>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
This is actually a very common issue that people don't think about until it happens to them. :-) The first thing I'd do would be to contact ISP 1 and see if they can provide any options. They should have the ability to advertise your more-specific route along with their aggregate. The next thing I'd do is....hmmm...umm... not sure. If ISP 1 refuses to advertise your /24 I'm not sure I see a great solution to your problem. Perhaps the real-world BGP gurus might have a suggestion. It's too late for you but I have one other suggestion. This is the sort of policy that needs to be researched before you even order a circuit with a provider. They usually state their aggregation policy in their BGP documentation and you should take a look at that before deciding on an ISP. As you can see, their aggregation can cause issues and you need to know up front how flexible they can be. Regards, John Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=61103&t=61095 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
