From: De Witt, Duane (duane.dewitt@siemens.com)
Date: Wed Nov 03 2004 - 18:21:05 GMT-3
Hi
The way I understand it is that because ISIS runs on the interface the interface IP range only enters the ISIS database on the neighbor routers. Therefore if you are redistributing into another protocol it won't show unless as stated you redistribute connected or include that interface range in the other routing protocol.
Regards
Duane
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of ccie2be
Sent: Wednesday, November 03, 2004 3:34 PM
To: Ivan Ostre9; ccielab@groupstudy.com
Cc: Ivan Ostre9
Subject: Re: ISIS to OSPF redist
Hi Ivan,
What you are noticing is one of the major differences in how Cisco
implements redistribution of ISIS compared to other routing protocols.
First, this is what happens when other routing protocols are redistributed.
The router (actually IOS), goes through the route table and finds all the
routes of the protocol being redistributed and redistributes them into the
other routing protocol. Then, IOS looks at which connected interfaces are
running the protocol being redistributed and redistributes those as well.
This example should make this concept very clear.
Suppose a router is running 2 IGP's, IGP 1 and IGP 2. IGP 1 is running on
Int 1 and IGP 2 is running on Int 2. Let's also assume that in the route
table there are 3 routes learned via IGP 2.
Now, you redist IGP 2 into IGP 1. What routes are redistributed?
If IGP 2 is rip, eigrp, or ospf, then the 3 routes learned via any of those
IGP's are redistributed AND the subnet assigned to Interface 2 is also
AUTOMATICALLY redistributed.
If, however, IGP 2 is ISIS, then only the 3 routes learned via ISIS are
redist, NOT the subnet assigned to Interface 2. When ISIS is redist into
another routing protocol, the interfaces on which ISIS is running are NOT
automatically redist.
To redist the subnet assigned to Interface 2 on which ISIS is running, you
must explicitly redist connected route-map CONN where route-map CONN matches
Interface 2.
If you're wondering WHY this is. I don't know. It may have something to do
with rfc standards or it may just be how Cisco choose to do this. Maybe
someone more knowledgable than me can tell you.
There's something else very important you should know.
Let's assume the same example as before and again you want to redist IGP 2
into IGP 1. And, in addition, there's int lo0 on which no routing protocol
is running. Also, assume that IGP 2 is not ISIS. So, here's your config.
router IGP 1
redist IGP 2
redist conn route-map CONN
route-map CONN
match int lo0
What routes are redist?
First, IOS finds the routes learned via IGP2 in the route table and redist
those 3 routes. Then, IOS processes the redist connected and sees the
route-map. It then redist the connected interfaces referenced in the
route-map. So, it then redist int lo0. But, then it stops redistributing.
Unlike before, IOS doesn't, in this case, AUTOMATICALLY redist the subnets
assigned to interfaces running IGP 2.
Why? Because the redist conn route-map conn stops the AUTOMATIC behavior
of IOS. Since you're now explicitly telling IOS which connected interfaces
to redist, IOS will only redist those connected interfaces you explicitly
told it to redist.
BTW, I must give credit for this where credit is due. I learned this when I
took the Internetwork Expert lab prep class. Those 2 Brian's are network
guru's and they explained this almost as clearly as above.
HTH, Tim
----- Original Message -----
From: "Ivan Ostre9" <ivan.ostres@snt.hr>
To: <ccielab@groupstudy.com>
Cc: "Ivan Ostre9" <ivan.ostres@snt.hr>
Sent: Wednesday, November 03, 2004 5:15 AM
Subject: ISIS to OSPF redist
> Hello all,
>
> I have the following topology:
>
> R1----------R2-----------R3
>
> R1 and R2 are running OSPF, while R2 and R3 are running ISIS (Level 2
only).
> I'm trying to redistribute from ISIS level-2 to OSPF and have all routes
from
> ISIS in OSPF EXCEPT the network that is specified on the link connecting
my
> ISIS routers (R2----R3). I've noticed the same behaviour on ASET Lab 6.
Why is
> this happening? How to redistribute all networks from ISIS to OSPF?
>
> Thanks,
> Ivan
>
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>
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