Margaret Wasserman wrote: > I think it depends what you mean by "filtering a prefix"... > > If you use a global prefix to number a private site, you > wouldn't necessarily advertise that prefix in global routing > tables.
Yes you would, because that private site is most likely part of a larger enterprise, so the parts that get advertised will be a /48 or shorter, while the parts that want to stay disconnected would be a /56 or longer. > In fact, it would be best not to. So, it wouldn't > be any more "routable" on the Internet than a site-local > prefix. Routers wouldn't have any path to it, so they'd drop it... This is only true if the site trying to stay out of the table was represented by a /48 or shorter. If not, the ISP filter will simply drop the longer advertisements and the part of the enterprise that didn't want to be globally accessable would suddenly find that they were reachable. > > Also, I am under the impression that ISPs do some filtering > at the customer bounday -- only allowing traffic from a > customers' global > prefix(es) out, and only letting traffic to the customers' global > prefix(es) in... How common is this? Not as common as it needs to be (see nanog discussion today on this topic), but even if it did happen everywhere, it does not mean that parts of a /48 can be globally routed while other parts are not. Tony > > Margaret > > > -------------------------------------------------------------------- > IETF IPng Working Group Mailing List > IPng Home Page: http://playground.sun.com/ipng > FTP archive: ftp://playground.sun.com/pub/ipng > Direct all administrative requests to [EMAIL PROTECTED] > -------------------------------------------------------------------- > -------------------------------------------------------------------- IETF IPng Working Group Mailing List IPng Home Page: http://playground.sun.com/ipng FTP archive: ftp://playground.sun.com/pub/ipng Direct all administrative requests to [EMAIL PROTECTED] --------------------------------------------------------------------
