From: Daniel Cisco Group Study (danielcgs@imc.net.au)
Date: Tue Apr 15 2003 - 06:39:20 GMT-3
I would tend to argue that no filtering would be necessary here..... Let me explain myself.
Specifically, this case calls for mutual redistribution between OSPF & EIGRP in two separate locations.
Scenario 1:
OSPF redistributed into EIGRP. Consider redistribution at one of the routers.
The OSPF routes end up getting an AD of 170 within the EIGRP cloud. Once these routes arrive at the second redistribution point, which routes will the router believe? The native OSPF routes with AD 110, or the redistributed (now EX EIGRP) routes with an AD of 170? The OSPF ones of course.... So there's no problem with this redistribution, and no risk of route feedback.
Scenario 2:
EIGRP redistributed into OSPF. Again, consider redistribution at one of the routers.
The EIGRP routes end up getting an AD of 110 within the OSPF cloud. Once the routes arrive at the second redistribution point, which routes will the router believe? The native EIGRP routes with AD 90, or the external OSPF routes, AD 110?
The EIGRP ones of course...... So, again, there's no problem, and no feedback risk.
Therefore, my conclusion would be that we don't need to worry about filtering are playing with administrative distances in this situation.
Now, if we are talking about RIP & OSPF, or RIP & EIGRP, that's a different story. I guess that Cisco was smart enough to made the AD of External EIGRP routes high enough to help avoid the feedback issues experienced with other routing protocols???
Comments? Any wild objections? Anyone agree? Would this reasoning get me the points in the lab?
Daniel
-----Original Message-----
From: Robert Yee [mailto:robert@bluespud.com]
Sent: Tuesday, 15 April 2003 13:51
To: ccielab@groupstudy.com
Subject: FW: Redistribution: Filter of not to filter
> Hi All,
>
> I just wanted to get your opinion as to whether or not you prefer to route filter on single point of redistribution when redistributing both ways? Especially, if there is no requirement to deny/permit a specific route.
>
> R2
> /\
> / \ OSPF
> / \
> ==R5====R6=== Filter? - YES!
> _|____|_
> | EIGRP
> |
> =====R7====== Filter? - NO?
> |
> | RIP v2
> R8
>
> I can understand controlling the routes when there are 2 points of redistribution, but on a single point, it would seem like a lot of work for no reason if you didn't have to.
>
> Just wondering?
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