From: Kenneth Wygand (KWygand@customonline.com)
Date: Sat Jul 10 2004 - 18:55:13 GMT-3
Howard,
When I typed "FIB", it was a typo, it meant to say "RIB". I just made the same typo three times... hey, it can happen! :)
Thanks for your diligence in terminology... it really is essential to proper understanding. And I learned a little bit more by your wonderful and thorough explanation. Thanks! :)
Ken
________________________________
From: nobody@groupstudy.com on behalf of Howard C. Berkowitz
Sent: Sat 7/10/2004 5:35 PM
To: ccielab@groupstudy.com
Subject: RE: distribute-list out (at the process-level)
At 4:34 PM -0400 7/10/04, Kenneth Wygand wrote:
>Adel,
>
>So basically the reference point is from the FIB even though the
>distribute-list is placed under the routing protocol process, if I
>understand correctly.
I would make the point that yes, the reference point is outside the
routing processes, but to say it is the FIB is misleading. "FIB" is
both a term specific to Cisco when referring to CEF, but also a
general routing theory term for the place in which destinations are
looked up for packet-by-packet forwarding.
The Routing Information Base is what is shown with "show ip route".
I would argue the RIB is the point of reference, because you are not
always using the CEF FIB. In process switching, the RIB and FIB are
the same table.
In fast (and, for that matter, autonomous, silicon and optimum in
older models) switching, the fast lookup "FIB" function is the fast
switching cache, which is a subset of the RIB. In these switching
modes, the FIB will occasionally be invalidated and rebuilt, so you
can't use it as a point of reference. CEF, in contrast, maintains a
FIB that is always in one-to-one correspondence with the RIB (with
some very special case exceptions).
>
>One question on your first bullet point (Only those OSPF previxes
>will be considered for redistribution, that are installed in FIB, in
>other words - you see them in the output of "show ip route ospf").
>
>Isn't all redistribution based upon routes that are active within
>the FIB? If I redistribute OSPF 1 into RIP, won't only routes
>active in the FIB be redistributed, as opposed to other routes in
>OSPF's LSA database?
>
>Thanks again, this was a great explanation!
>Ken
>
>________________________________
>
>From: Adel Abouchaev [mailto:adel@netmasterclass.net]
>Sent: Sat 7/10/2004 3:56 PM
>To: Kenneth Wygand
>Cc: ccielab@groupstudy.com
>Subject: Re: distribute-list out (at the process-level)
>
>
>
>1. Redistribution between two routing processes:
>
> You have OSPF 1 and RIP on your router. You want to limit prefixes
>redistributed from OSPF into RIP. So you configure "distribute-list 10
>out ospf 1" under RIP. By this, when you perform rediistribution under
>rip "redistribute ospf 1 metric 1":
> 1. Only those OSPF prefixes will be considered for
>redistribution, that are installed in FIB,
>in other words - you see them in the output of "show ip route ospf".
> 2. Only those OSPF prefixes will be redistributed into RIP
>_out_ of routing table, that are
>allowed by the access-list (10) that you reference in the
>distribute-list command.
>
>2. You have OSPF 1 process on the router. You want to filter some
>prefixes from being installed
>into the FIB, so you would not see them in "show ip route ospf". Then
>you configure an access-list,
>denying these networks, allowing everything else, then you configure
>"distribute-list 10 in", under router OSPF. Now, the denied prefixes
>will not be installed _in_ FIB.
>
>That's basically all about _in_'s and _out_'s :) It's not complicated at
>all, but is just a matter of watching the directions from the correct
>starting point.
>
>Cheers,
>
>Adel.
>
>Kenneth Wygand wrote:
>
>>Hi Adel,
>>
>>I'm sorry but I don't understand completely. Can you illustrate
>>with an example?
>>
>>Thanks very much in advance! :)
>>Ken
>>
>>________________________________
>>
>>From: Adel Abouchaev [mailto:adel@netmasterclass.net]
>>Sent: Sat 7/10/2004 3:44 PM
>>To: Kenneth Wygand
>>Cc: ccielab@groupstudy.com
>>Subject: Re: distribute-list out (at the process-level)
>>
>>
>>
>>It's better thought (when it's a redistribution distribute-list, not a
>>filtering distribute list) as "in" and "out" of FIB. Redistribution
>>takes prefixes from FIB for the source protocol and brings them into the
>>destination protocol. When doing just "in", for example, you will filter
>>prefixes from being installed into FIB.
>>
>>Cheers,
>>Adel Abouchaev
>>CCIE# 12037
>>www.netmasterclass.net
>>
>>
>>Kenneth Wygand wrote:
>>
>>
>>
>>>Hello everyone!
>>>
>>>I have a question regarding redistribution at the process level.
> >>
>>>Lets say we have the following situation:
>>>
>>><SNIP>
>>>router ospf 1
>>> distribute-list 1 out eigrp
>>>!
>>>router eigrp 1
>>> network x.x.x.x y.y.y.y
>>></SNIP>
>>>
>>>The way I remember what this command does is that it applies
>>>distribute-list 1 for routes redistribute "out -OF- EIGRP", so
>>>this would affect routes that are moving from the EIGRP routing
>>>process into the OSPF routing process.
>>>
>>>Now for my question: Does the "distribute-list" command work the
>>>same way within all routing processes? Are there any other type
>>>of "unintuitive" distribute-list process-level commands that might
>>>not work the way as expected?
>>>
>>>Thanks!
> >>Ken
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