So more specifics are sort of a sledge hammer approach. If you announce more
specifics over one link, assuming a prefix that long is widely readvertised,
you'll reroute all the traffic not just have a small effect. (more specifics
always win) (also it's bad form to not announce unified addressing at your
edges)
Further more, you'll have to have the more specifics in your IGP
somewhere to announce and they will have to route meaningfully else you'll have
issues reaching internal hosts in these ranges. If for example you had /24S
attached to different internal interfaces you could do a redistribute
connected, pass through a route map for appropriate tagging and use that to
source the more specifics.
One thing I bet you're bumping in to is that upstreams or peers of your
upstreams probably filter on shorter prefixes than /24 so assuming your IP
allocations are from your upstream they will install the larger say /19 that
your initial provider is announcing rather than the /24s or even the /23
because they filter on the edges at say /20. You want to use a looking glass
and make sure that you see both announcements equally announced and how widely
that's happening. Routeviews might be a good place to start. With prefixes
that long you may have issues balancing traffic meaningfully.
Make sure your upstream where you got the allocation is announcing your
space independently of the larger allocation. You might be announcing to your
upstream and they might not be passing on that more specific outside their AS.
Some carriers have communities that will allow you to announce or not
to announce to specific peers. You can try using communities to specifically
tag traffic and control how it's announced via the upstreams. You've got a
limited set of options though with prefixes that long.
Thanks
Scott
On Feb 28, 2013, at 10:11 PM, James Urwiller <[email protected]> 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 192.168.0.0/24
> Network 192.168.1.0/24
>
> OSPF:
> Network 192.168.0.0/23
>
> I would think in this scenario, the IP addresses 192.168.1.0 and
> 192.168.0.255 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
> [email protected]<mailto:[email protected]>
>
> _______________________________________________
> cisco-nsp mailing list [email protected]
> https://puck.nether.net/mailman/listinfo/cisco-nsp
> archive at http://puck.nether.net/pipermail/cisco-nsp/
_______________________________________________
cisco-nsp mailing list [email protected]
https://puck.nether.net/mailman/listinfo/cisco-nsp
archive at http://puck.nether.net/pipermail/cisco-nsp/
