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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: BGP4 on a /20
Security Administrator (or someone claiming to be) wrote... > If all the customers on a multi-billion dollar network could not reach my > network I would think about paying a different upstream provider to peer > with me. I announce a /19 and a /22 to NetRail and UUnet, and they both > do an excellent job of getting Sprint's customers routed to my network. > > Marcus R. Williams, Jr. > [email protected] > ISP Programmer / Engineer Suppose you are the provider with 2 customers with /20's in the same /19. Both do their own BGP4. You can choose to aggregate and announce the whole /19 or not. You can choose to pass the /20 announcements or not. 0. Block /20's and don't announce /19. In this case, nothing works. 1. Block /20's and announce the whole /19. You customers are unable to get routing to work right as this means their /20 announcement over their other provider(s) becomes the one(s) used, and not your network (but you might think that is good, not to put demand on your network). 2. Pass /20's and don't announce /19. Your customers cannot get through to providers that block long nets. 3. Pass /20's and announce /19. This results in the largest number of routes being added to the tables everyone else is keeping. If providers did NOT do any route filtering based on network length, then number 2 would not be a problem, and that method could be done. But since providers do block routes, number 2 has to be discarded and number 3 is done. What that means is that when providers block routes longer than /19 they are causing others to have to make choices that result in more routes than would otherwise be necessary. Thus, I assert that by doing such route blocking, they are not achieving the savings in routes they expect on their own networks, and are causing a greater number of routes for all the others who are not (yet) filtering. -- Phil Howard +-------------------------------------------------------------+ KA9WGN | House committee changes freedom bill to privacy invasion !! | phil at | more info: http://www.news.com/News/Item/0,4,14180,00.html | milepost.com +-------------------------------------------------------------+
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