set up all the protocols to not
redistribute, look at the databases and routing tables. Start one by
one and redistribute, then watch what happens. Make sure you use a variety
of masks and classfull and non-classfull networks.
Never never put in multiple redistribution statements without checking the
databases after adding each statement and making sure you do not need to
filter.
Julie Ann
At 09:01 AM 1/16/2001 -0500, ccie2b@usa.net wrote:
>Familiar with most issues, but this one keeps eluding me for some
>reason...never had anyone explain it...and yes, 2 weeks and
>closing...need help, not criticism...
>
>Devinator
>
>
>
> > You are walking into the lab in 2.5 weeks and you are unfamiliar with
> > classful versus classless issues?
>
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> > ccie2b@usa.net
> > Sent: Monday, January 15, 2001 7:37 PM
> > To: ccielab@groupstudy.com
> > Subject: aggregate addresses and redistribution
>
> > I keep hearing about having OSPF and igrp (or rip) having to have
> > matching masks or something. I don't understand what this is, applies
> > to, etc. Can someone enlighten me in layman's terms as to this
> > mask-matching thing?
>
> > Thanks ALOT,
>
> > Devinator
> > ccie2b@usa.net
>
>
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