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. security@tomco.net ISP Programmer / Engineer On Fri, 19 Sep 1997, Brian Horvitz wrote:
Date: Fri, 19 Sep 1997 10:54:05 -0400 From: Brian Horvitz <horvitz@nsa.shore.net> To: Security Administrator <security@tomco.net> Subject: Re: BGP4 on a /20
Because if all the customers on a multi-billion dollar network can't get to him it's not real good.
Brian
At 10:32 AM 9/19/97 -0400, you wrote:
Why should you concern yourself with the problems of a multi-billion dollar company like Sprint?
Marcus R. Williams, Jr. security@tomco.net ISP Programmer / Engineer
On Thu, 18 Sep 1997, Phil Howard wrote:
Date: Thu, 18 Sep 1997 18:22:19 -0500 From: Phil Howard <phil@charon.milepost.com> To: nanog@merit.edu Subject: BGP4 on a /20
I'm trying to understand what all the implications of running BGP4 on a network with a prefix longer than 19 bits. Here are some of the points I am thinking about.
<flameshields>
If I go ahead and announce a /20 via two backbones, one of which is the provider of the address space, then there will be redundant routes for this space as the backbone provider will be announcing the /19 (or shorter) block themselves.
If I do this, it adds to the routing table glut, among other things. The advantage gained is questionable. If my link to the provider that the space comes from goes down, they are still announcing and I'll only be able to reach where my path via the alternate provider is shorter than the path to the down provider itself.
OTOH
If the provider were to be convinced to stop announcing for my /20, then I'm going to get filtered at Sprint and AGIS and whoever else is doing this and there won't be any /19 announcement that I can use a default path on.
But the real catch here is that for the provider to stop announcing my /20 they have to split their /19 into two /20's. And if that was really a /18 that means they will be announcing a /19 and a /20 where before only a /18. This gets worse the larger their block was.
Even worse than that, by doing this, they now have a /20 (the other half of the /19 my /20 is in) with other customers who will now also be filtered out at Sprint and AGIS and whoever else. While it can be OK to me if I want to give up that reachability, this is also imposing this on the other customer(s) in the other /20. So that provider is not even likely to do that.
So, should I add to the glut of routes or should I add to the glut of routes?
This needs to be simpler.
</flameshields>
-- 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 +-------------------------------------------------------------+
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. security@tomco.net 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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