[c-nsp] BGP advertisements more specific than IGP

Andrew Miehs andrew at 2sheds.de
Thu Feb 28 23:30:04 EST 2013

You will need to have the two /24s in your IGP for BGP to announce them.
Advertising your 2x 24s on the one link, and the 1x 23 on the other link
would cause all the traffic to pass via your 2x /24 link - more specific.

Have you tried just announcing the same /23 to both providers? How bad is
the distribution?

On Fri, Mar 1, 2013 at 2:11 PM, James Urwiller <jurwiller at americanbb.com>wrote:

> I have a BGP multi-homed invironment that I am having problems balancing
> inbound traffic, besides prepends which don't seem to be helping anymore, I
> have heard that announcing my networks more specifically could also
> influence inbound traffic.  My question is, for example… If I have a /23
> that I am using as a /23 in OSPF, can I announce that in BGP more
> specifically (2, /24's)  without having to them break it up internally as
> well?  What I foresee happening is this..
> Example:
> BGP:
> Network
> Network
> Network
> I would think in this scenario, the IP addresses and
> would not have a route in BGP, even though they are valid
> addresses for use when used as a /23.  Since I would be multi-homed, I
> would still advertise the network as the aggregate /23 on the circuit I
> don't want to take as much traffic, so would those IP addresses in this
> scenario still work, but only through the circuit I advertise as the
> aggregate??
> James Urwiller
> Network Operations Manager
> CCNA 11567125
> American Broadband
> 402-426-6257 - Office
> 402-278-1875 - Cell
> 402-426-6273 - Fax
> jurwiller at americanbb.com<mailto:jurwiller at americanbb.com>
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