Re: OSPF & EIGRP redistribution

Yuri nailed it. You will need to specify ospf network type point-to-point
under your loopback.

On Tue, Jan 31, 2012 at 12:02 PM, Scott Strobeck <scott_at_strobeck.net> wrote:

> Nvnish - Yes, used the subnets keyword.
>
> -----Original Message-----
> From: nvnish_at_gmail.com
> Reply-to: nvnish_at_gmail.com
> To: Scott Strobeck <scott_at_strobeck.net>, ccielab
> <ccielab_at_groupstudy.com>
> Subject: Re: OSPF & EIGRP redistribution
> Date: Tue, 31 Jan 2012 19:25:54 +0000
>
>
> Hi Scott,
>
> Just to make sure... R1 & R2 : OSPF and R2 & R3 : EIGRP...
>
> Can you confirm you used the 'subnets' in the redistribute statement?
>
> Thanks,
>
> Sent from my BlackBerryB. wireless device
>
> -----Original Message-----
> From: Scott Strobeck <scott_at_strobeck.net>
> Sender: nobody_at_groupstudy.com
> Date: Tue, 31 Jan 2012 14:07:18
> To: ccielab<ccielab_at_groupstudy.com>
> Reply-To: Scott Strobeck <scott_at_strobeck.net>
> Subject: OSPF & EIGRP redistribution
>
> Hi everyone,
>
> I noticed today in my lab that I had an unexpected route. After chasing
> it down for a while, I found it seems to be an anomaly when
> redistributing ospf->eigrp.
>
> Consider a simple R1--R2--R3 lab where OSPF is running between R2&R3,
> and EIGRP between R2&R3. R1 & R2 have a loopback advertised into the
> OSPF with network statements. Full redistribution between OSPF & EIGRP
> is done on R2.
>
> R2's loopback, left at default, will have a network type of LOOPBACK and
> will show up in OSPF as a /32. However, in the EIGRP domain (on R3),
> this external route will show up as a /24.
>
> Is this expected behavior? Why would EIGRP have it as a /24 when OSPF,
> where it came from, has it as a /32. R1's loopback shows up as a /32 on
> R3, as expected, so why should this be different for R2's loopback?
>
> This may not seem like such a problem until you take R4 and connect it
> to both the OSPF and EIGRP domains, and perform full redistribution,
> again. Now, the /24 route from R2's loopback will get redistributed
> into OSPF as an external route since there's not an internal equivalent
> to cancel it out. Ultimately, the route will get advertised back to
> R2.
>
> If you add a 3rd point of redistribution between the two IGP's (R5), now
> you've created a routing loop for this /24 route and if you shut down
> R2, the /24 route created by R2's loopback remains.
>
> I'm tempted to go ahead and open a new ddts for this, but wanted to
> check on here, first. There may a good reason why this happens, but I
> can't, for the life of me, think of it.
>
> (BTW, as it stands, this would be a great 'gotcha' for the lab. . . a
> potential workaround might be to change the loopback's ospf network
> type, or to filter off the route in the EIGRP domain.)
>
> Thanks,
> Scott
>
>
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Received on Tue Jan 31 2012 - 12:32:33 ART