Jim, Continue to announce the /19 as before. You MAY want to also announce the /24 you've allocated to your downstream; depending upon the business relationship around this connectivity you may really want to announce the more specific /24. This is probably the critical choice you'll make. More details about the desired function of this interconnection would be needed to make intelligent comments on that.
Depending upon the specifics of the environment...The covering /19 will attract some traffic for this /24 regardless of the customer announcing the /24 via other providers. If you also propagate the announcement of this /24 then you will get a bigger % of the inbound traffic for this /24 depending upon the announcements made on the other interconnection(s) the customer AS has. Again....more specifics on the desired traffic flow would be helpful in deciding behaviour in various states. For some example of this .... When you give backup connectivity to a company which has sublet space from your shrinking dotcom, you'd not like to carry any of this downstream's traffic unless you have to. When you are billing the customer by the bit you'd like to bill them for as much traffic as you can carry without increasing your own costs enough to hurt your margins on the service. Suggestions: -Filter his announcements to you beyond just the as-path filter you've mentioned. Also use prefix list or such to limit the announcements you'll listen to be just the prefixes you've agreed to accept. This is probably just the /24(and nothing longer) you are allocating to him now. -Make sure you are allowing all your routers(especially border) to see this /24(or some covering aggregate) so that you don't create blackholes for some subset of the network. -Adjust your outbound route filters to permit the one /24(and nothing longer) to leak if you've decided you wanted this announced to the world via your network. This probably will require you to speak with your upstreams for them to adjust route filters on their side. -Regardless verify the announcements from outside your network by using a public looking glass. It is likely that all of the objectives for this interconnection will not be met with canned configuration or suggestions. It's also quite common that no one will notice that the objectives are failing to be met. This is usually due to the fact that "it works" right now and "it works" under simple failure modes. Best of luck and if you've got the time to share more details about what is desired the group can make more suggestions, Darrell Newcomb darrell(at)hayaitacosnet http://www.hayaitacos.net/mpeer/ Home of the Managed Peering Service ""Jim Devane"" wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > Hi all, > I am looking for some guidelines and I cannot find any relevant examples. I > have a situation where I have SWIP'd a /24 of my address block to a customer > downstream. They have their own AS and are multi-homed. > > My concern/question is: the /24 will originate from their AS and not mine. > Is there any special concerns I will need to take into accoutn for BGP > advertisements to my upstream providers? That is, I will peer with him and > allow his AS to originate the router and allow ^$ from him, but I am > concerned that this will mess up my advertisements of a /19. (the /24 I gave > him is out of my larger. Can I no longer advertise that? > > Are my concerns founded at all? Any advice? > > thanks, > Jim Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=62918&t=62914 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
