nanog mailing list archives
RE: FW: /8s and filtering
From: Brian <bri () sonicboom org>
Date: Tue, 10 Dec 2002 11:33:32 -0800 (PST)
Isn't it true that most bgp announcements with a mask longer than 24 bits hit the proverbial bit bucket? Brian On Tue, 10 Dec 2002, Harsha Narayan wrote:
Hello, But how will such an ISP justify this to the RIR? Thanks, Harsha. On Tue, 10 Dec 2002, Brian wrote:many isps will automatically give a /24 if their client is multihoming, even if their usage is well below the 254 usable ips allocated by the above block size. Brian On Tue, 10 Dec 2002, Harsha Narayan wrote:Hello, No, this is not the case. I enquired and it seems multihoming is not a justification for a /24 in any RIR. Does a network have to be able to fully utilize a /26 (25% of /24) in order to multihome? Harsha. On Tue, 10 Dec 2002, Ejay Hire wrote:Having a /24 doesn't indicate you are a network of any particular size, ARIN ratified a policy that allows multihoming as justification for a /24. -ej -----Original Message----- From: N [mailto:nathan () stonekitty net] Sent: Tuesday, December 10, 2002 1:01 PM To: Forrest Cc: nanog () merit edu Subject: Re: FW: /8s and filtering comments inline On Tue, Dec 10, 2002 at 12:36:39PM -0600, Forrest wrote:I was also curious about this - if I am a customer who wants to multihome and can justify only a /24, I would go to an ISP whichhas anallocation from the Class C space rather than one from the Class A space.It doesn't matter. For all practical purposes, basementmultihomersonly care that their two or three providers have their route.Maybe I'm missing something, but what good would it do for someone to multihome if only their own providers accept their route, but nobodyelsedoes? I realize that their block should be still announced with theirISP's larger aggregate, but what good does this do if your ISP goesdownand can't announce the large aggregate.For the assigned block to be part of the same aggregate(of both providers), that implys that the providers sharing the responsibility for the aggregate. It happens, but is rare. In this case, the providers must accept more specific routes from each other, that is within the space being aggregated. If they do not share specifics, one uplink down will cause a large percentage ~50% for the customer. This scenario is valid for load balancing, but redundancy is fragile. The only advantage I see is no limit to prefix length. You can do this with a /28 if you want... given the above caveats are addressed.If you're a smaller organization, perhaps you'll only have a /23 fromyourupstream provider. With the filtering that seems to be in place, itseemslike the only way you can truly multihome with a /23 is if it happenstobe in the old Class C space. Or is this wrong?In today's VLSM world... the old classes have no bearing on filtering in my experience. Prefix length discrimination knows no classfull boundaries.What seems to be needed is perhaps a /8 set aside by the RIRspecificallyto allocate to small organizations that wish to multihome that people would accept /24 and shorter from.There is value in the current filtering of longest prefixes... Allowing anyone to multihome with BGP, using any network size, is going to double our BGP tables overnight. Perhaps its good that you must be of some size to participate in public BGP. Many providers offer redundancy that is more appropriate for the smaller networks. -- ,N ~Nathan - routing & switching dude/fly-boy/sport biker - San Jose CA~
Current thread:
- Re: FW: /8s and filtering, (continued)
- Re: FW: /8s and filtering David Schwartz (Dec 10)
- Re: FW: /8s and filtering Harsha Narayan (Dec 10)
- Re: FW: /8s and filtering N (Dec 10)
- Re: FW: /8s and filtering David Schwartz (Dec 10)
- Re: FW: /8s and filtering Tim Thorne (Dec 11)
- Re: FW: /8s and filtering william (Dec 10)
- RE: FW: /8s and filtering Harsha Narayan (Dec 10)
- RE: FW: /8s and filtering Brian (Dec 10)
- RE: FW: /8s and filtering Harsha Narayan (Dec 10)
- RE: FW: /8s and filtering Brian (Dec 10)
- RE: FW: /8s and filtering Harsha Narayan (Dec 10)
- RE: FW: /8s and filtering Alec H. Peterson (Dec 10)
- RE: FW: /8s and filtering Harsha Narayan (Dec 10)
- RE: FW: /8s and filtering Harsha Narayan (Dec 10)