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RE: BGP - Controlling outboutbound routing decissions [7:81585] posted 12/30/2003
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Hi Duncan,

You can do this by prepending the AS-PATH of NET-A before advertising it to 
ISP-B.
Like this over the Internet the path for NetA via ISP-A will appear having 
shorter AS-PATh and will be prefered.

Redundancy still exists as NET-A is still adervertised via ISP-B also but 
with the modified prepended AS-PATh.

This will control your downstream from the Internet to NET-A.

Regards,
Yasser
>From: "Duncan Wallace" 

>
>I have 2 border routers each connected to a different ISPs. I am trying to
>control the exit point of one of my internal subnets. Sorry for the bad
>ascii art...What I would like to do is have NETA always utilize ISPA, never
>ISPB, unless ISPA is not available. Next, let BGP do its thing and let NETB
>,NETC, Etc. route where BGP has a best route to a destination net. I am
>rifling through Halabi, and cisco.com right now, but not getting very far,
>looking at route maps, policy maps, etc.  Any help or examples would be
>appreciated. I have tried Policy based routing from RTRC routing to RTRA,
>but using a BGP def local pref 200 kills that because RTA just sees the
>better route at RTRB anyway
>
>
>
>
>
>ISPA        ISPB
>  |    EBGP    |
>  |            |
>RTRA        RTRB
>  |    IBGP    |
>  |____________|
>  |            |
>  |     IGP    |
>RTRC_________RTRD_______
>  |            |       |
>NETA        NETB     NETC ...
>
>
>Thanks,
>
>Duncan Wallace
>FORTiX
>503-439-7661
>
>
>-----Original Message-----
>From: Bob Sinclair [mailto:bsin@xxxxxxx]
>Sent: Monday, December 29, 2003 7:42 AM
>To: cisco@xxxxxxxxxxxxxx
>Subject: Re: MLS on MSFC [7:81574]
>
>Jon,
>
>I think the follwowing points summarize the relevant  info from the white
>paper link supplied by Joseph.
>
>There are two kinds of Layer 3 switching done on the Cisco switches:  MLS
>(cache-based) and CEF (topology-based).
>
>Which one your 6000 uses as its method of L3 switching depends on whether
>you have a PFC (MLS) or a PFC2 (CEF).
>
>These layer 3 switching methods take most (MLS) or all (CEF) of the
>forwarding load off of the MSFC.
>
>In the case of a PFC doing MLS, the MSFC may itself use CEF as one of its
>switching methods (process, fast, CEF).
>
>If you enable MLS on the MSFC of a 6000 with PFC2, then you are allowing it
>to act as an external RP for a CAT 5000.  It does not affect the L3
>switching method on the 6000.
>
>
>HTH,
>
>Bob Sinclair
>
>
>
>----- Original Message -----
>From: "Jon Miles"
>To:
>Sent: Monday, December 29, 2003 10:17 AM
>Subject: RE: MLS on MSFC [7:81574]
>
>
> > I found another thread that is about the same topic:
> >
> > http://www.groupstudy.com/form/read.php?f=7&i=79810&t=79614
> >
> > One of the replies says that Sup1a (the switch I am practising on) does
>MLS
> > automatically, which proves your point Joe. The reply also states that
>Sup2
> > performs CEF instead of MLS, and that the MLS entries are purely for
>Netflow
> > data collection.
> >
> > 1. If this is the case, does CEF in this setup still = Layer 3 switching 
>?
> >
> > 2. If I did enable MLS on a MSFC attached to a Sup2, would this then be
> > running MLS or CEF ?
> >
> > Jon
> > **Please support GroupStudy by purchasing from the GroupStudy Store:
> > http://shop.groupstudy.com
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>http://www.groupstudy.com/list/cisco.html
>**Please support GroupStudy by purchasing from the GroupStudy Store:
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