From: ying chang (ying_c@xxxxxxxxxxx)
Date: Thu May 09 2002 - 10:00:55 GMT-3
Sorry, found a few mistakes from my post below, but the basic concept
presented is correct. In short, an external route will not get redistributed
if it's also an internal route or a local routing process.
Chang
>From: "ying chang" <ying_c@hotmail.com>
>Reply-To: "ying chang" <ying_c@hotmail.com>
>To: ccielab@groupstudy.com
>Subject: RE: Redistribute ospf external route into igrp
>Date: Thu, 09 May 2002 00:32:51 -0400
>
>After went through a few tests, I don't think the issue is not on
>split-horizon but on whose route is more trustworthy:
>
>Since mutual redistribution is always causing confusion, and this problem
>can be simulated without mutual redistribution, so I set up an environment
>like the following:
>
> R4<--igrp---R3<---rip---R5--172.16.155.0/24
> |
> ospf
> |
> R1<--rip----R2--172.16.125.0/24
>
>and below is what I got:
>
>Two external routes in R3:
>
>r3#sio d | b -5 <<<- both 125.0/24 and 155.0/24 are in ospf external db
> Type-5 AS External Link States
>
>Link ID ADV Router Age Seq# Checksum Tag
>172.16.125.0 172.16.200.1 48 0x80000001 0xC013 12
>172.16.155.0 172.16.146.1 610 0x80000002 0x8E45 35
>
>Only 172.16.155.0 is redistributed into igrp:
>
>r3#debug ip igrp tra <<<--sending 125.0/24 but not 155.0/24
>IGRP protocol debugging is on
>r3#
>13:28:22: IGRP: sending update to 255.255.255.255 via Ethernet0
>(172.16.52.3)
>13:28:22: subnet 172.16.144.0, metric=501
>13:28:22: subnet 172.16.145.0, metric=501
>13:28:22: subnet 172.16.146.0, metric=501
>13:28:22: subnet 172.16.53.0, metric=1100
>13:28:22: subnet 172.16.10.0, metric=8476
>13:28:22: subnet 172.16.125.0, metric=158250 <<<<----
>r3#
>r3#sh ip rip data <<<- r3 has 155.0/24 but not 125.0/24
>172.16.0.0/16 auto-summary
>172.16.145.0/24 directly connected, Loopback1
>...
>172.16.149.0/24
> [1] via 172.16.10.1, 00:00:08, Serial0
>172.16.155.0/24 <<<<------
> [1] via 172.16.53.1, 00:00:09, Ethernet1
>...
>r3#
>
>I think the reason 172.16.155.0/24 was not sending to IGRP is because from
>R3's point of view, 172.16.155.0/24 is in its rip database (know it by
>first
>hand), it also knows 172.16.155.0/24 is in ospf - but that's learn from
>some
>other protocol (second hand stuff), so the route is not cannot be trusted,
>and that's why when you redistribute ospf into igrp, you only see R1's rip
>routes but not R4's rip routes. 172.16.125.0/24 did not have this problem,
>because it's not in R3's local rip database.
>
>The moral for this problem: when you run more than two protocols in a
>router
>like this, not only you have to redistribute ospf into igrp, you also need
>to redistribute directly connected rip routes into igrp.
>
>Chang
>
>>From: "Jenkins, Buddy" <buddy.jenkins@csfb.com>
>>Reply-To: "Jenkins, Buddy" <buddy.jenkins@csfb.com>
>>To: ccielab@groupstudy.com
>>Subject: RE: Redistribute ospf external route into igrp
>>Date: Thu, 9 May 2002 07:25:00 +0900
>>
>>Jeff,
>>
>>Refer to Doyle Volume1 Chapter 11 on redistribution. In the questions at
>>the end of the chapter there is a question (I don't have the book with me
>>right now so I can't tell you the specific question) that has the same
>>scenario that you have. Doyle says that the reason for that type of
>>behaviour is because of the rule of split horizon. This makes sense for
>>you scanario below because IGRP would use split horizon and OSPF does not
>>use split horizon. However this is the part that still confuses me. I do
>>not know why split horizon is applied to a redistribution process. I
>>always though split horizon was implemented to not advertise a route out
>>an
>>interface from which that route was learned. Can any of the guru's out
>>there explain why split horizon is applied during mutual redistribution?
>>
>>Buddy
>>
>>-----Original Message-----
>>From: Jeff Szeto [mailto:jytszeto@hotmail.com]
>>Sent: Wednesday, May 08, 2002 5:20 PM
>>To: ccielab@groupstudy.com
>>Subject: Redistribute ospf external route into igrp
>>
>>
>>Hi,
>>
>>A router runs IGRP, OSPF and RIP. Mutual redistribution exist between
>>OSPF---RIP and OSPF---IGRP. But no redistribution between IGRP and RIP.
>>From the debug message I found that IGRP is no advertising the RIP routes
>>that are redistributed into OSPF while the OSPF routes are advertised
>>normally.
>>On the other hand, the IGRP routes are advertised into RIP through OSPF.
>>
>>Could someone explain the concept behind or point me to a document.
>>
>>Thanks in advance.
>>
>>Jeff
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