From: Gary Duncanson (gary.duncanson@googlemail.com)
Date: Tue Mar 04 2008 - 18:33:14 ARST
I don't use the IE workbooks but I have been trying to follow this. So far
as I can see the critical thing seems to be can the RIP routes redistributed
into OSPF on SW1 be fed back to SW1 somehow.
If Sadiq is right then they can and if so you will obviously want to prefer
the RIP routes to get to those places from SW1 not anything learned by OSPF.
Hence the AD of 109 for RIP routes on SW1. It will be prefered no matter
what OSPF routes transpire on SW1.
I presume the AD is set using the distance command under the RIP process on
SW1.
Gary
----- Original Message -----
From: "Scott Vermillion" <scott_ccie_list@it-ag.com>
To: "'Sadiq Yakasai'" <sadiqtanko@gmail.com>; "'Timothy Chin'"
<Tim@1c-solutions.com>
Cc: "'John'" <jgarrison1@austin.rr.com>; "'Hash Aminu'" <hashng@gmail.com>;
"'Carlos Alberto Trujillo Jimenez'" <carlos.trujillo.jimenez@gmail.com>;
<ccielab@groupstudy.com>
Sent: Tuesday, March 04, 2008 8:16 PM
Subject: RE: redistribution
> Yep, it makes perfect sense Sadiq! And I believe if you follow the IE
> solution to OSPF/EIGRP mutual redistribution, this distance 109 thing is
> likely required. Most found trouble with the solution as give, though,
> and
> wound up doing something different (such as tagging and filtering at the
> OSPF/EIGRP seam so that this isn't an issue). I obviously don't recall
> all
> of the details, but in reviewing quickly the postings on the IE forums,
> the
> solution as given fails when a backup link is active. Hence the
> alternative
> approaches that a good many of us wound up implementing before moving on
> to
> the remainder of this lab.
>
> IIRC, the solution given was meant to stretch our minds and show us a way
> of
> using distance in wacky ways to solve loops that result from massive
> mutual
> redistribution of practically everything everywhere. But in the end, it's
> not a very good approach and, as I said, actually fails when you bring up
> the backup link...
>
>
> -----Original Message-----
> From: Sadiq Yakasai [mailto:sadiqtanko@gmail.com]
> Sent: Tuesday, March 04, 2008 1:06 PM
> To: Timothy Chin
> Cc: John; Scott Vermillion; Hash Aminu; Carlos Alberto Trujillo Jimenez;
> ccielab@groupstudy.com
> Subject: Re: redistribution
>
> Guys,
>
> I have checked the lab and this comes back to what I said ealier:
>
> You are redistributing RIP into OSPF on SW1.
>
> Then you are mutually redistributing OSPF and EIGRP on three points;
> R2, R3, R4. Now, the rip routes you have redistributed into OSPF on
> SW1 go into OSPF and then;
>
> 1. on R2: they enter EIGRP and then come back into OSPF on R3 as
> externals. These LSAs would get sent everywhere and even down to SW1
> again (where they originally got redistributed into OSPF). SW1 would
> gladly put these routes into the routing table. Why? Because they
> would have a lower AD (OSPF 110) than the original prefixes (in RIP
> with AD of 120) and they would appear to have originated from EIGRP
> (which is false). This would now make these prefixes unreachable in
> the whole network because the originator of these prefixes into the
> OSPF no longer has the correct ones.
>
> 2. similar behaviour could be seen on R3, when the routes enter into
> EIGRP in R4 and come back into OSPF on R3 and these now get sent back
> to SW1.
>
> Now to mitigate this problem, you simply set the AD of RIP routes to
> 109 on SW1 so that no matter what, these prefixes will never be
> accepted on SW1 from OSPF even after they ahve gone through the EIGRP
> domain.
>
> Do you guys see the point?
>
> HTH
>
> Sadiq
>
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