From: Peter van Oene (pvo@usermail.com)
Date: Sat Mar 01 2003 - 19:20:13 GMT-3
At 12:07 PM 3/1/2003 -0800, Anthony Pace wrote:
>I am helping a friend who is developing an appliance to dynamically load
>balance BGP outbound advertisments using "the old PREPEND the AS-PATH on
>some networks going to one provider, and vice-versa going to the other".
>The "special" part is they will adjust this periodically based on a
>number of factors (load, latency etc...)
Routing protocols that link path determination to real time path attributes
tend to create race conditions. In BGP, this scenario will get you damped
in hurry (try ripe 210 to see how fast)
>I remember a year or two ago there were alot of problems in breaking up
>advertisments into blocks of less than /20. Some major providor(s) were
>dropping the routes and customers were getting "black holed".
Some providers may have filtered advertisements longer than /16 out of the
traditional Class B space. /24's otherwise tend to flow pretty well (in
the US anyway)
>DOES ANYONE KNOW THE SMALLEST BLOCKS WHICH ARE PRACTICAL WHEN ADVERTISING
>TO UPSTREAM PROVIDERS?
Transit upstreams will generally accept any length assuming you are using
space they give you. Most (hopefully all) will have strict ingress filters
that may or may not allow you to "leak" more specific routes that what you
have been allocated. Many of these same require you to register your
announcements in the RADB (or a mirror). /24's are generally health
assuming you are supposed to be advertising them.
Since this seems a pretty high priority item to you as you are yelling it
out to us, I might suggest you run, not walk (metaphorically that is) over
to something like http://www.irr.net/docs/rpsl.html and read the RPSL
docs. Hitting Arin or a similar registy and reading some IPv4 policies
might also help. Nanog/Ripe/Arin/ISP-BGP and similar are all also good
places to start. Google should lead you around.
>Halabi's book has alot of examples with /24 networks being advertised,
>but I am thinking it is just used as an example to conceptualize the
>concepts.
>
>Any help would be greatly appriciated.
>
>Anthony Pace CCIE #10349
>
>
>
>--
> Anthony Pace
> anthonypace@fastmail.fm
>
>--
>http://www.fastmail.fm - A fast, anti-spam email service.
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