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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: "Simple" Multi-Homing ? (was Re: CIDR Report)
Since I've been getting a few private email questions on this - here is what I was what I was able to find out...Basically it can work, but its dependent upon on you selecting appropriate ISP providers and that these provider peer (or I would assume are not too many ASs away)... Chris Williams had it correct all along in his mail: http://www.merit.edu/mailinglist/mailarchives/old_archive/msg02315.html Here is how I understand it: Yes, the /24s will be filtered out by some [big "meanies" - but give'm lots of $$ and they co-loc for ya - its for the greater good of the Internet...;-)...]. If Provider A (primay) has a /19 or larger, and you get you /24 from them, then when your link to them goes down - your /24 is withdrawn by A but Provider A's /19 or larger is still globablly visible and packets will still be sent to Provider A for your /24. If provider B is peered with Provider A, provider B is advertising your /24, then packets will be routed from A through B to your site. Note: In this case, Provider A must not filter /24s from his peers to their own address space. A must also export your /24 when your link is up with your AS (in addition to their /19). See the "BGP Multi-Homing to > 1 ISP Help Required" thread in the comp.protocols.tcp-ip if you want more info. Cheers... Todd Sandor wrote: > > This brings me back to my original "operational" question of whether a > non-aggregated /24 will be globablly visiable when our primary link fails...The > situation: > > "When a customer in one location is using a multi-homed setup to two providers A > and > B, with A being the primary (using a /24 from loaned from provider A) > and B being the secondary (updates via B would have a longer AS_path - using > default routes with > local-pref on the primary). When the customers link to A fails, will the /24 > that > needs to be now globably visible via B (a non-aggregate IP address for B) NOT be > globably > visible because of the BGP filtering policies of some other provider somewhere, > say C ? >
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