From: Brian McGahan (bmcgahan@internetworkexpert.com)
Date: Wed Nov 03 2004 - 16:23:48 GMT-3
Almost as clearly?!? ;)
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
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> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> ccie2be
> Sent: Wednesday, November 03, 2004 7:34 AM
> 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
> >
> > [GroupStudy removed an attachment of type application/ms-tnef which had
> a
> name of winmail.dat]
> >
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