From: Chuck Larrieu (chuck@xxxxxxxxxxxxx)
Date: Tue Dec 19 2000 - 01:48:55 GMT-3
Thanks to all those who provided some insight.
Let me say first of all, this exercise was one of the Mentor Tech Vlab
series - Lab 4010 to be precise.
The Vlab sample solution used a slight different numbering scheme than I
did, which changed a couple of things in a very minor way. Also, the Vlab
sample solution did not suggest any kind of distribute-list filtering. That
left a particular route leaking back into OSPF from the OSPF-IGRP
redistribution. Not that it mattered in this scenario. Everyone could still
ping everyone because the IGRP leak was less specific than the OSPF route in
the table.
Also, I was unable to re-create the pinging of IGRP interfaces from the OSPF
side with only one way redistribution from IGRP into OSPF. That means I was
either drunk or dreaming when I reported this phenomenon. Maybe I was
dreaming I was drunk?
In any case, I believe I have absorbed what the Vlab lesson was attempting
to teach- the issues around FLSM and VLSM redistribution. And where to place
summary addresses and area ranges. BTW, this is another place where the
Vlab suggested solution seems a bit strained. Vlab places ALL summarization
on the redistribution router. Being something of a purist, I like to place
summarization closest to the source. I.e. I like to use the area range
command on ABR's and summarize into the backbone. I like to use the
summary-address at the redistribution point. Although for this lab, given
the addressing scheme provided, I suppose this preference was irrelevant.
Thanks again, everyone.
Chuck
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Chuck Larrieu
Sent: Saturday, December 16, 2000 9:21 PM
To: CCIE_Lab Groupstudy List
Subject: Issue Spotting - FLSM and VLSM redistribution
These are my first looks into the issue of VLSM and FLSM redistribution. So
please forgive me if this is a bit of a naïve question.
Practice lab scenario - OSPF and IGRP redistribution
Redistribution router
-------------------------
OSPF..............................IGRP
172.16.1.0/24................172.16.24.0/24
172.16.4.64/26...............172.16.23.0/24
Other OSPF routes from elsewhere
----------------------
172.16.2.0/24
172.16.3.0/24
172.16.10.8/30
172.16.10.12/30
172.16.10.4/30
172.16.4.0/26
On the redistribution router, I configure the IGRP process and place the
172.16.0.0 network into it. The bad news is that the IGRP domain sees the
172.16.1.0 network, even though it shouldn't in that it is supposed to be
unique in the OSPF domain. The further bad news is that when I do a one way
redistribution into the OSPF domain, all OSPF routers can ping interfaces of
all routers in the IGRP domain, even though there is no redistribution of
the OSPF routes into the IGRP domain.
So I start fooling with distribute lists, and proceed to make a mess. Routes
disappear. Stop that.
Well, then I do mutual redistribution with no filters. I summarize all my
longer than /24 routes so they will be redistributed into the IGRP domain.
Life is good. I can ping all interfaces of either domain from the other.
But something is nagging at me. What did I miss? Is it true that there are
NO issues in a redistribution scenario if 1) there is only a single point
of redistribution AND 2) summarization at the IGRP (or any classful domain)
occurs at the point of redistribution?
Thanks for letting me think out loud here.
Chuck
----------------------
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