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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: your mail
On Thu, Nov 01, 2001 at 11:33:55AM -0600, Zhao, Xingguo wrote: > I have a question regarding to redistribute IGR routes into BGP. Currently > both Cisco > and Juniper support it. > > Here I don't understand what is the advantage of this redistribution? > Because BGP is > potentially injecting information into the IGP and then sending such > information back into BGP. > > Could anybody provide more description regarding the advantage and the > disadvantage > of redistribuing IGP routes into BGP? How is BGP potentially injecting information into the IGP? The only way that should be happening is if you are doing BGP -> IGP redistribution, in which case I'd surely hope you aren't doing IGP -> BGP as well. In my experience, most redistribution in either direction is used to overcome design issues (such as two iBGP neighbors whose paths to each other include a non-BGP-speaking router). I don't know that I would go so far as to say there is absolutely no valid use for it, but I've always seen it used strictly as a patch rather than as intended design. The main advantage IMHO is getting something working immediately instead of having to make design changes (when the boss wants it to work -now-), though this certainly comes with a cost if the proper path is not implemented shortly thereafter. The primary disadvantages I see are: 1) Loss of information. Whether you go IGP -> BGP or vice versa, you lose some of the specifics of routes. BGP and OSPF, for example, have different attributes, many of which can't be mapped to a corresponding attribute in either direction (AS-path is the most glaring example). 2) Risk of routing table pollution. More than one major ISP has had network meltdowns of varying degrees due to redistribution mishaps. Your policies and filters may seem to work fine, but you also may add some routes in the future that will trip them up. Again, I'm sure more than a few of us have used redistribution, but in general I see it as being used in lieu of a proper solution rather than being the proper solution itself. -c
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