nanog mailing list archives
Re: oh k can you see
From: Chris Woodfield <rekoil () semihuman com>
Date: Sat, 5 Nov 2005 13:11:21 -0500
Maybe I'm missing something, but the core issue is that the NO- EXPORT'ed anycast instance has a higher localpref inside the AS it's being advertised to, and as such supressing the non-NO_EXPORT'ed prefix. The "exportable" prefix gets suppressed at a point on the network such that the peering routers never see it, so it never makes it out of that AS.
Advertising the NO-EXPORT as a /25 (or two /25s) would serve the same purpose as tagging it NO-EXPORT, because as you say most peers filter on the /25. Incidentally it would obviate the need to assign it a higher localpref because it's a shorter prefix. However, unless I'm misunderstanding something, the /25 would not preempt the /24 advertisement, so the /24 would still make it out of the AS.
Just make sure you don't have anything numbered x.x.x.127 on the block...
On Nov 2, 2005, at 8:42 AM, Randy Bush wrote:
Is it an idea to have anycasted instances using NO_EXPORT announce /25's instead of /24's?many many folk filter on /24, so the /25 would not be seen.
Isn't that the point? The existing /24 is tagged NO-EXPORT after all...
Another possibility is for $LARGE_ISP to localpref the NO_EXPORTED down to $LOW valueand then how will the down-preffed prefix be seen within $large_isp? local-pref is a very heavy hammer. randy, at the clue edge i guess
-C
Current thread:
- Re: oh k can you see, (continued)
- Re: oh k can you see Sam Crooks (Nov 01)
- Re: oh k can you see Etaoin Shrdlu (Nov 01)
- Re: oh k can you see Joe Abley (Nov 01)
- Re: oh k can you see Randy Bush (Nov 01)
- Re: oh k can you see Etaoin Shrdlu (Nov 01)
- Re: oh k can you see Bill Woodcock (Nov 01)
- Re: oh k can you see Sam Crooks (Nov 01)
- Re: oh k can you see Sam Crooks (Nov 01)
- Re: oh k can you see Joe Maimon (Nov 01)
- Re: oh k can you see Randy Bush (Nov 01)
- Re: oh k can you see Joe Maimon (Nov 01)
- Re: oh k can you see Sabri Berisha (Nov 02)
- Re: oh k can you see Randy Bush (Nov 02)
- Re: oh k can you see Chris Woodfield (Nov 05)
- Re: oh k can you see Randy Bush (Nov 05)
- Re: oh k can you see Randy Bush (Nov 02)