Robert, I believe that you are kind of stuck with having ISP1 who filters everything of a /22 and below and ISP 2 filters at the /24. The first criteria is reachability (over all other algorithm criteria ... which are all just tie breakers as far as BGP is concerned). The reachability to your network behind both links is naturally always going to want to traverse ISP 2's link due to the uneven prefix filtering. What we would suggest to customers who had a similar problem is ask ISP 1 to get you a block (justified through ARIN of course) of a /22 (or whatever they will pass through) so that you can load balance traffic over both pipes using that one block. Then, in your justification to ARIN, make sure you detail the fact that you are handing back a /24 from ISP 2 due to the technical pitfall you have encountered and due to the nature of your traffic and business plan. Emphasize that you want to "load share" (not load balance)traffic over both links. Don't mention anything about ISP 2 going away ... need to know basis ... they don't need to know. Now ... if you get that /22 (or whatever size block) from ISP 1, you can announce the block in halves to both ISPs (eg. /23 to ISP 1 and /23 to ISP 2). Make sure that you know which traffic is most important and have that traverse your most reliable pipe ... then have the rest of the traffic traverse the to be backup pipe (aka ISP 2).
Hope any of this helps at all ... Please feel free to e-mail me if you have any other questions. Clay ----- Original Message ----- From: "Robert Fowler" To: Sent: Wednesday, January 15, 2003 9:31 AM Subject: BGP load balancing questions [7:61095] > Hello groupstudy, > > I've been banging my head against the wall and figured I would defer this > question to those of you more learned and experienced. Here is the the > scenario: > > 2 routers running BGP > Router 1 has a connection to ISP 1 and router 2 has a connection to ISP 2 > Each receives full routes. > Each provider has given us a class C address > Only the class C from provider 1 is actively used, because provider 2 will > probably be dropped eventually(ssshhh don't tell ARIN) > > > The class C is advertised to both ISPs, however ISP 1 aggregates this > address space so instead of being 1.1.1.x /24 it's 1.1.x.x /16 > This was checked using various looking glasses. > > What that means is that traffic to my Class C will arrive primarily via ISP > 2 because it will see the /24 I advertise though it. That is bad, for > various reasons. Mainly because we are charged by usage from ISP2, but also > because we are going to upgrade ISP1 to a fractional t3 and use ISP 2 > primarily as a backup eventually. Also the traffic coming in is 90% via ISP > 2 and 10% via ISP 1. > > If I remember from my studying so long ago, even prepending my AS number to > ISP 2 will not work, becuase it doesn't even make it to that criteria, but > rather see the /24 and chooses that route. > > I searched some newsgroups, but amazingly enough nobody seemed to have this > issue. I saw someone who had a larger block than /24 and some suggestions > there but that would not work in this case. > > > Options not available: > Using the Class C from Carrier 2 to load balance using IP space and traffic > types > Getting a class C independant of a provider from ARIN. (That costs money :)) > > > Robert Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=61107&t=61095 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
