BGP doesn't automatically pick up any routes.
There are three ways to do this:
1) network statements that enable advertising specific prefixes that
are present in the routing table.
2) aggregate statements that enable advertising prefixes for which there
may be more specific information available in the routing table
and/or BGP routes.
3) redistribution that enables advertising prefixes known to an IGP
(and therefore in the routing table, subject to selection via
a route-map or distribution list.
Each has it's role, and side effects. Redistribution exposes your
internal routing instabilities to the outside world, which probably
doesn't need to know. Aggregation creates confusing null routes.
Network statments don't neccessarily scale well as your network grows
and may require your to add your own null routes so that you can
announce aggregates.
For a mid-size network, you might redistribute connected routes into
your IGP (but not neccessarily statics!), and either aggregate or
use netowrk statements for what you adverties to the outside world.
George
> From cisco-nsp-request@puck.nether.net Sat Dec 16 16:09:51 2000
> Date: Sat, 16 Dec 2000 15:35:35 -0500
> X-From_: Vamsi_Gadireddy@satyam.com Sat Dec 16 15:35:33 2000
> Received-Date: Sat, 16 Dec 2000 15:35:30 -0500
> From: Vamsi_Gadireddy <Vamsi_Gadireddy@satyam.com>
> To: "'cisco-nsp@puck.nether.net'" <cisco-nsp@puck.nether.net>
> Old-Date: Sun, 17 Dec 2000 02:02:09 +0530
> Old-X-Envelope-To: cisco-nsp
> Resent-From: jared@puck.nether.net
> Resent-Date: Sat, 16 Dec 2000 15:57:09 -0500
> Resent-To: cisco-nsp@puck.nether.net
> Subject: [nsp] Redistribution
> X-Mailing-List: <cisco-nsp@puck.nether.net> archive/latest/4627
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> ------_=_NextPart_001_01C0679F.5AA51650
> Content-Type: text/plain
>
> Hi friends,
> I have an IGP (let it be OSPF) and am also running BGP on my routers
> connecting to external AS's.
> Do i have to redistribute my IGP into the BGP in order to enable routing
> of my internal networks? or will BGP automatically redistribute the IGP.
> This concept of redistribution is very confusing for me. Plese help me make
> it clear.
>
> Thanks & Regards,
> Vamsi
>
> ------_=_NextPart_001_01C0679F.5AA51650
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> Content-Transfer-Encoding: quoted-printable
>
> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
> <HTML>
> <HEAD>
> <META HTTP-EQUIV=3D"Content-Type" CONTENT=3D"text/html; =
> charset=3Dus-ascii">
> <META NAME=3D"Generator" CONTENT=3D"MS Exchange Server version =
> 5.5.2650.12">
> <TITLE>Redistribution</TITLE>
> </HEAD>
> <BODY>
>
> <P><FONT SIZE=3D2 FACE=3D"Arial">Hi friends,</FONT>
> <BR><FONT SIZE=3D2 FACE=3D"Arial"> I have an IGP (let =
> it be OSPF) and am also running BGP on my routers connecting to =
> external AS's.</FONT>
> <BR><FONT SIZE=3D2 FACE=3D"Arial"> Do i have to =
> redistribute my IGP into the BGP in order to enable routing of my =
> internal networks? or will BGP automatically redistribute the IGP. This =
> concept of redistribution is very confusing for me. Plese help me make =
> it clear.</FONT></P>
>
> <P><FONT SIZE=3D2 FACE=3D"Arial">Thanks & Regards,</FONT>
> <BR><FONT SIZE=3D2 FACE=3D"Arial">Vamsi</FONT>
> </P>
>
> </BODY>
> </HTML>
> ------_=_NextPart_001_01C0679F.5AA51650--
>
>
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